ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Search for Scalar Charm Quark Pair Production in pp Collisions at root s=8 TeV with the ATLAS Detector. Phys. Rev. Lett., 114(16), 161801–19pp.
Abstract: The results of a dedicated search for pair production of scalar partners of charm quarks are reported. The search is based on an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV recorded with the ATLAS detector at the LHC. The search is performed using events with large missing transverse momentum and at least two jets, where the two leading jets are each tagged as originating from c quarks. Events containing isolated electrons or muons are vetoed. In an R-parity-conserving minimal super-symmetric scenario in which a single scalar-charm state is kinematically accessible, and where it decays exclusively into a charm quark and a neutralino, 95% confidence-level upper limits are obtained in the scalar-charm-neutralino mass plane such that, for neutralino masses below 200 GeV, scalar-charm masses up to 490 GeV are excluded.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Search for Higgs and Z Boson Decays to J/psi gamma and Upsilon(nS)gamma with the ATLAS Detector. Phys. Rev. Lett., 114(12), 121801–19pp.
Abstract: A search for the decays of the Higgs and Z bosons to J/psi gamma and Upsilon(nS)gamma (n = 1,2,3) is performed with pp collision data samples corresponding to integrated luminosities of up to 20.3 fb(-1) collected at root s = 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above expected backgrounds and 95% C.L. upper limits are placed on the branching fractions. In the J/psi gamma final state the limits are 1.5 x 10(-3) and 2.6 x 10(-6) for the Higgs and Z boson decays, respectively, while in the Upsilon(1S, 2S, 3S)gamma. final states the limits are (1.3, 1.9, 1.3) x 10(-3) and (3.4, 6.5, 5.4) x 10(-6), respectively.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2015). Search for long-lived particles in e(+)e(-) collisions. Phys. Rev. Lett., 114(17), 171801–7pp.
Abstract: We present a search for a neutral, long-lived particle L that is produced in e(+)e(-)collisions and decays at a significant distance from the e(+)e(-) interaction point into various flavor combinations of two oppositely charged tracks. The analysis uses an e(+)e(-) data sample with a luminosity of 489.1 fb(-1) collected by the BABAR detector at the Upsilon(4S), Upsilon(3S), and Upsilon(2S) resonances and just below the Upsilon(4S). Fitting the two-track mass distribution in search of a signal peak, we do not observe a significant signal, and set 90% confidence level upper limits on the product of the L production cross section, branching fraction, and reconstruction efficiency for six possible two-body L decay modes as a function of the L mass. The efficiency is given for each final state as a function of the mass, lifetime, and transverse momentum of the candidate, allowing application of the upper limits to any production model. In addition, upper limits are provided on the branching fraction B(B -> XsL), where X-s is a strange hadronic system.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for a Charged Higgs Boson Produced in the Vector-Boson Fusion Mode with Decay H-+/- -> W(+/-)Z using pp Collisions at root S=8 TeV with the ATLAS Experiment. Phys. Rev. Lett., 114(23), 231801–18pp.
Abstract: A search for a charged Higgs boson, H-+/-, decaying to a W-+/- boson and a Z boson is presented. The search is based on 20.3 fb(-1) of proton-proton collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. The H-+/- boson is assumed to be produced via vector-boson fusion and the decays W-+/- -> q (q') over bar and Z -> e(+)e(-)/mu(+)mu(-) are considered. The search is performed in a range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the production of an H+ boson is observed. Upper limits of 31-1020 fb at 95% C.L. are placed on the cross section for vector-boson fusion production of an H-+/- boson times its branching fraction to W(+/-)Z. The limits are compared with predictions from the Georgi-Machacek Higgs triplet model.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Search for a Heavy Neutral Particle Decaying to e mu, e tau, or μtau in pp Collisions at root s=8 TeV with the ATLAS Detector. Phys. Rev. Lett., 115(3), 031801–18pp.
