Results on Multiple Coulomb Scattering from 12 and 20 GeV electrons on Carbon targets

Multiple scattering effects of 12 and 20 GeV electrons on 8 and 20 mm thickness carbon targets have been studied with high-resolution silicon microstrip detectors of the UA9 apparatus at the H8 line at CERN. Comparison of the scattering angle between data and GEANT4 simulation shows excellent agreement in the core of the distributions leaving some residual disagreement in the tails.Comment: 14 pages, 16 figures. Updated to match published versio

Breaking stress of neutron star crust

The breaking stress (the maximum of the stress-strain curve) of neutron star crust is important for neutron star physics including pulsar glitches, emission of gravitational waves from static mountains, and flares from star quakes. We perform many molecular dynamic simulations of the breaking stress at different coupling parameters (inverse temperatures) and strain rates. We describe our results with the Zhurkov model of strength. We apply this model to estimate the breaking stress for timescales ~1 s - 1 year, which are most important for applications, but much longer than can be directly simulated. At these timescales the breaking stress depends strongly on the temperature. For coupling parameter <200, matter breaks at very small stress, if it is applied for a few years. This viscoelastic creep can limit the lifetime of mountains on neutron stars. We also suggest an alternative model of timescale-independent breaking stress, which can be used to estimate an upper limit on the breaking stress.Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letter

First observation of proton reflection from bent crystals

We recently suggested using short bent crystals as primary collimators in a two stage cleaning system for hadron colliders, with the aim of providing larger impact parameters in the secondary bulk absorber, through coherent beam-halo deflection [1]. Tests with crystals a few mm long, performed with 70 GeV proton beams at IEHP in Protvino, showed a channeling efficiency exceeding 85 %. We also observed disturbing phenomena such as dechannelling at large impact angle, insufficient bending induced by volume capture inside the crystal, multiple scattering of non-channeled protons and, for the first time, a proton flux reflected by the crystalline planes. Indeed, protons with a tangent path to the curved planes somewhere inside the crystal itself are deflected in the opposite direction with respect to the channeled particles, with an angle almost twice as large as the critical angle. This effect, up to now only predicted by computer simulations [2], produces a flux of particles in the wrong direction with respect to the absorber, which may hamper the collimation efficiency if neglected

The UA9 experimental layout

The UA9 experimental equipment was installed in the CERN-SPS in March '09 with the aim of investigating crystal assisted collimation in coasting mode. Its basic layout comprises silicon bent crystals acting as primary collimators mounted inside two vacuum vessels. A movable 60 cm long block of tungsten located downstream at about 90 degrees phase advance intercepts the deflected beam. Scintillators, Gas Electron Multiplier chambers and other beam loss monitors measure nuclear loss rates induced by the interaction of the beam halo in the crystal. Roman pots are installed in the path of the deflected particles and are equipped with a Medipix detector to reconstruct the transverse distribution of the impinging beam. Finally UA9 takes advantage of an LHC-collimator prototype installed close to the Roman pot to help in setting the beam conditions and to analyze the efficiency to deflect the beam. This paper describes in details the hardware installed to study the crystal collimation during 2010.Comment: 15pages, 11 figure, submitted to JINS

Energy reconstruction with machine learning techniques in JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose liquid scintillator neutrino experiment under construction located in China. Although the main source of neutrinos in JUNO is two nuclear power plants located about 52.5 km away from the experiment, it will also be able to study solar and atmospheric neutrinos, geoneutrinos and neutrinos coming from supernovae. The determination of the neutrino mass ordering (NMO) with 3-4σ in 6 years is the main goal of the experiment. Moreover, another JUNO’s important aim is to measure neutrino oscillation parameters sin2 θ12,Δm2 21,Δm2 31 with sub-percent precision. The central detector of JUNO is an acrylic sphere filled with 20 kt of liquid-scintillator (LS) surrounded by 17612 20-inch photomultiplier tubes (PMTs) and 25600 3-inch PMTs, providing ∼78% coverage of the detector sphere. Thanks to the almost complete coverage of the sphere by the PMTs array, as well as high light yield leads to an unprecedented, for LS-based experiments, energy resolution of 3% at 1 MeV. Due to the need to take into account various effects, including the non-linearity of the energy response and the detector’s spatial non-uniformity, event energy reconstruction is not a straightforward task. In this study, energy reconstruction for reactor neutrino events with machine learning (ML) techniques is presented. The following two models are used: Boosted Decision Trees and Fully Connected Deep Neural Network. The models are trained on aggregated features extracted from charge and time information on PMTs

Volume reflection of a proton beam in a bent crystal

Volume reflection of 70 GeV proton beam from bent (111) atomic planes of silicon was observed in experiment devoted to the study of channeling in very short bent crystals. This phenomenon was predicted by A.M.Taratin and S.A.Vorobiev in 1987. Volume reflection is resulted from coherent interaction of incident protons with crystal lattice in tangency point of proton trajectories with bent atomic planes and has the same nature as channeling. Average deflection angle of reflected protons was found to be equal to 1.6 times the critical angle for channeling. The study fulfilled makes possible to develop new approach to crystal deflectors for high energy particle beams based on volume reflection phenomenon

Performance of the CMS Cathode Strip Chambers with Cosmic Rays

The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47 microns to 243 microns. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns