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Register a new userMeasurement of the forward Z boson production cross-section in pp collisions at $sqrt{s} = 13$ TeV
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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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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.
Using a data sample corresponding to an integrated luminosity of $2.0,fb^{-1}$, collected by the LHCb experiment, the production of the $eta_c(1S)$ state in proton-proton collisions at a centre-of-mass energy of $sqrt{s}=13 text{ TeV}$ is studied in the rapidity range ${2.0 < y < 4.5}$ and in the transverse momentum range ${6.5 < p_{T} < 14.0text{ GeV}}$. The cross-section for prompt production of $eta_c(1S)$ mesons relative to that of the $J/psi$ meson is measured using the ${pbar{p}}$ decay mode and is found to be ${sigma_{eta_c(1S)}/sigma_{J/psi} = 1.69 pm 0.15 pm 0.10 pm 0.18}$. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the ${J/psito p bar{p}}$ and ${eta_cto p bar{p}}$ decays. The prompt $eta_c(1S)$ production cross-section is determined to be ${sigma_{eta_c(1S)} = 1.26 pm 0.11pm 0.08 pm 0.14 ,mu b}$, where the last uncertainty includes that on the ${J/psi}$ meson cross-section. The ratio of the branching fractions of $b$-hadron decays to the $eta_c(1S)$ and ${J/psi}$ states is measured to be ${mathcal{B}_{btoeta_c X}/mathcal{B}_{bto J/psi X} = 0.48 pm 0.03 pm 0.03 pm 0.05}$, where the last uncertainty is due to those on the branching fractions of the ${J/psi to p bar{p}}$ and ${eta_cto p bar{p}}$ decays. The difference between the ${J/psi}$ and $eta_c(1S)$ masses is also determined to be ${113.0 pm 0.7 pm 0.1text{ MeV}}$, which is the most precise single measurement of this quantity to date.
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.
The production of $B^{pm}$ mesons is studied in $pp$ collisions at centre-of-mass energies of 7 and 13 TeV, using $B^{pm}rightarrow J/psi K^{pm}$ decays and data samples corresponding to 1.0 fb$^{-1}$ and 0.3 fb$^{-1}$, respectively. The production cross-sections summed over both charges and integrated over the transverse momentum range $0<p_{text{T}}< 40$ GeV/$c$ and the rapidity range $2.0<y<4.5$ are measured to be $sigma(pp rightarrow B^{pm} X, sqrt{s} = text{7 TeV}) = 43.0 pm 0.2 pm 2.5 pm 1.7mu b,$ $sigma(pp rightarrow B^{pm} X, sqrt{s} = text{13 TeV}) = 86.6 pm 0.5 pm 5.4 pm 3.4mu b,$ where the first uncertainties are statistical, the second are systematic, and the third are due to the limited knowledge of the $B^{pm}rightarrow J/psi K^{pm}$ branching fraction. The ratio of the cross-section at 13 TeV to that at 7 TeV is determined to be $2.02pm0.02text{(stat)}pm0.12text{(syst)}$. Differential cross-sections are also reported as functions of $p_{text{T}}$ and $y$. All results are in agreement with theoretical calculations based on the state-of-art fixed next-to-leading order quantum chromodynamics.
The production cross-section of $J/psi$ pairs is measured using a data sample of $pp$ collisions collected by the LHCb experiment at a centre-of-mass energy of $sqrt{s} = 13 ,{mathrm{TeV}}$, corresponding to an integrated luminosity of $279 pm 11 ,{mathrm{pb^{-1}}}$. The measurement is performed for $J/psi$ mesons with a transverse momentum of less than $10 ,{mathrm{GeV}}/c$ in the rapidity range $2.0<y<4.5$. The production cross-section is measured to be $15.2 pm 1.0 pm 0.9 ,{mathrm{nb}}$. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the $J/psi$ pair are measured and compared to theoretical predictions.
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