0000000000038964
AUTHOR
E. G. Thomas
GW170817: Implications for the Stochastic Gravitational-Wave Background from Compact Binary Coalescences
The LIGO Scientific and Virgo Collaborations have announced the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star background will add to the background from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude $\Omega_{\rm…
Deployment of the ATLAS high level trigger
The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS high-level triggers (HLT). The next steps are deployment on the pre-series farms in the experimental area during 2005, commissioning and cosmics tests in 2006 and collisions in 2007. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, selection algorithms, testing, software distribution, installation and improvements
Model-Independent Evidence forJ/ψpContributions toΛb0→J/ψpK−Decays
The data sample of Lambda(0)(b) -> J/psi pK(-) decays acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb(-1), is inspected for the presence of J/psi p or J/psi K- contributions with minimal assumptions about K(-)p contributions. It is demonstrated at more than nine standard deviations that Lambda(0)(b) -> J/psi pK(-) decays cannot be described with K- p contributions alone, and that J/psi K- contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for P-c(+)-> J/psi p charmonium-pentaquark states in the same data sample.
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually-unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generic…
Overview of the high-level trigger electron and photon selection for the ATLAS experiment at the LHC
texte intégral : http://cdsweb.cern.ch/record/846438; The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of efficiently selecting interesting candidate events in$pp$collisions at 14 TeV center-of-mass energy, whilst rejecting the enormous number of background events. The High-Level Trigger (HLT$=$second level trigger and Event Filter), which is a software based trigger will need to reduce the level-1 output rate of$approx75$kHz to$approx200$Hz written out to mass storage. In this talk an overview of the current physics and system performance of the HLT selection for electrons and photons is given. The performance has been evaluated using Monte Carlo simulations …
Tests of General Relativity with GW170817
The recent discovery by Advanced LIGO and Advanced Virgo of a gravitational wave signal from a binary neutron star inspiral has enabled tests of general relativity (GR) with this new type of source. This source, for the first time, permits tests of strong-field dynamics of compact binaries in presence of matter. In this paper, we place constraints on the dipole radiation and possible deviations from GR in the post-Newtonian coefficients that govern the inspiral regime. Bounds on modified dispersion of gravitational waves are obtained; in combination with information from the observed electromagnetic counterpart we can also constrain effects due to large extra dimensions. Finally, the polari…
First observation of the rareB+→D+K+π−decay
The B+→D+K+π- decay is observed in a data sample corresponding to 3.0 fb-1 of pp collision data recorded by the LHCb experiment during 2011 and 2012. The signal significance is 8σ and the branching fraction is measured to be B(B+→D+K+π-)=(5.31±0.90±0.48±0.35)×10-6, where the uncertainties are statistical, systematic and due to the normalization mode B+→D-K+π+, respectively. The Dalitz plot appears to be dominated by broad structures. Angular distributions are exploited to search for quasi-two-body contributions from B+→D2∗(2460)0K+ and B+→D+K∗(892)0 decays. No significant signals are observed and upper limits are set on their branching fractions.
Measurement ofCPviolation parameters inB0→DK*0decays
An analysis of B0→DK*0 decays is presented, where D represents an admixture of D0 and D¯0 mesons reconstructed in four separate final states: K−π+, π−K+, K+K− and π+π−. The data sample corresponds to 3.0 fb−1 of proton-proton collision, collected by the LHCb experiment. Measurements of several observables are performed, including CP asymmetries. The most precise determination is presented of rB(DK*0), the magnitude of the ratio of the amplitudes of the decay B0→DK+π− with a b→u or a b→c transition, in a Kπ mass region of ±50 MeV/c2 around the K∗(892) mass and for an absolute value of the cosine of the K*0 helicity angle larger than 0.4.
Deployment of the ATLAS High-Level Trigger
The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS High-Level Trigger (HLT). The next steps are deployment on the pre-series farms in the experimental area during 2005, commissioning and cosmics tests with the full detector in 2006 and collisions in 2007. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, integration of selection algorithms, testing, software distribution, installation and improvements.
Studies of the resonance structure inD0→KS0K±π∓decays
Amplitude models are constructed to describe the resonance structure of D0→ K-π+π+π- and D0→ K+π-π-π+ decays using pp collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb- 1. The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes D0→ a1(1260) +K- and D0→ K1(1270 / 1400) +π- being prominent in D0→ K-π+π+π- and D0→ K+π-π-π+, respectively. Precise measurements of the lineshape parameters and couplings of the a1(1260) +, K1(1270) - and K(1460) - resonances are made, and a quasi model-independent study of the K(1460) - resonance is performed. The coher…
GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence
On August 14, 2017 at 10 30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of 1 in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30.5-3.0+5.7M and 25.3-4.2+2.8M (at the 90% credible level). The luminosity distance of the source is 540-210+130 Mpc, corresponding to a redshift of z=0.11-0.04+0.03. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible regio…
Measurement of the Ratio of Branching FractionsB(B¯0→D*+τ−ν¯τ)/B(B¯0→D*+μ−ν¯μ)
The branching fraction ratio R(D-*) = B((B) over bar (0) -> D-*(+)tau(-)(nu) over bar (tau))/B((B) over bar (0) -> D-*(+)mu(-)(nu) over bar (mu)) is measured using a sample of proton-proton collision data corresponding to 3.0 fb(-1) of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode tau(-) -> mu(-)(nu) over bar (mu)nu(tau). The semitauonic decay is sensitive to contributions from non-standard-model particles that preferentially couple to the third generation of fermions, in particular, Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate (B) over bar (0) decays gives R(D-*) =…
Constraining the p -Mode– g -Mode Tidal Instability with GW170817
We analyze the impact of a proposed tidal instability coupling p modes and g modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: An overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes factor (lnB!pgpg) comparing our p-g model to a standard one. We find that the observed signal is consistent with waveform models that neglect p-g effects, with lnB!pgpg=…
Search for weakly decaying b -flavored pentaquarks
Investigations of the existence of pentaquark states containing a single $b$ (anti)quark decaying weakly into four specific final states J/$\psi K^+\pi^- p$, J/$\psi K^- \pi^- p$, J/$\psi K^- \pi^+ p$, and $J/\psi \phi (1020) p$ are reported. The data sample corresponds to an integrated luminosity of 3.0/fb in 7 and 8 TeV pp collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the $\Lambda_b$.
