High-statistics study of f0(1500) decay into π0π0

Abstract A partial-wave analysis of the reaction p p →π 0 π 0 π 0 has been performed using a high-quality high-statistics data set of 712 000 events. In addition to the f0(975) and f0(1300), the scalar resonance with mass m = (1500 ± 15) MeV and width Γ = (120 ± 25) MeV is necessary to describe the data.

E decays to ηππ in annihilation at rest

Abstract We have observed the ηπ + π − and ηπ 0 π 0 decay modes of the E meson in p p annihilation at rest into π + π − π 0 π 0 η . The mass and width of the E meson are 1409 ± 3 and 86 ± 10 MeV. The production and decay branching ratio is B( p p → Eππ)B(E → ηππ) = (3.3 ± 1.0) × 10 −3 . With a spin-parity analysis we determine that J P = 0 − . The observation of the ηπ 0 π 0 decay mode establishes that E is isoscalar ( C = +1). We find that E decays to η ( ππ ) s (where ( ππ ) s is an S-wave dipion) and πa 0 (980)(→ πη ) with a relative branching ratio of (78 ± 16) %. Using the K K π production and decay branching ratio measured earlier we determine that B[E → K K π] B[E → ηππ] = 0.61 ± 0.1…

Study of annihilation at rest into ωηπ0

Abstract We have studied p p annihilations at rest in liquid hydrogen into the final state ωηπ 0 where ω decays to π 0 γ . This reaction is dominated by the production of α 0 (980) and contributions from a 2 (1320) and b 1 0 (1235). Upper limits for the production of an axial vector h ′ 1 (1380) meson and vector mesons ω(1390), ω(1600), and φ(1680) decaying to ωη are given. The branching ratio of p p annihilation into ωηπ 0 was determined to be (0.68±0.01±0.05)%.

The pseudoscalar mixing angle ΘPS from ν and ν′ production in annihiltion at rest

Abstract We have determined ratios of branching ratios for p p annihilations at rest into π0η and π0η′, into ηη and ηη′, and into ωη and ωη′. All reactins are observed in two different all-neutral final states. The ratios permit a determination of the pseudoscalar mixing angle. We find ΘPS = −(17.3±1.8)°.

T2K neutrino flux prediction

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations using an off-axismuon neutrino beam with a peak energy of about 0.6 GeV that originates at the Japan Proton Accelerator Research Complex accelerator facility. Interactions of the neutrinos are observed at near detectors placed at 280 m from the production target and at the far detector-Super-Kamiokande-located 295 km away. The flux prediction is an essential part of the successful prediction of neutrino interaction rates at the T2K detectors and is an important input to T2K neutrino oscillation and cross section measurements. A FLUKA and GEANT3-based simulation models the physical processes involved in the neutrino producti…

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 …

New states as observed by the Crystal Barrel experiment

Abstract The Crystal Barrel Detector has been in operation since October 1989. Results on the analysis of the annihilation of protonium at rest into three pseudoscalars is presented. The π 0 π 0 π 0 final state confirms the existence of ƒ 2 (1520)→π 0 π 0 . In the ηη system of the π 0 ηη final state an isoscalar J PC = 0 ++ resonance with a mass of 1560 MeV/c 2 and a width of 245 MeV/c 2 is observed. The identification with ƒ 0 (1590) is doubtful since the ηη' decay is not observed with the corresponding strength. Our analysis yields an upper limit for the relative branching ratio BR(ƒ 0 (1560)→ηη') BR(ƒ 0 (1560)→ηη) .

