Muon Charge Research Articles

Cosmic ray studies with the L3-cosmics program at CERN

The L3 detector at the CERN electron-positron collider had a muon spectrometer which was employed during the last years of LEP operation for cosmic ray studies. The results of this program include a precise muon spectrum and charge ratio between 20 GeV and 3 TeV, a limit on TeV primary antiprotons from a study of the Moon’s shadow, the (possible) observation of a are signal from a fixed position in the northern hemisphere through muons, a solar anisotropy of 200 GeV protons, and other results. Negative limits on muons associated with known H.E. gamma sources or gamma bursts, the search for anomalous H.E. interaction or decay events such as reported from the Kolar Gold Fields, and a search for muons correlated with a solar are are also noted.

Determining the neutrino mass hierarchy with atmospheric neutrinos

The possibility to determine the type of neutrino mass hierarchy by studying atmospheric neutrino oscillations with a detector capable to distinguish between neutrino and antineutrino events, such as magnetized iron calorimeters, is considered. We discuss how the ability to distinguish between the neutrino mass spectrum with normal and inverted hierarchy depends on detector characteristics like neutrino energy and direction resolutions or charge miss-identification, and on the systematical uncertainties related to the atmospheric neutrino fluxes. We show also how the neutrino mass hierarchy determination depends on the true values of θ 13 and θ 23 , as well as on the type of the true hierarchy. We find that for μ-like events, an accurate reconstruction of the energy and direction of the neutrino greatly improves the sensitivity to the type of neutrino mass spectrum. For sin 2 2 θ 13 ≅ 0.1 and a precision of 5% in the reconstruction of the neutrino energy and 5° in the neutrino direction, the type of neutrino mass hierarchy can be identified at the 2 σ C.L. with approximately 200 events. For resolutions of 15% for the neutrino energy and 15° for the neutrino direction roughly one order of magnitude larger event numbers are required. For a detector capable to distinguish between ν e and ν ¯ e induced events the requirements on energy and direction resolutions are, in general, less demanding than for a detector with muon charge identification.

AN ALTERNATIVE METHOD TO OBTAIN THE MUON CHARGE RATIO AT SEA LEVEL

The vertical muon charge ratio generated from hadron showers in the earth's atmosphere is obtained accurately in the energy range from a few GeV to several TeV. To solve the hadron diffusion equations we apply the analytical method based on depth-like ordered exponential operator. A comparison among our calculations (with and without scaling violation) with the measured ratio and Lipari's analytical calculation is made. Our differential muon fluxes are also compared with data at sea level.

Atmospheric muon measurements using the OKAYAMA telescope

The atmospheric muon spectrum has been measured at sea level using a magnet spectrometer called the OKAYAMA telescope. The OKAYAMA telescope is able to point at any azimuth and zenith angle and to measure the muon energy and charge sign. We report the absolute atmospheric muon differential energy spectrum, charge ratio and azimuthal angular dependences.

Low energy muons in the cosmic radiation

A review of measurements of the muon energy spectra for different altitudes, height and directions performed with devices placed at various geomagnetic latitudes is presented. The muon spectra and the muon charge ratio, defined as the ratio of positive to negative muon fluxes, are analysed taking into account the geomagnetic field, in view of the East-West effect. Fluxes of both positive and negative muons are analysed.

The precision tracker of the OPERA detector

The Precision Tracker of the muon spectrometer of the OPERA detector consists of ∼ 10000 aluminum drift tubes of 8 m length. They have an outer diameter of 38 mm and a wall thickness of 0.85 mm. The challenge of the detector design originates from the 8 m length of the drift tubes, a detector length, which has not been used before. Tight mechanical tolerances for positioning and alignment of the signal wires are required in order to make a significant measurement of the sign of the muon charge. The detector is manufactured in modules, which are 50 cm wide, each consisting of four adjacent drift tube planes. This guarantees high efficiency and complete rejection of the left–right ambiguity. The details of the novel mechanical design are described in this paper. For safety reasons, the drift tubes are operated with an Argon / CO 2 gas mixture. The gas volume of the drift tubes is entirely sealed with O-rings, in order to avoid ageing problems. The total gas volume amounts to about 80 m 3 . The front end electronics of the drift tubes consist of a bootstrap amplifier followed by a commercial ultrafast comparator. Thus only digital LVDS signals are transmitted over large distances. We report on the development and performance of the first two prototype modules of the precision tracker including test measurements of the resolution and efficiency obtained.

