LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of the properties of the Xi(b)(*0) baryon. J. High Energy Phys., 05(5), 161–19pp.
Abstract: We perform a search for near-threshold I (b) (0) resonances decaying to I (b) (-) pi (+) in a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb(-1) collected by the LHCb experiment. We observe one resonant state, with the following properties: m(Xi b*0) – m (Xi b-) – m (pi+) = 15.727 +/- 0.068 (stat) +/- 0.023 (syst) MeV/c2, Gamma(Xi b*0) = 0.90 +/- 0.16 (stat) +/- 0.08 (syst) MeV. This confirms the previous observation by the CMS collaboration. The state is consistent with the J (P) = 3/2(+)aEuro integral I (b) (au 0) resonance expected in the quark model. This is the most precise determination of the mass and the first measurement of the natural width of this state. We have also measured the ratio sigma(pp -> Xi b*0 X)B(Xi b*0 -> Xi b-pi+)/sigma(pp -> Xi b- X) = 0.28 +/- 0.03 (stat.) +/- 0.01 (syst).
|
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).
|
LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the forward Z boson production cross-section in pp collisions at root s=7 TeV. J. High Energy Phys., 08(8), 039–37pp.
Abstract: A measurement of the production cross-section for Z bosons that decay to muons is presented. The data were recorded by the LHCb detector during pp collisions at a centre-of-mass energy of 7 TeV, and correspond to an integrated luminosity of 1.0 fb(-1). The cross-section is measured for muons in the pseudorapidity range 2.0 < eta < 4.5 with transverse momenta p(T) >20 GeV/e. The dimuon mass is restricted to 60 < M mu+mu- < 120 GeV/c(2). The measured cross-section is sigma(Z ->mu+mu-) = (76.0 +/- 0.3 +/- 0.5 +/- 1.0 +/- 1.3) pb where the uncertainties are due to the sample size, systematic effects, the beam energy and the luminosity. This result is in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. The cross-section is also measured differentially as a function of kinematic variables of the Z boson. Ratios of the production cross-sections of electroweak bosons are presented using updated LHCb measurements of W boson production. A precise test of the Standard Model is provided by the measurement of the ratio sigma(W+) -> mu(+) nu(mu) + sigma(W) -> mu(+) (nu) over bar (mu)/sigma(Z ->mu+mu-) = 0.09 +/- 0.12 +/- 0.05, where the uncertainty due to luminosity cancels.
|
LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Angular analysis of the B-0 -> K*(0) e(+) e(-) decay in the low-q(2) region. J. High Energy Phys., 04(4), 064–23pp.
Abstract: An angular analysis of the B-0 -> K(*0)e(+) e(-) decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 fb(-1), collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared (q(2)) interval between 0.002 and 1.120 GeV2/c(4). The angular observables F-L and A(T)(Re) which are related to the K-*0 polarisation and to the lepton forward-backward asymmetry, are measured to be F-L = 0.16 +/- 0.06 +/- 0.03 and A(T)(Re) = 0.10 +/- 0.18 +/- 0.05, where the first uncertainty is statistical and the second systematic. The angular observables A(T)((2)) and A(T)(Im) which are sensitive to the photon polarisation in this q(2) range, are found to be A(T)((2)) = – 0.23 +/- 0.23 +/- 0.05 and A(T)(Im) = 0.14 +/- 0.22 +/- 0.05. The results are consistent with Standard Model predictions.
|
LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of forward W and Z boson production in pp collisions at root s=8TeV. J. High Energy Phys., 01(1), 155–45pp.
Abstract: Measurements are presented of electroweak boson production using data from pp collisions at a centre-of-mass energy of root s = 8TeV. The analysis is based on an integrated luminosity of 2.0 fb(-1) recorded with the LHCb detector. The bosons are identified in the W -> μnu and Z -> mu(+)mu(-) decay channels. The cross-sections are measured for muons in the pseudorapidity range 2.0 < eta < 4.5, with transverse momenta p(T) > 20 GeV/c and, in the case of the Z boson, a dimuon mass within 60 < M mu+mu- < 120 GeV/c(2). The results are sigma(W+) -> mu(+)nu(-) = 1093.6 +/- 2.1 +/- 7.2 +/- 10.9 +/- 12.7 pb, sigma(W-) -> mu(-)nu(-) = 818.4 +/- 1.9 +/- 5.0 +/- 7.0 +/- 9.5 pb, sigma(Z) -> mu(+)mu(-) = 95.0 +/- 0.3 +/- 0.7 +/- 1.1 +/- 1.1 pb, where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the W and Z boson cross-sections with centre-of-mass energy is studied using previously reported measurements with 1.0 fb(-1) of data at 7 TeV. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.
|
