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Register a new userMeasurement of the Z+b-jet cross-section in pp collisions at $sqrt{s}=7{mathrm{,Tekern -0.1em V}}$ in the forward region
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The associated production of a Z boson or an off-shell photon $gamma^*$ with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of $7{mathrm{,Tekern -0.1em V}}$. The Z bosons are reconstructed in the ${text{Z}/gamma^*}!rightarrow{mu^{+}mu^{-}}$ final state from muons with a transverse momentum larger than $20{mathrm{,Gekern -0.1em V}}$, while two transverse momentum thresholds are considered for jets ($10{mathrm{,Gekern -0.1em V}}$ and $20{mathrm{,Gekern -0.1em V}}$). Both muons and jets are reconstructed in the pseudorapidity range $2.0 < eta < 4.5$. The results are based on data corresponding to $1.0{,mbox{fb}^{-1}}$ recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet cross-section is normalized to the Z+jet cross-section. The measured cross-sections are begin{equation*} sigma(text{$text{Z}/gamma^*(mu^{+}mu^{-})$+b-jet}) = 295 pm 60~(text{stat}) pm 51~(text{syst}) pm 10~(text{lumi}) {,mbox{fb}} end{equation*} for ${p_{rm T}}$(jet)$>10{mathrm{,Gekern -0.1em V}}$, and begin{equation*} sigma(text{$text{Z}/gamma^*(mu^{+}mu^{-})$+b-jet}) = 128 pm 36~(text{stat}) pm 22~(text{syst}) pm 5~(text{lumi}) {,mbox{fb}} end{equation*} for ${p_{rm T}}$(jet)$>20{mathrm{,Gekern -0.1em V}}$.
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Measurements are presented of electroweak boson production using data from $pp$ collisions at a centre-of-mass energy of $sqrt{s} = 8mathrm{,Tekern -0.1em V}$. The analysis is based on an integrated luminosity of $2.0mathrm{,fb}^{-1}$ recorded with the LHCb detector. The bosons are identified in the $Wrightarrowmu u$ and $Zrightarrowmu^{+}mu^{-}$ decay channels. The cross-sections are measured for muons in the pseudorapidity range $2.0 < eta < 4.5$, with transverse momenta $p_{rm T} > 20{mathrm{,Gekern -0.1em V!/}c}$ and, in the case of the $Z$ boson, a dimuon mass within $60 < M_{mu^{+}mu^{-}} < 120{mathrm{,Gekern -0.1em V!/}c^{2}}$. The results are begin{align*} sigma_{W^{+}rightarrowmu^{+} u} &= 1093.6 pm 2.1 pm 7.2 pm 10.9 pm 12.7{rm ,pb} , , sigma_{W^{-}rightarrowmu^{-}bar{ u}} &= phantom{0}818.4 pm 1.9 pm 5.0 pm phantom{0}7.0 pm phantom{0}9.5{rm ,pb} , , sigma_{Zrightarrowmu^{+}mu^{-}} &= phantom{00}95.0 pm 0.3 pm 0.7 pm phantom{0}1.1 pm phantom{0}1.1{rm ,pb} , , end{align*} 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 $1.0mathrm{,fb}^{-1}$ of data at $7mathrm{,Tekern -0.1em V}$. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.
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/c. The dimuon mass is restricted to $60 < M_{mu^{+}mu^{-}} < 120$ GeV/c$^{2}$. The measured cross-section is $$sigma_{Zrightarrowmu^{+}mu^{-}} = (76.0 pm 0.3 pm 0.5 pm 1.0 pm 1.3) , text{pb}$$ 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 $$frac{sigma_{W^{+}rightarrowmu^{+} u_{mu}} + sigma_{W^{-}rightarrowmu^{-}bar{ u}_{mu}}}{sigma_{Zrightarrowmu^{+}mu^{-}}} = 20.63pm0.09pm0.12pm0.05,$$ where the uncertainty due to luminosity cancels.
The production of B+- mesons in proton-proton collisions at sqrt(s)=7 TeV is studied using 35 pb-1 of data collected by the LHCb detector. The B+- mesons are reconstructed exclusively in the B+- -> J/psi K+- mode, with J/psi -> mu+ mu-. The differential production cross-section is measured as a function of the B+- transverse momentum in the fiducial region 0 < pT < 40 GeV/c and with rapidity 2.0 < y < 4.5. The total cross-section, summing up B+ and B-, is measured to be sigma(pp -> B+- X, 0 < pT < 40 GeV/c, 2.0 < y < 4.5) = 41.4 +- 1.5 (stat.) +- 3.1 (syst.) mub.
A measurement of the inclusive $W to mu u$ production cross-section using data from $pp$ collisions at a centre-of-mass energy of $sqrt{s} = 7 {rm , TeV}$ is presented. The analysis is based on an integrated luminosity of about $1.0 {rm , fb}^{-1}$ recorded with the LHCb detector. Results are reported for muons with a transverse momentum greater than $20 {rm , Gekern -0.1em V!/}c$ and pseudorapidity between 2.0 and 4.5. The $W^{+}$ and $W^{-}$ production cross-sections are measured to be $$sigma_{W^{+} to mu^{+} u} = 861.0 pm 2.0 pm 11.2 pm 14.7 {rm , pb},$$ $$sigma_{W^{-} to mu^{-}overline{ u}} = 675.8 pm 1.9 pm 8.8 pm 11.6 {rm , pb},$$ where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity determination. Cross-section ratios and differential distributions as functions of the muon pseudorapidity are also presented. The ratio of $W^{+}$ to $W^{-}$ cross-sections in the same fiducial kinematic region is determined to be $$frac{sigma_{W^{+} to mu^{+} u}}{sigma_{W^{-} to mu^{-}overline{ u}}} = 1.274 pm 0.005 pm 0.009,$$ where the uncertainties are statistical and systematic, respectively. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.
A measurement of the production cross-section of Z bosons in pp collisions at $sqrt{s} = 13$ TeV is presented using dimuon and dielectron final states in LHCb data. The cross-section is measured for leptons with pseudorapidities in the range $2.0 < eta < 4.5$, transverse momenta $p_text{T} > 20$ GeV and dilepton invariant mass in the range $60<m(ellell)<120$ GeV. The integrated cross-section from averaging the two final states is begin{equation*}sigma_{text{Z}}^{ellell} = 194.3 pm 0.9 pm 3.3 pm 7.6text{ pb,}end{equation*} where the first uncertainty is statistical, the second is due to systematic effects, and the third is due to the luminosity determination. In addition, differential cross-sections are measured as functions of the Z boson rapidity, transverse momentum and the angular variable $phi^*_eta$.
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