(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Measurements are presented of electroweak boson production using data from pp collisions at a centre-of-mass energy of ... ...TeV. The analysis is based on an integrated luminosity of 2.0 fb super(-1) recorded with the LHCb detector. The bosons are identified in the W arrow right mu nu and Z arrow right mu super(+) mu super(-) decay channels. The cross-sections are measured for muons in the pseudorapidity range 2.0 < eta < 4.5, with transverse momenta p sub(T) > 20 GeV/c and, in the case of the Z boson, a dimuon mass within ... GeV/c super(2). The results are ... ... ... ... ... ... ... ... 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 super(-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. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A measurement of the Z(arrow right mu ^sup +^ mu ^sup -^) + jet production cross-section in pp collisions at a ...centre-of-mass energy ... = 7 TeV is presented. The analysis is based on an integrated luminosity of 1.0 fb^sup -1^ recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction (2.0 < eta < 4.5). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction. Figure not available: see fulltext.
The LHCb measurement of the lifetime ratio of the Λb0 baryon to the B¯0 meson is updated using data corresponding to an integrated luminosity of 3.0 fb−1 collected using 7 and 8 TeV centre-of-mass ...energy pp collisions at the LHC. The decay modes used are Λb0→J/ψpK− and B¯0→J/ψπ+K−, where the π+K− mass is consistent with that of the K¯⁎0(892) meson. The lifetime ratio is determined with unprecedented precision to be 0.974±0.006±0.004, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the B¯0 lifetime, the Λb0 lifetime is found to be 1.479±0.009±0.010 ps.
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/ψK_{S}^{0} and B_{s}^{0}→J/ψK^{+}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 Δa_{μ} 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.
Two structures are observed close to the kinematic threshold in the Ξ(b)(0)π(-) mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), ...recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content bds are expected in this mass region: the spin-parity J(P)=(1/2)(+) and J(P)=(3/2)(+) states, denoted Ξ(b)('-) and Ξ(b)(*-). Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be m(Ξ(b)('-))-m(Ξ(b)(0))-m(π(-))=3.653±0.018±0.006 MeV/c(2), m(Ξ(b)(*-))-m(Ξ(b)(0))-m(π(-))=23.96±0.12±0.06 MeV/c(2), Γ(Ξ(b)(*-))=1.65±0.31±0.10 MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of Γ(Ξ(b)('-))<0.08 MeV at 95% confidence level. Relative production rates of these states are also reported.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Charged particle multiplicities are studied in proton-proton collisions in the forward region at a centre-of-mass energy of ......TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of ... in pseudorapidity, momenta greater than ... and transverse momenta greater than ... The measurements are performed using events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators.
We present a measurement of the ratio of the B¯s⁰ meson lifetime, in the flavor-specific decay to Ds⁺π⁻, to that of the B¯⁰ meson. The pp collision data used correspond to an integrated luminosity of ...1 fb(-1), collected with the LHCb detector, at a center-of-mass energy of 7 TeV. Combining our measured value of 1.010±0.010±0.008 for this ratio with the known B¯⁰ lifetime, we determine the flavor-specific B¯s⁰ lifetime to be τ(B¯s⁰ )=1.535±0.015±0.014 ps, where the uncertainties are statistical and systematic, respectively. This is the most precise measurement to date, and is consistent with previous measurements and theoretical predictions.
Abstract Production of ... mesons in proton-lead collisions at a nucleon-nucleon centre-of-mass energy ... = 5 TeV is studied with the LHCb detector. The analysis is based on a data sample ...corresponding to an integrated luminosity of 1.6 nb-1. The ... mesons of transverse momenta up to 15 GeV/c are reconstructed in the dimuon decay mode. The rapidity coverage in the centre-of-mass system is 1.5 < y < 4.0 (forward region) and -5.0 < y < -2.5 (backward region). The forward-backward production ratio and the nuclear modification factor for ...(1S) mesons are determined. The data are compatible with the predictions for a suppression of ...(1S) production with respect to proton-proton collisions in the forward region, and an enhancement in the backward region. The suppression is found to be smaller than in the case of prompt J/psi mesons. Figure not available: see fulltext.
The production cross-section of J/ψ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of s√=13TeV, corresponding to an integrated ...luminosity of 279±11pb−1. The measurement is performed for J/ψ mesons with a transverse momentum of less than 10GeV/c in the rapidity range 2.0<y<4.5. The production cross-section is measured to be 13.5±0.9±0.8nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/ψ pair are measured and compared to theoretical predictions.
A study of indirect CP violation in $D^0$ mesons through the determination of the parameter $A_\Gamma$ is presented using a data sample of $pp$ collisions, corresponding to an integrated luminosity ...of 1.0 fb$^{-1}$, collected with the LHCb detector and recorded at the centre-of-mass energy of 7 TeV at the LHC. The parameter $A_\Gamma$ is the asymmetry of the effective lifetimes measured in decays of $D^0$ and $\bar{D}^0$ mesons to the CP eigenstates $K^-K^+$ and $\pi^-\pi^+$. Fits to the data sample yield $A_\Gamma(KK)=(-0.35\pm0.62\pm0.12)\times 10^{-3}$ and $A_\Gamma(\pi\pi)=(0.33\pm1.06\pm0.14)\times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results represent the world's best measurements of these quantities. They show no difference in $A_\Gamma$ between the two final states and no indication of CP violation.
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