Measurement of Coherent π+ Production in Low Energy Neutrino-Carbon Scattering

We report the first measurement of the flux-averaged cross section for charged current coherent π+ production on carbon for neutrino energies less than 1.5 GeV, and with a restriction on the final state phase space volume in the T2K near detector, ND280. Comparisons are made with predictions from the Rein-Sehgal coherent production model and the model by Alvarez-Ruso et al., the latter representing the first implementation of an instance of the new class of microscopic coherent models in a neutrino interaction Monte Carlo event generator. We observe a clear event excess above background, disagreeing with the null results reported by K2K and SciBooNE in a similar neutrino energy region. The …

Systematic study of charged-pion and kaon femtoscopy in Au + Au collisions atsNN=200GeV

We present a systematic study of charged-pion and kaon interferometry in Au + Au collisions at root s(NN) = 200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.

Search for short baseline nu(e) disappearance with the T2K near detector

8 pages.- 6 figures

Medium Modification of Jet Fragmentation inAu+AuCollisions atsNN=200  GeVMeasured in Direct Photon-Hadron Correlations

The jet fragmentation function is measured with direct photon-hadron correlations in p + p and Au + Au collisions at root S-NN = 200 GeV. The P-T of the photon is an excellent approximation to the initial P-T of the jet and the ratio Z(T) = P-T(h)/P-T(gamma) is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au + Au collisions while a photon isolation cut is applied in p + p. I-AA, the ratio of hadron yield opposite the photon in Au + Au to that in p + p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high Z(T). The associated h…

The PHENIX Collaboration

Cross Section and Parity-Violating Spin Asymmetries ofW±Boson Production in Polarizedp+pCollisions ats=500  GeV

Large parity-violating longitudinal single-spin asymmetries A(L)(e+) = 0.86(-0.14)(+0.30) and Ae(L)(e-) = 0.88(-0.71)(+0.12) are observed for inclusive high transverse momentum electrons and positrons in polarized p + p collisions at a center-of-mass energy of root s = 500 GeV with the PHENIX detector at RHIC. These e(+/-) come mainly from the decay of W-+/- and Z(0) bosons, and their asymmetries directly demonstrate parity violation in the couplings of the W-+/- to the light quarks. The observed electron and positron yields were used to estimate W-+/- boson production cross sections for the e(+/-) channels of sigma(pp -> W+X) X BR(W+ -> e(+) nu(e)) = 144.1 +/- 21.2(stat)(-10.3)(+3.4)(syst)…

Cross section forbb¯production via dielectrons ind+ Au collisions atsNN=200GeV

We report a measurement of e+e− pairs from semileptonic heavy-flavor decays in d+Au collisions at sNN−−−√=200 GeV. By exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to pythia and mc@nlo simulations. The resulting bb¯-production cross section is σdAubb¯=1.37±0.28(stat)±0.46(syst) mb, which is equivalent to a nucleon-nucleon cross section of σNNbb=3.4±0.8(stat)±1.1(syst)μb.

Υ(1S+2S+3S)production ind+Au andp+pcollisions atsNN=200GeV and cold-nuclear-matter effects

The three gamma states, gamma (1S + 2S + 3S), are measured in d + Au and p + p collisions at root s(NN) = 200 GeV and rapidities 1.2 < vertical bar y vertical bar < 2.2 by the PHENIX experiment at the Relativistic Heavy Ion Collider. Cross sections for the inclusive gamma (1S + 2S + 3S) production are obtained. The inclusive yields per binary collision for d + Au collisions relative to those in p + p collisions (R-dAu) are found to be 0.62 +/- 0.26 (stat) +/- 0.13 (syst) in the gold-going direction and 0.91 +/- 0.33 (stat) +/- 0.16 (syst) in the deuteron-going direction. The measured results are compared to a nuclear-shadowing model, EPS09 [Eskola et al., J. High Energy Phys. 04 (2009) 065]…

Combined Analysis of Neutrino and Antineutrino Oscillations at T2K.

T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beams. The data include all runs from January 2010 to May 2016 and comprise 7.482 ×10^(20) protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 μ-like events, and 7.471 × 10^(20) protons on target in antineutrino mode, which yielded 4 e-like and 66 μ-like events. Reactor measurements of sin(2)2θ(13) have been used as an additional constraint. The one-dimensional confidence interval at 90% for the phase δCP spans the range (−3.13, −0.39) for normal mass ordering. The CP conservation hypothesis …

Meson production inp+U, O+U and S+U interactions at 200 GeV/nucleon

Meson production in proton, oxygen and sulphur interactions with uranium targets at 200 GeV/nucleon is studied. We measure the inclusive meson cross-section d σ/dPT2 and its evolution fromp+U to S+U. The cross-section fitted with an exponential gives an inverse slopePT0 of the order of 210 MeV/c. As a function of the neutral transverse energy,PT0 values show a slight rise followed by a plateau. The normalized difference (σ+−σ−)/σ− between positive and negative meson cross-sections is found to increase withET.

Measurement ofΥ(1S+2S+3S)production inp+pand Au + Au collisions atsNN=200GeV

Measurements of bottomonium production in heavy-ion and p + p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three states, (1S + 2S + 3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au + Au and p + p collisions at root sNN = 200 GeV. The (1S + 2S + 3S) -> e(+)e(-) differential cross section at midrapidity was found to be B(ee)d sigma/dy = 108 +/- 38 (stat) +/- 15 (syst) +/- 11 (luminosity) pb in p + p collisions. The nuclear modification factor in the 30% most central Au + Au collisions indicates a suppression of the total. state yield relative to the extrapolation from p + p collision data. …

Study of J/$\psi$ production in p-U, O-U and S-U interactions at 200 GeV per nucleon

Abstract In a search for quark-gluon plasma formation, the production of J/ψ and muon pairs in the mass continuum region is studied in oxygen-uranium and sulphur-uranium interactions. The yield of J/ψ relative to the continuum is measured to be a decreasing function of the neutral transverse energy produced in the collision, i.e. of the energy density. A comparison is made with proton-uranium reactions.

Search for Electron Antineutrino Appearance in a Long-baseline Muon Antineutrino Beam

Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40 σ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and a…

Cross section and transverse single-spin asymmetry ofηmesons inp↑+pcollisions ats=200  GeVat forward rapidity

We present a measurement of the cross section and transverse single-spin asymmetry (AN) for. mesons at large pseudorapidity from root s = 200 GeV p up arrow + p collisions. The measured cross section for 0.5 = 0.061 +/- 0.014. The results are consistent with prior transverse single-spin measurements of forward eta and pi(0) mesons at various energies in overlapping x(F) ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p up arrow + p collisions.

