Electron Neutrino Pair Annihilation: A New Source for Muon and Tau Neutrinos in Supernovae

We show that in a supernova core the annihilation process nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar is always more important than the traditional reaction e^+ e^- -> nu_{mu,tau} nu_{mu,tau}-bar as a source for muon and tau neutrino pairs. We study the impact of the new process by means of a Monte Carlo transport code with a static stellar background model and by means of a self-consistent hydrodynamical simulation with Boltzmann neutrino transport. Nucleon bremsstrahlung NN -> NN nu_{mu,tau} nu_{mu,tau}-bar is also included as another important source term. Taking into account nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar increases the nu_mu and nu_tau luminosities by as much as 20% while the spectra remain almost unaffected. In our hydrodynamical simulation the shock was somewhat weakened. Elastic nu_{mu,tau} nu_e and nu_{mu,tau} nu_e scattering is not negligible but less important than nu_{mu,tau} e^+ or e^- scattering. Its influence on the nu_{mu,tau} fluxes and spectra is small after all other processes have been included.Comment: 11 pages, 9 eps-figs, submitted to Ap

Large-angle scattering of multi-GeV muons on thin Lead targets

The probability of large-angle scattering for multi-GeV muons in thin ($t/X_0 \sim 10^{-1}$) lead targets is studied. The new estimates presented here are based both on simulation programs (GEANT4 libraries) and theoretical calculations. In order to validate the results provided by simulation, a comparison is drawn with experimental data from the literature. This study is particularly relevant when applied to muons originating from $\nu_\mu^{CC}$ interactions of CNGS beam neutrinos. In that circumstance the process under study represents the main background for the $\nu_\mu \to \nu_\tau$ search in the $\tau \to \mu$ channel for the OPERA experiment at LNGS. Finally, we also investigate, in the CNGS context, possible contributions from the muon photo-nuclear process which might in principle also produce a large-angle muon scattering signature in the detector

Energy dependence of exclusive J/ψJ/\psi photoproduction off protons in ultra-peripheral p-Pb collisions at sNN\sqrt{s_{\rm{NN}}} = 5.02 TeV

The ALICE Collaboration has measured the energy dependence of exclusive photoproduction of $J/\psi$ vector mesons off proton targets in ultra-peripheral p-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV. The e$^+$e$^-$ and $\mu^+\mu^-$ decay channels are used to measure the cross section as a function of the rapidity of the $J/\psi$ in the range $-2.5 < y < 2.7$, corresponding to an energy in the $\gamma$p centre-of-mass in the interval $40 < W_{\gamma\mathrm{p}}<550$ GeV. The measurements, which are consistent with a power law dependence of the exclusive $J/\psi$ photoproduction cross section, are compared to previous results from HERA and the LHC and to several theoretical models. They are found to be compatible with previous measurements.Comment: 25 pages, 3 captioned figures, 3 tables, authors from page 19, published version, figures at http://alice-publications.web.cern.ch/node/455

Sensitivity and background estimates towards Phase-I of the COMET muon-to-electron conversion search

COMET is a future high-precision experiment searching for charged lepton flavour violation through the muon-to-electron conversion process. It aims to push the intensity frontier of particle physics by coupling an intense muon beam with cutting-edge detector technology. The first stage of the experiment, COMET Phase-I, is currently being assembled and will soon enter its data acquisition period. It plans to achieve a single event sensitivity to μ-e conversion in aluminium of 3.1x10⁻¹⁵. This thesis presents a study of the sensitivity and backgrounds of COMET Phase-I using the latest Monte Carlo simulation data produced. The background contribution from cosmic ray-induced atmospheric muons is estimated using a backward Monte Carlo approach, which allows computational resources to be focused on the most critical signal-mimicking events. Analysis of a μ-e conversion simulation sample suggests that COMET Phase-I will reach a single event sensitivity of 3.6x10⁻¹⁵ within 146 days of data acquisition. Our results suggest that, in that period, on the order of 10³ atmospheric muons will enter the detector system and produce an event similar enough to the conversion signal to pass all the signal selection criteria. Most of these events will be rejected by the Cosmic Ray Veto system, however, we expect at least 2.2 background events to sneak in unnoticed. It is vital for the conversion search that these events be discriminated from conversion electrons, for instance by using Cherenkov threshold counters to distinguish between muons and electrons or, alternatively, by developing a direction identification algorithm to reject some fraction of the μ⁺-induced events.Open Acces

A Three-Dimensional Code for Muon Propagation through the Rock: MUSIC

We present a new three-dimensional Monte-Carlo code MUSIC (MUon SImulation Code) for muon propagation through the rock. All processes of muon interaction with matter with high energy loss (including the knock-on electron production) are treated as stochastic processes. The angular deviation and lateral displacement of muons due to multiple scattering, as well as bremsstrahlung, pair production and inelastic scattering are taken into account. The code has been applied to obtain the energy distribution and angular and lateral deviations of single muons at different depths underground. The muon multiplicity distributions obtained with MUSIC and CORSIKA (Extensive Air Shower simulation code) are also presented. We discuss the systematic uncertainties of the results due to different muon bremsstrahlung cross-sections.Comment: 24 pages, 11 Postscript figures, LaTeX, to be published in Astroparticle Physic

Distributions of secondary muons at sea level from cosmic gamma rays below 10 TeV

The FLUKA Monte Carlo program is used to predict the distributions of the muons which originate from primary cosmic gamma rays and reach sea level. The main result is the angular distribution of muons produced by vertical gamma rays which is necessary to predict the inherent angular resolution of any instrument utilizing muons to infer properties of gamma ray primaries. Furthermore, various physical effects are discussed which affect these distributions in differing proportions.Comment: 36 pages, 13 figures, minor revision, new layou