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Register a new userThermal behavior and entanglement in Pb-Pb and p-p collisions
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The thermalization of the particles produced in collisions of small size objects can be achieved by quantum entanglement of the partons of the initial state as it was analyzed recently in proton-proton collisions. We extend such study to Pb-Pb collisions and to different multiplicities of proton-proton collisions. We observe that, in all cases, the effective temperature is approximately proportional to the hard scale of the collision. We show that such relation between the thermalization temperature and the hard scale can be explained as a consequence of the clustering of the color sources. The fluctuations on the number of parton states decreases with multiplicity in Pb-Pb collisions as far as the width of the transverse momentum distributions decreases, contrary to the p-p case. We relate these fluctuations to the temperature time fluctuations by means of a Langevin equation for the white noise due to the quench of a hard parton collision.
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% An analysis is made of the particle composition (hadrochemistry) of the final state in proton-proton (p-p), proton-lead (p-Pb) and lead-lead (Pb-Pb) collisions as a function of the charged particle multiplicity ($dNchdeta$). The thermal model is used to determine the chemical freeze-out temperature as well as the radius and strangeness saturation factor $gamma_s$. Three different ensembles are used in the analysis namely, the grand canonical ensemble, the canonical ensemble with exact strangeness conservation and the canonical ensemble with exact baryon number, strangeness and electric charge conservation. It is shown that for high multiplicities (at least 20 charged hadrons in the mid-rapidity interval considered) the three ensembles lead to the same results.
Recently the ALICE collaboration has observed an interesting systematic behaviour of ratios of identified particles to pions yields at the LHC, showing that they depend solely on the charged-particle multiplicity in pp, pPb and PbPb collisions. In particular, the yields of (multi)strange particles relative to pions, increases with multiplicity and the enhancement is mode pronounced with increasing strangeness content. We will argue, that such a pattern of arises naturally in the thermal model taking into account exact strangeness conservation. Furthermore, extending the thermal model by including hadron interactions within the S-matrix approach, the ALICE data can be well quantified by the thermal particle yields at the chiral-crossover temperature, as previously found in central Pb-Pb collisions.
Predictions for particle production at LHC are discussed in the context of the statistical model. Moreover, the capability of particle ratios to determine the freeze-out point experimentally is studied, and the best suited ratios are specified. Finally, canonical suppression in p-p collisions at LHC energies is discussed in a cluster framework. Measurements with p-p collisions will allow us to estimate the strangeness correlation volume and to study its evolution over a large range of incident energies.
In a framework of a semi-analytic model with longitudinally extended strings of fluctuating end-points, we demonstrate that the rapidity spectra and two-particle correlations in collisions of Pb-Pb, p-Pb, and p-p at the energies of the Large Hadron Collider can be universally reproduced. In our approach, the strings are pulled by wounded constituents appearing in the Glauber modeling at the partonic level. The obtained rapidity profile for the emission of hadrons from a string yields bounds for the distributions of the end-point fluctuations. Then, limits for the two-particle-correlations in pseudorapidity can be obtained. Our results are favorably compared to recent experimental data from the ATLAS Collaboration.
We calculate various azimuthal angle distributions for three jets produced in the forward rapidity region with transverse momenta $p_T>20,mathrm{GeV}$ in proton-proton (p-p) and proton-lead (p-Pb) collisions at center of mass energy $5.02,,mathrm{TeV}$. We use the multi-parton extension of the so-called small-$x$ Improved Transverse Momentum Dependent factorization (ITMD). We study effects related to change from the standard $k_T$-factorization to ITMD factorization as well as changes as one goes from p-p collision to p-Pb. We observe rather large differences in the distribution when we change the factorization approach, which allows to both improve the small-$x$ TMD gluon distributions as well as validate and improve the factorization approach. We also see significant depletion of the nuclear modification ratio, indicating a possibility of searches for saturation effects using trijet final states in a more exclusive way than for dijets.
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