Transverse momentum dependence ofηmeson suppression in Au+Au collisions atsNN=200GeV

New measurements by the PHENIX experiment at the Relativistic Heavy Ion Collider for. production at midrapidity as a function of transverse momentum ((PT)) and collision centrality in root s(NN) = 200 GeV Au + Au and p + p collisions are presented. They indicate nuclear modification factors (R-AA) which are similar in both magnitude and trend to those found in earlier pi(0) measurements. Linear fits to R-AA as a function of (PT) in 5-20 GeV/c show that the slope is consistent with zero within two standard deviations at all centralities, although a slow rise cannot be excluded. Having different statistical and systematic uncertainties, the pi(0) and eta measurements are complementary at high…

Measurements of ν̅ μ and ν̅ μ + ν μ charged-current cross-sections without detected pions or protons on water and hydrocarbon at a mean anti-neutrino energy of 0.86 GeV

Abstract We report measurements of the flux-integrated ν̅μ and ν̅μ + νμ charged-current cross-sections on water and hydrocarbon targets using the T2K anti-neutrino beam with a mean beam energy of 0.86 GeV. The signal is defined as the (anti-)neutrino charged-current interaction with one induced $\mu^\pm$ and no detected charged pion or proton. These measurements are performed using a new WAGASCI module recently added to the T2K setup in combination with the INGRID Proton Module. The phase space of muons is restricted to the high-detection efficiency region, $p_{\mu}&amp;gt;400~{\rm MeV}/c$ and $\theta_{\mu}&amp;lt;30^{\circ}$, in the laboratory frame. An absence of pions and protons in the …

Measurements of the T2K neutrino beam properties using the INGRID on-axis near detector

Precise measurement of neutrino beam direction and intensity was achieved based on a new concept with modularized neutrino detectors. INGRID (Interactive Neutrino GRID) is an on-axis near detector for the T2K long baseline neutrino oscillation experiment. INGRID consists of 16 identical modules arranged in horizontal and vertical arrays around the beam center. The module has a sandwich structure of iron target plates and scintillator trackers. INGRID directly monitors the muon neutrino beam profile center and intensity using the number of observed neutrino events in each module. The neutrino beam direction is measured with accuracy better than 0.4 mrad from the measured profile center. The …

Azimuthal correlations of electrons from heavy-flavor decay with hadrons inp+pand Au+Au collisions atsNN=200GeV

Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled p+p collisions. These measurements indicate that charm and bottom quarks interact with the hot dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whet…

J/ψsuppression at forward rapidity in Au+Au collisions atsNN=200GeV

Heavy quarkonia are observed to be suppressed in relativistic heavy-ion collisions relative to their production in p + p collisions scaled by the number of binary collisions. In order to determine if this suppression is related to color screening of these states in the produced medium, one needs to account for other nuclear modifications including those in cold nuclear matter. In this paper, we present new measurements from the PHENIX 2007 data set of J/psi yields at forward rapidity (1.2 < vertical bar y vertical bar < 2.2) in Au + Au collisions at root s(NN) = 200 GeV. The data confirm the earlier finding that the suppression of J/. at forward rapidity is stronger than at midrapidity, whi…

Cold-Nuclear-Matter Effects on Heavy-Quark Production at Forward and Backward Rapidity ind+AuCollisions atsNN=200  GeV

The PHENIX experiment has measured open heavy-flavor production via semileptonic decay over the transverse momentum range 1 < p(T) < 6 GeV/c at forward and backward rapidity (1.4 < vertical bar y vertical bar < 2.0) in d + Au and p + p collisions at root s(NN) = 200 GeV. In central d + Au collisions, relative to the yield in p + p collisions scaled by the number of binary nucleon-nucleon collisions, a suppression is observed at forward rapidity (in the d-going direction) and an enhancement at backward rapidity (in the Au-going direction). Predictions using nuclear-modified-parton-distribution functions, even with additional nuclear-p(T) broadening, cannot simultaneously reproduce the data a…

Measurement of the muon neutrino inclusive charged-current cross section in the energy range of 1–3 GeV with the T2K INGRID detector

International audience; We report a measurement of the $\nu_{\mu}$-nucleus inclusive charged current cross section (=$\sigma^{cc}$) on iron using data from exposed to the J-PARC neutrino beam. The detector consists of 14 modules in total, which are spread over a range of off-axis angles from 0$^\circ$ to 1.1$^\circ$. The variation in the neutrino energy spectrum as a function of the off-axis angle, combined with event topology information, is used to calculate this cross section as a function of neutrino energy. The cross section is measured to be $\sigma^{cc}(1.1\text{ GeV}) = 1.10 \pm 0.15$ $(10^{-38}\text{cm}^2/\text{nucleon})$, $\sigma^{cc}(2.0\text{ GeV}) = 2.07 \pm 0.27$ $(10^{-38}\te…

Heavy-quark production and elliptic flow in Au + Au collisions atsNN=62.4GeV

We present measurements of electrons and positrons from the semileptonic decays of heavy-flavor hadrons at midrapidity (|y|< 0.35) in Au+Au collisions at sNN−−−−√=62.4 GeV. The data were collected in 2010 by the PHENIX experiment that included the new hadron-blind detector. The invariant yield of electrons from heavy-flavor decays is measured as a function of transverse momentum in the range 1<peT<5 GeV/c. The invariant yield per binary collision is slightly enhanced above the p+p reference in Au+Au 0%–20%, 20%–40%, and 40%–60% centralities at a comparable level. At this low beam energy this may be a result of the interplay between initial-state Cronin effects, final-state flow, and energy …

Cold-Nuclear-Matter Effects on Heavy-Quark Production ind+AuCollisions atsNN=200  GeV

The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d+Au and p+p collisions at sqrt[S(NN)]=200 GeV in the transverse-momentum range 0.85 ≤ p(T)(e) ≤ 8.5 GeV/c. In central d+Au collisions, the nuclear modification factor R(dA) at 1.5<p(T)<5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p+p collisions, and shows that the mass-dependent Cronin enhancement observed at the Relativistic Heavy Ion Collider extends to the heavy D meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-…

Trends in Yield and Azimuthal Shape Modification in Dihadron Correlations in Relativistic Heavy Ion Collisions

Fast parton probes produced by hard scattering and embedded within collisions of large nuclei have shown that partons suffer large energy loss and that the produced medium may respond collectively to the lost energy. We present measurements of neutral pion trigger particles at transverse momenta p^t_T = 4-12 GeV/c and associated charged hadrons (p^a_T = 0.5-7 GeV/c) as a function of relative azimuthal angle Delta Phi at midrapidity in Au+Au and p+p collisions at sqrt(s_NN) = 200 GeV. These data lead to two major observations. First, the relative angular distribution of low momentum hadrons, whose shape modification has been interpreted as a medium response to parton energy loss, is found to…

Measurement of transverse single-spin asymmetries forJ/ψproduction in polarizedp+pcollisions ats=200  GeV

