Abstract
The transverse momentum spectra of hadrons are calculated from the unintegrated gluon distribution (UGD) within the ${k}_{T}$-factorization framework at small $x$. Starting from $pp$ collisions, the modification caused by the nuclear medium is incorporated in the UGD at high energies, which is related to the nuclear shadowing phenomenon. Moreover, we consider that particle production from minijet decay is not enough to explain the ${p}_{T}$ spectra in $AA$ collisions due to collective phenomena that take place after the hard collision. The Boltzmann-Gibbs blast wave distribution is utilized in order to evaluate the distribution of particle production in equilibrium. Data from the ALICE Collaboration for PbPb collisions at $\sqrt{s}=2.76\text{ }\text{ }\mathrm{TeV}$ are analyzed, and the nuclear modification factor for pion production is computed.
Highlights
The modification of nuclear structure functions at small Bjorken x, compared to those for free nucleon observed in deep inelastic scattering (DIS) [1] (i.e., European Muon Collaboration effect, antishadowing, and shadowing), can be attributed to distinct phenomena [2,3,4]
We propose a nuclear unintegrated gluon distribution that embeds the shadowing verified in DIS
We investigated the role of nuclear shadowing incorporated in the gluon distribution through the saturation or color glass condensate (CGC) formalism applied to the spectra of produced gluons in heavy ion collisions at high energies
Summary
The modification of nuclear structure functions at small Bjorken x, compared to those for free nucleon observed in deep inelastic scattering (DIS) [1] (i.e., European Muon Collaboration effect, antishadowing, and shadowing), can be attributed to distinct phenomena [2,3,4]. While the collinear factorization mechanism is well established at large Q2, the saturation formalism or CGC makes use of kT factorization in the small x domain in order to describe minijet production of gluons where the UGD, φðx; kTÞ, depends on the transverse momentum kT This distribution is related to the dipole cross section σdpðx; rÞ, the latter being directly extracted from DIS at small x. As already pointed out, such a scenario might not be appropriate for collisions of heavy ions, where there are collective effects that modify the pT spectra of produced hadrons with respect to the initial state UGD φAðx; kTÞ from the free nucleon distribution φpðx; kTÞ This is achieved using the multiple scattering formalism as well as the predictions of the spectra of produced hadrons using the kT factorization with these modifications.
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