No Arabic abstract
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.
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.
A measurement of $Zrightarrowtau^+tau^-$ production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb$^{-1}$, from $pp$ collisions at $sqrt{s}=8$ TeV collected by the LHCb experiment. The $tau^+tau^-$ candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for $Z$ bosons with invariant mass between 60 and 120 GeV/$c^2$, which decay to tau leptons with transverse momenta greater than 20 GeV/$c$ and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be $sigma_{pprightarrow{}Zrightarrow{}tau^+tau^-} = 95.8 pm 2.1 pm 4.6 pm 0.2 pm 1.1 mathrm{pb}$, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for $Zrightarrowtau^+tau^-$ to $Zrightarrowmu^+mu^-$ ($Zrightarrow{}e^+e^-$), determined to be $1.01 pm 0.05$ ($1.02 pm 0.06$), is consistent with the lepton-universality hypothesis in $Z$ decays.
In this paper, we report the production cross-section of forward photons in the pseudorapidity regions of $eta,>,10.94$ and $8.99,>,eta,>,8.81$, measured by the LHCf experiment with proton--proton collisions at $sqrt{s}$ = 13 TeV. The results from the analysis of 0.191 $mathrm{nb^{-1}}$ of data obtained in June 2015 are compared to the predictions of several hadronic interaction models that are used in air-shower simulations for ultra-high-energy cosmic rays. Although none of the models agree perfectly with the data, EPOS-LHC shows the best agreement with the experimental data among the models.