We report the first measurement of transverse single-spin asymmetries in J/psi production from transversely polarized p + p collisions at root s = 200 GeV with data taken by the PHENIX experiment in 2006 and 2008. The measurement was performed over the rapidity ranges 1.2 < vertical bar y vertical bar < 2.2 and vertical bar y vertical bar < 0.35 for transverse momenta up to 6 GeV/c. J/psi production at the Relativistic Heavy Ion Collider is dominated by processes involving initial-state gluons, and transverse single-spin asymmetries of the J/psi can provide access to gluon dynamics within the nucleon. Such asymmetries may also shed light on the long-standing question in QCD of the J/psi pro…

Search for heavy neutrinos with the T2K near detector ND280

This paper reports on the search for heavy neutrinos with masses in the range 140<MN<493  MeV/c2 using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are N→ℓ±απ∓ and N→ℓ+αℓ−β(−)ν(α,β=e,μ). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heav…

Updated T2K measurements of muon neutrino and antineutrino disappearance using 1.5×1021 protons on target

We report measurements by the T2K experiment of the parameters $\theta_{23}$ and $\Delta m^{2}_{32}$ governing the disappearance of muon neutrinos and antineutrinos in the three flavor neutrino oscillation model. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, the parameters are measured separately for neutrinos and antineutrinos. Using $7.482 \times 10^{20}$ POT in neutrino running mode and $7.471 \times 10^{20}$ POT in antineutrino mode, T2K obtained, $\sin^{2}(\theta_{23})=0.51^{+0.08}_{-0.07}$ and $\Delta m^{2}_{32} = 2.53^{+0.15}_{-0.13} \times 10^{-3}$eV$^{2}$/c$^{4}$ for neutrinos, and $\sin^{2}({\overline{\theta}}_{23})=0.4…

Low-momentum direct-photon measurement in Cu + Cu collisions at sNN=200GeV

We measured direct photons for pT<5GeV/c in minimum bias and 0%–40% most-central events at midrapidity for Cu+Cu collisions at sNN=200GeV. The e+e− contribution from quasireal direct virtual photons has been determined as an excess over the known hadronic contributions in the e+e− mass distribution. A clear enhancement of photons over the binary scaled p+p fit is observed for pT<4GeV/c in Cu+Cu data. The pT spectra are consistent with the Au+Au data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the p+p baseline are 285±53(stat)±57(syst)MeV/c and 333±72(stat)±45(syst)MeV/c for minimum bias and 0%–40% most-central even…

Measurement of the $\nu_{\mu}$ charged current quasi-elastic cross-section on carbon with the T2K on-axis neutrino beam

17 pages.- 21 figures

Quadrupole Anisotropy in Dihadron Azimuthal Correlations in Centrald+AuCollisions atsNN=200  GeV

The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in d + Au collisions at root s(NN) = 200 GeV. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central p + Pb collisions at root s(NN) = 5.02 TeV, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies in d + Au collisions at RHIC compared to those seen…

φ, ϱ, and ω production in pU, OU and SU reactions at 200 GeV per nucleon

Abstract Low mass muon pair production at high P T and low X F studied in pU, OU and SU 200 GeV per nucleon react ions. When energy density or projectile mass are increased, φ production is enhanced as compared with the yield of muon pairs in the mass continuum (1.7 M μμ c 2 ), whereas the production of ω and ϱ, experimentally unresolved, remains approximately constant. This φ enhancement is in agreement with predictions based on quark-gluon plasma formation and, together with the previously reported J/Ψ suppression, puts severe constraints on a purely hadronic description of nucleus-nucleus collisions.

Cold Nuclear Matter Effects onJ/ψYields as a Function of Rapidity and Nuclear Geometry ind+ACollisions atsNN=200  GeV

We present measurements of J/psi yields in d + Au collisions at root S-NN = 200 GeV recorded by the PHENIX experiment and compare them with yields in p + p collisions at the same energy per nucleon-nucleon collision. The measurements cover a large kinematic range in J/psi rapidity (-2.2 < y < 2.4) with high statistical precision and are compared with two theoretical models: one with nuclear shadowing combined with final state breakup and one with coherent gluon saturation effects. In order to remove model dependent systematic uncertainties we also compare the data to a simple geometric model. The forward rapidity data are inconsistent with nuclear modifications that are linear or exponentia…

Centrality categorization forRp(d)+Ain high-energy collisions

High-energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, including modifications of parton distribution functions in nuclei, gluon saturation, and color neutralization and hadronization in a nuclear environment, among others. All of these effects are expected to have a significant dependence on the size of the nuclear target and the impact parameter of the collision, also known as the collision centrality. In this article, we detail a method for determining centrality classes in p(d) + A collisions via cuts on the multiplicity at backward rapidity (i.e., the nucleus-going direction) and for determining systematic uncertainti…

Production ofωmesons inp+p,d+ Au, Cu + Cu, and Au + Au collisions atsNN=200GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured omega meson production via leptonic and hadronic decay channels in p + p, d + Au, Cu+ Cu, and Au + Au collisions at root s(NN) = 200 GeV. The invariant transverse momentum spectra measured in different decay modes give consistent results. Measurements in the hadronic decay channel in Cu Cu and Au + Au collisions show that. production has a suppression pattern at high transverse momentum, similar to that of pi(0) and eta in central collisions, but no suppression is observed in peripheral collisions. The nuclear modification factors, R-AA, are consistent in Cu + Cu and Au + Au collisions at similar numbers of participan…

Measurements of e+e− pairs from open heavy flavor in p+p and d+A collisions at sNN=200 GeV

We report a measurement of e+e− pairs from semileptonic heavy-flavor decays in p+p collisions at sNN=200 GeV. The e+e− pair yield from bb¯ and cc¯ is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and pT. We used three different event generators, pythia, mc@nlo, and powheg, to simulate the e+e− spectra from cc¯ and bb¯ production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4π, significant differences are observed for the total cross section. These difference are less pronounced for bb¯ than for cc¯. The same model dependence was observed in alr…

Measurement of double-differential muon neutrino charged-current interactions onC8H8without pions in the final state using the T2K off-axis beam

We report the measurement of muon neutrino charged-current interactions on carbon without pions in the final state at the T2K beam energy using 5.734×1020 protons on target. For the first time the measurement is reported as a flux-integrated, double-differential cross section in muon kinematic variables (cosθμ, pμ), without correcting for events where a pion is produced and then absorbed by final state interactions. Two analyses are performed with different selections, background evaluations and cross-section extraction methods to demonstrate the robustness of the results against biases due to model-dependent assumptions. The measurements compare favorably with recent models which include n…

Measurement of the inclusive $\nu_{\mu}$ charged current cross section on iron and hydrocarbon in the T2K on-axis neutrino beam

We report a measurement of the $\nu_\mu$ inclusive charged current cross sections on iron and hydrocarbon in the T2K on-axis neutrino beam. The measured inclusive charged current cross sections on iron and hydrocarbon averaged over the T2K on-axis flux with a mean neutrino energy of 1.51 GeV are $(1.444\pm0.002(stat.)_{-0.157}^{+0.189}(syst.))\times 10^{-38}\mathrm{cm}^2/\mathrm{nucleon}$, and $(1.379\pm0.009(stat.)_{-0.147}^{+0.178}(syst.))\times 10^{-38}\mathrm{cm}^2/\mathrm{nucleon}$, respectively, and their cross section ratio is $1.047\pm0.007(stat.)\pm0.035(syst.)$. These results agree well with the predictions of the neutrino interaction model, and thus we checked the correct treatme…

Cold-nuclear-matter effects on heavy-quark production at forward and backward rapidity in d + Au collisions at √sNN = 200  GeV.

