Phys.Lett.B

A measurement of angular correlations in Drell-Yan lepton pairs via the @f_@h^@? observable is presented. This variable probes the same physics as the Z/@c^@? boson transverse momentum with a better experimental resolution. The Z/@c^@?->e^+e^- and Z/@c^@?->@m^+@m^- decays produced in proton-proton collisions at a centre-of-mass energy of s=7 TeV are used. The data were collected with the ATLAS detector at the LHC and correspond to an integrated luminosity of 4.6 fb^-^1. Normalised differential cross sections as a function of @f_@h^@? are measured separately for electron and muon decay channels. These channels are then combined for improved accuracy. The cross section is also measured double differentially as a function of @f_@h^@? for three independent bins of the Z boson rapidity. The results are compared to QCD calculations and to predictions from different Monte Carlo event generators. The data are reasonably well described, in all measured Z boson rapidity regions, by resummed QCD predictions combined with fixed-order perturbative QCD calculations or by some Monte Carlo event generators. The measurement precision is typically better by one order of magnitude than present theoretical uncertainties.

Phys. Lett. B

The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons.

Phys.Rev.D

A search for nonresonant new phenomena, originating from either contact interactions or large extra spatial dimensions, has been carried out using events with two isolated electrons or muons. These events, produced at the LHC in proton-proton collisions at s=7  TeV, were recorded by the ATLAS detector. The data sample, collected throughout 2011, corresponds to an integrated luminosity of 4.9 and 5.0  fb-1 in the e+e- and μ+μ- channels, respectively. No significant deviations from the Standard Model expectation are observed. Using a Bayesian approach, 95% confidence level lower limits ranging from 9.0 to 13.9 TeV are placed on the energy scale of ℓℓqq contact interactions in the left-left isoscalar model. Lower limits ranging from 2.4 to 3.9 TeV are also set on the string scale in large extra dimension models. After combining these limits with results from a similar search in the diphoton channel, slightly more stringent limits are obtained.

Phys.Lett.B

A search has been performed for the experimental signature of an isolated photon with high transverse momentum, at least one jet identified as originating from a bottom quark, and high missing transverse momentum. Such a final state may originate from supersymmetric models with gauge-mediated supersymmetry breaking in events in which one of a pair of higgsino-like neutralinos decays into a photon and a gravitino while the other decays into a Higgs boson and a gravitino. The search is performed using the full dataset of 7 TeV proton-proton collisions recorded with the ATLAS detector at the LHC in 2011, corresponding to an integrated luminosity of 4.7 fb^-^1. A total of 7 candidate events are observed while 7.5+/-2.2 events are expected from the Standard Model background. The results of the search are interpreted in the context of general gauge mediation to exclude certain regions of a benchmark plane for higgsino-like neutralino production.

Phys.Lett.B

A search for long-lived particles is performed using a data sample of 4.7 fb −1 from proton–proton collisions at a centre-of-mass energy s=7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% confidence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tanβ=5–20 . Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R -hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R -hadrons are obtained that are less sensitive to the interaction model for R -hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone.

JHEP

The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at . The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb(−1), is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (|η| < 1.37 and 1.52 < |η| < 2.37) and with an angular separation ΔR > 0.4, is pb. The differential cross sections as a function of the di-photon invariant mass, transverse momentum, azimuthal separation, and cosine of the polar angle of the largest transverse energy photon in the Collins-Soper di-photon rest frame are also measured. The results are compared to the prediction of leading-order parton-shower and next-to-leading-order and next-to-next-to-leading-order parton-level generators.

JHEP

A search for resonances produced in 7 TeV proton-proton collisions and decaying into top-quark pairs is described. In this Letter events where the top-quark decay produces two massive jets with large transverse momenta recorded with the ATLAS detector at the Large Hadron Collider are considered. Two techniques that rely on jet substructure are used to separate top-quark jets from those arising from light quarks and gluons. In addition, each massive jet is required to have evidence of an associated bottom-quark decay. The data are consistent with the Standard Model, and limits can be set on the production cross section times branching fraction of a Z' boson and a Kaluza-Klein gluon resonance. These limits exclude, at the 95% credibility level, Z' bosons with masses 0.70-1.00 TeV as well as 1.28-1.32 TeV and Kaluza-Klein gluons with masses 0.70-1.62 TeV.

