752 research outputs found
STAR Barrel Electromagnetic Calorimeter Absolute Calibration Using "Minimum Ionizing Particles" from Collisions at RHIC
The procedure for the STAR Barrel Electromagnetic Calorimeter (BEMC) absolute
calibrations, using penetrating charged particle hits (MIP-hits) from physics
events at RHIC, is presented. Its systematic and statistical errors are
evaluated. It is shown that, using this technique, the equalization and
transfer of the absolute scale from the test beam can be done to a percent
level accuracy in a reasonable amount of time for the entire STAR BEMC.
MIP-hits would also be an effective tool for continuously monitoring the
variations of the BEMC tower's gains, virtually without interference to STAR's
main physics program. The method does not rely on simulations for anything
other than geometric and some other small corrections, and also for estimations
of the systematic errors. It directly transfers measured test beam responses to
operations at RHIC.Comment: 19 pages, 7 figures, Accepted to NIM-
Simulation of large photomultipliers for experiments in astroparticle physics
We have developed an accurate simulation model of the large 9 inch
photomultiplier tubes (PMT) used in water-Cherenkov detectors of cosmic-ray
induced extensive air-showers. This work was carried out as part of the
development of the Offline simulation software for the Pierre Auger Observatory
surface array, but our findings may be relevant also for other astrophysics
experiments that employ similar large PMTs.
The implementation is realistic in terms of geometrical dimensions, optical
processes at various surfaces, thin-film treatment of the photocathode, and
photon reflections on the inner structure of the PMT. With the quantum
efficiency obtained for this advanced model we have calibrated a much simpler
and a more rudimentary model of the PMT which is more practical for massive
simulation productions. We show that the quantum efficiency declared by
manufactures of the PMTs is usually determined under conditions substantially
different from those relevant for the particular experiment and thus requires
careful (re)interpretation when applied to the experimental data or when used
in simulations. In principle, the effective quantum efficiency could vary
depending on the optical characteristics of individual events.Comment: 8 pages, 11 figure
Anomalous prompt photon production in hadronic collisions at low-
We investigate the discrepancy that exists at low- between
the next--to--leading order QCD calculations of prompt photon production and
the measured cross section. The central values of the measured cross section
are of order 100\% larger than QCD predictions in this region. It has been
suggested that the bremsstrahlung contribution may account for this
discrepancy. The quark fragmentation function has not been
measured and an exactly known asymptotic form is normally used in calculations.
We examine the effect of much larger fragmentation functions on the QCD
predictions. After illustrating the effect of the large fragmentation functions
in some detail for recent CDF data at =1.8~TeV, we perform a
fit to 8 prompt photon data sets ranging in CMS energy from 24~GeV to 1.8~TeV.
While a large fragmentation function normalization may prove to play an
important role in resolving the discrepancy, the present theoretical and
experimental uncertainties prevent any definite normalization value from being
determined.Comment: 14 pages, LBL-33122 and UCB-PTH-92/38. 13 figures available by email,
specify postscript or topdrawe
Atmospheric MUons from PArametric formulas: a fast GEnerator for neutrino telescopes (MUPAGE)
Neutrino telescopes will open, in the next years, new opportunities in
observational high energy astrophysics. For these experiments, atmospheric
muons from primary cosmic ray interactions in the atmosphere play an important
role, because they provide the most abundant source of events for calibration
and test. On the other side, they represent the major background source.
In this paper a fast Monte Carlo generator (called MUPAGE) of bundles of
atmospheric muons for underwater/ice neutrino telescopes is presented. MUPAGE
is based on parametric formulas [APP25(2006)1] obtained from a full Monte Carlo
simulation of cosmic ray showers generating muons in bundle, which are
propagated down to 5 km w.e. It produces the event kinematics on the surface of
a user-defined virtual cylinder, surrounding the detector. The multiplicity of
the muons in the bundle, the muon spatial distribution and energy spectrum are
simulated according to a specific model of primary cosmic ray flux, with
constraints from measurements of the muon flux with underground experiments. As
an example of the application, the result of the generation of events on a
cylindrical surface of 3 km^2 at a depth of 2450 m of water is presented.Comment: 20 pages, 4 figure
First Measurement of Near-Threshold J/ᴪ Exclusive Photoproduction Off the Proton
We report on the measurement of the γp -\u3e J/ψp cross section from Eγ = 11.8 GeV down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment. We find that the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section dσ/dt has an exponential slope of 1.67 ± 0.39 GeV-2 at 10.7 GeV average energy. The LHCb pentaquark candidates P+c can be produced in the s channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions β(P+c → J/ψp) and cross sections σ(γp → P+c ) x β(P+c → J/ψp)
Pion Structure Function in the Nambu and Jona-Lasinio model
The pion structure function is studied in the Nambu and Jona-Lasinio (NJL)
model. We calculate the forward scattering amplitude of a virtual photon from a
pion target in the Bjorken limit, and obtain valence quark distributions of the
pion at the low energy hadronic scale, where the NJL model is supposed to work.