The PHENIX experiment has measured open heavy-flavor production via semileptonic decay over the transverse momentum range 1p(T)6  GeV/c at forward and backward rapidity (1.4|y|2.0) in d+Au and p + p collisions at √sNN = 200  GeV. In central d+Au collisions, relative to the yield in p + p collisions scaled by the number of binary nucleon-nucleon collisions, a suppression is observed at forward rapidity (in the d-going direction) and an enhancement at backward rapidity (in the Au-going direction). Predictions using nuclear-modified-parton-distribution functions, even with additional nuclear-p(T) broadening, cannot simultaneously reproduce the data at both rapidity ranges, which implies that t…

Suppression of away-side jet fragments with respect to the reaction plane in Au + Au collisions atsNN=200GeV

Pair correlations between large transverse momentum neutral pion triggers (p(T) = 4-7 GeV/c) and charged hadron partners (p(T) = 3-7 GeV/c) in central (0%-20%) and midcentral (20%-60%) Au + Au collisions at root s(NN) = 200 GeV are presented as a function of trigger orientation with respect to the reaction plane. The particles are at larger momentum than where jet shape modifications have been observed, and the correlations are sensitive to the energy loss of partons traveling through hot densematter. An out-of-plane trigger particle produces only 26 +/- 20% of the away-side pairs that are observed opposite of an in-plane trigger particle for midcentral (20%-60%) collisions. In contrast, ne…

Observation of Electron Neutrino Appearance in a Muon Neutrino Beam

The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of 7.3$\sigma$ when compared to 4.92 $\pm$ 0.55 expected background events. In the PMNS mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles $\theta_{12}$, $\theta_{23}$, $\theta_{13}$, a mass difference $\Delta m^2_{32}$ and a CP violating phase $\delta_{\mathrm{CP}}$. In this neutrino oscillation scenario, assuming $…

Search for Lorentz and CPT violation using sidereal time dependence of neutrino flavor transitions over a short baseline

A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations was performed using the T2K on-axis near detector. Two complementary methods were used in this study, both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms from the Standard Model extension have been derived by taking into account their correlations in this model for the first time. These results imply such symmetry violations are suppressed by a factor of more than 1020 at the GeV scale.

Transverse energy distributions in nucleus-nucleus collisions at 200 GeV/nucleon

Abstract The transverse energy ET distributions of nucleus-nucleus collisions are studied in the framework of a simple geometrical model. The distributions for inclusive production of J ψ and muon pairs in the mass continuum are analyzed. The shape of the ET distribution of the continuum agreed with the model. The previously oberved decrease of the ratio ( J ψ )/continuum with increasing ET is due to the behavior of the J ψ .

Measurement of the higher-order anisotropic flow coefficients for identified hadrons in Au + Au collisions atsNN=200GeV

Measurements of the anisotropic flow coefficients v2{Ψ2},v3{Ψ3},v4{Ψ4}, and v4{Ψ2} for identified particles (π±,K±, and p+p) at midrapidity, obtained relative to the event planes Ψm at forward rapidities in Au + Au collisions at sNN=200GeV, are presented as a function of collision centrality and particle transverse momenta pT. The vn coefficients show characteristic patterns consistent with hydrodynamical expansion of the matter produced in the collisions. For each harmonic n, a modified valence quark-number Nq scaling [plotting vn{Ψm}/(Nq)n/2 versus transverse kinetic energies (KET)/Nq] is observed to yield a single curve for all the measured particle species for a broad range of KET. A si…

Direct photon production ind+Au collisions atsNN=200GeV

Direct photons have been measured in root s(NN) = 200 GeV d + Au collisions at midrapidity. A wide p(T) range is covered by measurements of nearly real virtual photons (1 < p(T) < 6 GeV/c) and real photons (5 < p(T) < 16 GeV/c). The invariant yield of the direct photons in d + Au collisions over the scaled p + p cross section is consistent with unity. Theoretical calculations assuming standard cold-nuclear-matter effects describe the data well for the entire p(T) range. This indicates that the large enhancement of direct photons observed in Au + Au collisions for 1.0 < p(T) < 2.5 GeV/c is attributable to a source other than the initial-state nuclear effects.

Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K

Authors: K. Abe,56 N. Akhlaq,45 R. Akutsu,57 A. Ali,32 C. Alt,11 C. Andreopoulos,54,34 L. Anthony,21 M. Antonova,19 S. Aoki,31 A. Ariga,2 T. Arihara,59 Y. Asada,69 Y. Ashida,32 E. T. Atkin,21 Y. Awataguchi,59 S. Ban,32 M. Barbi,46 G. J. Barker,66 G. Barr,42 D. Barrow,42 M. Batkiewicz-Kwasniak,15 A. Beloshapkin,26 F. Bench,34 V. Berardi,22 L. Berns,58 S. Bhadra,70 S. Bienstock,53 S. Bolognesi,6 T. Bonus,68 B. Bourguille,18 S. B. Boyd,66 A. Bravar,13 D. Bravo Berguño,1 C. Bronner,56 S. Bron,13 A. Bubak,51 M. Buizza Avanzini ,10 T. Campbell,7 S. Cao,16 S. L. Cartwright,50 M. G. Catanesi,22 A. Cervera,19 D. Cherdack,17 N. Chikuma,55 G. Christodoulou,12 M. Cicerchia,24,† J. Coleman,34 G. Collazu…

Evolution ofπ0Suppression inAu+AuCollisions fromsNN=39to 200 GeV

Neutral-pion pi(0) spectra were measured at midrapidity (vertical bar y vertical bar < 0.35) in Au + Au collisions at root s(NN) = 39 and 62.4 GeV and compared with earlier measurements at 200 GeV in a transverse-momentum range of 1 < p(T) < 10 GeV/c. The high-p(T) tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for p + p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and p(T) dependence. Above p(T) = 7 GeV/c, R-AA is similar for root sNN = 62.4 and 200 GeV at …

Azimuthal Anisotropy ofπ0Production inAu+AuCollisions atsNN=200  GeV: Path-Length Dependence of Jet Quenching and the Role of Initial Geometry