JHEP

A measurement of the ZZ production cross section in proton-proton collisions at TeV using data recorded by the ATLAS experiment at the Large Hadron Collider is presented. In a data sample corresponding to an integrated luminosity of 4.6 fb(−1) collected in 2011, events are selected that are consistent either with two Z bosons decaying to electrons or muons or with one Z boson decaying to electrons or muons and a second Z boson decaying to neutrinos. The ZZ ((*)) → ℓ (+) ℓ (−) ℓ (′+) ℓ (′−) and cross sections are measured in restricted phase-space regions. These results are then used to derive the total cross section for ZZ events produced with both Z bosons in the mass range 66 to 116 GeV, pb, which is consistent with the Standard Model prediction of pb calculated at next-to-leading order in QCD. The normalized differential cross sections in bins of various kinematic variables are presented. Finally, the differential event yield as a function of the transverse momentum of the leading Z boson is used to set limits on anomalous neutral triple gauge boson couplings in ZZ production.

Phys. Rev. D

A generic search for anomalous production of events with at least three charged leptons is presented. The search uses a pp-collision data sample at a center-of-mass energy of s=7  TeV corresponding to 4.6  fb-1 of integrated luminosity collected in 2011 by the ATLAS detector at the CERN Large Hadron Collider. Events are required to contain at least two electrons or muons, while the third lepton may either be an additional electron or muon, or a hadronically decaying tau lepton. Events are categorized by the presence or absence of a reconstructed tau-lepton or Z-boson candidate decaying to leptons. No significant excess above backgrounds expected from Standard Model processes is observed. Results are presented as upper limits on event yields from non-Standard-Model processes producing at least three prompt, isolated leptons, given as functions of lower bounds on several kinematic variables. Fiducial efficiencies for model testing are also provided. The use of the results is illustrated by setting upper limits on the production of doubly charged Higgs bosons decaying to same-sign lepton pairs.

JHEP

A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb(−1) to 4.8 fb(−1). Higgs boson decays into oppositely-charged muon or τ lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits are for the production cross-section of a generic neutral Higgs boson, ϕ, as a function of the Higgs boson mass and for h/A/H production in the MSSM as a function of the parameters m ( )A( ) and tan β in the scenario for m ( )A( ) in the range of 90 GeV to 500 GeV.

Eur.Phys.J.C

A measurement of the top quark pair production cross section in the final state with a hadronically decaying tau lepton and jets is presented. The analysis is based on proton-proton collision data recorded by the ATLAS experiment at the LHC, with a centre-of-mass energy of 7 TeV. The data sample corresponds to an integrated luminosity of 1.67 inverse femtobarns. The cross section is measured to be $\sigma_{t\bar{t}}$ = 194 +/- 18 (stat.) +/- 46 (syst.) pb and is in agreement with other measurements and with the Standard Model prediction.

Phys. Rev. D

Using 1.8  fb-1 of pp collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the Large Hadron Collider, we present measurements of the production cross sections of Υ(1S,2S,3S) mesons. Υ mesons are reconstructed using the dimuon decay mode. Total production cross sections for pT<70  GeV and in the rapidity interval |yΥ|<2.25 are measured to be, 8.01±0.02±0.36±0.31  nb, 2.05±0.01±0.12±0.08  nb, and 0.92±0.01±0.07±0.04  nb, respectively, with uncertainties separated into statistical, systematic, and luminosity measurement effects. In addition, differential cross section times dimuon branching fractions for Υ(1S), Υ(2S), and Υ(3S) as a function of Υ transverse momentum pT and rapidity are presented. These cross sections are obtained assuming unpolarized production. If the production polarization is fully transverse or longitudinal with no azimuthal dependence in the helicity frame, the cross section may vary by approximately ±20%. If a nontrivial azimuthal dependence is considered, integrated cross sections may be significantly enhanced by a factor of 2 or more. We compare our results to several theoretical models of Υ meson production, finding that none provide an accurate description of our data over the full range of Υ transverse momenta accessible with this data set.