Abstract: This Letter presents a search for a heavy neutral particle decaying into an opposite-sign different-flavor dilepton pair, e(+/-) mu(-/+), e(+/-) tau(-/+), or mu(+/-) tau(-/+) using 20.3 fb(-1) of pp collision data at root s = 8 TeV collected by the ATLAS detector at the LHC. The numbers of observed candidate events are compatible with the standard model expectations. Limits are set on the cross section of new phenomena in two scenarios: the production of (nu) over tilde (tau) in R-parity-violating supersymmetric models and the production of a lepton-flavor-violating Z' vector boson.
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Maiezza, A., Nemevsek, M., & Nesti, F. (2015). Lepton Number Violation in Higgs Decay at LHC. Phys. Rev. Lett., 115(8), 081802–7pp.
Abstract: We show that within the left-right symmetric model, lepton number violating decays of the Higgs boson can be discovered at the LHC. The process is due to the mixing of the Higgs boson with the triplet that breaks parity. As a result, the Higgs boson can act as a gateway to the origin of the heavy Majorana neutrino mass. To assess the LHC reach, a detailed collider study of the same-sign dileptons plus jets channel is provided. This process is complementary to the existing nuclear and collider searches for lepton number violation and can probe the scale of parity restoration even beyond other direct searches.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of CP Violation in B-0 -> J/psi K-S(0) Decays. Phys. Rev. Lett., 115(3), 031601–9pp.
Abstract: Measurements are presented of the CP violation observables S and C in the decays of B-0 and (B) over bar (0) mesons to the J/psi K-S(0) final state. The data sample corresponds to an integrated luminosity of 3.0 fb(-1) collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B-0 and (B) over bar (0) decays. The analysis of the time evolution of these decays yields S = 0.731 +/- 0.035(stat) +/- 0.020(syst) and C = -0.038 +/- 0.032(stat) +/- 0.005(syst). In the standard model, S equals sin(2 beta) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Observation of the B-s(0) -> eta 'eta ' Decay. Phys. Rev. Lett., 115(5), 051801–9pp.
Abstract: The first observation of the B-s(0) -> eta'eta' decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0 fb(-1) of integrated luminosity collected with the LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be [3.31 +/- 0.64(stat) +/- 0.28(syst) +/- 0.12(norm)] x 10(-5), where the third uncertainty comes from the B-+/- -> eta'K-+/- branching fraction that is used as a normalization. In addition, the charge asymmetries of B-+/- -> eta'K-+/- and B-+/- -> phi K-+/-, which are control channels, are measured to be (-0.2 +/- 1.3)% and (+1.7 +/- 1.3)%, respectively. All results are consistent with theoretical expectations.
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ATLAS and CMS Collaborations(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Combined Measurement of the Higgs Boson Mass in pp Collisions at root s=7 and 8 TeV with the ATLAS and CMS Experiments. Phys. Rev. Lett., 114(19), 191803–33pp.
Abstract: A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H --> gamma gamma and H --> ZZ --> 4l decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is m(H) = 125.09 +/- 0.21 (stat) +/- 0.11 (syst) GeV.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for New Phenomena in Dijet Angular Distributions in Proton-Proton Collisions at root s=8 TeV Measured with the ATLAS Detector. Phys. Rev. Lett., 114(22), 221802–17pp.
Abstract: A search for new phenomena in LHC proton-proton collisions at a center-of-mass energy of root s = 8 TeV was performed with the ATLAS detector using an integrated luminosity of 17.3 fb(-1). The angular distributions are studied in events with at least two jets; the highest dijet mass observed is 5.5 TeV. All angular distributions are consistent with the predictions of the standard model. In a benchmark model of quark contact interactions, a compositeness scale below 8.1 TeV in a destructive interference scenario and 12.0 TeV in a constructive interference scenario is excluded at 95% C.L.; median expected limits are 8.9 TeV for the destructive interference scenario and 14.1 TeV for the constructive interference scenario.
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