We have measured the azimuthal anisotropy of pi(0) production for 1 < p(T) < 18 GeV/c for Au + Au collisions at root s(NN) = 200 GeV. The observed anisotropy shows a gradual decrease for 3 less than or similar to p(T) less than or similar to 7-10 GeV/c, but remains positive beyond 10 GeV/c. The magnitude of this anisotropy is underpredicted, up to at least similar to 10 GeV/c, by current perturbative QCD (PQCD) energy-loss model calculations. An estimate of the increase in anisotropy expected from initial-geometry modification due to gluon saturation effects and fluctuations is insufficient to account for this discrepancy. Calculations that implement a path-length dependence steeper than wh…

Neutral pion production with respect to centrality and reaction plane in Au+Au collisions atsNN=200GeV

The PHENIX experiment has measured the production of pi(0)s in Au + Au collisions at root S-NN = 200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, p(T), to 20 GeV/c. The production ratio of eta/pi(0) is 0.46 +/- 0.01(stat) +/- 0.05(syst), constant with p(T) and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p + p and d + Au values. pi(0) are suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor R-AA vs p(T), with a slope of 0.0106 +/-(0…

Nuclear Modification ofψ′,χc, andJ/ψProduction ind+AuCollisions atsNN=200  GeV

We present results for three charmonia states (psi' chi(c), and J/ psi) in d + Au collisions at vertical bar y vertical bar < 0.35 and root s(NN) = 200 GeV. We find that the modification of the psi' yield relative to that of the J/ psi scales approximately with charged particle multiplicity at midrapidity across p + A, d + Au, and A + A results from the Super Proton Synchrotron and the Relativistic Heavy Ion Collider. In large-impact-parameter collisions we observe a similar suppression for the psi' and J/ psi, while in small-impact-parameter collisions the more weakly bound psi' is more strongly suppressed. Owing to the short time spent traversing the Au nucleus, the larger psi' suppressio…

Inclusive cross section and double-helicity asymmetry forπ0production at midrapidity inp+pcollisions ats=510  GeV

PHENIX measurements are presented for the cross section and double-helicity asymmetry (A(LL)) in inclusive pi(0) production at midrapidity from p + p collisions at root s = 510 GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The pi(0)A(LL) results follow an increasingly positive asymmetry trend with p(T) and root s with respect to the predictions and are …

Inclusive double-helicity asymmetries in neutral-pion and eta-meson production inp→+p→collisions ats=200  GeV

Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, A(LL), for pi(0) and eta production in root s = 200 GeV polarized p + p collisions. Comparison of the pi(0) results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, Delta G, in the proton in the probed Bjorken x range. The effect of adding the new 2009 pi(0) data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit Delta G(DSSV)([0.05,0.2]) = 0.06(-0.15)(+0.11) in the range 0.05 < x < 0.2, with the unce…

Transverse momentum of produced in pCu, pU, 16OCu, 16OU and 32SU collisions at 200 GeV per nucleon

Suppression of Back-to-Back Hadron Pairs at Forward Rapidity ind+AuCollisions atsNN=200  GeV

Back-to-back hadron pair yields in d + Au and p + p collisions at root S-NN = 200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity vertical bar eta vertical bar < 0: 35 and the associated hadron at forward rapidity (deuteron direction, 3.0< eta < 3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case, the yield of back-to-back hadron pairs in d + Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p + p collisions. The kinematics of these pairs is expected to probe partons in the Au nu…

Indication of electron neutrino appearance from an accelerator-produced off-axis muon neutrino beam

The T2K experiment observes indications of $\nu_\mu\rightarrow \nu_e$ appearance in data accumulated with $1.43\times10^{20}$ protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with $|\Delta m_{23}^2|=2.4\times10^{-3}$ eV$^2$, $\sin^2 2\theta_{23}=1$ and $\sin^2 2\theta_{13}=0$, the expected number of such events is 1.5$\pm$0.3(syst.). Under this hypothesis, the probability to observe six or more candidate events is 7$\times10^{-3}$, equivalent to 2.5$\sigma$ significance. At 90% C.L., the data are consistent with 0.03(0.04)$<\sin^2 2\theta_{13}<$ 0.28(0.34) for $\delta_{\rm CP}=0$ and a normal (inverted) hierarchy.

Low-mass vector-meson production at forward rapidity inp+pcollisions ats=200  GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson ,omega, rho, and phi, production through the dimuon decay channel at forward rapidity (1.2 mu mu) = 80 +/- 6(stat) +/- 12(syst)nb and d sigma/dy(phi -> mu mu) = 27 +/- 3(stat) +/- 4(syst)nb. These results are compared with midrapidity measurements and calculations.

Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K

This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C$_8$H$_8$) target. The data were taken between years 2010 and 2013, corresponding to approximately 6$\times10^{20}$ protons on target. Thanks to their exploration of the proton kinematics and of kinematic imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measureme…

Measurement of theνμcharged-current quasielastic cross section on carbon with the ND280 detector at T2K

We thank the J-PARC staff for superb accelerator performance and the CERN NA61 Collaboration for providing valuable particle production data. We acknowledge the support of MEXT, Japan; NSERC, NRC, and CFI, Canada; CEA and CNRS/IN2P3, France; DFG, Germany; INFN, Italy; National Science Centre (NCN), Poland; RSF, RFBR, and MES, Russia; MINECO and ERDF funds, Spain; SNSF and SER, Switzerland; STFC, UK; and DOE, USA. We also thank CERN for the UA1/NOMAD magnet, DESY for the HERA-B magnet mover system, NII for SINET4, the WestGrid and SciNet consortia in Compute Canada, GridPP, UK. In addition participation of individual researchers and institutions has been further supported by funds from ERC (…

Measurement of Long-Range Angular Correlation and Quadrupole Anisotropy of Pions and (Anti)Protons in Centrald+AuCollisions atsNN=200GeV

We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central d+Au and minimum bias p+p collisions at sqrt[s_{NN}]=200 GeV. The charged hadron is measured at midrapidity |η| 2.75 is observed in d+Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength v_{2} for inclusive charged hadrons at midrapidity up to p_{T}=4.5 GeV/c. We also present the measurement of v_{2} for identified π^{±} and (anti)protons in central d+Au collisions, and observe a mass-ordering pattern similar to that seen in heavy-ion collisions. These results are compared with viscous hydrodynamic calc…

First Muon-Neutrino Disappearance Study with an Off-Axis Beam

We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43 × 10(20) protons on target, we observe 31 fully-contained single μ-like ring events in Super-Kamiokande, compared with an expectation of 104 ± 14(syst) events without neutrino oscillations. The best-fit point for two-flavor νμ → ντ oscillations is sin 2(2θ(23)) = 0.98 and |Δm(2)(32)| = 2.65 × 10(−3) eV2. The boundary of the 90% confidence region includes the points (sin2 (2θ(23)), |Δm(2)(32)|) = (1.0, 3.1 × 10(−3) eV2), (0.84, …

Precise measurement of the neutrino mixing parameter θ23 from muon neutrino disappearance in an off-axis beam

