LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). First Observation of Top Quark Production in the Forward Region. Phys. Rev. Lett., 115(11), 112001–10pp.
Abstract: Top quark production in the forward region in proton-proton collisions is observed for the first time. The W + b final state with W -> μnu is reconstructed using muons with a transverse momentum, p(T), larger than 25 GeV in the pseudorapidity range 2.0 < eta < 4.5. The b jets are required to have 50 < p(T) < 100 GeV and 2.2 < eta < 4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p(T) > 20 GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0 fb(-1) collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross sections in the fiducial region are sigma(top)[7 TeV] = 239 +/- 53(stat) +/- 33(syst) +/- 24(theory) fb; sigma(top)[8 TeV ] = 289 +/- 43(stat) +/- 40(syst) +/- 29(theory) fb: These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order standard model predictions.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for Hidden-Sector Bosons in B-0 -> K*(0)mu(+)mu(-) Decays. Phys. Rev. Lett., 115(16), 161802–10pp.
Abstract: A search is presented for hidden-sector bosons, chi, produced in the decay B-0 -> K*(892)(0)chi, with K*(892)(0) -> K+pi(-) and chi -> mu(+)mu(-). The search is performed using pp-collision data corresponding to 3.0 fb(-1) collected with the LHCb detector. No significant signal is observed in the accessible mass range 214 <= m(chi) <= 4350 MeV, and upper limits are placed on the branching fraction product B(B-0 -> K*(892)(0)chi) X B(chi -> mu(+)mu(-)) as a function of the mass and lifetime of the chi boson. These limits are of the order of 10(-9) for chi lifetimes less than 100 ps over most of the m(chi) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Evidence for the Strangeness-Changing Weak Decay Xi(-)(b) -> Lambda(0)(b)pi(-). Phys. Rev. Lett., 115(24), 241801–10pp.
Abstract: Using a pp collision data sample corresponding to an integrated luminosity of 3.0 fb(-1), collected by the LHCb detector, we present the first search for the strangeness-changing weak decay Xi(-)(b) -> Delta(0)(b)pi(-). No b hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be f Xi(-)(b)/f Lambda B-0(b)(Xi(-)(b) -> Lambda(0)(b)pi(-)) = (5.7 +/- 1.8(-0.9)(+0.8)) x 10(-4) where f Xi(-)(b) and f Lambda(0)(b) are the b -> Xi(-)(b) and b -> Lambda(0)(b) fragmentation fractions, and B(Xi(-)(b) -> Lambda(0)(b)pi(-)) is the branching fraction. Assuming f Xi(-)(b)/f Lambda(0)(b) is bounded between 0.1 and 0.3, the branching fraction B(Xi(-)(b) -> Lambda(0)(b)pi(-)) would lie in the range from (0.57 +/- 0.21)% to (0.19 +/- 0.07)%.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Model-Independent Evidence for J/psi p Contributions to Lambda(0)(b) -> J/psi pK(-) Decays. Phys. Rev. Lett., 117(8), 082002–9pp.
Abstract: The data sample of Lambda(0)(b) -> J/psi pK(-) decays acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb(-1), is inspected for the presence of J/psi p or J/psi K- contributions with minimal assumptions about K(-)p contributions. It is demonstrated at more than nine standard deviations that Lambda(0)(b) -> J/psi pK(-) decays cannot be described with K- p contributions alone, and that J/psi K- contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for P-c(+)-> J/psi p charmonium-pentaquark states in the same data sample.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Observation of B-s(0) -> (D)over-bar(0)K(S)(0) and Evidence for B-s(0) -> (D)over-bar*K-0(S)0 Decays. Phys. Rev. Lett., 116(16), 161802–9pp.
Abstract: The first observation of the B-s(0) -> (D) over bar K-0(S)0 decay mode and evidence for the B-s(0) -> (D) over bar*K-0(S)0 decay mode are reported. The data sample corresponds to an integrated luminosity of 3.0 fb-1 collected in pp collisions by LHCb at center-of-mass energies of 7 and 8 TeV. The branching fractions are measured to be B(B-s(0) -> (D) over bar (0)(K) over bar (0)) = [4.3 +/- 0.5(stat) +/- 0.3 (syst) +/- 0.3(frag) +/- 0.6(norm)] x 10(-4), B(B-s(0) -> (D) over bar*(0)(K) over bar (0)) = [2.8 +/- 1.0(stat) +/- 0.3 (syst) +/- 0.2(frag) +/- 0.4(norm)] x 10(-4), where the uncertainties are due to contributions coming from statistical precision, systematic effects, and the precision of two external inputs, the ratio f(s)/f(d) and the branching fraction of B-0 (D) over bar K-0(S)0, which is used as a calibration channel.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of the Difference of Time-Integrated CP Asymmetries in D-0 -> K-K+ and D-0 -> pi(-)pi(+) Decays. Phys. Rev. Lett., 116(19), 191601–10pp.