Eur.Phys.J.C

The production of D* and D mesons in inelastic scattering of 160 GeV/c muons off a ^6LiD target has been investigated with the COMPASS spectrometer at CERN for 0.003 (GeV/c)^2 < Q^2 < 10 (GeV/c)^2 and 3x10^-5< x_Bj < 0.1. The study is based on 8100 events where a D^0 or anti D^0 is detected subsequently to a D*+ or D*- decay, and on 34000 events, where only a D^0 or anti D^0 is detected. Kinematic distributions of D*, D and K*_2 are given as a function of their energy E, transverse momentum p_T, energy fraction z, and of the virtual photon variables nu, Q^2 and x_Bj. Semi-inclusive differential D* production cross-sections are compared with theoretical predictions for D* production via photon-gluon fusion into open charm. The total observed production cross-section for D*+/- mesons with laboratory energies between 22 and 86 GeV is 1.9 nb. Significant cross-section asymmetries are observed between D*+ and D*- production for nu<40 GeV and z>0.6.

Phys. Rev. D

The gluon polarization in the nucleon was measured using open charm production by scattering 160  GeV/c polarized muons off longitudinally polarized protons or deuterons. The data were taken by the COMPASS Collaboration between 2002 and 2007. A detailed account is given of the analysis method that includes the application of neural networks. Several decay channels of D0 mesons are investigated. Longitudinal spin asymmetries of the D meson production cross sections are extracted in bins of D0 transverse momentum and energy. At leading order QCD accuracy, the average gluon polarization is determined as ⟨Δg/g⟩LO=-0.06±0.21(stat.)±0.08(syst.) at the scale ⟨μ2⟩≈13  (GeV/c)2 and an average gluon momentum fraction ⟨x⟩≈0.11. The average gluon polarization is also obtained at next-to-leading order QCD accuracy as ⟨Δg/g⟩ NLO=-0.13±0.15(stat.)±0.15(syst.) at the scale ⟨μ2⟩≈13  (GeV/c)2 and ⟨x⟩≈0.20.

Phys. Rev. D

We present new measurements of the inclusive forward-backward tt¯ production asymmetry, AFB, and its dependence on several properties of the tt¯ system. The measurements are performed with the full Tevatron data set recorded with the CDF II detector during pp¯ collisions at s=1.96  TeV, corresponding to an integrated luminosity of 9.4  fb-1. We measure the asymmetry using the rapidity difference Δy=yt-yt¯. Parton-level results are derived, yielding an inclusive asymmetry of 0.164±0.047(stat+syst). We establish an approximately linear dependence of AFB on the top-quark pair mass Mtt¯ and the rapidity difference |Δy| at detector and parton levels. Assuming the standard model, the probabilities to observe the measured values or larger for the detector-level dependencies are 7.4×10-3 and 2.2×10-3 for Mtt¯ and |Δy| respectively. Lastly, we study the dependence of the asymmetry on the transverse momentum of the tt¯ system at the detector level. These results are consistent with previous lower-precision measurements and provide additional quantification of the functional dependencies of the asymmetry.

Phys. Rev. D

We measure the polarization of W bosons from top-quark (t) decays into final states with a charged lepton and jets, tt¯→W+bW-b¯→ℓνbqq¯′b¯, using the full Run II data set collected by the CDF II detector, corresponding to an integrated luminosity of 8.7  fb-1. A model-independent method simultaneously determines the fraction of longitudinal (f0) and right-handed (f+) W bosons to yield f0=0.726±0.066(stat)±0.067(syst) and f+=-0.045±0.044(stat)±0.058(syst) with a correlation coefficient of -0.69. Additional results are presented under various standard model assumptions. No significant discrepancies with the standard model are observed.

Phys.Rev.Lett.