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…

Test of chiral perturbation theory in η decays

The decay of the η-meson into three pions plays an important role as a test of low-energy QCD calculations in the framework of chiral perturbation theory. Previous experiments show results that are inconclusive or even contradictory. The Crystal Barrel experiment at LEAR has determined the braching ratiosΓ(η→3π0)/Γ(η→π+π−π0)=1.47±0.09±0.15 andΓ(η→γγ)/Γ(η→π+π−π0)=1.88±0.10±0.17 using its unique features to detect charged particles as well as neutral particles. The value for the first ratio agrees nicely with the theoretical predictions and solves previous experimental uncertainties. The second value, which yields a partial width ofΓ(η→π+π−π0)=(0.24±0.03) keV, shows that the same next-to-lead…

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 …

First T2K measurement of transverse kinematic imbalance in the muon-neutrino charged-current single- π+ production channel containing at least one proton

This paper reports the first T2K measurement of the transverse kinematic imbalance in the single-$\pi^+$ production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single $\pi^+$ and at least one proton in the final state, at the ND280 off-axis near detector of the T2K experiment. The extracted cross sections are compared to the predictions from different neutrino-nucleus interaction event generators. Overall, the results show a preference for models which have a more realistic treatment of nuclear medium effects including the initial nuclear state and final-state interactions.

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…

Antiproton-proton annihilation in-flight

This is an overview of the preliminary results of\(\bar pp\) annihilation at incident\(\bar p\) momenta of 600, 1200 and 1940 MeV/c(*). The data was taken at LEAR with the Crystal Barrel Detector (E. Akeret al.:Nucl. Instrum. Methods A,321, 108 (1992)). In the two pseudoscalar final states seven different channels are observable and their angular distributions are measured. They are compared to older data, if existent, and are found to be equal within the experimental errors. In the three-meson final states, an overview of the already examined final states is given. Striking signals in the Dalitz plots and invariant-mass projections for a set of final states are observed. In the final state…

Momentum dependence of the decay η→π+π−π0

Abstract The π 0 momentum dependence of the decay η → π + π − π 0 has been measured with the Crystal Barrel detector. The analysis is based on 3230 events. The results of this independent measurement are compared to new chiral perturbation theory calculations and previous measurements.

Antiproton annihilation at rest in liquid deuterium into π−π0π0pS

With the Crystal Barrel detector, the final state π−π0π0pS at rest in liquid deuterium was measured for the first time. A preliminary partial-wave analysis was performed, which required two interesting features: besides the ρ(770), a second pole was needed in the ππP-wave and a narrow resonance in the ππS-wave, slightly above 1500 MeV/c2. With the same parametrization a high-statistics π+π−π0 data set could also be well described.

Branching ratios for p annihilation at rest into two-body final states

Abstract Measurements of two-body branching ratios for p p annihilations at rest in liquid and gaseous (12 ρ STP ) hydrogen are reported. Channels studied are p p →π 0 π 0 ,π 0 η , K 0 S K 0 L , K + K − . The branching ratio for the π 0 π 0 channel in liquid H 2 is measured to be ( 6.14±0.40)×10 −4 . The results are compared with those from other experiments. The fraction of P-state annihilation for a range of target densities from 0.002 ρ STP to liquid H 2 is determined. Values obtained include 0.11±0.02 in liquid H 2 and 0.48±0.04 in 12 ρ STP H 2 gas.

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 $…

Evidence for two isospin zeroJ PC=2−+ mesons at 1645 and 1875 MeV

Data on\(\bar pp \to \eta \pi ^0 \pi ^0 \pi ^0 \) taken at beam momenta of 1.2 and 1.94 GeV/c reveal evidence for twoI=0JPC=2−+ resonances inηππ. The first, at 1645±14(stat.)±15(syst.) MeV with width 180−21+40±25 MeV, decays toα2(1320)π withL=0. It may be interpreted as the\(q\bar q^1 \)D2 partner ofπ2(1670). A strong signal is also observed just above threshold inf2(1270)η withL=0. It is 11–22 times stronger than is expected for the high mass tail of the 1645 MeV resonance. It can be fitted as a second 2−+ resonance at 1875±20±35 MeV with width 200±25±45 MeV. A third resonance havingJPC=2++ is observed at 2135±20±45 MeV withΛ=250±25±45 MeV, decaying to botha2(1320)π andf2(1270)η withL=1. T…

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…

New results from crystal barrel

Results are presented on meson spectroscopy, two-body final states and meson decay modes observed in\(\bar pp\) annhilation at rest by the Crystal Barrel experiment at LEAR.

