Muon Charge Asymmetry Research Articles

Observation of nuclear modifications in W± boson production in pPb collisions at [formula omitted

The production of W± bosons is studied in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of sNN=8.16TeV. Measurements are performed in the W±→μ±νμ channel using a data sample corresponding to an integrated luminosity of 173.4±6.1nb−1, collected by the CMS Collaboration at the LHC. The number of positively and negatively charged W bosons is determined separately in the muon pseudorapidity region in the laboratory frame |ηlabμ|<2.4 and transverse momentum pTμ>25GeV/c. The W± boson differential cross sections, muon charge asymmetry, and the ratios of W± boson yields for the proton-going over the Pb-going beam directions are reported as a function of the muon pseudorapidity in the nucleon-nucleon centre-of-mass frame. The measurements are compared to the predictions from theoretical calculations based on parton distribution functions (PDFs) at next-to-leading-order. The results favour PDF calculations that include nuclear modifications and provide constraints on the nuclear PDF global fits.

Prompt neutrinos and intrinsic charm at SHiP

We present a new evaluation of the far-forward neutrino plus antineutrino flux and number of events from charm hadron decays in a 400 GeV proton beam dump experiment like the Search for Hidden Particles (SHiP). Using next-to-leading order perturbative QCD and a model for intrinsic charm, we include intrinsic transverse momentum effects and other kinematic angular corrections. We compare this flux to a far-forward flux evaluated with next-to-leading order perturbative QCD, without intrinsic transverse momentum, that used the angular distribution of charm quarks rather than the neutrinos from their decays. The tau neutrino plus antineutrino number of events in the perturbative QCD evaluation is reduced by a factor of about three when intrinsic transverse momentum and the full decay kinematics are included. We show that intrinsic charm contributions can significantly enhance the number of events from neutrinos from charm hadron decays. Measurements of the number of events from tau neutrino plus antineutrino interactions and of the muon charge asymmetry as a function of energy can be used to constrain intrinsic charm models.

Interference Effects in a Very Precise Measurement of the Muon Charge Asymmetry at FCC-ee

At the future high luminosity electron-positron collider FCC-ee proposed for CERN, the precise measurement of the charge asymmetry in $e^+ e^- \to \mu^+ \mu^-$ near the Z resonance is of special interest. In particular, such a measurement at $M_Z \pm 3.5$ GeV may provide a very precise measurement of the electromagnetic coupling at the scale $\sim M_Z$, a fundamental constant of the Standard Model. However, this charge asymmetry is plagued by a large trivial contribution from the interference of photon emission from initial state electrons and final state muons. We address the question whether this interference can be reliably calculated and subtracted with the help of a resummed QED calculation.

Measurement of the muon charge asymmetry in inclusive pp → W + X production at [formula omitted] at CMS and an improved determination of light parton distribution functions

Measurements of the muon charge asymmetry in inclusive pp→WX production at s=7 TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 fb-1 recorded with the CMS detector at the LHC. With a sample of more than twenty million W→μν events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10-3 to 10-1. These measurements are used together with the cross sections for inclusive deep inelastic ep scattering at HERA in a next-to-leading-order QCD analysis.

Measurement of the muon charge asymmetry in inclusivepp→W+Xproduction ats=7 TeVand an improved determination of light parton distribution functions

Measurements of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 inverse femtobarns recorded with the CMS detector at the LHC. With a sample of more than twenty million W to mu nu events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10E-3 to 10E-1. These measurements and the recent CMS measurement of associated W + charm production are used together with the cross sections for inclusive deep inelastic ep scattering at HERA in a next-to-leading-order QCD analysis. The determination of the valence quark distributions is improved, and the strange-quark distribution is probed directly through the leading-order process g + s to W + c in proton-proton collisions at the LHC.

Measurement of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV

Measurement of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV

Study ofCP-violating charge asymmetries of single muons and like-sign dimuons inpp¯collisions

We measure the inclusive single muon charge asymmetry and the like-sign dimuon charge asymmetry in $p \bar{p}$ collisions using the full data set of 10.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron. The standard model predictions of the charge asymmetries induced by CP violation are small in magnitude compared to the current experimental precision, so non-zero measurements could indicate new sources of CP violation. The measurements differ from the standard model predictions of CP violation in these asymmetries with a significance of 3.6 standard deviations. These results are interpreted in a framework of $B$ meson mixing within the CKM formalism to measure the relative width difference $\dgg$ between the mass eigenstates of the $\Bd$ meson system, and the semileptonic charge asymmetries $\asld$ and $\asls$ of $\Bd$ and $\Bs$ mesons respectively.

