Speaker
Jianhui Zhu
(Central China Normal University CCNU (CN))
Description
The high collision energies available at the LHC allow for an abundant production of hard probes, such as quarkonia, high-$p_{\rm T}$ jets and vector bosons (W, Z). The latter are produced in initial hard parton scattering processes and they decay before the formation of the Quark-Gluon Plasma (QGP), which is a deconfined phase of QCD matter produced in high-energy heavy-ion collisions. Furthermore, their leptonic decay products do not interact strongly with the QGP. The electroweak boson introduces a way for benchmarking in-medium modifications to coloured probes. In Pb--Pb and p--Pb collisions, precise measurements of W and Z-boson production can constrain the Nuclear Parton Distribution Functions (nPDFs), which could be modified with respect to the nucleon due to shadowing or gluon saturation, and they can be used to test the scaling of hard particle production with the number of binary nucleon--nucleon collisions. Especially in p--Pb collisions, the measurement of W yields at forward and backward rapidity allows us to probe the modification of nPDFs at small and large Bjorken-$x$, respectively. Such measurements can be benchmarked in pp collisions, where W and Z-boson production is theoretically known with good precision. Also, the charge asymmetry of leptons from W-boson decays is a sensitive probe of up and down quark densities in a nucleon inside a nucleus.
The production of W and Z bosons in p--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV is measured with the ALICE muon spectrometer via the inclusive $p_{\rm T}$-differential muon yield and the invariant mass of opposite-sign muon pairs, respectively. The rapidity coverage of the muon spectrometer is -4.46 $< y^\mu_{\rm cms} <$ -2.96 and 2.03 $< y^\mu_{\rm cms} <$ 3.53, which is complementary to the one of ATLAS and CMS. The results are compared with model calculations accounting for the nuclear modification of the PDFs. The W production as a function of the event activity will be discussed as well.
| On behalf of collaboration: | ALICE |
|---|
Primary author
Jianhui Zhu
(Central China Normal University CCNU (CN))
