Measurement of the longitudinal spin asymmetries for weak boson production in proton-proton collisions at s=510\u2009\u2009GeV

We report new STAR measurements of the single-spin asymmetries AL for W+ and W- bosons produced in polarized proton-proton collisions at s=510\u2009\u2009GeV as a function of the decay-positron and decay-electron pseudorapidity. The data were obtained in 2013 and correspond to an integrated luminosity of 250\u2009\u2009pb-1. The results are combined with previous results obtained with 86\u2009\u2009pb-1. A comparison with theoretical expectations based on polarized lepton-nucleon deep-inelastic scattering and prior polarized proton-proton data suggests a difference between the u\uaf and d\uaf quark helicity distributions for 0.05<x<0.25. In addition, we report new results for the double-spin asymmetries ALL for W\ub1, as well as AL for Z/\u3b3* production and subsequent decay into electron-positron pairs

Measurements of the charge asymmetry in top-quark pair production in the dilepton final state at s √ =8 TeV with the ATLAS detector

Measurements of the top-antitop quark pair production charge asymmetry in the dilepton channel, characterized by two high-pT leptons (electrons or muons), are presented using data corresponding to an integrated luminosity of 20.3  fb−1 from pp collisions at a center-of-mass energy s√=8  TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the tt¯ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: AℓℓC based on the selected leptons and Att¯C based on the reconstructed tt¯ final state. The inclusive asymmetries are measured in the full phase space to be AℓℓC=0.008±0.006 and Att¯C=0.021±0.016, which are in agreement with the Standard Model predictions of AℓℓC=0.0064±0.0003 and Att¯C=0.0111±0.0004

Measurement of CP violation and constraints on the CKM angle γ in B± → DK± with D → K0Sπ+π− decays

A model-dependent amplitude analysis of B± → DK± with D → K0 Sπ+π− decays is performed using proton–proton collision data, corresponding to an integrated luminosity of 1 fb−1, recorded by LHCb at a centre-of-mass energy of 7 TeV in 2011. Values of the CP violation observables x± and y±, which are sensitive to the CKM angle γ, are measured to be x− = +0.027 ± 0.044+0.010 −0.008 ± 0.001, y− = +0.013 ± 0.048+0.009 −0.007 ± 0.003, x+ = −0.084 ± 0.045 ± 0.009 ± 0.005, y+ = −0.032 ± 0.048+0.010 −0.009 ± 0.008, where the first uncertainty is statistical, the second systematic and the third arises from the uncertainty of the D → K0 Sπ+π− amplitude model. The value of γ is determined to be (84+49 −42)◦, including all sources of uncertainty. Neutral D meson mixing is found to have negligible effect

Search for heavy particles decaying into a top-quark pair in the fully hadronic final state in pp collisions at s=13\u2009\u2009TeV with the ATLAS detector

A search for new particles decaying into a pair of top quarks is performed using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of root s = 13 TeV corresponding to an integrated luminosity of 36.1 fb(-1). Events consistent with top-quark pair production and the fully hadronic decay mode of the top quarks are selected by requiring multiple high transverse momentum jets including those containing b-hadrons. Two analysis techniques, exploiting dedicated top-quark pair reconstruction in different kinematic regimes, are used to optimize the search sensitivity to new hypothetical particles over a wide mass range. The invariant mass distribution of the two reconstructed top-quark candidates is examined for resonant production of new particles with various spins and decay widths. No significant deviation from the Standard Model prediction is observed and limits are set on the production cross-section times branching fraction for new hypothetical Z' bosons, dark-matter mediators, Kaluza-Klein gravitons and Kaluza-Klein gluons. By comparing with the predicted production cross sections, the Z' boson in the topcolor-assisted-technicolor model is excluded for masses up to 3.1-3.6 TeV, the dark-matter mediators in a simplified framework are excluded in the mass ranges from 0.8 to 0.9 TeV and from 2.0 to 2.2 TeV, and the Kaluza-Klein gluon is excluded for masses up to 3.4 TeV, depending on the decay widths of the particles

Search for the standard model Higgs boson produced in association with top quarks and decaying into a b¯b pair in pp collisions at √s=13 TeV with the ATLAS detector

