802 research outputs found
Nuclear recoil measurements in Superheated Superconducting Granule detectors
The response of Superheated Superconducting Granule (SSG) devices to nuclear
recoils has been explored by irradiating SSG detectors with a 70MeV neutron
beam. In the past we have tested Al SSG and more recently, measurements have
been performed with Sn and Zn detectors. The aim of the experiments was to test
the sensitivity of SSG detectors to recoil energies down to a few keV. In
this paper, the preliminary results of the neutron irradiation of a SSG
detector made of Sn granules 15-20m in diameter will be discussed. For the
first time, recoil energy thresholds of 1keV have been measured.Comment: 7pages in Latex format, Preprint Bu-He 93/6 (University of Berne,
Switzerland), four figures available upon request via
[email protected] or [email protected]
Stable quark stars beyond neutran stars : can they account for the missing matter ?
The structure of a spherically symmetric stable dark 'star' is discussed, at
zero temperature, containing 1) a core of quarks in the deconfined phase and
antileptons 2) a shell of hadrons in particular , , and
and leptons or antileptons and 3) a shell of hydrogen in the
superfluid phase. If the superfluid hydrogen phase goes over into the
electromagnetic plasma phase at densities well below one atom / ,
as is usually assumed, the hydrogen shell is insignificant for the mass and the
radius of the 'star'. These quantities are then determined approximatively :
mass = 1.8 solar masses and radius = 9.2 km. On the contrary if densities of
the order of one atom / do form a stable hydrogen superfluid
phase, we find a large range of possible masses from 1.8 to 375 solar masses.
The radii vary accordingly from 9 to 1200 km.Comment: 5 pages, 2 figures, contribution to Strange Quark Matter conference,
Frankfurt, Germany, Sept. 200
Antimatter and Matter Production in Heavy Ion Collisions at CERN (The NEWMASS Experiment NA52)
Besides the dedicated search for strangelets NA52 measures light
(anti)particle and (anti)nuclei production over a wide range of rapidity.
Compared to previous runs the statistics has been increased in the 1998 run by
more than one order of magnitude for negatively charged objects at different
spectrometer rigidities. Together with previous data taking at a rigidity of
-20 GeV/c we obtained 10^6 antiprotons 10^3 antideuterons and two antihelium3
without centrality requirements. We measured nuclei and antinuclei
(p,d,antiprotons, antideuterons) near midrapidity covering an impact parameter
range of b=2-12 fm. Our results strongly indicate that nuclei and antinuclei
are mainly produced via the coalescence mechanism. However the centrality
dependence of the antibaryon to baryon ratios show that antibaryons are
diminished due to annihilation and breakup reactions in the hadron dense
environment. The volume of the particle source extracted from coalescence
models agrees with results from pion interferometry for an expanding source.
The chemical and thermal freeze-out of nuclei and antinuclei appear to coincide
with each other and with the thermal freeze-out of hadrons.Comment: 12 pages, 8 figures, to appear in the proceedings of the conference
on 'Fundamental Issues in Elementary Matter' Bad Honnef, Germany, Sept.
