|
|
ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Search for a Light Higgs Boson Decaying to Long-Lived Weakly Interacting Particles in Proton-Proton Collisions at root s=7 TeV with the ATLAS Detector. Phys. Rev. Lett., 108(25), 251801–18pp.
Abstract: A search for the decay of a light Higgs boson (120-140 GeV) to a pair of weakly interacting, long-lived particles in 1.94 fb(-1) of proton-proton collisions at root s = 7 TeV recorded in 2011 by the ATLAS detector is presented. The search strategy requires that both long-lived particles decay inside the muon spectrometer. No excess of events is observed above the expected background and limits on the Higgs boson production times branching ratio to weakly interacting, long-lived particles are derived as a function of the particle proper decay length.
|
|
|
|
ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in pp Collisions at root s=7 TeV. Phys. Rev. Lett., 108(24), 241802–19pp.
Abstract: A search is presented for gluinos decaying via the supersymmetric partner of the top quark using events with two same-sign leptons, jets, and missing transverse momentum. The analysis is performed with 2: 05 fb(-1) of integrated luminosity from pp collisions at root s = 7 TeV collected by the ATLAS detector at the LHC. No excess beyond the standard model expectation is observed, and exclusion limits are derived for simplified models where the gluino decays via the supersymmetric partner of the top quark and in the minimal supergravity and constrained minimal supersymmetric standard model framework. In those scenarios, gluino masses below 550 GeV are excluded at 95% C.L. within the parameter space considered, significantly extending the coverage with respect to existing limits. Depending on the model parameters, gluino masses up to 750 GeV can also be excluded at 95% C.L.
|
|
|
|
ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Observation of Spin Correlation in t(t)over-bar Events from pp Collisions at root s=7 TeV Using the ATLAS Detector. Phys. Rev. Lett., 108(21), 212001–19pp.
Abstract: A measurement of spin correlation in t (t) over bar production is reported using data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 2.1 fb(-1). Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. The difference in azimuthal angle between the two charged leptons in the laboratory frame is used to extract the correlation between the top and antitop quark spins. In the helicity basis the measured degree of correlation corresponds to A(helicity) = 0.40(-0.08)(+0.09), in agreement with the next-to-leading-order standard model prediction. The hypothesis of zero spin correlation is excluded at 5.1 standard deviations.
|
|
|
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2012). Search for Direct Top Squark Pair Production in Final States with One Isolated Lepton, Jets, and Missing Transverse Momentum in root s=7 TeV pp Collisions Using 4.7 fb(-1) of ATLAS Data. Phys. Rev. Lett., 109(21), 211803–18pp.
Abstract: A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at root s = 7 TeV. The measurement is based on 4.7 fb(-1) of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.
|
|
|
|
ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Search for Production of Resonant States in the Photon-Jet Mass Distribution Using pp Collisions at root s=7 TeV Collected by the ATLAS Detector. Phys. Rev. Lett., 108(21), 211802–18pp.
Abstract: This Letter describes a model-independent search for the production of new resonant states in photon + jet events in 2.11 fb(-1) of proton-proton collisions at root s = 7 TeV. We compare the photon + jet mass distribution to a background model derived from data and find consistency with the background-only hypothesis. Given the lack of evidence for a signal, we set 95% credibility level limits on generic Gaussian-shaped signals and on a benchmark excited-quark (q*) model, excluding 2 TeV Gaussian resonances with cross section times branching fraction times acceptance times efficiency near 5 fb and excluding q* masses below 2.46 TeV, respectively.
|
|
|
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2012). Search for a Supersymmetric Partner to the Top Quark in Final States with Jets and Missing Transverse Momentum at root s=7 TeV with the ATLAS Detector. Phys. Rev. Lett., 109(21), 211802–18pp.