The calculated distribution functions are evolved to the experimental momentum
scale using the Altarelli-Parisi equation. The resulting distributions are in a
reasonable agreement with experiment. We calculate also the kaon structure
function and compare the ratio of kaon to pion valence u-quark distributions
with experiment.Comment: 15 pages with 5 figures as uuencoded postscript files, TMU-NT-930301
(plain LaTeX
Meson Structure in Deep Inelastic Scattering
We study the deep inelastic structure functions of mesons within the Nambu
and Jona-Lasinio model. We calculate the valence quark distributions in ,
, and mesons at the low energy model scale, which are evoluted to
the experimental momentum scale in terms of the Altarelli-Parisi equation. The
resulting distribution functions show reasonable agreements with experiment. We
also discuss the semi-inclusive lepton nucleon scattering process with a slow
nucleon in coincidence in the final state, which reveals the off-shell
structure of the pion.Comment: 31 pages with 16 figures as uuencoded postscript files, TMU-NT-940101
(plain LaTeX
Energy calibration of large underwater detectors using stopping muons
We propose to use stopping cosmic-ray muons in the energy calibration of planned and deployed large underwater detectors. The method is based on the proportionality between the incident muon energy and the length of the muon path before it stops. Simultaneous measurements of the muon path and the amplitude of the signal from the photomultiplier tubes allow a relation between the energy deposited in the sensitive volume of the detector and the observed signal to be derived, and also provide a test of detector simulations. We describe the proposed method and present the results of simulations
Light tracking through ice and water -- Scattering and absorption in heterogeneous media with Photonics
In the field of neutrino astronomy, large volumes of optically transparent
matter like glacial ice, lake water, or deep ocean water are used as detector
media. Elementary particle interactions are studied using in situ detectors
recording time distributions and fluxes of the faint photon fields of Cherenkov
radiation generated by ultra-relativistic charged particles, typically muons or
electrons.
The Photonics software package was developed to determine photon flux and
time distributions throughout a volume containing a light source through Monte
Carlo simulation. Photons are propagated and time distributions are recorded
throughout a cellular grid constituting the simulation volume, and Mie
scattering and absorption are realised using wavelength and position dependent
parameterisations. The photon tracking results are stored in binary tables for
transparent access through ANSI-C and C++ interfaces. For higher-level physics
applications, like simulation or reconstruction of particle events, it is then
possible to quickly acquire the light yield and time distributions for a
pre-specified set of light source and detector properties and geometries
without real-time photon propagation.
In this paper the Photonics light propagation routines and methodology are
presented and applied to the IceCube and Antares neutrino telescopes. The way
in which inhomogeneities of the Antarctic glacial ice distort the signatures of
elementary particle interactions, and how Photonics can be used to account for
these effects, is described.Comment: 22 pages, 8 Postscript figures, uses elsart.cl
Supernova pointing with low- and high-energy neutrino detectors
A future galactic SN can be located several hours before the optical
explosion through the MeV-neutrino burst, exploiting the directionality of
--scattering in a water Cherenkov detector such as Super-Kamiokande. We
study the statistical efficiency of different methods for extracting the SN
direction and identify a simple approach that is nearly optimal, yet
independent of the exact SN neutrino spectra. We use this method to quantify
the increase in the pointing accuracy by the addition of gadolinium to water,
which tags neutrons from the inverse beta decay background. We also study the
dependence of the pointing accuracy on neutrino mixing scenarios and initial
spectra. We find that in the ``worst case'' scenario the pointing accuracy is
at 95% C.L. in the absence of tagging, which improves to
with a tagging efficiency of 95%. At a megaton detector, this accuracy can be
as good as . A TeV-neutrino burst is also expected to be emitted
contemporaneously with the SN optical explosion, which may locate the SN to
within a few tenths of a degree at a future km high-energy neutrino
telescope. If the SN is not seen in the electromagnetic spectrum, locating it
in the sky through neutrinos is crucial for identifying the Earth matter
effects on SN neutrino oscillations.Comment: 13 pages, 7 figures, Revtex4 format. The final version to be
published in Phys. Rev. D. A few points in the original text are clarifie
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