25-29, 200
Strangelet spectra from type II supernovae
We study in this work the fate of strangelets injected as a contamination in
the tail of a "strange matter-driven" supernova shock. A simple model for the
fragmentation and braking of the strangelets when they pass through the
expanding oxygen shell is presented and solved to understand the reprocessing
of this component. We find that the escaping spectrum is a scaled-down version
of the one injected at the base of the oxygen shell. The supernova source is
likely to produce low-energy particles of quite independently
of the initial conditions. However, it is difficult that ultrarrelativistic
strangelets (such as the hypothetical Centauro primaries) can have an origin in
those explosive events.Comment: RevTex file, 5 pp., no figure
High-speed analysis of nuclear emulsion films with the use of dry objective lenses
The extensive use of nuclear emulsions as precise tracking detectors in experimental physics has been made possible due to recent advances in the production of novel emulsion films and to the development of automatic scanning devices. The scanning speed of such systems has exceeded the level of 20 cm2 of emulsion surface per hour. High-speed automatic scanning systems, such as those developed by the OPERA Collaboration, are able to reconstruct particle tracks in nuclear emulsions with excellent accuracy. However, the high-magnification oil immersion objectives used in these systems assume deposition and removal of oil onto and from the emulsion films. This is a major technological obstacle in the automatization of the emulsion feeding to the microscope, as required for large scale use as in the case of the OPERA neutrino oscillation experiment. In order to overcome this problem, an innovative technique of nuclear emulsion films scanning with the use of dry objective lenses has been developed and successfully applied to the experiment
Centrality dependence of K+ produced in Pb+Pb collisions at 158 GeV per nucleon
The NA52 collaboration searches for a discontinuous behaviour of charged
kaons produced in Pb+Pb collisions at 158 A GeV as a function of the impact
parameter, which could reveal a hadron to quark-gluon plasma (QGP) phase
transition. The K+ yield is found to grow proportional to the number of
participating ('wounded') nucleons N, above N=100. Previous NA52 data agree
with the above finding and show a discontinuous behaviour in the kaon
centrality dependence near N=100, marking the onset of strangeness enhancement
-over e.g. p+A data at the same \sqrt{s}- in a chemically equilibrated phase.Comment: 2 pages, 2 figures, submitted to the XXXth International Conference
on High Energy Physics, 27 July - 2 August, 2000, Osaka, Japa
Charged pion production in fixed target Pb + Pb collisions at 158 GeV per nucleon
Changes in pion production as a function of the impact parameter of the collision or the incident energy, may reveal characteristics of a possible first-order phase transition from nuclear to quark matter, as predicted by lattice quantum chromodynamics. In this paper we investigate charged pion production in Pb+Pb collisions at 158 GeV/nucleon near 0° production angle and at forward rapidity . The centrality dependence of pion production is shown in the impact parameter range ~ 2-12 fm at the rapidities y = 5.7 and 6.3. An enhancement in the pi-/pi+ ratio has been measured near beam rapidity, indicating Coulomb interaction of charged pions with the spectator protons. The charged pion yield per nucleon participating in the collision (N_p) at y = 5.7 increases faster than linearly with N_p, up to N_p~100 and then it saturates, while at y = 6.3 it does not exhibit any sudden change as a function of N_p
Evidence for appearance in the CNGS neutrino beam with the OPERA experiment
The OPERA experiment is designed to search for oscillations in appearance mode i.e. through the direct observation
of the lepton in charged current interactions. The
experiment has taken data for five years, since 2008, with the CERN Neutrino to
Gran Sasso beam. Previously, two candidates with a decaying
into hadrons were observed in a sub-sample of data of the 2008-2011 runs. Here
we report the observation of a third candidate in the
decay channel coming from the analysis of a sub-sample of the
2012 run. Taking into account the estimated background, the absence of
oscillations is excluded at the 3.4
level.Comment: 9 pages, 5 figures, 1 table
Emulsion sheet doublets as interface trackers for the OPERA experiment
New methods for efficient and unambiguous interconnection between electronic
counters and target units based on nuclear photographic emulsion films have
been developed. The application to the OPERA experiment, that aims at detecting
oscillations between mu neutrino and tau neutrino in the CNGS neutrino beam, is
reported in this paper. In order to reduce background due to latent tracks
collected before installation in the detector, on-site large-scale treatments
of the emulsions ("refreshing") have been applied. Changeable Sheet (CSd)
packages, each made of a doublet of emulsion films, have been designed,
assembled and coupled to the OPERA target units ("ECC bricks"). A device has
been built to print X-ray spots for accurate interconnection both within the
CSd and between the CSd and the related ECC brick. Sample emulsion films have
been extensively scanned with state-of-the-art automated optical microscopes.
Efficient track-matching and powerful background rejection have been achieved
in tests with electronically tagged penetrating muons. Further improvement of
in-doublet film alignment was obtained by matching the pattern of low-energy
electron tracks. The commissioning of the overall OPERA alignment procedure is
in progress.Comment: 19 pages, 19 figure
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