New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter theta_{23}. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57 x 10^{20} protons on target, T2K has fit the energy-dependent nu_mu oscillation probability to determine oscillation parameters. Marginalizing over the values of other oscillation parameters yields sin^2 (theta_{23}) = 0.514 +0.055/-0.056 (0.511 +- 0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Delta m^2_{32} = (2.51 +- 0.10) x 10^{-3} eV^2/c^4 (inverted hierarchy: Delta m^2_{13} = (2.48 +- 0.10) …

Measurements of Higher Order Flow Harmonics inAu+AuCollisions atsNN=200  GeV

Flow coefficients nu(n) for n = 2, 3, 4, characterizing the anisotropic collective flow in Au + Au collisions at root s(NN) = 200 GeV, are measured relative to event planes Psi(n), determined at large rapidity. We report nu(n) as a function of transverse momentum and collision centrality, and study the correlations among the event planes of different order n. The nu(n) are well described by hydrodynamic models which employ a Glauber Monte Carlo initial state geometry with fluctuations, providing additional constraining power on the interplay between initial conditions and the effects of viscosity as the system evolves. This new constraint can serve to improve the precision of the extracted …

Spectra and ratios of identified particles in Au+Au andd+Au collisions atsNN=200GeV

The transverse momentum (p(T)) spectra and ratios of identified charged hadrons (pi(+/-), K-+/-, p, (p) over bar) produced in root s(NN) = 200 GeV Au + Au and d + Au collisions are reported in five different centrality classes for each collision species. The measurements of pions and protons are reported up to p(T) = 6 GeV/c (5 GeV/c), and the measurements of kaons are reported up to p(T) = 4 GeV/c (3.5 GeV/c) in Au + Au (d + Au) collisions. In the intermediate p(T) region, between 2 and 5 GeV/c, a significant enhancement of baryon-to-meson ratios compared to those measured in p + p collisions is observed. This enhancement is present in both Au + Au and d + Au collisions and increases as th…

Deviation from quark number scaling of the anisotropy parameterv2of pions, kaons, and protons inAu+Aucollisions atsNN=200GeV

Measurements of the anisotropy parameter v(2) of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum p(T), and transverse kinetic energy KET at midrapidity (vertical bar eta vertical bar < 0.35) in Au + Au collisions at root s(N N) = 200 GeV are presented. Pions and protons are identified up to p(T) = 6 GeV/c, and kaons up to p(T) = 4 GeV/c, by combining information from time-of-flight and aerogel Cerenkov detectors in the PHENIX Experiment. The scaling of v(2) with the number of valence quarks (n(q)) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observ…

Nuclear modification factors ofϕmesons ind+Au,Cu+Cu, andAu+Aucollisions atsNN=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed systematic measurements of phi meson production in the K+K- decay channel at midrapidity in p + p, d + Au, Cu + Cu, and Au + Au collisions at root s(NN) = 200 GeV. Results are presented on the phi invariant yield and the nuclear modification factor R-AA for Au + Au and Cu + Cu, and R-dA for d + Au collisions, studied as a function of transverse momentum (1 < p(T) < 7 GeV/c) and centrality. In central and midcentral Au + Au collisions, the R-AA of phi exhibits a suppression relative to expectations from binary scaled p + p results. The amount of suppression is smaller than that of the pi(0) and the. in the intermediat…

Azimuthal anisotropy ofπ0andηmesons in Au + Au collisions atsNN=200GeV

The azimuthal anisotropy coefficients v2 and v4 of p 0 and. mesons are measured in Au + Au collisions at root s(NN) = 200 GeV as a function of transverse momentum p(T) (1-14 GeV/c) and centrality. The extracted v(2) coefficients are found to be consistent between the two meson species over the measured p(T) range. The ratio of v(4)/v(2)(2) for pi(0) mesons is found to be independent of p(T) for 1- 9 GeV/c, implying a lack of sensitivity of the ratio to the change of underlying physics with p(T). Furthermore, the ratio of v(4)/v(2)(2) is systematically larger in central collisions, which may reflect the combined effects of fluctuations in the initial collision geometry and finite viscosity i…

Search for CP Violation in Neutrino and Antineutrino Oscillations by the T2K Experiment with 2.2×1021 Protons on Target

The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of $14.7(7.6)\times 10^{20}$ protons on target in neutrino (antineutrino) mode, 89 $\nu_e$ candidates and 7 anti-$\nu_e$ candidates were observed while 67.5 and 9.0 are expected for $\delta_{CP}=0$ and normal mass ordering. The obtained $2\sigma$ confidence interval for the $CP$ violating phase, $\delta_{CP}$, does not include the $CP$-conserving cases ($\delta_{CP}=0,\pi$). The best-fit values of other parameters are $\sin^2\theta_{23} = 0.526^{+0.032}_{-0.036}$ and $\Delta m^2_{32}=2.463\pm0.065\times10^{-3} \mathrm{eV}^2/c^4$.

Observation of Direct-Photon Collective Flow inAu+AuCollisions atsNN=200  GeV

The second Fourier component v(2) of the azimuthal anisotropy with respect to the reaction plane is measured for direct photons at midrapidity and transverse momentum (p(T)) of 1-12 GeV/c in Au + Au collisions at root s(NN) = 200 GeV. Previous measurements of this quantity for hadrons with p(T) 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for p(T) > 4 GeV/c the anisotropy for direct photons is consistent with zero, which is as expected if the dominant source of direct photons is initial hard scattering. However, in the p(T) < 4 GeV/c re…

Measurement of the neutrino-oxygen neutral-current interaction cross section by observing nuclear deexcitation gamma rays

We report the first measurement of the neutrino-oxygen neutral-current quasielastic (NCQE) cross section. It is obtained by observing nuclear deexcitation $\gamma$-rays which follow neutrino-oxygen interactions at the Super-Kamiokande water Cherenkov detector. We use T2K data corresponding to $3.01 \times 10^{20}$ protons on target. By selecting only events during the T2K beam window and with well-reconstructed vertices in the fiducial volume, the large background rate from natural radioactivity is dramatically reduced. We observe 43 events in the $4-30$ MeV reconstructed energy window, compared with an expectation of 51.0, which includes an estimated 16.2 background events. The background …

First measurement of the charged current ν¯μ double differential cross section on a water target without pions in the final state

We thank the J-PARC staff for superb accelerator performance. We thank the CERN NA61/SHINE Collaboration for providing valuable particle production data. We acknowledge the support of MEXT, Japan; NSERC (Grant No. SAPPJ-2014-00031), the NRC and CFI, Canada; the CEA and CNRS/IN2P3, France; the DFG, Germany; the INFN, Italy; the National Science Centre and Ministry of Science and Higher Education, Poland; the RSF (Grant No. 19-12-00325) and the Ministry of Science and Higher Education, Russia; MINECO and ERDF funds, Spain; the SNSF and SERI, Switzerland; the STFC, UK; and the DOE, USA. We also thank CERN for the UA1/NOMAD magnet, DESY for the HERA-B magnet mover system, NII for SINET4, the We…

Cross section and longitudinal single-spin asymmetry AL for forward W±→μ±ν production in polarized p+p collisions at s=510  GeV

We have measured the cross section and single-spin asymmetries from forward W±→μ±ν production in longitudinally polarized p+p collisions at s=510 GeV using the PHENIX detector at the Relativistic Heavy Ion Collider. The cross sections are consistent with previous measurements at this collision energy, while the most forward and backward longitudinal single spin asymmetries provide new insights into the sea quark helicities in the proton. The charge of the W bosons provides a natural flavor separation of the participating partons. © 2018 authors. Published by the American Physical Society.