This Letter reports a search for a narrow resonant state decaying into two W bosons and two b quarks where one W boson decays leptonically and the other decays into a quark-antiquark pair. The search is particularly sensitive to top-antitop resonant production. We use the full data sample of proton-antiproton collisions at a center-of-mass energy of 1.96 TeV collected by the CDF II detector at the Fermilab Tevatron, corresponding to an integrated luminosity of 9.45  fb-1. No evidence for resonant production is found, and upper limits on the production cross section times branching ratio for a narrow resonant state are extracted. Within a specific benchmark model, we exclude a Z′ boson with mass, MZ′, below 915  GeV/c2 decaying into a top-antitop pair at the 95% credibility level assuming a Z′ boson decay width of ΓZ′=0.012MZ′. This is the most sensitive search for a narrow qq¯-initiated tt¯ resonance in the mass region below 750  GeV/c2.

Phys. Rev. D

We present a search for charged massive long-lived particles (CMLLPs) that are pair produced in pp¯ collisions at s=1.96  TeV collected by the D0 experiment at the Fermilab Tevatron collider. Our result is a combination of two searches where either one or both CMLLPs are reconstructed in the detector. We select events with muonlike particles that have both speed and ionization energy loss (dE/dx) different from muons produced in pp¯ collisions. In the absence of evidence for CMLLPs corresponding to 6.3  fb-1 of integrated luminosity, we set limits on the CMLLP masses in several supersymmetric models, excluding masses below 278 GeV for long-lived gaugino-like charginos, and masses below 244 GeV for long-lived Higgsino-like charginos at the 95% C.L. We also set limits on the cross section for pair production of long-lived scalar tau leptons that range from 0.04 to 0.008 pb for scalar tau lepton masses of 100–300 GeV.

Phys.Rev.D

We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with two or more jets using 9.7  fb-1 of Run II Fermilab Tevatron Collider data collected with the D0 detector. The analysis is sensitive to Higgs boson production via gluon fusion, associated vector boson production, and vector boson fusion, followed by the Higgs boson decay to tau lepton pairs or to W boson pairs. The ratios of 95% C.L. upper limits on the cross section times branching ratio to those predicted by the standard model are obtained for orthogonal subsamples that are enriched in either H→ττ decays or H→WW decays, and for the combination of these subsample limits. The observed and expected limit ratios for the combined subsamples at a Higgs boson mass of 125 GeV are 11.3 and 9.0, respectively.

Phys.Rev.D

Using 106×106 ψ′ decays collected with the BESIII detector at the BEPCII, three decays of χcJ (J=0, 1, 2) with baryon pairs (ΛΛ¯, Σ0Σ¯0, Σ+Σ¯-) in the final state have been studied. The branching fractions are measured to be B(χc0,1,2→ΛΛ¯)=(33.3±2.0±2.6)×10-5, (12.2±1.1±1.1)×10-5, (20.8±1.6±2.3)×10-5; B(χc0,1,2→Σ0Σ¯0)=(47.8±3.4±3.9)×10-5, (3.8±1.0±0.5)×10-5, (4.0±1.1±0.5)×10-5; and B(χc0,1,2→Σ+Σ¯-)=(45.4±4.2±3.0)×10-5, (5.4±1.5±0.5)×10-5, (4.9±1.9±0.7)×10-5, where the first error is statistical and the second is systematic. Upper limits on the branching fractions for the decays of χc1,2→Σ0Σ¯0, Σ+Σ¯- are estimated to be B(χc1→Σ0Σ¯0)<6.2×10-5, B(χc2→Σ0Σ¯0)<6.5×10-5, B(χc1→Σ+Σ¯-)<8.7×10-5 and B(χc2→Σ+Σ¯-)<8.8×10-5 at the 90% confidence level.

Phys.Rev.D

Using a sample of 225.3 million J/ψ events collected with the BESIII detector at the BEPCII e+e- collider in 2009, searches for the decays of η and η′→π+e-ν¯e+c.c. in J/ψ→ϕη and ϕη′ are performed. The ϕ signals, which are reconstructed in K+K- final states, are used to tag η and η′ semileptonic decays. No signals are observed for either η or η′, and upper limits at the 90% confidence level are determined to be 7.3×10-4 and 5.0×10-4 for the ratios B(η→π+e-ν¯e+c.c.)B(η→π+π-π0) and B(η′→π+e-ν¯e+c.c.)B(η′→π+π-η), respectively. These are the first upper-limit values determined for η and η′ semileptonic weak decays.

