219 research outputs found
Physics Opportunities of a Fixed-Target Experiment using the LHC Beams
We outline the many physics opportunities offered by a multi-purpose
fixed-target experiment using the LHC proton and Pb beams extracted by a bent
crystal. In a proton run with the LHC 7-TeV beam, one can analyze pp, pd and pA
collisions at sqrt(s_NN)~115 GeV and even higher using the Fermi motion in a
nuclear target. In a Pb run with a 2.76 TeV-per-nucleon beam, sqrt(s_NN) is as
high as 72 GeV. Bent crystals can be used to extract about 5x10^8 protons/s;
the integrated luminosity over a year reaches 0.5fb-1 on a typical 1 cm-long
target without species limitation. Such an extraction mode does not alter the
performance of the collider experiments at the LHC. By instrumenting the
target-rapidity region, gluon and heavy-quark proton and neutron PDFs can be
accessed at large x and even at x larger than 1 in the nuclear case. Single
diffractive physics and, for the first time, the large negative-xF domain can
be accessed. The nuclear target-species versatility provides a unique
opportunity to study nuclear matter vs. the features of the hot and dense
matter formed in heavy-ion collisions, which can be studied in PbA collisions
over the full range of target-rapidity domain with a large variety of nuclei.
The polarization of hydrogen and nuclear targets allows an ambitious spin
program, including measurements of the QCD lensing effects which underlie the
Sivers single-spin asymmetry, the study of transversity distributions and
possibly of polarized PDFs. We also emphasize the potential offered by pA
ultra-peripheral collisions where the nucleus target A is used as a coherent
photon source, mimicking photoproduction processes in ep collisions. Finally,
we note that W and Z bosons can be produced and detected in a fixed-target
experiment and in their threshold domain for the first time, providing new ways
to probe the partonic content of the proton and the nucleus.Comment: 14 pages, 2 figures, 5 tables. Comments are welcom
Study of the reaction pbar p -> phi phi from 1.1 to 2.0 GeV/c
A study has been performed of the reaction pbar p -> 4K using in-flight
antiprotons from 1.1 to 2.0 GeV/c incident momentum interacting with a hydrogen
jet target. The reaction is dominated by the production of a pair of phi
mesons. The pbar p -> phi phi cross section rises sharply above threshold and
then falls continuously as a function of increasing antiproton momentum. The
overall magnitude of the cross section exceeds expectations from a simple
application of the OZI rule by two orders of magnitude. In a fine scan around
the xi/f_J(2230) resonance, no structure is observed. A limit is set for the
double branching ratio B(xi -> pbar p) * B(xi -> phi phi) < 6e-5 for a spin 2
resonance of M = 2.235 GeV and Width = 15 MeV.Comment: 13 pages, 13 figures, 2 tables, Latex. To be published in Phys. Rev.
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Formation processes of a reopened early Bronze Age inhumation grave in Austria: the soil thin section analyses
Early Bronze Age and early medieval inhumation graves in (central) Europe had often been re-opened a short time after burial and, inmost cases, grave goods were removed. To improve the understanding of the archaeological evidence of these graves, one re-opened grave from a large early Bronze Age (Wieselburg/Gáta culture) cemetery
in Weiden am See, eastern Austria, was excavated using a microstratigraphic protocol to maximize data collection for the reconstruction of the context formation process and, consequently, the interpretation of the re-opening process. In this article the results of the soil thin section analyses are presented and discussed
The -dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron, proton and neutron
The Gerasimov-Drell-Hearn (GDH) sum rule connects the anomalous contribution
to the magnetic moment of the target nucleus with an energy-weighted integral
of the difference of the helicity-dependent photoabsorption cross sections. The
data collected by HERMES with a deuterium target are presented together with a
re-analysis of previous measurements on the proton. This provides a measurement
of the generalised GDH integral covering simultaneously the nucleon-resonance
and the deep inelastic scattering regions. The contribution of the
nucleon-resonance region is seen to decrease rapidly with increasing . The
DIS contribution is sizeable over the full measured range, even down to the
lowest measured . As expected, at higher the data are found to be in
agreement with previous measurements of the first moment of . From data on
the deuteron and proton, the GDH integral for the neutron has been derived and
the proton--neutron difference evaluated. This difference is found to satisfy
the fundamental Bjorken sum rule at GeV.Comment: 12 pages, 10 figure
Flavor decomposition of the sea quark helicity distributions in the nucleon from semi-inclusive deep-inelastic scattering
Double-spin asymmetries of semi-inclusive cross sections for the production
of identified pions and kaons have been measured in deep-inelastic scattering
of polarized positrons on a polarized deuterium target. Five helicity
distributions including those for three sea quark flavors were extracted from
these data together with re-analyzed previous data for identified pions from a
hydrogen target. These distributions are consistent with zero for all three sea
flavors. A recently predicted flavor asymmetry in the polarization of the light
quark sea appears to be disfavored by the data.Comment: 5 pages, 3 figure
Nuclear Polarization of Molecular Hydrogen Recombined on a Non-metallic Surface
The nuclear polarization of molecules formed by recombination
of nuclear polarized H atoms on the surface of a storage cell initially coated
with a silicon-based polymer has been measured by using the longitudinal
double-spin asymmetry in deep-inelastic positron-proton scattering. The
molecules are found to have a substantial nuclear polarization, which is
evidence that initially polarized atoms retain their nuclear polarization when
absorbed on this type of surfac
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