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Register a new userParticle Production at Large Transverse Momentum with ALICE
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Authors
Harald Appelshauser
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We present transverse momentum distributions of inclusive charged particles and identified hadrons in $pp$ and Pb--Pb collisions at $rs= 2.76$ TeV, measured by ALICE at the LHC. The Pb--Pb data are presented in intervals of collision centrality and cover transverse momenta up to 50 GeV/$c$. Nuclear medium effects are studied in terms of the nuclear modification factor raa. The results indicate a strong suppression of high-$p_T$ particles in Pb--Pb collisions, consistent with a large energy loss of hard-scattered partons in the hot, dense and long-lived medium created at the LHC. We compare the preliminary results for inclusive charged particles to previous results from RHIC and calculations from energy loss models. Furthermore, we compare the nuclear modification factors of inclusive charged particles to those of identified $pi^0$, $pi^{pm}$, K$^0_s$, and $Lambda$.
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We determine rapidity asymmetry in the production of charged pions, protons and anti-protons for large transverse momentum (pT) for d+Au collisions at sqrt s_NN = 200 GeV. The identified hadrons are measured in the rapidity regions |y| < 0.5 and 0.5 < |y| < 1.0 for the pT range 2.5 < pT < 10 GeV/c. We observe significant rapidity asymmetry for charged pion and proton+anti-proton production in both rapidity regions. The asymmetry is larger for 0.5 < |y| < 1.0 than for |y|< 0.5 and is almost independent of particle type. The measurements are compared to various model predictions employing multiple scattering, energy loss, nuclear shadowing, saturation effects, and recombination, and also to a phenomenological parton model. We find that asymmetries are sensitive to model parameters and show model-preference. The rapidity dependence of pi^{-}/pi^{+} and bar{p}/p ratios in peripheral d+Au and forward neutron-tagged events are used to study the contributions of valence quarks and gluons to particle production at high pT. The results are compared to calculations based on NLO pQCD and other measurements of quark fragmentation functions.
Strange quark and particle production is studied at the LHC with unprecedented high beam energies in both heavy-ion and proton-proton collisions: on the one hand, strangeness is used for investigating chemical equilibration and bulk properties; on the other hand, strange particles contribute to probe different kinematical domains, from the one where collective phenomena are at play up to the region dominated by pQCD-calculable processes. We highlight the suitability of the ALICE experiment for this topic, presenting our latest measurements and comparing them to models.
The ALICE collaboration at the LHC has measured the transverse momentum spectra of neutral pions via their two photon decay in pp and Pb$-$Pb collisions at $sqrt{s_{NN}}=2.76$ TeV over a broad transverse momentum range with different subsystems: with the electromagnetic calorimeters PHOS and EMCAL and with photon
We revisit the `hybrid formalism for particle production used recently to study saturation effects in single hadron multiplicities at forward rapidities at RHIC and LHC. We point out that at leading twist there is an extra contribution to the formulae used so far, which corresponds to particle production via inelastic scattering of the projectile partons on the target fields. This contribution is expected to be small due to kinematics at very forward rapidities/very high transverse momenta, but should be significant at high momenta and very high energies. This contribution is expected to be most affected by saturation effects and is therefore an interesting object of study in the context of possible onset of saturation at high energies.
Proton-proton (pp) collisions have been used extensively as a reference for the study of interactions of larger colliding systems at the LHC. Recent measurements performed in high-multiplicity pp and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. In this context, the study of identified particle spectra and yields as a function of multiplicity is a key tool for the understanding of similarities and differences between small and large systems. We report on the production of pions, kaons, protons, $K^{0}_{rm S}$, $Lambda$, $Xi$, $Omega$ and $K^{*0}$ as a function of multiplicity in pp collisions at $sqrt{s}=$ 7 TeV measured with the ALICE experiment. The work presented here represents the most comprehensive set of results on identified particle production in pp collisions at the LHC. Spectral shapes, studied both for individual particles and via particle ratios as a function of $p_{rm T}$, exhibit an evolution with charged particle multiplicity that is similar to the one observed in larger systems. In addition, results on the production of light flavour hadrons in pp collisions at $sqrt{s}=$ 13 TeV, the highest centre-of-mass energy ever reached in the laboratory, are also presented and compared with previous, lower energy results.
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