171 research outputs found
Some indication for a missing chiral partner eta_4 around 2 GeV
The high-lying mesons in the light quark sector previously obtained from the
partial wave analysis of the proton-antiproton annihilation in flight at 1.9 -
2.4 GeV region at CERN reveal a very high degree of degeneracy. This degeneracy
can be explained as due to an effective restoration of both SU(2)_L * SU(2)_R
and U(1)_A symmetries combined with a principal quantum number n + J. In this
case there must be chiral partners for the highest spin states in the 2 and 2.3
GeV bands presently missing in the data. Here we reanalyze the Crystal Barrel
data and show an indication for existence of the missing state around
2 GeV. This result calls for further experimental search of the missing states
both in the proton-antiproton annihilation and in the production reactions.Comment: 4 pp. A fit with the energy-dependent width has been added that
agrees with the previous analysis. Accepted by PR
The two-pion spectra for the reaction \pi^- p -> \pi^0\pi^0 n at 38 GeV/c pion momentum and combined analysis of the GAMS, Crystal Barrel and BNL data
We perform the K-matrix analysis of meson partial waves with IJ^{PC}
=00^{++}, 10^{++}, 02^{++}, 12^{++} basing on GAMS data on \pi^-p -> \pi^0\pi^0
n, \eta\eta n, \eta\eta' n together with BNL data on \pi^-p -> K\bar K n and
Crystal Barrel data on p\bar p (at rest) -> \pi^0\pi^0\pi^0, \pi^0\eta\eta,
\pi^0\pi^0\eta. The positions of the amplitude poles (physical resonances) are
determined as well as the positions of the K-matrix poles (bare states) and the
values of bare state couplings to two-meson channels. Nonet classification of
the determined bare states is discussed.Comment: LaTex, 15 pages and 10 figure
Unquenching the scalar glueball
Computations in the quenched approximation on the lattice predict the
lightest glueball to be a scalar in the 1.5-1.8 GeV region. Here we calculate
the dynamical effect the coupling to two pseudoscalars has on the mass, width
and decay pattern of such a scalar glueball. These hadronic interactions allow
mixing with the scalar nonet, which is largely fixed by the
well-established K_0^*(1430). This non-perturbative mixing means that, if the
pure gluestate has a width to two pseudoscalar channels of ~100 MeV as
predicted on the lattice, the resulting hadron has a width to these channels of
only ~30 MeV with a large eta-eta component. Experimental results need to be
reanalyzed in the light of these predictions to decide if either the f_0(1500)
or an f_0(1710) coincides with this dressed glueball.Comment: 12 pages, LaTex, 3 Postscript figure
Study of the system in the mass range up to 1200 MeV
The reaction has been studied with GAMS-2000
spectrometer in the secondary 38 GeV/c -beam of the IHEP U-70
accelerator. Partial wave analysis of the reaction has been performed in the
mass range up to 1200 MeV. The -meson is seen as a sharp
peak in S-wave. The -dependence of production cross section has
been studied. Dominant production of the at a small transfer
momentum confirms the hypothesis of Achasov and Shestakov about significant
contribution of the exchange () in the mechanism
of meson production in -channel of the reaction.Comment: 4 pages, 3 figures, talk given at HADRON'9
Process pi p -> pi pi N at high energies and moderate momenta transferred to the nucleon and the determination of parameters of the f_0(980) and f_0(1300)
We present the results of simultaneous analysis of the S-wave pi pi-spectra
in the reactions pi^- p -> (pi^0 pi^0)_S n at p_{lab}=38 GeV/c (GAMS) and pi^-
p -> (pi^+ pi^-)_S n at p_{lab}=18 GeV/c (E852 Collaboration) at moderate
momenta transferred to the nucleon, |t| < 1.5 (GeV/c)^2. The t-distributions
are described by the reggeized pi- and a_1-exchanges provided by the leading
and daughter trajectories, while the M_{pi pi}-spectra are determined by a set
of scalar-isoscalar resonances. With M_{pi pi}-distributions averaged over
t-intervals, we have found several solutions given by different t-channel
exchange mechanisms at |t| ~ (0.5-1.5) (GeV/c)^2, with resonance parameters
close to each other. We conclude that despite a poor knowledge of the structure
of the t-exchange, the characteristics of resonances such as masses and widths
can be reliably determined using the processes under discussion. As to pole
positions, we have found (1031 +/- 10) - i(35 +/- 6) MeV for f_0(980) and (1315
+/- 20) - i(150 +/- 30) MeV for f_0(1300).Comment: 17 pages, RevTeX, 10 EPS figures, misprints correcte
Hadroproduction and Polarization of Charmonium
In the limit of heavy quark mass, the production cross section and
polarization of quarkonia can be calculated in perturbative QCD. We study the
-averaged production of charmonium states in collisions at
fixed target energies. The data on the relative production rates of \jp and
is found to disagree with leading twist QCD. The polarization of the
\jp indicates that the discrepancy is not due to poorly known parton
distributions nor to the size of higher order effects (-factors). Rather,
the disagreement suggests important higher twist corrections, as has been
surmised earlier from the nuclear target -dependence of the production cross
section.Comment: 19 page
The COMPASS Experiment at CERN
The COMPASS experiment makes use of the CERN SPS high-intensitymuon and
hadron beams for the investigation of the nucleon spin structure and the
spectroscopy of hadrons. One or more outgoing particles are detected in
coincidence with the incoming muon or hadron. A large polarized target inside a
superconducting solenoid is used for the measurements with the muon beam.