Abstract: A search for CP violation in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is performed using pp collision data, corresponding to an integrated luminosity of 3 fb(-1), collected using the LHCb detector at center-of-mass energies of 7 and 8 TeV. The flavor of the charm meson is inferred from the charge of the pion in D*(+) -> D-0 pi(+) and D*(-) -> (D) over bar (0)pi(-) decays. The difference between the CP asymmetries in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays, Delta A(CP) A(CP)(K-K+) – A(CP)(pi(-)pi(+)), is measured to be [-0.10 +/- 0.08(stat) +/- 0.03(syst)]%. This is the most precise measurement of a time-integrated CP asymmetry in the charm sector from a single experiment.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Search for violations of Lorentz invariance and CPT symmetry in B-(s)(0) mixing. Phys. Rev. Lett., 116(24), 241601–10pp.
Abstract: Violations of CPT symmetry and Lorentz invariance are searched for by studying interference effects in B-0 mixing and in B-s(0) mixing. Samples of B-0 -> J/psi K-S(0) and B-0(s) -> J/psi K+K- decays are recorded by the LHCb detector in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). No periodic variations of the particle-antiparticle mass differences are found, consistent with Lorentz invariance and CPT symmetry. Results are expressed in terms of the standard model extension parameter Delta a(mu) with precisions of O(10(-15)) and O(10(-14)) GeV for the B-0 and B-s(0) systems, respectively. With no assumption on Lorentz (non) invariance, the CPT-violating parameter z in the B-s(0) system is measured for the first time and found to be Re(z) = -0.022 +/- 0.033 +/- 0.005 and Im(z) = 0.004 +/- 0.011 +/- 0.002, where the first uncertainties are statistical and the second systematic.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). First Observation of D-0 – (D)over-bar(0) Oscillations in D-0 -> K+pi(-)pi(+)pi(-) Decays and Measurement of the Associated Coherence Parameters. Phys. Rev. Lett., 116(24), 241801–10pp.
Abstract: Charm meson oscillations are observed in a time-dependent analysis of the ratio of D-0 -> K+pi(-)pi(+)pi(-) to D-0 -> K-pi(+)pi(-)pi(+) decay rates, using data corresponding to an integrated luminosity of 3.0 fb(-1) recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favored amplitudes r(D)(K3 pi) and the product of the coherence factor R-D(K3 pi) and a charm mixing parameter y'(K3 pi). The constraints measured are r(D)(K3 pi) = (5.67 +/- 0.12) x 10(-2), which is the most precise determination to date, and R-D(K3 pi) y'(K3 pi) = (0.3 +/- 1.8) x 10(-3), which provides useful input for determinations of the CP-violating phase gamma in B-+/- -> DK +/-, D -> K--/+pi(+/-)pi(-/+)pi(+/-) decays. The analysis also gives the most precise measurement of the D-0 -> K+pi(-)pi(+)pi(-) branching fraction, and the first observation of D-0-(D) over bar (0) oscillations in this decay mode, with a significance of 8.2 standard deviations.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Evidence for Exotic Hadron Contributions to Lambda(0)(b) -> J/psi p pi(-) Decays. Phys. Rev. Lett., 117(8), 082003–10pp.
Abstract: A full amplitude analysis of Lambda(0)(b) -> J/psi pi(-) decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb(-1). A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations N -> p pi(-), either the P-c(43800)(+) and P-c(4450)(+) -> J/psi p states, previously observed in Lambda(0)(b) -> J/psi pK(-) decays, or the Z(c)(4200)(-) -> J/psi pi(-) state, previously reported in B-0 -> J/psi K+pi(-) decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the P-c(4380)(+) and P-c(4 450)(+) production rates expected from their previous observation taking account of Cabibbo suppression.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of the CP Asymmetry in B-s(0) – (B)over-bar(s)(0) Mixing. Phys. Rev. Lett., 117(6), 061803–9pp.
Abstract: The CP asymmetry in the mixing of B-s(0) and (B) over bar (0)(s) mesons is measured in proton-proton collision data corresponding to an integrated luminosity of 3.0 fb(-1), recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV. Semileptonic B-s(0) and (B) over bar (s) (0) decays are studied in the inclusive mode D-s(-/+)mu(+/-)nu((-)) X-mu with the D-s(-/+) mesons reconstructed in the K+K-pi(-/+) final state. Correcting the observed charge asymmetry for detection and background effects, the CP asymmetry is found to be a(sl)(s) = (0.39 +/- 0.26 +/- 0.20)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of a(sl)(s) to date. It is consistent with the prediction from the standard model and will constrain new models of particle physics.
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