835 research outputs found
The high-intensity hyperon beam at CERN
A high-intensity hyperon beam was constructed at CERN to deliver Sigma- to
experiment WA89 at the Omega facility and operated from 1989 to 1994. The setup
allowed rapid changeover between hyperon and conventional hadron beam
configurations. The beam provided a Sigma-flux of 1.4 x 10^5 per burst at mean
momenta between 330 and 345 Gev/c, produced by about 3 x 10^10 protons of 450
GeV/c . At the experiment target the beam had a Sigma-/pi- ratio close to 0.4
and a size of 1.6 x 3.7 cm^2. The beam particle trajectories and their momenta
were measured with a scintillating fibre hodoscope in the beam channel and a
silicon microstrip detector at the exit of the channel. A fast transition
radiation detector was used to identify the pion component of the beam.Comment: 20 pages, 13 figures. Submitted to Nucl. Instr. Meth.
Beam losses from ultra-peripheral nuclear collisions between Pb ions in the Large Hadron Collider and their alleviation
Electromagnetic interactions between colliding heavy ions at the Large Hadron
Collider (LHC) at CERN will give rise to localized beam losses that may quench
superconducting magnets, apart from contributing significantly to the
luminosity decay. To quantify their impact on the operation of the collider, we
have used a three-step simulation approach, which consists of optical tracking,
a Monte-Carlo shower simulation and a thermal network model of the heat flow
inside a magnet. We present simulation results for the case of Pb ion operation
in the LHC, with focus on the ALICE interaction region, and show that the
expected heat load during nominal Pb operation is 40% above the quench level.
This limits the maximum achievable luminosity. Furthermore, we discuss methods
of monitoring the losses and possible ways to alleviate their effect.Comment: 17 pages, 20 figure
First observations of beam losses due to bound-free pair production in a heavy-ion collider
We report the first observations of beam losses due to bound-free pair
production at the interaction point of a heavy-ion collider. This process is
expected to be a major luminosity limit for the Large Hadron Collider (LHC)
when it operates with 208Pb82+ ions because the localized energy deposition by
the lost ions may quench superconducting magnet coils. Measurements were
performed at the Relativistic Heavy Ion Collider (RHIC) during operation with
100 GeV/nucleon 63Cu29+ ions. At RHIC, the rate, energy and magnetic field are
low enough so that magnet quenching is not an issue. The hadronic showers
produced when the single-electron ions struck the RHIC beampipe were observed
using an array of photodiodes. The measurement confirms the order of magnitude
of the theoretical cross section previously calculated by others.Comment: 4 pages, 5 figures. Added journal ref. Corrected typos. Fixed fig 1.
Minor improvements to fig. 1,3,4. Rephrased a small number of sentences
(p1,3,4). Added numerical values of the aperture and the displacement for Au
(p 2). Changed reference 5, added name in acknowledgments (p 4
Hadron beam test of a scintillating fibre tracker system for elastic scattering and luminosity measurement in ATLAS
A scintillating fibre tracker is proposed to measure elastic proton
scattering at very small angles in the ATLAS experiment at CERN. The tracker
will be located in so-called Roman Pot units at a distance of 240 m on each
side of the ATLAS interaction point. An initial validation of the design
choices was achieved in a beam test at DESY in a relatively low energy electron
beam and using slow off-the-shelf electronics. Here we report on the results
from a second beam test experiment carried out at CERN, where new detector
prototypes were tested in a high energy hadron beam, using the first version of
the custom designed front-end electronics. The results show an adequate
tracking performance under conditions which are similar to the situation at the
LHC. In addition, the alignment method using so-called overlap detectors was
studied and shown to have the expected precision.Comment: 12 pages, 8 figures. Submitted to Journal of Instrumentation (JINST
First observation of the deflection of a 33 TeV Pb ion beam in a bent silicon crystal
For the first time, the deflection of an ultra-relativistic, fully stripped Pb82+ ion beam in a bent silicon crystal has been observed. The ions were provided by the CERN-SPS in the H4 beam at a momentum of 400 GeV/c per unit of charge. A 60 mm long silicon crystal, bent over 50 mm to give a 4 mrad deflection angle, was used in this experiment. The measured Pb ion deflection efficiency is comparable to the one obtained with protons at an equivalent ratio of momentum per charge, and is found to be about 15\% for a beam with a divergence of 35 microradians (FWHM). The interaction rate observed in a background counter is found to drop when the crystal is well aligned with the beam. This corroborates further the channeling model, which predicts that channeled ions are steered away from regions of high electron densities as well as the nuclei in the crystal
Record deflection efficiencies measured for high energy protons in a bent germanium crystal
New experimental results on the deflection of high energy protons in a bent germanium crystal are presented. At 450 GeV/c, the 50 mm long crystal gave record deflection efficiencies up to 60% for small angles (1 mrad), while at angles as large as 12 mrad, the efficiency is about 25 times larger than for a silicon crystal of the same size. The experimental results are in good agreement with a model for channeling and deflection developed by Ellison and give - together with a similar comparison for a 200 GeV/c beam - confidence in extrapolations to higher energies (e.g. to LHC), other crystal materials or different deflection angles
Measurement of the Omega_c Lifetime
We present the measurement of the lifetime of the Omega_c we have performed
using three independent data samples from two different decay modes. Using a
Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c
decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts
normally used in charm analysis. The short but measurable lifetime of the
Omega_c is demonstrated by a clear enhancement of the signals at short but
finite decay lengths. Using a continuous maximum likelihood method we
determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs.
This makes the Omega_c the shortest living weakly decaying particle observed so
far. The short value of the lifetime confirms the predicted pattern of the
charmed baryon lifetimes and demonstrates that the strong interaction plays a
vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip
Search for the exotic Resonance in 340GeV/c -Nucleus Interactions
We report on a high statistics search for the resonance in
-nucleus collisions at 340GeV/c. No evidence for this resonance is
found in our data sample which contains 676000 candidates above
background. For the decay channel and the
kinematic range 0.150.9 we find a 3 upper limit for the
production cross section of 3.1 and 3.5 b per nucleon for reactions with
carbon and copper, respectively.Comment: 5 pages, 4 figures, modification of ref. 43 and 4
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