Abstract: A search for direct pair production of supersymmetric top squarks ((t) over tilde (1)) is presented, assuming the (t) over tilde (1) decays into a top quark and the lightest supersymmetric particle, (chi) over tilde (0)(1), and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13.5(-3.6)(+3.7) (4.4(-1.3)(+1.7)) events in two signal regions based on integral Ldt = 4.7 fb(-1) of pp collision data taken at root s = 7 TeV with the ATLAS detector at the LHC. An exclusion region in the (t) over tilde (1) versus (chi) over tilde (0)(1) mass plane is evaluated: 370 < m(<(t)over tilde>1) < 465 GeV is excluded for m(<(chi)over tilde>10) similar to 0 GeV while m((t) over tilde1) = 445 GeV is excluded for m((chi) over tilde 10) <= 50 GeV.
|
|
|
|
BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2012). Search for Low-Mass Dark-Sector Higgs Bosons. Phys. Rev. Lett., 108(21), 211801–7pp.
Abstract: Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516 fb(-1) of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the standard model-dark-sector mixing angle and the dark-sector coupling constant.
|
|
|
|
BABAR Collaboration(Lees, J. P. et al), Bernabeu, J., Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2012). Observation of Time-Reversal Violation in the B-0 Meson System. Phys. Rev. Lett., 109(21), 211801–8pp.
Abstract: Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time-reversal violation. The decays of entangled neutral B mesons into definite flavor states (B-0 or (B) over bar (0)), and J/psi K-L(0) or c (c) over barK(S)(0) final states (referred to as B+ or B-), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, (B) over bar (0) -> B- and B- -> (B) over bar (0), as a function of the time difference between the two B decays. Using 468 X 10(6) B (B) over bar pairs produced in Y(4S) decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding Delta S-T(+) = -137 +/- 0.14(stat) +/- 0.06(syst) and Delta S-T(-) = 1.17 +/- 0.18(stat) +/- 0.11(syst). These nonzero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.
|
|
|
|
Fallot, M., Cormon, S., Estienne, M., Algora, A., Bui, V. M., Cucoanes, A., et al. (2012). New Antineutrino Energy Spectra Predictions from the Summation of Beta Decay Branches of the Fission Products. Phys. Rev. Lett., 109(20), 202504–5pp.
Abstract: In this Letter, we study the impact of the inclusion of the recently measured beta decay properties of the Tc-102;104;105;106;107, Mo-105, and Nb-101 nuclei in an updated calculation of the antineutrino energy spectra of the four fissible isotopes U-235,U-238 and Pu-239,Pu-241. These actinides are the main contributors to the fission processes in pressurized water reactors. The beta feeding probabilities of the above-mentioned Tc, Mo, and Nb isotopes have been found to play a major role in the gamma component of the decay heat of Pu-239, solving a large part of the gamma discrepancy in the 4-3000 s range. They have been measured by using the total absorption technique, insensitive to the pandemonium effect. The calculations are performed by using the information available nowadays in the nuclear databases, summing all the contributions of the beta decay branches of the fission products. Our results provide a new prediction of the antineutrino energy spectra of U-235, Pu-239,Pu-241, and, in particular, U-238 for which no measurement has been published yet. We conclude that new total absorption technique measurements are mandatory to improve the reliability of the predicted spectra.
|
|
|
|
BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2012). Precision Measurement of the B -> Xs gamma Photon Energy Spectrum, Branching Fraction, and Direct CP Asymmetry ACP(B -> Xs+d gamma). Phys. Rev. Lett., 109(19), 191801–8pp.
Abstract: The photon spectrum in the inclusive electromagnetic radiative decays of the B meson, B --> X-s gamma plus B --> X-d gamma, is studied using a data sample of (382.8 +/- 4.2) x 10(6)Y(4S) --> B (B) over bar decays collected by the BABAR experiment at SLAC. The spectrum is used to extract the branching fraction B(B --> X-s gamma) = (3.21 +/- 0.33) x 10(-4) for E-gamma > 1.8 GeV and the direct CP asymmetry A(CP)(B --> Xs+d gamma) = 0.057 +/- 0.063. The effects of detector resolution and Doppler smearing are unfolded to measure the photon energy spectrum in the B meson rest frame.
|
|