Outgoing particles are detected by a two-stage, large angle and large momentum
range spectrometer. The setup is built using several types of tracking
detectors, according to the expected incident rate, required space resolution
and the solid angle to be covered. Particle identification is achieved using a
RICH counter and both hadron and electromagnetic calorimeters. The setup has
been successfully operated from 2002 onwards using a muon beam. Data with a
hadron beam were also collected in 2004. This article describes the main
features and performances of the spectrometer in 2004; a short summary of the
2006 upgrade is also given.Comment: 84 papes, 74 figure
Search for Point Sources of High Energy Neutrinos with AMANDA
This paper describes the search for astronomical sources of high-energy
neutrinos using the AMANDA-B10 detector, an array of 302 photomultiplier tubes,
used for the detection of Cherenkov light from upward traveling
neutrino-induced muons, buried deep in ice at the South Pole. The absolute
pointing accuracy and angular resolution were studied by using coincident
events between the AMANDA detector and two independent telescopes on the
surface, the GASP air Cherenkov telescope and the SPASE extensive air shower
array. Using data collected from April to October of 1997 (130.1 days of
livetime), a general survey of the northern hemisphere revealed no
statistically significant excess of events from any direction. The sensitivity
for a flux of muon neutrinos is based on the effective detection area for
through-going muons. Averaged over the Northern sky, the effective detection
area exceeds 10,000 m^2 for E_{mu} ~ 10 TeV. Neutrinos generated in the
atmosphere by cosmic ray interactions were used to verify the predicted
performance of the detector. For a source with a differential energy spectrum
proportional to E_{nu}^{-2} and declination larger than +40 degrees, we obtain
E^2(dN_{nu}/dE) <= 10^{-6}GeVcm^{-2}s^{-1} for an energy threshold of 10 GeV.Comment: 46 pages, 22 figures, 4 tables, submitted to Ap.
Antideuterons as a probe of primordial black holes
In most cosmological models, primordial black holes (PBHs) should have formed
in the early Universe. Their Hawking evaporation into particles could
eventually lead to the formation of antideuterium nuclei. This paper is devoted
to a first computation of this antideuteron flux. The production of these
antinuclei is studied with a simple coalescence scheme, and their propagation
in the Galaxy is treated with a well-constrained diffusion model. We compare
the resulting primary flux to the secondary background, due to the spallation
of protons on the interstellar matter. Antideuterons are shown to be a very
sensitive probe for primordial black holes in our Galaxy. The next generation
of experiments should allow investigators to significantly improve the current
upper limit, nor even provide the first evidence of the existence of
evaporating black holes.Comment: Final version, published in Astronomy & Astrophysic
New hadrons as ultra-high energy cosmic rays
Ultra-high energy cosmic ray (UHECR) protons produced by uniformly
distributed astrophysical sources contradict the energy spectrum measured by
both the AGASA and HiRes experiments, assuming the small scale clustering of
UHECR observed by AGASA is caused by point-like sources. In that case, the
small number of sources leads to a sharp exponential cutoff at the energy
E<10^{20} eV in the UHECR spectrum. New hadrons with mass 1.5-3 GeV can solve
this cutoff problem. For the first time we discuss the production of such
hadrons in proton collisions with infrared/optical photons in astrophysical
sources. This production mechanism, in contrast to proton-proton collisions,
requires the acceleration of protons only to energies E<10^{21} eV. The diffuse
gamma-ray and neutrino fluxes in this model obey all existing experimental
limits. We predict large UHE neutrino fluxes well above the sensitivity of the
next generation of high-energy neutrino experiments. As an example we study
hadrons containing a light bottom squark. These models can be tested by
accelerator experiments, UHECR observatories and neutrino telescopes.Comment: 17 pages, revtex style; v2: shortened, as to appear in PR
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