Neutrino Physics with JUNO

The Jiangmen Underground Neutrino Observatory (JUNO), a 20 kton multi-purpose underground liquid scintillator detector, was proposed with the determination of the neutrino mass hierarchy as a primary physics goal. It is also capable of observing neutrinos from terrestrial and extra-terrestrial sources, including supernova burst neutrinos, diffuse supernova neutrino background, geoneutrinos, atmospheric neutrinos, solar neutrinos, as well as exotic searches such as nucleon decays, dark matter, sterile neutrinos, etc. We present the physics motivations and the anticipated performance of the JUNO detector for various proposed measurements. By detecting reactor antineutrinos from two power plan…

Search for dark photons from neutral meson decays inp+pandd+Aucollisions atsNN=200 GeV

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g−2)μ deviates from SM calculations by 3.6σ. Several theoretical models attribute this to the existence of a “dark photon,” an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in π0,η→γe+e− decays and obtained upper limits of O(2×10−6) on U−γ mixing at 90% C.L. for the mass range 30<mU<90 MeV/c2. Combined with other experimental limits, the remaining region in the U−γ mixing parameter space that can explain the (g−2)μ deviation from its SM…

Nonperturbative-transverse-momentum effects and evolution in dihadron and direct photon-hadron angular correlations in p+p collisions at s=510  GeV

Dihadron and isolated direct photon-hadron angular correlations are measured in $p$$+$$p$ collisions at $\sqrt{s}=510$ GeV. Correlations of charged hadrons of $0.7<p_T<10$ GeV/$c$ with $\pi^0$ mesons of $4<p_T<15$ GeV/$c$ or isolated direct photons of $7<p_T<15$ GeV/$c$ are used to study nonperturbative effects generated by initial-state partonic transverse momentum and final-state transverse momentum from fragmentation. The nonperturbative behavior is characterized by measuring the out-of-plane transverse momentum component $p_{\rm out}$ perpendicular to the axis of the trigger particle, which is the high-$p_T$ direct photon or $\pi^0$. Nonperturbative evolution effects are extracted from …

Nuclear matter effects onJ/ψproduction in asymmetric Cu + Au collisions atsNN=200GeV

We report on J/psi production from asymmetric Cu + Au heavy-ion collisions at root S-NN = 200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of J/psi yields in Cu + Au collisions in the Au-going direction is found to be comparable to that inAu + Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, J/psi production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-x gluon suppression in the larger Au nucleus.

Dielectron production in Au + Au collisions atsNN=200GeV

We present measurements of e+e- production at midrapidity in Au+Au collisions at sNN=200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (mee<5 GeV/c2) and pair transverse momentum (pT<5 GeV/c) for minimum bias and for five centrality classes. The e+e- yield is compared to the expectations from known sources. In the low-mass region (mee=0.30-0.76 GeV/c2) there is an enhancement that increases with centrality and is distributed over the entire pair pT range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to 2.3±0.4(stat)±0.4(syst)±0.2(model) or to 1.7±0.3(stat)±0.3(syst)±0.2(model) for min…

Transverse-momentum dependence of theJ/ψnuclear modification ind+Au collisions atsNN=200GeV

We present measured J/psi production rates in d + Au collisions at root s(NN) = 200 GeV over broad ranges of transverse momentum (p(T) = 0-14 GeV/c) and rapidity (-2.2 1) for p(T) > 2 GeV/c. The observed enhancement at negative rapidity has implications for the interpretation of the observed modification in heavy-ion collisions at high p(T). DOI: 10.1103/PhysRevC.87.034904

Measurement ofKS0andK*0inp+p,d+Au, and Cu + Cu collisions atsNN=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of K-S(0) and K*(0) meson production at midrapidity in p + p, d + Au, and Cu + Cu collisions at root s(NN) = 200 GeV. The K-S(0) and K*(0) mesons are reconstructed via their K-S(0) -> pi(0)(-> gamma gamma) pi(0)(-> gamma gamma) and K*(0) -> K-+/-pi(-/+) decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of K-S(0) and K*(0) mesons in d + Au and Cu + Cu collisions at different centralities. In the d + Au collisions, the nuclear modification factor of K-S(0) and K*(0) mesons is almost constant as a function of transverse momentum a…

Measurement of jet-medium interactions via direct photon-hadron correlations in Au+Au and d+Au collisions at sNN=200 GeV

We present direct photon-hadron correlations in 200 GeV/A Au+Au, d+Au, and p+p collisions, for direct photon pT from 5–12 GeV/c, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in d+Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au+Au compared to p+p and d+Au. As the momentum fraction decreases, the yield of hadrons in Au+Au increases to an excess over the yield in p+p collisions. The excess is at large angles and at low hadron pT and is most pronounced for hadrons associated with lower momentum direct …

J/ψsuppression at forward rapidity in Au+Au collisions atsNN=39and 62.4 GeV

We present measurements of the J/psi invariant yields in root s(NN) = 39 and 62.4 GeV Au + Au collisions at forward rapidity (1.2 < vertical bar y vertical bar < 2.2). Invariant yields are presented as a function of both collision centrality and transverse momentum. Nuclear modifications are obtained for central relative to peripheral Au + Au collisions (R-CP) and for various centrality selections in Au + Au relative to scaled p + p cross sections obtained from other measurements (R-AA). The observed suppression patterns at 39 and 62.4 GeV are quite similar to those previously measured at 200 GeV. This similar suppression presents a challenge to theoretical models that contain various compe…

Centrality dependence of low-momentum direct-photon production inAu+Aucollisions atsNN=200 GeV

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au+Au collisions at sNN−−−√=200 GeV down to pT=0.4 GeV/c. Photons are detected via photon conversions to e+e− pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT. We find an excess of direct photons above the Ncoll-scaled yield measured in p+p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240MeV/c in the pT range 0.6–2.0 GeV/c. While the shape of the pT distribution is independent of centrality within the experimental uncert…

Charged-pion cross sections and double-helicity asymmetries in polarizedp+pcollisions ats=200  GeV

We present midrapidity charged-pion invariant cross sections, the ratio of the pi(-) to pi(+) cross sections and the charge-separated double-spin asymmetries in polarized p + p collisions at root s = p + 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The char…

Transverse momentum of j/$\psi$ produced in oxygen-uranium collisions at 200 GeV per nucleon

Abstract The study of the J ψ transverse momentum distribution in oxygen-uranium reactions at 200 GeV/nucleon shows that 〈PT〉 and 〈PT2〉 increase with the transverse energy of the reaction. Muon pairs in the mass continuum do not exhibit the same behaviour. The comparison of the J ψ production rates in central and peripheral collisions shows a significant diminution for low PT central events.