Measurement of the muon charge asymmetry inpp¯→W+X→μν+Xevents ats=1.96 TeV

We present a measurement of the muon charge asymmetry from the decay of the W boson via W→μν using 7.3 fb−1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider at s=1.96 TeV. The muon charge asymmetry is presented in two kinematic regions in muon transverse momentum and event missing transverse energy: (pTμ>25 GeV, E̸T>25 GeV) and (pTμ>35 GeV, E̸T>35 GeV). The measured asymmetries are compared with theory predictions made using three parton distribution function sets. The data at pTμ>35 GeV, E̸T>35 GeV, and larger values of |ημ| favor an increased d(x)/u(x) ratio at higher values of x than is predicted.Received 11 September 2013DOI:https://doi.org/10.1103/PhysRevD.88.091102© 2013 American Physical Society

W and Z in heavy ion collisions with CMS

Abstract Electroweak W and Z boson measurements in PbPb collisions at nucleon–nucleon center of mass energy s = 2.76 TeV at the LHC using the CMS detector are presented. The W analysis is based on 2010 PbPb data corresponding to an integrated luminosity of 7.3 μ b − 1 and also on 2011 pp data corresponding to an integrated luminosity of 231 n b − 1 . The Z analysis is based on 2011 PbPb data with an integrated luminosity of 150 μ b − 1 . The dependence of W and Z production as a function of PbPb collision centrality is studied and shown to scale with the number of NN binary collisions. W + and W − yields in PbPb and pp collisions are in agreement once we take into account the proton and neutron composition in Pb nuclei. The muon charge asymmetry is measured as a function of pseudo-rapidity and is in agreement with next-to-leading order perturbative QCD calculations.

W and Z bosons measurement in PbPb collisions with CMS

The electroweak bosons W and Z produced in PbPb collisions at LHC at = 2.76 TeV have been measured and studied through their leptonic decay channel with the CMS detector. In the following we present the measurement of the Z yields as a function of pT, rapidity and centrality based on 2011 PbPb data with an integrated luminosity of 150 μb−1, and the W yield as a function of centrality as well as the muon charge asymmetry using 2010 PbPb data corresponding to an integrated luminosity of 7.3 μ/b−1. The dependence of W and Z production as a function of PbPb collision centrality is shown to scale with the number of NN binary collisions.

Leptonic observables in TeV Pb+Pb collisions measured with the ATLAS detector at the LHC

We report on the first measurements of J/ψ, W and Z boson production in lead–lead collisions measured by the ATLAS detector at the nucleon–nucleon centre of mass energy TeV. These measurements are performed via the J/ψ and electroweak boson decays to muon final states. We present a measurement of W boson yields produced in heavy-ion collisions as function of centrality, ratios of W+/W− and W/Z. For a subset of the W → μν decays, we report on muon rapidity and charge asymmetry measurements. These measurements are the first ATLAS results on W measurements in lead–lead collisions at the LHC.

Measurement of the W charge asymmetry in the [formula omitted] decay mode in pp collisions at [formula omitted] with the ATLAS detector

This Letter reports a measurement of the muon charge asymmetry from W bosons produced in proton–proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The asymmetry is measured in the W→μν decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb−1. The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton.

Measurement of the muon charge asymmetry fromWboson decays

We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb−1 of data collected at s=1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron pp¯ Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.Received 27 September 2007DOI:https://doi.org/10.1103/PhysRevD.77.011106©2008 American Physical Society

The sign of Δm312 and the muon-charge asymmetry for atmospheric neutrinos

The sign of Δm312 and the muon-charge asymmetry for atmospheric neutrinos

The sign of Δ m312 and the muon-charge asymmetry for atmospheric neutrinos

We discuss the possibility to measure the sign of δ m 31 2 from matter-induced charge asymmetries in atmospheric neutrino oscillations. The main conclusion is that an impact on the ν μ survival probability requires the action of the MSW resonance, which becomes visible for baselines above ∼ 7000 km.

The earth Mantle-Core effect in charge-asymmetries for atmospheric neutrino oscillations

Earth medium effects in the three-neutrino oscillations of atmospheric neutrinos are observable under appropriate conditions. This paper generalizes the study of the medium effects and the possibility of their observation in the atmospheric neutrino oscillations from the case of neutrinos traversing only the Earth mantle, where the density is essentially constant, to the case of atmospheric neutrinos crossing also the Earth core. In the latter case new resonance-like effects become apparent. We calculate the CPT-odd asymmetry for the survival probability of muon neutrinos and the observable muon-charge asymmetry, taking into account the different atmospheric neutrino fluxes, and show the dependence of these asymmetries on the sign of $\Delta m^{2}_{3 1}$ and on the magnitude of the mixing angle $\theta_{13}$. A magnetized detector with a sufficiently good neutrino momentum resolution is required for the observation of the muon-charge asymmetry generated by the Earth mantle-core effect.

Study of the e+e− → μ+μ−γ reaction at center-of-mass energies between 54 and 64 GeV

Abstract The cross section and forward-backward muon charge asymmetry for the e+e−→μ+μ−γ reaction were measured to be σ=2.82±0.35 pb and A=−0.34±0.10 with the VENUS detector at TRISTAN at 〈√s〉=59.2GeV for an integrated luminosity of 53.5 pb−1. The measured cross section agrees with the theoretical prediction. The asymmetry result is consistent with the electroweak prediction but not with the QED prediction at the level of 2σ.