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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the time-dependent CP asymmetries in B-s(0) -> J/psi K-S(0). J. High Energy Phys., 06(6), 131–22pp.
Abstract: The first measurement of decay-time-dependent CP asymmetries in the decay B-S(0) -> J/psi K-S(0) and an updated measurement of the ratio of branching fractions B(B-S(0) -> J/psi K-S(0))/B(B-0 -> J/psi K-S(0)) are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fb(-1) of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The results on the CP asymmetries are A(Delta Gamma)(B-S(0) -> J/psi K-S(0)) = 0.49 +/- (0.77)(0.65)(stat) +/- 0.06(syst), C-dir(B-S(0) -> J/psi K-S(0)) = -0.28 +/- 0.41(stat) +/- 0.08(syst), S-mix(B-S(0) -> J/psi K-S(0)) = -0.08 +/- 0.40(stat) +/- 0.08(syst). The ratio B(B-S(0) -> J/psi K-S(0))/B(B-0 -> J/psi K-S(0)) is measured to be 0.0431 +/- 0.0017(stat) +/- 0.0012(syst) +/- 0.0025(f(s)/f(d)), where the last uncertainty is due to the knowledge of the B-S(0) and B-0 production fractions.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Differential branching fraction and angular analysis of Lambda(0)(b) -> Lambda mu(+)mu(-) decays. J. High Energy Phys., 06(6), 115–29pp.
Abstract: The differential branching fraction of the rare decay Lambda(0)(b) -> Lambda mu(+)mu(-) is measured as a function of q(2), the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), collected by the LHCb experiment. Evidence of signal is observed in the q(2) region below the square of the J/psi mass. Integrating over 15 < q(2) < 20 GeV2/c(4) the differential branching fraction is measured as dB(Lambda(0)(b) -> Lambda mu(+)mu(-))/dq(2) = (1.18(-0.08)(+0.09) +/- 0.03 +/- 0.27) x 10(-7) (GeV2/c(4))(-1) where the uncertainties are statistical, systematic and due to the normalisation mode Lambda(0)(b) -> J/psi Lambda , respectively. In the q(2) intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon (A(FB)(l)) and hadron (A(FB)(h)) systems are measured for the first time. In the range 15 < q(2) < 20GeV(2)/c(4) they are found to be A(FB)(l) = -0.05 +/- 0.09 (stat) +/- 0.03 (syst) and A(FB)(h) = -0.29 +/- 0.07 (stat) +/- 0.03 (syst).
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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 asymmetries and polarisation fractions in B-s(0) -> K*(0)(K)over-bar*(0) decays. J. High Energy Phys., 07(7), 166–28pp.
Abstract: An angular analysis of the decay B-s(0) -> K*(0)(K) over bar*(0) is performed using pp collisions corresponding to an integrated luminosity of 1.0 fb(-1) collected by the LHCb experiment at a centre-of-mass energy root s = 7TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction f(L) = 0.201 +/- 0.057 (stat.) +/- 0.040 (syst.) for the B-s(0) -> K*(892)(0)(K) over bar*(892)(0) decay. A large scalar contribution from the K*(0) (1430) and K*(0) (800) resonances is found, allowing the determination of additional CP asymmetries. Triple product and direct CP asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction B(B-s(0) -> K*(892)(0)(K) over bar*(892)(0)) is measured to be (10.8 +/- 2.1 (stat.) +/- 1.4 (syst.) +/- 0.6 (f(d)/f(s))) x 10(-6).
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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 heavy Majorana neutrinos with the ATLAS detector in pp collisions at root s=8 TeV. J. High Energy Phys., 07(7), 162–44pp.
Abstract: A search for heavy Majorana neutrinos in events containing a pair of high-p(T) leptons of the same charge and high-p(T) jets is presented. The search uses 20.3 fb(-1) of pp collision data collected with the ATLAS detector at the CERN Large Hadron Collider with a centre-of-mass energy of root s = 8TeV. The data are found to be consistent with the background-only hypothesis based on the Standard Model expectation. In the context of a Type-I seesaw mechanism, limits are set on the production cross-section times branching ratio for production of heavy Majorana neutrinos in the mass range between 100 and 500 GeV. The limits are subsequently interpreted as limits on the mixing between the heavy Majorana neutrinos and the Standard Model neutrinos. In the context of a left-right symmetric model, limits on the production cross-section times branching ratio are set with respect to the masses of heavy Majorana neutrinos and heavy gauge bosons W-R and Z'.
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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). A search for high-mass resonances decaying to tau(+)tau(-) in pp collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 157–44pp.
Abstract: A search for high-mass resonances decaying into tau(+)tau(-) final states using proton-proton collisions at root s = 8 TeV produced by the Large Hadron Collider is presented. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 19.5-20.3 fb(-1). No statistically significant excess above the Standard Model expectation is observed; 95% credibility upper limits are set on the cross section times branching fraction of Z' resonances decaying into tau(+)tau(-) pairs as a function of the resonance mass. As a result, Z' bosons of the Sequential Standard Model with masses less than 2.02 TeV are excluded at 95% credibility. The impact of the fermionic couplings on the Z' acceptance is investigated and limits are also placed on a Z' model that exhibits enhanced couplings to third-generation fermions.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for the decay B-s(0) -> (D)over-bar(0) f(0)(980). J. High Energy Phys., 08(8), 005–19pp.