High statistics study of ƒ0(1500)s decay into ηη

Abstract A partial wave analysis of the reaction p p →π o ηη has been performed, using a high quality, high statistics data set of 198,000 events. In addition to the ƒ 0 (1370), a second scalar resonance decaying into ηη, the ƒ 0 (1500), with mass m = (1505 ± 15) MeV and width Γ = (120 ± 30) MeV has to be introduced to describe the data.

High-statistics analysis of $$\bar pp \to \pi ^0 \pi ^0 \pi ^0 $$ at restat rest

Antiproton-proton annihilation at rest into 3π0 is analysed based on a data sample of about 500 000 high-quality 3π0 events. In this high-statistics Dalitz plot two structures in the region of π0π0 invariant masses of about 1500 MeV show up, a small band and a blob at higher masses. In a first attempt to describe the data two different models are used to parametrize the dynamical amplitudes leading to the same conclusion: the data require a 0+ + and also a 2+ + resonance in the 1500 MeV region.

Antiproton-proton annihilation at rest into KKπ0π0

Abstract The annihilation channel p p →K + K − π 0 in liquid hydrogen at rest has been studied with the Crystal Barrel detector at LEAR. The measured branching ratio is: BR ( p p → K + K − π 0 )=(2.37±0.15)×10 −3 . A partial wave analysis shows that this reaction is dominated by the π (K K ) S , K K ∗ (892) and π φ (1020) intermediate states. Weak signals are observed for π a 2 (1320), π f 2 (1270), π f 2 ′(1525) and K(Kπ) S . A satisfactory description of the Dalitz plot requires the introduction of π (K K ) P intermediate states with at least one pole.

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.

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) …

First observation of the production of nucleon resonances in antiproton annihilation in liquid deuterium

High-mass ϱ-meson states from p̄d-annihilation at rest into π−π0π0pspectator

Abstract A study of p -annihilation in liquid deuterium into π − π 0 π 0 and a spectator-proton is presented. A cut on the proton-momentum of ≤ 100 MeV/ c ensures that annihilation takes place on a quasi-free neutron. A partial wave analysis shows contributions from three vector mesons, with masses and widths of (763.7 ± 3.2; 152.8 ± 4.3), (1411 ± 14; 343 ± 20); (1780 −29 +37 ; 275 ± 45) MeV/ c 2 , respectively.

Measurement of the decay distribution of η′ → π+π−γ and evidence for the box anomaly

Abstract The distribution of m ( π + π − ) in the decay η ′ → π + π − γ has been measured with the Crystal Barrel detector. The results are based on a total of 7392 observed η′ decays. The box anomaly constant is extracted from this and its value is found to agree well with theoretical expectations. The pseudoscalar nonet parameters ( f 1 , f 8 and θ PS ) are determined. Finally, we find that there is a problem of consistency between QCD and the standard VDM assumption.

Partial-wave analysis of ππη in $$\bar pp$$ annihilation at restannihilation at rest

A new isovector scalar πη resonance with a mass of 1450 MeV is observed in a high-statistics study of\(\bar pp\) annihilation at rest into π0π0η.

P- versus S-wave at rest in LH2

Abstract The annihilation p p →π 0 π 0 was measured for antiprotons stopped in liquid hydrogen (LH2). This reaction is only allowed from odd angular momentum states of the p p - atom . The resulting branching ratio BR ( p p →π 0 π 0 ) LH 2 =(6.93±0.22 stat ±0.37 syst )×10 −4 , combined with a previous measurement of the branching ratio BR ( p p →π + π − ) 2 P in gas from the 2P-state of p p suggests a fraction of P-wave annihilation in LH2 of (28.8±3.5)%, much larger than the values obtained from other annihilation channels. A method of reconciling the contradictory results is discussed.

Antiproton-proton annihilation at rest into two mesons

Abstract Branching ratios for antiproton-proton annihilations at rest into two mesons are given. The data were obtained at LEAR by stopping antiprotons in a liquid hydrogen target. Both charged and neutral annihilation products were detected in the Crystal Barrel detector. Representative data are presented, and their bearing on the general picture of annihilation dynamics is discussed. In addition, preliminary branching ratios for two-body radiative annihilations are given.

