Muon Charge Research Articles

Experimental results on the atmospheric muon charge ratio

The atmospheric muon charge ratio, defined as the number of positive over negative charged muons, is a highly informative observable both for cosmic rays and particle physics. It allows studying the features of high-energy hadronic interactions in the forward region and the composition of primary cosmic rays. In this review results from underground experiments measuring the charge ratio around 1 TeV are discussed. The measurements in the TeV energy region constrain the associated kaon production, which is particularly important e.g. for the calculation of the atmospheric neutrino flux.

The OPERA experiment

The OPERA experiment was designed to study νμ→ντ oscillations in appearance mode using the CERN to Gran Sasso high energy neutrino beam. From 2008 to 2012, 19505 CNGS neutrino interactions were recorded in the OPERA detector. At the present status of the analysis, 4 ντ candidate events have been observed, establishing the oscillation mechanism in the atmospheric sector with a significance of 4.2 σ. The oscillation analysis will be presented in detail and the candidate events will be described. The final measurement of the atmospheric muon charge ratio in the TeV region will be also reported.

Altitude profile of atmospheric muons in a location with relatively high cut-off rigidity

We have investigated the differential and integrated muon fluxes, muon charge ratios and the zenith angle dependence of the integrated muon intensities at sea level and various depths in the atmosphere of Tsukuba, Japan, for muons with momenta below 400GeV/c using the Geant4 simulation package. The simulated sea level muon spectrum and charge ratio have been seen to be in good agreement, throughout the momentum interval of the interest, with those from the measurements made by the BESS-TeV spectrometer. Integrated muon intensities have been found to increase as the atmospheric depth decreases up to slightly above 200g/cm2, and then they have a trend to decrease at lower atmospheric depths. Muon charge ratios at each of the atmospheric depth of interest have been shown to have a very similar behavior with the one at sea level. Simulation results for the zenith angle dependence of muon intensity have been quite compatible with the existing information in the literature for sea level. It has also been shown that the zenith angular dependence of muon intensity has a tendency to disappear (to obey the secθ distribution) as the atmospheric depth decreases for muons with relatively low (high) momenta.

Results from the OPERA experiment at the CNGS beam

The OPERA experiment at the Gran Sasso underground laboratory is searching for νμ → ντ oscillations in appearance mode in the CNGS neutrino beam. Four ντ candidate events have been found so far, using a sub-sample of data from the 2008-2012 runs. Given the number of analysed events and the low background, νμ → ντ oscillations are established with a significance of 4.2 σ. In this paper the data analysis is discussed, with emphasis on the background constraints obtained using dedicated data-driven control samples. We present also the analysis of the τ neutrino and electron neutrino data in the framework of the 3+1 sterile neutrino model. The measurement of the muon charge ratio in the collected cosmic ray sample is also reported.

Atmospheric lepton fluxes

This review of atmospheric muons and neutrinos emphasizes the high energy range relevant for backgrounds to high-energy neutrinos of astrophysical origin. After a brief historical introduction, the main distinguishing features of atmospheric νμ and νe are discussed, along with the implications of the muon charge ratio for the νµ / νµ ratio. Methods to account for effects of the knee in the primary cosmic-ray spectrum and the energy-dependence of hadronic interactions on the neutrino fluxes are discussed and illustrated in the context of recent results from IceCube. A simple numerical/analytic method is proposed for systematic investigation of uncertainties in neutrino fluxes arising from uncertainties in the primary cosmic-ray spectrum/composition and hadronic interactions.

Muonium states in Cu2ZnSnS4 solar cell material

We investigated bulk and thin-film samples of the quaternary p-type semiconductor Cu2ZnSnS4 (CZTS) by μSR, in order to characterize the existing muonium signals. We find that the majority of the implanted muons form a diamagnetic state broadened by an interaction with the Cu nuclear moments, which we interpret as Mu+ bound to sulphur. A paramagnetic fraction is also present at low temperatures and the ratio between the two muon charge states, Mu+ and Mu0, varies between 20 and 40% prior to the onset of muon diffusion, which occurs at around 150 K. The fraction of Mu0 is found to be sensitive to the defect content of the sample. The paramagnetic fraction has two different contributions and their origin is discussed and related with the muon role as a probe for charge carriers in the material.

