Abstract
Abstract Photons and weak bosons do not interact strongly and, thus, their production yields provide direct tests of scaling with a number of binary nucleon–nucleon collisions in the heavy-ion environment. In addition, they should be sensitive to the nuclear modification of parton distribution functions (nPDF). Proton-lead collisions also provide an excellent opportunity to test nPDF in a less dense environment than lead–lead via looking at forward–backward production of weak bosons. The ATLAS detector has proven to be an excellent apparatus in measurements involving photons, electrons and muons, the latter being products of weak boson decays, in the high occupancy environment produced in heavy-ion collisions. The experiment has recorded 30 nb − 1 of proton–lead data and 140 μb − 1 of lead–lead data, both of which have similar integrated partonic luminosities. We present the prompt photon, Z and W boson yields as a function of centrality, and also differentially in transverse momentum and rapidity, in lead–lead and proton–lead collisions from the ATLAS experiment. For W ± bosons, a lepton charge asymmetry has also been studied, which may also shed light on nPDF.
Highlights
Binary collision scaling appears to hold true à no interac@on with quark-‐gluon plasma (QGP) pT and η distributions of Z’s in Pb+Pb à Each decay channel corrected and background subtracted, channels combined à PYTHIA normalized to the Zà l+l-‐ cross sec@on in p+p from NNLO calcula@ons and
Electroweak (EW) bosons are produced in hard processes before quark-‐gluon plasma (QGP) is formed
Leptons which are produced as decay products of weak bosons are colorless as well à QGP is transparent to them
Summary
Electroweak (EW) bosons are produced in hard processes before quark-‐gluon plasma (QGP) is formed. Leptons which are produced as decay products of weak bosons are colorless as well à QGP is transparent to them. One can explore jet quenching in EW+jet events using EW bosons as calibra@on tools. In addi@on, the EW boson produc@on mechanism (e.g. via qq-‐bar annihila@on) makes them sensi@ve to parton distribu=on func=ons (PDFs). Since studies are done in the heavy-‐ion (HI) environment, one can inves@gate nuclear modifica@ons to PDFs (nPDFs). Proton-‐lead collisions are a perfect tool to disentangle ini@al-‐ from final-‐state effects
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