The first study of W boson production in pPb collisions is presented, for bosons decaying to a muon or electron, and a neutrino. The measurements are based on a data sample corresponding to an integrated luminosity of 34.6 nb −1 at a nucleon-nucleon centre-of-mass energy of √ s NN = 5.02 TeV, collected by the CMS experiment. The W boson differential cross sections, lepton charge asymmetry, and forward-backward asymmetries are measured for leptons of transverse momentum exceeding 25 GeV/c, and as a function of the lepton pseudorapidity in the |η lab | < 2.4 range. Deviations from the expectations based on currently available parton distribution functions are observed, showing the need for including W boson data in nuclear parton distribution global fits.The direction of the proton beam was initially opposite to the positive direction of the CMS longitudinal axis [15], and was reversed after 60% of the data were taken. The beam energies were 4 TeV for protons and 1.58 TeV per nucleon for lead nuclei, resulting in a centre-of-mass energy per nucleon pair of √ s NN = 5.02 TeV. As a result of the energy difference of the colliding beams, the NN centre-of-mass frame in pPb collisions was not at rest with respect to the laboratory frame. Massless particles emitted at pseudorapidity η in the NN centre-of-mass frame are detected at η lab = η − 0.465 (first proton beam orientation) and η lab = η + 0.465 (second proton A The CMS Collaboration

No abstract

The production of Z bosons in pPb collisions at √ s NN = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions.

We discuss the prospects of probing the Lµ − Lτ gauge boson at the MUonE experiment. The Lµ − Lτ gauge boson Z with a mass of 200 MeV, which can explain the discrepancy between the measured value of the muon g − 2 and the value calculated in the Standard Model, can be produced at the MUonE experiment through the process µe → µeZ . The Z in the final state decays into a pair of neutrinos, and therefore we cannot observe the decay of Z directly. It is, however, still possible to probe this signature by searching for events with a large scattering angle of muon and a less energetic final-state electron. The background events coming from the elastic scattering µe → µe as well as radiative process µe → µeγ can be removed by the kinematical cuts on the muon scattering angle and the electron energy, in addition to a photon veto. The background events from the electroweak process µe → µeν ν are negligible. With our selection criteria, the number of signal events µe → µeZ is found to be as large as ∼ 10 3 in the parameter region motivated by the muon g − 2 discrepancy. It is, therefore, quite feasible to probe the Lµ − Lτ gauge boson at the MUonE experiment-without introducing additional devices-and we strongly recommend recording the events relevant to this Z production process.

No abstract