Phys.Rev.D

We report on a study of the isospin-violating and isospin-conserving decays of the J/ψ and ψ′ charmonium state to ΛΛ¯π0 and ΛΛ¯η, respectively. The data are based on 225 million J/ψ and 106 million ψ′ events that were collected with the BESIII detector. The most accurate measurement of the branching fraction of the isospin-violating process J/ψ→ΛΛ¯π0 is obtained, and the isospin-conserving processes J/ψ→ΛΛ¯η and ψ′→ΛΛ¯η are observed for the first time. The branching fractions are measured to be B(J/ψ→ΛΛ¯π0)=(3.78±0.27stat±0.30sys)×10-5, B(J/ψ→ΛΛ¯η)=(15.7±0.80stat±1.54sys)×10-5 and B(ψ′→ΛΛ¯η)=(2.48±0.34stat±0.19sys)×10-5. No significant signal events are observed for ψ′→ΛΛ¯π0 decay resulting in an upper limit of the branching fraction of B(ψ′→ΛΛ¯π0)<0.29×10-5 at the 90% confidence level. The two-body decay of J/ψ→Σ(1385)0Λ¯+c.c. is searched for, and the upper limit is B(J/ψ→Σ(1385)0Λ¯+c.c.)<0.82×10-5 at the 90% confidence level.

Phys.Rev.D

Using a sample of 1.06×108 ψ′ mesons collected with the BESIII detector at the BEPCII e+e- collider and χcJ mesons produced via radiative transitions from the ψ′, we report the first observation for ψ′→p¯K+Σ0+c.c. (charge conjugate), as well as improved measurements for the χcJ hyperon decays χcJ→p¯K+Λ+c.c. The branching fractions are measured to be B(ψ′→p¯K+Σ0+c.c.)=(1.67±0.13±0.12)×10-5, B(χc0→p¯K+Λ+c.c.)=(13.2±0.3±1.0)×10-4, B(χc1→p¯K+Λ+c.c.)=(4.5±0.2±0.4)×10-4, and B(χc2→p¯K+Λ+c.c.)=(8.4±0.3±0.6)×10-4, where the first error is statistical, and the second is systematic. In the decay of χc0→p¯K+Λ+c.c., an anomalous enhancement near threshold is observed in the invariant mass distribution of p¯Λ+c.c., which cannot be explained by phase space.

Phys.Rev.D

A 2.25×108 J/ψ event sample accumulated with the BESIII detector is used to study the doubly Okubo-Zweig-Iizuka-suppressed decay modes J/ψ→γωϕ, ω→π+π-π0, ϕ→K+K-. A strong deviation (>30σ) from three-body J/ψ→γωϕ phase space is observed near the ωϕ mass threshold that is consistent with a previous observation reported by the BESII experiment. A partial wave analysis with a tensor covariant amplitude that assumes that the enhancement is due to the presence of a resonance, the X(1810), is performed and confirms that the spin-parity of the X(1810) is 0++. The mass and width of the X(1810) are determined to be M=1795±7(stat)-5+13(syst)±19(mod)  MeV/c2 and Γ=95±10(stat)-34+21(syst)±75(mod)  MeV/c2, respectively, and the product branching fraction is measured to be B(J/ψ→γX(1810))×B(X(1810)→ωϕ)=(2.00±0.08(stat)-1.00+0.45(syst)±1.30(mod))×10-4. These results are consistent within errors with those of the BESII experiment.

JINST

The ``Neutrino Experiment with a Xenon Time-Projection Chamber'' (NEXT) is intended to investigate the neutrinoless double beta decay of (136)Xe, which requires a severe suppression of potential backgrounds. An extensive screening and material selection process is underway for NEXT since the control of the radiopurity levels of the materials to be used in the experimental set-up is a must for rare event searches. First measurements based on Glow Discharge Mass Spectrometry and gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterr&apos,aneo de Canfranc (Spain) are described here. Activity results for natural radioactive chains and other common radionuclides are summarized, being the values obtained for some materials like copper and stainless steel very competitive. The implications of these results for the NEXT experiment are also discussed.