Measurement of the Inclusive NuMu Charged Current Cross Section on Carbon in the Near Detector of the T2K Experiment

T2K has performed the first measurement of nu(mu) inclusive charged current interactions on carbon at neutrino energies of similar to 1 GeV where the measurement is reported as a flux-averaged double differential cross section in muon momentum and angle. The flux is predicted by the beam Monte Carlo and external data, including the results from the NA61/SHINE experiment. The data used for this measurement were taken in 2010 and 2011, with a total of 10.8 x 10(19) protons-on-target. The analysis is performed on 4485 inclusive charged current interaction candidates selected in the most upstream fine-grained scintillator detector of the near detector. The flux-averaged total cross section is (…

Ground and excited state charmonium production inp+pcollisions ats=200  GeV

We report on charmonium measurements [J/psi (1S), psi' (2S), and chi(c) (1P)] in p + p collisions at root s = 200 GeV. We find that the fraction of J/psi coming from the feed-down decay of psi' and chi(c) in the midrapidity region (vertical bar y vertical bar < 0: 35) is 9.6 +/- 2.4% and 32 +/- 9%, respectively. We also present the p(T) and rapidity dependencies of the J/psi yield measured via dielectron decay at midrapidity (vertical bar y vertical bar < 0.35) and via dimuon decay at forward rapidity (1.2 < vertical bar y vertical bar < 2.2). The statistical precision greatly exceeds that reported in our previous publication [Phys. Rev. Lett. 98, 232002 (2007)]. The new results are compare…

First measurement of the muon neutrino charged current single pion production cross section on water with the T2K near detector

The T2K off-axis near detector, ND280, is used to make the first differential cross section measurements of muon neutrino charged current single positive pion production on a water target at energies ∼0.8  GeV. The differential measurements are presented as a function of the muon and pion kinematics, in the restricted phase space defined by pπ+>200  MeV/c, pμ>200  MeV/c, cos(θπ+)>0.3 and cos(θμ)>0.3. The total flux integrated νμ charged current single positive pion production cross section on water in the restricted phase space is measured to be ⟨σ⟩ϕ=4.25±0.48(stat)±1.56(syst)×10-40  cm2/nucleon. The total cross section is consistent with the NEUT prediction (5.03×10-40  cm2/nucleon) and 2σ…

Measurement of the Inclusive Electron Neutrino Charged Current Cross Section on Carbon with the T2K Near Detector

The T2K off-axis near detector, ND280, is used to make the first differential cross-section measurements of electron neutrino charged current interactions at energies ~1 GeV as a function of electron momentum, electron scattering angle and four-momentum transfer of the interaction. The total flux-averaged $\nu_e$ charged current cross-section on carbon is measured to be $1.11\pm0.09~(stat)\pm0.18~(syst)\times10^{-38} cm^2/nucleon$. The differential and total cross-section measurements agree with the predictions of two leading neutrino interaction generators, NEUT and GENIE. The NEUT prediction is $1.23\times10^{-38} cm^2/nucleon$ and the GENIE prediction is $1.08\times10^{-38} cm^2/nucleon$…

Measurements of Elliptic and Triangular Flow in High-MultiplicityHe3+AuCollisions atsNN=200  GeV

We present the first measurement of elliptic ($v_2$) and triangular ($v_3$) flow in high-multiplicity $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in $^{3}$He$+$Au and in $p$$+$$p$ collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the $^{3}$He$+$Au system. The collective behavior is quantified in terms of elliptic $v_2$ and triangular $v_3$ anisotropy coefficients measured with respect to their corresponding event planes. The $v_2$ values are comparable to those previously measured in $d$$+$Au collis…

The T2K Experiment

The T2K experiment is a long-baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle {\theta}_{13} by observing {\nu}_e appearance in a {\nu}_{\mu} beam. It also aims to make a precision measurement of the known oscillation parameters, {\Delta}m^{2}_{23} and sin^{2} 2{\theta}_{23}, via {\nu}_{\mu} disappearance studies. Other goals of the experiment include various neutrino cross section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande)…

Evidence of Electron Neutrino Appearance in a Muon Neutrino Beam

The T2K Collaboration reports evidence for electron neutrino appearance at the atmospheric mass splitting, vertical bar Delta m(32)(2)vertical bar approximate to 2.4 X 10(-3) eV(2). An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beam's origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of 3.3 +/- 0.4(syst) events is expected. The background-only hypothesis is rejected with a p value of 0.0…

Measurement of the single π0 production rate in neutral current neutrino interactions on water

The single π0 production rate in neutral current neutrino interactions on water in a neutrino beam with a peak neutrino energy of 0.6 GeV has been measured using the POD, one of the subdetectors of the T2K near detector. The production rate was measured for data taking periods when the POD contained water (2.64×1020 protons-on-target) and also periods without water (3.49×1020 protons-on-target). A measurement of the neutral current single π0 production rate on water is made using appropriate subtraction of the production rate with water in from the rate with water out of the target region. The subtraction analysis yields 106±41±69 signal events where the uncertainties are statistical (stat.…

Elliptic and Hexadecapole Flow of Charged Hadrons inAu+AuCollisions atsNN=200  GeV

Differential measurements of the elliptic (upsilon(2)) and hexadecapole (upsilon(4)) Fourier flow coefficients are reported for charged hadrons as a function of transverse momentum (p(T)) and collision centrality or number of participant nucleons (N-part) for Au + Au collisions at root s(NN) = 200 GeV/ The upsilon(2,4) measurements at pseudorapidity vertical bar eta vertical bar <= 0.35, obtained with four separate reaction-plane detectors positioned in the range 1.0 < vertical bar eta vertical bar < 3.9, show good agreement, indicating the absence of significant Delta eta-dependent nonflow correlations. Sizable values for upsilon(4)(p(T)) are observed with a ratio upsilon(4)(p(T), N-part)/…

Production of π0 and η mesons in Cu+Au collisions at sNN=200GeV

Production of π0 and η mesons has been measured at midrapidity in Cu+Au collisions at sNN=200GeV. Measurements were performed in π0(η)→γγ decay channel in the 1(2)-20GeV/c transverse momentum range. A strong suppression is observed for π0 and η meson production at high transverse momentum in central Cu+Au collisions relative to the p+p results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au+Au with comparable nuclear overlap. The η/π0 ratio measured as a function of transverse momentum is consistent with mT-scaling parametrization down to pT=2GeV/c, its asymptotic value is constant and consistent with Au+Au and p+p and does not show…