Neutrons and antiprotons in ultrahigh-energy cosmic rays

The neutron fraction in the very high energy cosmic rays near the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy is analyzed by taking into account the time dilation effect of the neutron decays and also the pion photoproduction behaviors above the GZK cutoff. We predict a non-trivial neutron fraction above the GZK cutoff and a negligibly small neutron fraction below. However, there should be a large antiproton fraction in the high energy cosmic rays below the GZK cutoff in several existing models for the observed cosmic-ray events above and near the GZK cutoff. Such a large antiproton fraction can manifest itself by the muon charge ratio $\mu^+/\mu^-$ in the collisions of the primary nucleon cosmic rays with the atmosphere, if there is no neutron contribution. We suggest to use the muon charge ratio as one of the information to detect the composition of the primary cosmic rays near or below the GZK cutoff.

Experimental studies of positive and negative atmospheric muons with a cosmic rays telescope

An experiment has been developed for the measurement of the muon charge ratio (ratio of positive to negative muons) in the cosmic ray flux in energy range 0.236–0.242 GeV. The muon charge ratio is found to be 1.35 ± 0.10 with a mean zenith angle of 32° ± 5°. Meanwhile, the distributions of muons in zenith ( θ) and azimuth angles have been studied. A cos n θ distribution with n = 1.95 ± 0.13 has been obtained. An asymmetry has been observed in East–West directions because of geomagnetic field.

Measurement of the Atmospheric Muon Spectrum from 20 to 3000 GeV

The absolute muon flux between 20 and 3000 GeV was measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0 0 to 58 0 . Due to the large exposure of about 150 m 2 sr d and the excellent momentum resolution of the L3 muon chamber system, the muon flux was determined with a precision of 2.3 % at 150 GeV in the vertical direction. The ratio of positive to negative muons was studied between 20 and 500 GeV. The average vertical muon charge ratio is found to be 1.285 ± 0.003 (stat.)± 0.019 (sys.)

New measurement of the altitude dependence of the atmospheric muon intensity

We present a new measurement of atmospheric muons made during an ascent of the High Energy Antimatter Telescope balloon experiment. The muon charge ratio ${\ensuremath{\mu}}^{+}/{\ensuremath{\mu}}^{\ensuremath{-}}$ as a function of atmospheric depth in the momentum interval 0.3--0.9 GeV/c is presented. The differential ${\ensuremath{\mu}}^{\ensuremath{-}}$ intensities in the 0.3--50 GeV/c range and for atmospheric depths between $4--960\text{ }\text{ }\mathrm{g}/{\mathrm{c}\mathrm{m}}^{2}$ are also presented. We compare these results with other measurements and model predictions. We find that our charge ratio is $\ensuremath{\sim}1.1$ for all atmospheric depths and is consistent, within errors, with other measurements and the model predictions. We find that our measured ${\ensuremath{\mu}}^{\ensuremath{-}}$ intensities are also consistent with other measurements, and with the model predictions, except at shallow atmospheric depths.

Measurement of charm production in antineutrino charged-current interactions

During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS collecting about 106 neutrino interactions. A measurement of ν¯μ-induced charm production is performed by using the presence of a 5% ν¯μ component in the νμ beam. The measurement takes advantage of the capability to observe the decay topology in the emulsion. The analysis is based on a sample of charged-current interactions with at least one identified muon. About 100 000 were located in the emulsion target and fully reconstructed. By requiring a positive muon charge as determined by the CHORUS muon spectrometer, 32ν¯μ-induced charm events were observed with an estimated background of 3.2 events. At an average antineutrino energy in the neutrino beam of 18 GeV, the charm production rate induced by antineutrinos is measured to be σ(ν¯μN→μ+c¯X)/σ(ν¯μN→μ+X)=(5.0−0.9+1.4(stat)±0.7(syst))%. The ratio between neutral and charged charm production rates in this process is (2.6−1.0+1.7(stat)±0.8(syst)). The charm production rate as a function of the antineutrino energy is found to be in good agreement with previous results derived from di-lepton data.

Measurement of the atmospheric muon spectrum from 20 to 3000 GeV

The absolute muon flux between 20 and 3000 GeV is measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0° to 58°. Due to the large exposure of about 150m2sr d, and the excellent momentum resolution of the L3 muon chambers, a precision of 2.3% at 150 GeV in the vertical direction is achieved. The ratio of positive to negative muons is studied between 20 and 500 GeV, and the average vertical muon charge ratio is found to be 1.285±0.003(stat.)±0.019(syst.).

Measurement of the atmospheric muon spectrum from 20 to 3000 GeV

The absolute muon flux between 20 and 3000 GeV is measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0° to 58°. Due to the large exposure of about 150 m2sr d, and the excellent momentum resolution of the L3 muon chambers, a precision of 2.3% at 150 GeV in the vertical direction is achieved.The ratio of positive to negative muons is studied between 20 and 500 GeV, and the average vertical muon charge ratio is found to be 1.285±0.003(stat.)±0.019(syst.).