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.

A simulations study of the muon response of the Iron Calorimeterdetector at the India-based Neutrino Observatory

The magnetised Iron CALorimeter detector (ICAL), proposed to be builtat the India-based Neutrino Observatory (INO), is designed to studyatmospheric neutrino oscillations. The ICAL detector is optimized tomeasure the muon momentum, its direction and charge. A GEANT4-basedpackage has been developed by the INO collaboration to simulate the ICALgeometry and propagation of particles through the detector. The simulatedmuon tracks are reconstructed using the Kalman Filter algorithm. Herewe present the first study of the response of the ICAL detector tomuons using this simulations package to determine the muon momentumand direction resolutions as well as their reconstruction and chargeidentification efficiencies. For 1–20 GeV/c muons in the central regionof the detector, we obtain an average angle-dependent momentum resolutionof 9–14%, an angular resolution of about a degree, reconstructionefficiency of about 80% and a correct charge identification of about98%.

Measurement of the TeV atmospheric muon charge ratio with the complete OPERA data set

The OPERA detector, designed to search for $\nu_{\mu} \to \nu_{\tau}$ oscillations in the CNGS beam, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale cosmic rays. For the analysis here presented, the detector was used to measure the atmospheric muon charge ratio in the TeV region. OPERA collected charge-separated cosmic ray data between 2008 and 2012. More than 3 million atmospheric muon events were detected and reconstructed, among which about 110000 multiple muon bundles. The charge ratio $R_{\mu} \equiv N_{\mu^+}/N_{\mu^-}$ was measured separately for single and for multiple muon events. The analysis exploited the inversion of the magnet polarity which was performed on purpose during the 2012 Run. The combination of the two data sets with opposite magnet polarities allowed minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Data were fitted to obtain relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region. In the surface energy range 1-20 TeV investigated by OPERA, $R_{\mu}$ is well described by a parametric model including only pion and kaon contributions to the muon flux, showing no significant contribution of the prompt component. The energy independence supports the validity of Feynman scaling in the fragmentation region up to $200$ TeV/nucleon primary energy.

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

The cosmic ray veto system of the Mario Schenberg gravitational wave detector

The Mario Schenberg gravitational wave antenna is a spherical cryogenic resonant mass detector located at IFUSP, São Paulo. It is well known that cosmic rays interact with cryogenic resonant mass detectors generating acoustic signals. Depending on the shower energy, they could provide a substantial background noise which should be vetoed to reduce the false alarm rate. For this purpose, in December 2011, we have installed a cosmic ray veto system which is, since then, acquiring data. The cosmic ray veto system is composed of three particle detectors containing each one a scintillator, a photomultiplier and a tension divider.As the shower number of particles is used to define a threshold for the veto, it is important that the cosmic ray veto provides a linear response to high-energy cosmic ray events. The veto setup response was optimized and allows measurements up to 23,000 equivalent muon charge particles per square meter.We present here the experimental setup, its calibration and performance. Finally, to confirm the linearity of the data acquisition we show the measured particle multiplicity.

Alignment methods for the OPERA drift tube detector

The goal of the OPERA experiment is to give the first direct evidence for neutrino oscillations in the channel νμ→ντ. The OPERA detector is designed to observe the appearance of tau neutrinos in the originally pure muon neutrino CNGS beam. An important part of the magnetic spectrometer is the Precision Tracker (PT), a drift tube detector consisting of 9504 drift tubes. Its main task is the determination of the muon charge and momentum. The alignment strategy for the PT consists of two parts: the hardware measurement by theodolite and the software alignment using long muon tracks. In this paper, the hardware and the software alignment are described, and the track-based alignment methods are explained in detail. Results of the software alignment are presented with a focus on the analysis of cosmic particles.