Abstract: A search for B-s(0) -> (D) over bar (0) f(0)(980) decays is performed using 3.0 fb(1-) of pp collision data recorded by the LHCb experiment during 2011 and 2012. The f(0)(980) meson is reconstructed through its decay to the pi(+)pi(-) final state in the mass window 900 MeV/c(2) < m (pi(+)pi(-)) < 1080 MeV/c(2). No significant signal is observed. The first upper limits on the branching fraction of B (B-s(0) -> (D) over bar (0) f(0)(980)) < 3.1 (3.4) x 10(-6) are set at 90% (95 %) confidence level.
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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 production of vector-like quark pairs and of four top quarks in the lepton-plus-jets final state in pp collisions at root 8=8 TeV with the ATLAS detector. J. High Energy Phys., 08(8), 105–86pp.
Abstract: A search for pair production of vector-like quarks, both up-type (T) and down-type (B), as well as for four-top-quark production, is presented. The search is based on pp collisions at TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 20.3 fb(-1). Data are analysed in the lepton-plus-jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets. Dedicated analyses are performed targeting three cases: a T quark with significant branching ratio to a W boson and a b-quark , and both a T quark and a B quark with significant branching ratio to a Higgs boson and a third-generation quark ( respectively). No significant excess of events above the Standard Model expectation is observed, and 95% CL lower limits are derived on the masses of the vector-like T and B quarks under several branching ratio hypotheses assuming contributions from T -> Wb, Zt, Ht and B -> Wt, Zb, Hb decays. The 95% CL observed lower limits on the T quark mass range between 715 GeV and 950 GeV for all possible values of the branching ratios into the three decay modes, and are the most stringent constraints to date. Additionally, the most restrictive upper bounds on four-top-quark production are set in a number of new physics scenarios.
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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 new phenomena in events with three or more charged leptons in pp collisions at TeV with the ATLAS detector. J. High Energy Phys., 08(8), 138–60pp.
Abstract: A generic search for anomalous production of events with at least three charged leptons is presented. The data sample consists of pp collisions at TeV collected in 2012 by the ATLAS experiment at the CERN Large Hadron Collider, and corresponds to an integrated luminosity of 20.3 fb(-1). Events are required to have at least three selected lepton candidates, at least two of which must be electrons or muons, while the third may be a hadronically decaying tau. Selected events are categorized based on their lepton flavour content and signal regions are constructed using several kinematic variables of interest. No significant deviations from Standard Model predictions are observed. Model-independent upper limits on contributions from beyond the Standard Model phenomena are provided for each signal region, along with prescription to re-interpret the limits for any model. Constraints are also placed on models predicting doubly charged Higgs bosons and excited leptons. For doubly charged Higgs bosons decaying to e tau or μtau, lower limits on the mass are set at 400 GeV at 95% confidence level. For excited leptons, constraints are provided as functions of both the mass of the excited state and the compositeness scale I >, with the strongest mass constraints arising in regions where the mass equals I >. In such scenarios, lower mass limits are set at 3.0 TeV for excited electrons and muons, 2.5 TeV for excited taus, and 1.6 TeV for every excited-neutrino flavour.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the exclusive gamma production cross-section in pp collisions at root s=7 TeV and 8 TeV. J. High Energy Phys., 09(9), 084–20pp.
Abstract: A study is presented of central exclusive production of gamma(n S) states, where the gamma (n S) resonances decay to the mu(+) mu(-) final state, using p p collision data recorded by the LHCb experiment. The cross-section is measured in the rapidity range 2 < y (gamma) < 4.5 where the muons are reconstructed in the pseudorapidity range 2 < eta (mu(+/-)) < 4.5. The data sample corresponds to an integrated luminosity of 2.9 fb(-1) and was collected at centreof- mass energies of 7TeV and 8TeV. The measured gamma(1 S) and gamma(2 S) production crosssections are sigma(pp -> p gamma(1S)p) = 9.0 +/- 1.7 pb and sigma(pp -> p gamma(2S)p) = 1.3 +/- 0.3 pb, where the first uncertainties are statistical and the second are systematic. The gamma (1S) cross-section is also measured as a function of rapidity and is found to be in good agreement with Standard Model predictions. An upper limit is set at 3.4 pb at the 95% confidence level for the exclusive gamma(3 S) production cross-section, including possible contamination from chi b (3P) -> gamma (3S)gamma decays.
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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). Measurement of charged-particle spectra in Pb plus Pb collisions at root s(NN)=2.76 TeV with the ATLAS detector at the LHC. J. High Energy Phys., 09(9), 050–51pp.
Abstract: Charged-particle spectra obtained in Pb+Pb interactions at root s(NN) = 2.76TeV and pp interactions at root s(NN) = 2.76TeV with the ATLAS detector at the LHC are presented, using data with integrated luminosities of 0.15 nb(-1) and 4.2 pb(-1), respectively, in a wide transverse momentum (0.5 < p(T) < 150 GeV) and pseudorapidity (vertical bar eta vertical bar < 2) range. For Pb+Pb collisions, the spectra are presented as a function of collision centrality, which is determined by the response of the forward calorimeters located on both sides of the interaction point. The nuclear modification factors R-AA and R-CP are presented in detail as a function of centrality, p(T) and eta. They show a distinct p(T)-dependence with a pronounced minimum at about 7 GeV. Above 60 GeV, R-AA is consistent with a plateau at a centrality-dependent value, within the uncertainties. The value is 0.55 +/- 0.01(stat.) +/- 0.04(syst.) in the most central collisions. The R-AA distribution is consistent with flat vertical bar eta vertical bar dependence over the whole transverse momentum range in all centrality classes.
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