Long-term operation of a multi-channel cosmic muon system based on scintillation counters with MRS APD light readout

A Cosmic Ray Test Facility (CRTF) is the first large-scale implementation of a scintillation triggering system based on a new scintillation technique known as START. In START, the scintillation light is collected and transported by WLS optical fibers, while light detection is performed by pairs of avalanche photodiodes with the Metal-Resistor-Semiconductor structure operated in the Geiger mode (MRS APD). START delivers 100% efficiency of cosmic muon detection, while its intrinsic noise level is less than 10^{-2} Hz. CRTF, consisting of 160 START channels, has been continuously operated by the ALICE TOF collaboration for more than 25 000 hours, and has demonstrated a high level of stability. Fewer than 10% of MRS APDs had to be replaced during this period.Comment: Proceedings of NDIP-2008. 8 pages, 8 figures, 6 reference

Spontaneous symmetry breaking for long-wave gravitons in the early Universe

It is shown that nonlinear terms in equations of gravitons on the background of curved space-time of the expanding Universe can solve the problem of the negative square of the effective mass formally arising in linear approximation for gravitons. Similar to well known spontaneous breaking of symmetry in Goldstone model one must take another vacuum so that nonzero vacuum expectation value of the quantized graviton field leads to change of spectrum for gravitons. There appears two graviton fields, one with the positive mass, another with the zero mass. Energy density and the density of particles created by gravitation of the expanding Universe are calculated for some special cases of the scale factor. Numerical results are obtained for the dust universe case.Comment: 13 page

Scintillation counter with MRS APD light readout

START, a high-efficiency and low-noise scintillation detector for ionizing particles, was developed for the purpose of creating a high-granular system for triggering cosmic muons. Scintillation light in START is detected by MRS APDs (Avalanche Photo-Diodes with Metal-Resistance-Semiconductor structure), operated in the Geiger mode, which have 1 mm^2 sensitive areas. START is assembled from a 15 x 15 x 1 cm^3 scintillating plastic plate, two MRS APDs and two pieces of wavelength-shifting optical fiber stacked in circular coils inside the plastic. The front-end electronic card is mounted directly on the detector. Tests with START have confirmed its operational consistency, over 99% efficiency of MIP registration and good homogeneity. START demonstrates a low intrinsic noise of about 10^{-2} Hz. If these detectors are to be mass-produced, the cost of a mosaic array of STARTs is estimated at a moderate level of 2-3 kUSD/m^2.Comment: 6 pages, 5 figure

RPC with low-resistive phosphate glass electrodes as a candidate for the CBM TOF

Usage of electrodes made of glass with low bulk resistivity seems to be a promising way to adapt the Resistive Plate Chambers (RPC) to the high-rate environment of the upcoming CBM experiment. A pilot four-gap RPC sample with electrodes made of phosphate glass, which has bulk resistivity in the order of 10^10 Ohm cm, has been studied with MIP beam for TOF applications. The tests have yielded satisfactory results: the efficiency remains above 95% and the time resolution stays within 120 ps up to the particle rate of 18 kHz/cm2. The increase in rate from 2.25 to 18 kHz/cm2 leads to an increase of estimated "tails" fraction in the time spectrum from 1.5% to 4%.Comment: 8 pages, 6 figures, submitted to Elsevier Scienc

START as the detector of choice for large-scale muon triggering systems

Further progress in building high-granular large-scale systems based on Scintillation Tiles with MRS APD light readout (START) became possible thanks to the creation of an improved version of MRS APD. The cost of the system may now be significantly reduced by using inexpensive extruded scintillator. More than 160 START samples were assembled based on this design modification and proved to possess 100% MIP detection efficiency and the intrinsic noise rate of less than 0.08 Hz. Long-term stability of START characteristics was confirmed after 3.5 months of operation

Study of QGP signatures with the phi->K+K- signal in Pb-Pb ALICE events

The phi->K+K- decay channel in Pb-Pb collisions at LHC is studied through a full simulation of the ALICE detector. The study focuses on possible signatures in this channel of quark-gluon plasma (QGP) formation. On a basis of 10^6 collisions at high centrality some proposed QGP signatures are clearly visible both in K+K- invariant mass and transverse mass distributions. The high significance of this observation appears to reside heavily on the use of the TOF (Time Of Flight) system of ALICE in addition to its central tracking detectors.Comment: 9 pages, 7 figures, to appear in EPJ

A parallel-plate chamber as a detector for time-of-flight measurements

The possibility of measuring the time of flight of minimum-ionizing particles with high accuracy and efficiency using a gaseous parallel- plate detector operating in avalanche gas-amplification mode is demonstrated in principle. (9 refs)

Data on light-fragment correlations in 40^{40}Ar + 58^{58}Ni at 77 MeV/nucleon

Results of the experimental study of p 4 He, d 3 He, dT, pT, p 3 He and, for the first time, nT, n 3 He, n 4 He correlations in the region of small relative momenta are presented. The data analysis provides an estimate of the effective source size or emission time. (Springer