Implementation and performance of the third level muon trigger of the ATLAS experiment at LHC
The trigger system of the ATLAS experiment at the LHC aims at a high selectivity in order to keep the full physics potential while reducing the 40 MHz initial event rate imposed by the LHC bunch crossing down to /spl sim/100 Hz, as required by the data acquisition system. Algorithms working in the final stage of the trigger environment (Event Filter) are implemented to run both in a "wrapped" mode (reconstructing tracks in the entire Muon Spectrometer) and in a "seeded" mode (according to a dedicated strategy that performs pattern recognition only in regions of the detector where trigger hypotheses have been produced at earlier stages). The working principles of the offline muon reconstruct…
GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
On August 17, 2017 at 12-41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per 8.0×104 years. We infer the component masses of the binary to be between 0.86 and 2.26 M, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17-1.60 M, with the total mass of the system 2.74-0.01+0.04M. The source was localized within a sky region of 28 deg2 (90% probabili…
Measurement of the Difference of Time-IntegratedCPAsymmetries inD0→K−K+andD0→π−π+Decays
A search for CP violation in $D^0 \rightarrow K^{-} K^{+} $ and $D^0 \rightarrow \pi^{-} \pi^{+} $ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of $3~fb^{-1}$, collected using the LHCb detector at centre-of-mass energies of 7 and $8~$TeV. The flavour of the charm meson is inferred from the charge of the pion in $D^{*+}\rightarrow D^0\pi^+$ and $D^{*-}\rightarrow \bar{D^0}\pi^{-}$ decays. The difference between the CP asymmetries in $D^0 \rightarrow K^{-} K^{+} $ and $D^0 \rightarrow \pi^{-} \pi^{+} $ decays, $\Delta A_{CP} \equiv A_{CP}(K^{-} K^{+}) - A_{CP}(\pi^{-} \pi^{+})$, is measured to be $\left( -0.10 \pm 0.08(stat) \pm 0.03(syst) \right) \…
Amplitude analysis ofB−→D+π−π−decays
The Dalitz plot analysis technique is used to study the resonant substructures of $B^{-} \to D^{+} \pi^{-} \pi^{-}$ decays in a data sample corresponding to 3.0 ${\rm fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. A model-independent analysis of the angular moments demonstrates the presence of resonances with spins 1, 2 and 3 at high $D^{+}\pi^{-}$ mass. The data are fitted with an amplitude model composed of a quasi-model-independent function to describe the $D^{+}\pi^{-}$ S-wave together with virtual contributions from the $D^{*}(2007)^{0}$ and $B^{*0}$ states, and components corresponding to the $D^{*}_{2}(2460)^{0}$, $D^{*}_{1}(2680)^{0}$, $D^{*}_…
Study of J/ψ Production in Jets
The production of $J/\psi$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J/\psi$ meson, $z \equiv p_{\rm T}(J/\psi)/p_{\rm T}({\rm jet})$, is measured using jets with $p_{\rm T}({\rm jet}) > 20$ GeV in the pseudorapidity range $2.5 < \eta({\rm jet}) < 4.0$. The observed $z$ distribution for $J/\psi$ mesons produced in $b$-hadron decays is consistent with expectations. However, the results for prompt $J/\psi$ production do not agree with predictions based on fixed-order non-relativistic QCD. This is the first measurement o…
A Fermi Gamma-Ray Burst Monitor Search for Electromagnetic Signals Coincident with Gravitational-wave Candidates in Advanced LIGO's First Observing Run
We present a search for prompt gamma-ray counterparts to compact binary coalescence gravitational wave (GW) candidates from Advanced LIGO's first observing run (O1). As demonstrated by the multimessenger observations of GW170817/GRB 170817A, electromagnetic and GW observations provide complementary information about the astrophysical source and, in the case of weaker candidates, may strengthen the case for an astrophysical origin. Here we investigate low-significance GW candidates from the O1 compact-binary coalescence searches using the Fermi Gamma-ray Burst Monitor (GBM), leveraging its all-sky and broad energy coverage. Candidates are ranked and compared to background to measure signific…
GW170817: Measurements of Neutron Star Radii and Equation of State
On 17 August 2017, the LIGO and Virgo observatories made the first direct detection of gravitational waves from the coalescence of a neutron star binary system. The detection of this gravitational-wave signal, GW170817, offers a novel opportunity to directly probe the properties of matter at the extreme conditions found in the interior of these stars. The initial, minimal-assumption analysis of the LIGO and Virgo data placed constraints on the tidal effects of the coalescing bodies, which were then translated to constraints on neutron star radii. Here, we expand upon previous analyses by working under the hypothesis that both bodies were neutron stars that are described by the same equation…