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Register a new userObservation of $Z$ production in proton-lead collisions at LHCb
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The first observation of $Z$ boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of $sqrt{s_{NN}}=5~text{TeV}$ is presented. The data sample corresponds to an integrated luminosity of $1.6~text{nb}^{-1}$ collected with the LHCb detector. The $Z$ candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above $20~text{GeV}/c$. The invariant dimuon mass is restricted to the range $60-120~text{GeV}/c^2$. The $Z$ production cross-section is measured to be begin{eqnarray*} sigma_{Ztomu^+mu^-}(text{fwd})&=&13.5^{+5.4}_{-4.0}text{(stat.)}pm1.2text{(syst.)}~text{nb} end{eqnarray*} in the direction of the proton beam and begin{eqnarray*} sigma_{Ztomu^+mu^-}(text{bwd}) & =&10.7^{+8.4}_{-5.1}text{(stat.)}pm1.0text{(syst.)}~text{nb} end{eqnarray*} in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.
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A study of prompt charm-hadron pair production in proton-lead collisions at $sqrt{s_mathrm{NN}}= 8.16$ TeV is performed using data corresponding to an integrated luminosity of about 30 nb${}^{-1}$, collected with the LHCb experiment. Production cross-sections for different pairs of charm hadrons are measured and kinematic correlations between the two charm hadrons are investigated. This is the first measurement of associated production of two charm hadrons in proton-lead collisions. The results confirm the predicted enhancement of double parton scattering production in proton-lead collisions compared to the single parton scattering production.
The production of charged hadrons within jets recoiling against a $Z$ boson is measured in proton-proton collision data at $sqrt{s}=8$ TeV recorded by the LHCb experiment. The charged-hadron structure of the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum $p_{mathrm{T}}>20$ GeV and in the pseudorapidity range $2.5<eta<4$. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a $Z$ boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics.
Production of $B_c^+$ mesons in proton-proton collisions at a center-of-mass energy of 8 TeV is studied with data corresponding to an integrated luminosity of $2.0~{rm fb}^{-1}$ recorded by the LHCb experiment. The ratio of production cross-sections times branching fractions between the $B_c^+to J/psi pi^+$ and $B^+to J/psi K^+$ decays is measured as a function of transverse momentum and rapidity in the regions $0 < p_{rm T} < 20~{rm GeV}/c$ and $2.0 < y < 4.5$. The ratio in this kinematic range is measured to be $(0.683pm0.018pm0.009)%$, where the first uncertainty is statistical and the second systematic.
The production of $W$ and $Z$ bosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $pm$ 0.02 fb$^{-1}$. The $W$ boson is identified using its decay to a muon and a neutrino, while the $Z$ boson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios of $W+$jet and $Z$+jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.
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