The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities ( ) in proton-proton collisions at three center-of-mass energies, Formula omitted 0.9, ...2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 Formula omitted 0.3 % (stat) 8.8 % (sys) and 61.2 Formula omitted 0.3 % (stat) 7.6 % (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The production of the strange and double-strange baryon resonances (..., ...) has been measured at mid-rapidity (... ...) ...in proton-proton collisions at ... ... 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the ... pentaquark, decaying in the ... channel, has been carried out but no evidence is seen.
The production of the strange and double-strange baryon resonances (Formula: see text, Formula: see text) has been measured at mid-rapidity (Formula: see textFormula: see text) in proton-proton ...collisions at Formula: see text Formula: see text 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the Formula: see text pentaquark, decaying in the Formula: see text channel, has been carried out but no evidence is seen.
The measurement of primary Formula: see text, Formula: see text, Formula: see text and Formula: see text production at mid-rapidity (Formula: see text 0.5) in proton-proton collisions at Formula: see ...textFormula: see text 7 TeV performed with a large ion collider experiment at the large hadron collider (LHC) is reported. Particle identification is performed using the specific ionisation energy-loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/Formula: see text for pions, from 0.2 up to 6 GeV/Formula: see text for kaons and from 0.3 up to 6 GeV/Formula: see text for protons. The measured spectra and particle ratios are compared with quantum chromodynamics-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Furthermore, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies.
We present the first measurement at the LHC of exclusive J/ψ photoproduction off protons, in ultraperipheral proton-lead collisions at sqrts_{NN}=5.02 TeV. Events are selected with a dimuon pair ...produced either in the rapidity interval, in the laboratory frame, 2.5<y<4 (p-Pb) or -3.6<y<-2.6 (Pb-p), and no other particles observed in the ALICE acceptance. The measured cross sections σ(γ+p→J/ψ+p) are 33.2±2.2(stat)±3.2(syst)±0.7(theor) nb in p-Pb and 284±36(stat)_{-32}^{+27}(syst)±26(theor) nb in Pb-p collisions. We measure this process up to about 700 GeV in the γp center of mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the J/ψ photoproduction cross section in γp energies from about 20 to 700 GeV, or equivalently, from Bjorken x scaling variable between ∼2×10^{-2} and ∼2×10^{-5}, thus indicating no significant change in the gluon density behavior of the proton between HERA and LHC energies.
The production of \({\rm J}/\psi\) and \(\psi^\prime\) charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were ...collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The \({\rm J}/\psi\) and \(\psi^\prime\) production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the \(\psi^\prime\) than for the \({\rm J}/\psi\). Given the high statistics of the data samples, the \(x_{\rm F}\) (or rapidity) differential cross-sections of the \({\rm J}/\psi\) and \(\psi^\prime\) states have also been studied, for each of the target nuclei.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The ALICE Collaboration at the LHC has measured the J/ψ and ψ' photoproduction at mid-rapidity in ultra-peripheral Pb-Pb ...collisions at ... The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 mub^sup -1^. The cross section for coherent and incoherent J/ψ production in the rapidity interval -0.9<y<0.9, are ... and ..., respectively. The results are compared to theoretical models for J/ψ production and the coherent cross section is found to be in good agreement with those models incorporating moderate nuclear gluon shadowing at Bjorken-x around 10^sup -3^, such as EPS09 parametrization. In addition the cross section for the process γγarrow righte ^sup +^ e ^sup -^ has been measured and found to be in agreement with models implementing QED at leading order.
Spike production is studied in pp and π
+p/K
+p collisions in the beam-momentum range of 205–360 GeV/c. The pseudorapidity distribution of spike centers exhibits two narrow peaks in pp interactions, ...while having one wide bump in πp and Kp interactions. The position of the peaks is consistent with the expectation from a model of coherent gluon radiation at finite length. The interference between the quark color amplitudes obtained within this model causes two off-center peaks in pp data, but only one central peak in πp and Kp data.
The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at sqrts_{NN}=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative ...slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta p_{T} between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even p_{T} shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.
PDF