A search for the standard model Higgs boson produced in association with a top-quark pair, t¯tH, is presented. The analysis uses 36.1  fb−1 of pp collision data at √s=13  TeV collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H→b¯b decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain b-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by t¯t+jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured t¯tH signal cross-section to the standard model expectation is found to be μ=0.84+0.64−0.61. A value of μ greater than 2.0 is excluded at 95% confidence level (C.L.) while the expected upper limit is μ<1.2 in the absence of a t¯tH signal.We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZS, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, USA. In addition, individual groups and members have received support from BCKDF, the Canada Council, CANARIE, CRC, Compute Canada, FQRNT, and the Ontario Innovation Trust, Canada; EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Sklodowska-Curie Actions, European Union; Investissements d'Avenir Labex and Idex, ANR, Region Auvergne and Fondation Partager le Savoir, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF; BSF, GIF and Minerva, Israel; BRF, Norway; CERCA Programme Generalitat de Catalunya, Generalitat Valenciana, Spain; the Royal Society and Leverhulme Trust, United Kingdom. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), Ainfo:eu-repo/semantics/publishedVersio

Beam Spin Asymmetry in Semi-Inclusive Electroproduction of Hadron Pairs

International audienceA first measurement of the longitudinal beam spin asymmetry ALU in the semi-inclusive electroproduction of pairs of charged pions is reported. ALU is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function e(x). Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498-GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the ALUsinϕR moments are extracted for the kinematic variables of interest in the valence quark region. The understanding of dihadron production is essential for the interpretation of observables in single-hadron production in semi-inclusive DIS, and pioneering measurements of single-spin asymmetries in dihadron production open a new avenue in studies of QCD dynamics

Erratum: Measurement of the -Quark Production Cross Section in 7 and 13 TeV Collisions [Phys. Rev. Lett. 118 , 052002 (2017)]

No abstract available

Excess electronic recoil events in XENON1T

We report results from searches for new physics with low-energy electronic recoil data recorded with the XENON1T detector. With an exposure of 0.65 tonne-years and an unprecedentedly low background rate of 76\ub12stat\u2009\u2009events/(tonne 7year 7keV) between 1 and 30 keV, the data enable one of the most sensitive searches for solar axions, an enhanced neutrino magnetic moment using solar neutrinos, and bosonic dark matter. An excess over known backgrounds is observed at low energies and most prominent between 2 and 3 keV. The solar axion model has a 3.4\u3c3 significance, and a three-dimensional 90% confidence surface is reported for axion couplings to electrons, photons, and nucleons. This surface is inscribed in the cuboid defined by gae&lt;3.8 710-12, gaeganeff&lt;4.8 710-18, and gaega\u3b3&lt;7.7 710-22\u2009\u2009GeV-1, and excludes either gae=0 or gaega\u3b3=gaeganeff=0. The neutrino magnetic moment signal is similarly favored over background at 3.2\u3c3, and a confidence interval of \u3bc\u3bd 08(1.4,2.9) 710-11\u2009\u2009\u3bcB (90% C.L.) is reported. Both results are in strong tension with stellar constraints. The excess can also be explained by \u3b2 decays of tritium at 3.2\u3c3 significance with a corresponding tritium concentration in xenon of (6.2\ub12.0) 710-25\u2009\u2009mol/mol. Such a trace amount can neither be confirmed nor excluded with current knowledge of its production and reduction mechanisms. The significances of the solar axion and neutrino magnetic moment hypotheses are decreased to 2.0\u3c3 and 0.9\u3c3, respectively, if an unconstrained tritium component is included in the fitting. With respect to bosonic dark matter, the excess favors a monoenergetic peak at (2.3\ub10.2)\u2009\u2009keV (68% C.L.) with a 3.0\u3c3 global (4.0\u3c3 local) significance over background. This analysis sets the most restrictive direct constraints to date on pseudoscalar and vector bosonic dark matter for most masses between 1 and 210\u2009\u2009keV/c2. We also consider the possibility that Ar37 may be present in the detector, yielding a 2.82 keV peak from electron capture. Contrary to tritium, the Ar37 concentration can be tightly constrained and is found to be negligible

Precision measurement of the ratio of the Lambda(0)(b) to (B)over-bar(0) lifetimes

The LHCb measurement of the lifetime ratio of the Lambda(0)(b) baryon to the (B) over bar (0) meson is updated using data corresponding to an integrated luminosity of 3.0 fb(-1) collected using 7 and 8 TeV centre-of-mass energy pp collisions at the LHC. The decay modes used are Lambda(0)(b) -> J/psi pK(-) and (B) over bar (0) -> J/psi pi K-+(-), where the pi K-+(-) mass is consistent with that of the (K) over bar*(0)(892) meson. The lifetime ratio is determined with unprecedented precision to be 0.974 +/- 0.006 +/- 0.004, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the (B) over bar (0) lifetime, the Lambda(0)(b) lifetime is found to be 1.479 +/- 0.009 +/- 0.010 ps