The ATLAS Collaboration has measured the inclusive production of $Z$ bosons via their decays into electron and muon pairs in $p+$Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV at the Large Hadron Collider. The measurements are made using data corresponding to integrated luminosities of 29.4 nb$^{-1}$ and 28.1 nb$^{-1}$ for $Z \rightarrow ee$ and $Z \rightarrow \mu\mu$, respectively. The results from the two channels are consistent and combined to obtain a cross section times the $Z \rightarrow \ell\ell$ branching ratio, integrated over the rapidity region $|y^{*}_{Z}|<3.5$, of 139.8 $\pm$ 4.8 (stat.) $\pm$ 6.2 (syst.) $\pm$ 3.8 (lumi.) nb. Differential cross sections are presented as functions of the $Z$ boson rapidity and transverse momentum, and compared with models based on parton distributions both with and without nuclear corrections. The centrality dependence of $Z$ boson production in $p+$Pb collisions is measured and analyzed within the framework of a standard Glauber model and the model's extension for fluctuations of the underlying nucleon-nucleon scattering cross section.
We report on the measurement of $\rm{J}/\psi$ production in the dielectron channel at mid-rapidity (|y|<1) in p+p and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment at the Relativistic Heavy Ion Collider. The transverse momentum $p_{T}$ spectra in p+p for $p_{T}$ < 4 GeV/c and d+Au collisions for $p_{T}$ < 3 GeV/c are presented. These measurements extend the STAR coverage for $\rm{J}/\psi$ production in p+p collisions to low $p_{T}$. The $<p_{T}^{2}>$ from the measured $\rm{J}/\psi$ invariant cross section in p+p and d+Au collisions are evaluated and compared to similar measurements at other collision energies. The nuclear modification factor for $\rm{J}/\psi$ is extracted as a function of $p_{T}$ and collision centrality in d+Au and compared to model calculations using the modified nuclear Parton Distribution Function and a final-state $\rm{J}/\psi$ nuclear absorption cross section.
We have studied the inclusive production of the hadrons π ± , K ± , p, p , Λ, Λ , ρ and ⋉ in the central region at the ISR s = 53 GeV , in both pp and p p collisions. Differences are observed only for K ± , p, and p production. We then study also correlations between low- p T pp and p p pairs in the two types of collisions, separating the contribution from baryon pair production and from the incident particles (stopping protons). We observe a positive correlation between two stopping protons; between the production of two pairs, and between a stopping proton and a pair production, there are negative correlations.
The production rate of charged D* mesons in jets has been measured in 1.8-TeV p¯p collisions at the Fermilab Tevatron with the Collider Detector at Fermilab. In a sample of approximately 32 300 jets with a mean transverse energy of 47 GeV obtained from an exposure of 21.1 nb−1, a signal corresponding to 25.0±7.5(stat)±2.0(syst) D*±→K∓π±π± events is seen above background. This corresponds to a ratio N(D*++D*−)/N(jet) =0.10±0.03±0.03 for D* mesons with fractional momentum z greater than 0.1.
The inclusive cross section for larger p T π 0 production near 90° in p-p collisions at the CERN ISR is presented for centre-of-mass energies 30.7, 53.1 and 62.4 GeV. The data are inconsistent with scaling of the form p T − n F ( x T ), with constant n or with n allowed to depend on x T = 2p T / s . For s = 53.1 and 62.4 GeV , the value of n found for 3.5 < p T < 7.0 GeV/ c is n = 8.0 ± 0.5, in agreement with previous experiments. However, for 7.5 < p T < 14.0 GeV/ c the value becomes n = 5.1 ± 0.4.
The cross section for the production and subsequent decay to electron and neutrino of the W intermediate vector boson has been measured in 1.8-TeV p¯p collisions at the Fermilab Tevatron Collider. An analysis of events with missing transverse energy greater than 25 GeV and with an electron of transverse energy greater than 15 GeV from a datum sample of 25.3 nb−1 gives σB=2.6±0.6±0.5 nb.
We present a measurement of jet shapes in p¯p collisions at √s =1.8 TeV at the Fermilab Tevatron using the Collider Detector at Fermilab (CDF). Qualitative agreement is seen with the predictions of recent next-to-leading [O(αs3)] calculations and with leading logarithm QCD based Monte Carlo simulations. The dependence of the jet shape on transverse energy is studied.
An analysis of high-transverse-momentum electrons using data from the Collider Detector at Fermilab (CDF) of p¯p collisions at s=1800 GeV yields values of the production cross section times branching ratio for W and Z0 bosons of σ(p¯p→WX→eνX)=2.19±0.04(stat)±0.21(syst) nb and σ(p¯p→Z0X→e+e−X)=0.209±0.013(stat)±0.017(syst) nb. Detailed descriptions of the CDF electron identification, background, efficiency, and acceptance are included. Theoretical predictions of the cross sections that include a mass for the top quark larger than the W mass, current values of the W and Z0 masses, and higher-order QCD corrections are in good agreement with these measured values.
An apparatus consisting of a superconducting solenoid magnet, cylindrical drift-chambers, and two arrays of lead-glass Čerenkov counters has been used at the CERN ISR to study the production of e + e − pairs of invariant mass above 6.5 GeV/ c 2 . Cross sections for the continuum and the ϒ family of resonances are presented, as well as the mean transverse momentum 〈 p T 〉 of the electron-positron pairs in the continuum and resonance region.
An analysis of proton-antiproton collisions at √s =1.8 TeV recorded with the Collider Detector at Fermilab (CDF) yields σ(pp¯→WX)B(W→μν)=2.21±0.22 nb and σ(pp¯→ZX)B(Z →μ+μ−)=0.226±0.032 nb. The ratio is Rμ=σWB(W→μν)/σZB(Z→μ+μ−)=9.8±1.2. Combining with previous CDF electron results gives σWB(W→lν)=2.20±0.20 nb, σZB(Z→l+l−)=0.214±0.023 nb, and Rl=10.0±0.8. We extract the ratios of the coupling constants gμ/ge and gτ/gμ. Using standard model assumptions we deduce the inverse branching ratio B−1(W→lν), the width Γ(W), and a decay-mode-independent lower bound on the top quark mass of 45 GeV/c2 (95% C.L.).