Atmospheric neutrinos as a probe of CPT violation

We show that atmospheric neutrinos can provide a sensitive and robust probe of CPT violation (CPTV). We perform realistic event-rate calculations and study the variations of the ratio of total muon to antimuon survival rates with L/E and L (L≡ baseline length, E ≡ neutrino energy) in a detector capable of identifying the muon charge. We demonstrate that measurements of these ratios when coupled with the significant L and E range which characterizes the atmospheric neutrino spectrum provides a method of both detecting the presence of such violations and putting bounds on them which compare very favorably with those possible from a future neutrino factory.

The cosmic ray muon spectrum and charge ratio in CosmoALEPH

The ALEPH experiment at the LEP e +e − storage ring at CERN has been used to measure the momentum spectrum of cosmic ray muons. ALEPH is located at a vertical depth of 320 m.w.e. underground close to the Jura mountains. The high resolution of the time projection chamber (TPC) of ALEPH allows to reconstruct muon tracks with momenta up to the TeV region. The measured muon momentum spectrum and the charge ratio in the range from 80 to 2500 GeV are presented. After corrections for energy loss in the overburden the sea level muon spectrum at nearly vertical incidence is obtained. The experimental data are compared to theoretical expectations and results from other experiments.

The East-West effect of the muon charge ratio at energies relevant to the atmospheric neutrino anomaly

The charge ratio of atmospheric muons is rather sensitive to effects of the geomagnetic field and to the hadronic interaction. Experimental information about this quantity is very useful for tuning the ingredients of models used for calculations of atmospheric neutrino fluxes. For experimental observations, and in particular regarding the asymmetry in the charge ratio of muons from the east and West directions (East-West effect) a rotatable device has been installed in NIPNE-HH (National Institute of Physics and Nuclear Engineering — Horia Hulubei) Bucharest (44° 26'N, 26° 04' E, 85 m above sea-level at a vertical cut-off rigidity of 5.6 GV). The detector is mounted in a rotatable frame, consisting of a stack of 16 modules, 90 × 90 cm 2, formed by plastic scintillator layers (3 cm thick) and aluminum support (1.2 cm thick), surrounded by 4 lateral veto counters. The measurements are based on observation of the life time of muons stopped in the absorber layers of the detector. At a mean zenith angle of 35° the East West asymmetry in the ratio has been found to decrease from 0.25 to 0.20, in the momentum range 0.35 – 0.50 GeV/c.

Charge ratio of muons from atmospheric neutrinos

We calculate the intensities and angular distributions of positive and negative muons produced by atmospheric neutrinos. We comment on some sources of uncertainty in the charge ratio. We also draw attention to a potentially interesting signature of neutrino oscillations in the muon charge ratio, and we discuss the prospects for its observation (which are not quite within the reach of currently planned magnetized detectors).

Cosmic rays with the LEP detectors

The LEP detectors are well suited for different studies on cosmic ray induced muons. In here, several aspects of the muon spectrum are reported. The vertical as well as the zenith-angle dependence of both the absolute muon spectrum and the muon charge ratio have been measured. High and low muon multiplicities have been measured, the latter in combination with the electromagnetic shower size. All of this has been compared to simulations.

Radio-frequency techniques for muon charge state conversion measurements

Radio-frequency (RF) methods have proved to be an important tool for making final muon charge state determinations in μSR spectroscopy. To date, however, most experiments have been concerned with measuring the final-state fractions; charge state transition parameters being determined by modelling techniques. This paper, instead, considers a novel RF experiment where the excitation is delayed relative to muon implantation. Varying this time delay enables the formation of the final state to be displayed explicitly—this new scheme is clearly uniquely suited to implementation at a pulsed muon source. The technique has been demonstrated by following the ionisation of the bond-centred muonium state in silicon.

Precise measurements of atmospheric muon fluxes with the BESS spectrometer

The vertical absolute fluxes of atmospheric muons and muon charge ratio have been measured precisely at different geomagnetic locations by using the BESS spectrometer. The observations had been performed at sea level (30 m above sea level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada. The vertical cutoff rigidities in Tsukuba (36.2°N, 140.1°E) and in Lynn Lake (56.5°N, 101.0°W) are 11.4 and 0.4 GV, respectively. We have obtained vertical fluxes of positive and negative muons in a momentum range from 0.6 to 20 GeV/ c with systematic errors <3% in both measurements. By comparing the data collected at two different geomagnetic latitudes, we have seen an effect of cutoff rigidity. The dependence on the atmospheric pressure and temperature, and the solar modulation effect have been also clearly observed. We also clearly observed the decrease of charge ratio of muons at low momentum side with at higher cutoff rigidity region.