95 research outputs found
An Optical Readout TPC (O-TPC) for Studies in Nuclear Astrophysics With Gamma-Ray Beams at HIgS
We report on the construction, tests, calibrations and commissioning of an
Optical Readout Time Projection Chamber (O-TPC) detector operating with a
CO2(80%) + N2(20%) gas mixture at 100 and 150 Torr. It was designed to measure
the cross sections of several key nuclear reactions involved in stellar
evolution. In particular, a study of the rate of formation of oxygen and carbon
during the process of helium burning will be performed by exposing the chamber
gas to intense nearly mono-energetic gamma-ray beams at the High Intensity
Gamma Source (HIgS) facility. The O-TPC has a sensitive target-drift volume of
30x30x21 cm^3. Ionization electrons drift towards a double parallel grid
avalanche multiplier, yielding charge multiplication and light emission.
Avalanche induced photons from N2 emission are collected, intensified and
recorded with a Charge Coupled Device (CCD) camera, providing two-dimensional
track images. The event's time projection (third coordinate) and the deposited
energy are recorded by photomultipliers and by the TPC charge-signal,
respectively. A dedicated VME-based data acquisition system and associated data
analysis tools were developed to record and analyze these data. The O-TPC has
been tested and calibrated with 3.183 MeV alpha-particles emitted by a 148Gd
source placed within its volume with a measured energy resolution of 3.0%.
Tracks of alpha and 12C particles from the dissociation of 16O and of three
alpha-particles from the dissociation of 12C have been measured during initial
in-beam test experiments performed at the HIgS facility at Duke University. The
full detection system and its performance are described and the results of the
preliminary in-beam test experiments are reported.Comment: Supported by the Richard F. Goodman Yale-Weizmann Exchange Program,
ACWIS, NY, and USDOE grant Numbers: DE-FG02-94ER40870 and DE-FG02-97ER4103
Unambiguous Identification of the Second 2+ State in 12C and the Structure of the Hoyle State
The second 2+ state of 12C, predicted over fifty years ago as an excitation
of the Hoyle state, has been unambiguously identified using the 12C(g,a_0)8Be
reaction. The alpha particles produced by the photodisintegration of 12C were
detected using an Optical Time Projection Chamber (O-TPC). Data were collected
at beam energies between 9.1 and 10.7 MeV using the intense nearly
mono-energetic gamma-ray beams at the HIgS facility. The measured angular
distributions determine the cross section and the E1-E2 relative phases as a
function of energy leading to an unambiguous identification of the second 2+
state in 12C at 10.03(11) MeV, with a total width of 800(130) keV and a ground
state gamma-decay width of 60(10) meV; B(E2: 2+ ---> gs) = 0.73(13) e2fm4 [or
0.45(8) W.u.]. The Hoyle state and its rotational 2+ state that are more
extended than the ground state of 12C presents a challenge and constraints for
models attempting to reveal the nature of three alpha particle states in 12C.
Specifically it challenges the ab-initio Lattice Effective Field Theory (L-EFT)
calculations that predict similar r.m.s. radii for the ground state and the
Hoyle state.Comment: Accepted for Publication in the Physical Review Lette
Associated Charm Production in Neutrino-Nucleus Interactions
In this paper a search for associated charm production both in neutral and
charged current -nucleus interactions is presented. The improvement of
automatic scanning systems in the {CHORUS} experiment allows an efficient
search to be performed in emulsion for short-lived particles. Hence a search
for rare processes, like the associated charm production, becomes possible
through the observation of the double charm-decay topology with a very low
background. About 130,000 interactions located in the emulsion target
have been analysed. Three events with two charm decays have been observed in
the neutral-current sample with an estimated background of 0.180.05. The
relative rate of the associated charm cross-section in deep inelastic
interactions, has been
measured. One event with two charm decays has been observed in charged-current
interactions with an estimated background of 0.180.06 and the
upper limit on associated charm production in charged-current interactions at
90% C.L. has been found to be .Comment: 10 pages, 4 figure
Leading order analysis of neutrino induced dimuon events in the CHORUS experiment
We present a leading order QCD analysis of a sample of neutrino induced
charged-current events with two muons in the final state originating in the
lead-scintillating fibre calorimeter of the CHORUS detector. The results are
based on a sample of 8910 neutrino and 430 antineutrino induced opposite-sign
dimuon events collected during the exposure of the detector to the CERN Wide
Band Neutrino Beam between 1995 and 1998. % with GeV
and GeV collected %between 1995 and 1998. The analysis yields a
value of the charm quark mass of \mc = (1.26\pm 0.16 \pm 0.09) \GeVcc and a
value of the ratio of the strange to non-strange sea in the nucleon of , improving the results obtained in similar analyses
by previous experiments.Comment: Submitted to Nuclear Physics
High intensity neutrino oscillation facilities in Europe
The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Fréjus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of μ+ and μ− beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular He6 and Ne18, also stored in a ring. The far detector is also the MEMPHYS detector in the Fréjus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive
Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions
The CHORUS experiment, designed to search for
oscillations, consists of a nuclear emulsion target and electronic detectors.
In this paper, results on the production of charged particles in a small sample
of charged-current neutrino-- and anti-neutrino--nucleus interactions at high
energy are presented. For each event, the emission angle and the ionization
features of the charged particles produced in the interaction are recorded,
while the standard kinematic variables are reconstructed using the electronic
detectors. The average multiplicities for charged tracks, the pseudo-rapidity
distributions, the dispersion in the multiplicity of charged particles and the
KNO scaling are studied in different kinematical regions. A study of
quasi-elastic topologies performed for the first time in nuclear emulsions is
also reported. The results are presented in a form suitable for use in the
validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure
The Acceleration and Storage of Radioactive Ions for a Beta-Beam Facility
The term beta-beam has been coined for the production of a pure beam of
electron neutrinos or their antiparticles through the decay of radioactive ions
circulating in a storage ring. This concept requires radioactive ions to be
accelerated to as high Lorentz gamma as 150. The neutrino source itself
consists of a storage ring for this energy range, with long straight sections
in line with the experiment(s). Such a decay ring does not exist at CERN today,
nor does a high-intensity proton source for the production of the radioactive
ions. Nevertheless, the existing CERN accelerator infrastructure could be used
as this would still represent an important saving for a beta-beam facility.Comment: beta-beam working group website at http://cern.ch/beta-bea
Measurement of charm production in neutrino charged-current interactions
The nuclear emulsion target of the CHORUS detector was exposed to the
wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy from
1994 to 1997. In total about 100000 charged-current neutrino interactions with
at least one identified muon were located in the emulsion target and fully
reconstructed, using newly developed automated scanning systems. Charmed
particles were searched for by a program recognizing particle decays. The
observation of the decay in nuclear emulsion makes it possible to select a
sample with very low background and minimal kinematical bias. 2013
charged-current interactions with a charmed hadron candidate in the final state
were selected and confirmed through visual inspection. The charm production
rate induced by neutrinos relative to the charged-current cross-section is
measured to be sigma(nu_mu N -> mu- C X)/sigma(CC) = (5.75 +-0.32 stat +-0.30
syst)%. The charm production cross-section as a function of the neutrino energy
is also obtained. The results are in good agreement with previous measurements.
The charm-quark hadronization produces the following charmed hadrons with
relative fractions (in %): f_Dzero = 43.7+-4.5, f_Lambda_c^plus = 19.2+-4.2,
f_Dplus = 25.3+-4.2, and f_D_splus = 11.8+-4.7.Comment: 16 pages, 5 figure
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