Hidden and open $$\bar ss$$ production in $$\bar pp$$ annihilation at restannihilation at rest

New branching ratios for\(\bar pp\) annihilation at rest into final states with a\(K\bar K\) pair or φ-meson are being measured with the Crystal Barrel detector at LEAR. The yield of φγ, relative to ωγ, appears to violate the OZI rule as strongly as φπ relative to ωπ.

Final states with strangeness from Crystal Barrel and Asterix

Abstract We discuss φ production in p p annihilation at rest from the Asterix and Crystal Barrel experiments and compare the branching ratios to similar final states without strangeness. The ωπ 0 φπ 0 production ratio is unexpectedly low. In the search for new states, the φπ0 mass spectrum shows no evidence for a resonance in the 1450 MeV/c2 mass range but the K☆K0π0 Dalitz plot shows interesting structure.

Annihilation at rest of antiprotons and protons into neutral particles

Abstract Annihilation of antiprotons and protons at rest into neutral particles has been studied with the Crystal Barrel detector at LEAR. Annihilation frequencies are determined for final states containing π 0 , η , η ′ and ω mesons using a liquid and a room temperature, 12 bar, gaseous hydrogen target. Including annihilation frequencies for production of neutral kaons from other experiments, the identified reactions for annihilation in liquid hydrogen add up to a branching fraction of (3.56±0.28)% per annihilation compared to the frequency of (3.50±0.30)% with which we observe the all-neutral decay modes inclusively. Since the exclusive final states are normalized to the Crystal Barrel me…

The ρ-mass, width and line shape in annihilation at rest into π+π−π0

The rho mass, width and line shape in p(over)-bar-p annihilation at rest into pi(+)pi(-)pi(0)

Large underground, liquid based detectors for astro-particle physics in Europe: scientific case and prospects

This document reports on a series of experimental and theoretical studies conducted to assess the astro-particle physics potential of three future large-scale particle detectors proposed in Europe as next generation underground observatories. The proposed apparatus employ three different and, to some extent, complementary detection techniques: GLACIER (liquid Argon TPC), LENA (liquid scintillator) and MEMPHYS (\WC), based on the use of large mass of liquids as active detection media. The results of these studies are presented along with a critical discussion of the performance attainable by the three proposed approaches coupled to existing or planned underground laboratories, in relation to…

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 $1.08\times10^{-38} cm^2/nucleon$…

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…

Search for a new light gauge boson in decays of π0 and η

Abstract We have searched for new light gauge bosons produced in π 0 and η decays by studying the kinematically well-constrained reactions p p→π 0 π 0 π 0 and p p→π 0 π 0 η , where one π 0 or the η decays through the emission of a single photon recoiling against a missing state X (where X is a long-lived weakly interacting particle or X →ν ν ). No signal has been observed and branching ratio upper limits of 6 × 10 −5 at 90% C.L. have been obtained for masses of the gauge boson lying between ∼65 MeV and 125 MeV ( π 0 decay), and 6 × 10 −5 at 90% C.L. for X masses between ∼200 MeV and 525 MeV (η decay). The π 0 -decay limit represents a factor of 4 to 8 improvement when compared to the existi…

First observations of Pontecorvo reactions with a recoiling neutron

We report the first observations of Pontecorvo reactions of the type ¯pd →Xn. We fully reconstruct the outgoing meson and, for antiprotons stopped in liquid deuterium, we measure: BR(¯pd→π0)=(7.03±0.72)×10−6, BR(¯pd→ηn)=(3.19+0.48)×10−6, BR(¯pd→ωn)=(22.8+4.1)×10−6, BR(¯pd→η′n)14×10−6 (at 95% confidence level). Assuming charge independence, our result for¯ pd→π0n is compatible with measurements of the only other observed Pontecorvo reaction ¯pd → π−p. The experimental ratios between the above branching ratios are in fair agreement with both the statistical model and dynamical two-step models (assumingN¯ N annihilation into two mesons, with subsequent absorption of one meson on the remaining …