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

ICARUS-NESSiE: a sensitive search for sterile neutrinos at CERN SPS

A new experimental search for sterile neutrinos beyond the Standard Model at a new CERN-SPS neutrino beam aiming at measuring the electron and muon neutrino events with a Near and Far detectors (1600 and 330 m from the proton target) is presented. The project will exploit the ICARUS T600 LAr-TPC moved from LNGS to the CERN Far position and a new additional LAr-TPC detector, 1/4 of the T600, located in the Near position. Two magnetic spectrometers will be placed downstream of the two LAr-TPC detectors to greatly complement the physics capabilities. Comparing the two detectors, in absence of oscillations, all cross sections and experimental biases cancel out. Any difference of the event distributions at the two locations should be attributed to the possible existence of oscillations, presumably due to additional neutrinos with a mixing angle sin2(2θnew) and a mass squared difference Δm2new larger than the measured for the standard neutrinos. The superior quality of the LAr imaging TPC, in particular its unique electron-π0 discrimination allows for full rejection of backgrounds and offers a lossless νe detection capability. The determination of the muon charge with the spectrometers allows for the full separation of νμ from ν̄μ and therefore controlling systematics from muon mis-identification mainly at high momenta.

Superconducting curved transport solenoid with dipole coils for charge selection of the muon beam

At the J-PARC Muon Science Facility (MUSE) the Super-Omega muon beamline is now under construction in the experimental hall No. 2 of the Materials and Life Science Facility building. Muons up to 45MeV/c will be extracted with a large acceptance solid angle to produce the world highest intensity pulsed muon beam. This beamline comprises three parts, a normal-conducting capture solenoid, a superconducting curved transport solenoid and an axial focusing solenoid. Since only solenoids are used, both surface μ+ and cloud μ− are extracted simultaneously. To accommodate future experiments that would only require either μ+ or μ− beam, two dipole coils located on the straight section of the curved solenoid provide the muon charge selection by directing one of the beam onto the solenoid inner-wall. The design parameters, the construction status and the initial beam commissioning are reported.

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.

ICARUS+NESSiE: A proposal for short baseline neutrino anomalies with innovative LAr imaging detectors coupled with large muon spectrometers

The proposal for an experimental search for sterile neutrinos beyond the Standard Model with a new CERN-SPS neutrino beam is presented. The experiment is based on two identical LAr-TPCʼs followed by magnetized spectrometers, observing the electron and muon neutrino events at 1600 and 300 m from the proton target. This project will exploit the ICARUS T600, moved from LNGS to the CERN “Far” position. An additional 1/4 of the T600 detector will be constructed and located in the “Near” position. Two spectrometers will be placed downstream of the two LAr-TPC detectors to greatly complement the physics capabilities. Comparing the two detectors, in absence of oscillations, all cross sections and experimental biases cancel out. Any difference of the event distributions at the locations of the two detectors might be attributed to the possible existence of ν-oscillations, presumably due to additional neutrinos with a mixing angle sin2(2θnew) and a larger mass difference Δmnew2. The superior quality of the LAr imaging TPC, in particular its unique electron-π0 discrimination allows full rejection of backgrounds and offers a lossless νe detection capability. The determination of the muon charge with the spectrometers allows the full separation of νμ from anti-νμ and therefore controlling systematics from muon mis-identification largely at high momenta.

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.

Study of atmospheric muons using a cosmic ray telescope

The charge ratio of cosmic muons holds important information for both the atmospheric neutrino anomaly and hadronic interaction models. In this paper we measured the muon charge ratio () in the cosmic ray flux in the momenta range 0.76–1.60 GeV/c by using a cosmic ray telescope. The delayed coincidence method is used based on the reduced mean lifetime of negative muons due to nuclear capture in matter. The systematic time-dependent effects of the muon charge ratio are considered by grouping the decay data into different time intervals. We compared the experimental data with the predictions of CORSIKA simulations using a high energy interaction model (QGSJET-II) and two low energy interaction models (UrQMD and GHEISHA) in the energy range 1011–1016 eV for primary particles. In addition, by considering the muon flux in different zenithal and azimuthal angles, the muon angular distribution is obtained as I(θ) = I(0)cos nθ with average n = 1.91 ± 0.07. Dependence of the muon flux on the azimuth angle (the East–West effect) is also observed, due to the influence of the geomagnetic field in particular on low energy muons.