Abstract
The respective contributions of cold-matter and hot-medium effects to the suppression of $\Upsilon(1S)$ and $\Upsilon(2S)$ mesons in pPb collisions at energies reached at the Large Hadron Collider (LHC) are investigated. Whereas known alterations of the parton density functions in the lead nucleus and coherent parton energy loss account for the leading fraction of the modifications in cold nuclear matter (CNM), the hot-medium (quark-gluon plasma, QGP) effects turn out to be relevant in spite of the small initial spatial extent of the fireball. We compare our transverse-momentum-, rapidity-, and centrality-dependent theoretical results for the $\Upsilon$ suppression in pPb collisions at a center-of-mass energy of $\sqrt{s_\text{NN}} = 8.16$ TeV with recent LHCb and preliminary ALICE data from the Large Hadron Collider (LHC). Both cold-matter and hot-medium effects are needed to account for the data. The initial central temperature of the fireball is found to be $T_0 \simeq 460$ MeV.
Highlights
The successive suppression of the bottomonia statesΥ(1S), Υ(2S), and Υ(3S) in the hot quark-gluon plasma (QGP) that is created in symmetric high-energy heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) [1]and the CERN Large Hadron Collider (LHC) [2,3,4,5] is a valuable indicator for its properties, such as the initial central temperature T0 [6,7,8,9,10,11,12,13]
Regarding the cold nuclear matter (CNM) effects, we consider the modification of the parton distribution functions (PDFs) in a nucleus compared to free nucleons, and the coherent energy loss of the bottomonia on their paths through the medium [14]
Before we proceed to investigate the influence of the hot fireball in asymmetric systems at LHC energies on the Υ suppression, we mention that our calculations for the CNM effects due to both, modifications of the PDFs and coherent energy loss in the nuclear medium
Summary
Υ(1S), Υ(2S), and Υ(3S) in the hot quark-gluon plasma (QGP) that is created in symmetric high-energy heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) [1]. Regarding the CNM effects, we consider the modification of the parton distribution functions (PDFs) in a nucleus compared to free nucleons, and the coherent energy loss of the bottomonia on their paths through the medium [14]. These coldmatter effects are not expected to be much different for ground and excited bottomonia states; the ALICE Collaboration measurement of the cross section ratio Υ(2S)/Υ(1S) in.
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