518 research outputs found
Higher Twist Distribution Amplitudes of the Nucleon in QCD
We present the first systematic study of higher-twist light-cone distribution
amplitudes of the nucleon in QCD. We find that the valence three-quark state is
described at small transverse separations by eight independent distribution
amplitudes. One of them is leading twist-3, three distributions are twist-4 and
twist-5, respectively, and one is twist-6. A complete set of distribution
amplitudes is constructed, which satisfies equations of motion and constraints
that follow from conformal expansion. Nonperturbative input parameters are
estimated from QCD sum rules.Comment: 29 pages, 4 figures, eqn in (3.19) corrected, table 3 accordingly
changed, some typos fixe
Jet color chemistry and anomalous baryon production in -collisions
We study anomalous high- baryon production in -collisions due to
formation of the two parton collinear system in the anti-sextet color
state for quark jets and system in the decuplet/anti-decuplet color states
for gluon jets. Fragmentation of these states, which are absent for
-collisions, after escaping from the quark-gluon plasma leads to baryon
production. Our qualitative estimates show that this mechanism can be
potentially important at RHIC and LHC energies.Comment: 20 pages, 4 figures, Eur.Phys.J. versio
A Chiral Effective Lagrangian for Nuclei
An effective hadronic lagrangian consistent with the symmetries of quantum
chromodynamics and intended for applications to finite-density systems is
constructed. The degrees of freedom are (valence) nucleons, pions, and the
low-lying non-Goldstone bosons, which account for the intermediate-range
nucleon-nucleon interactions and conveniently describe the nonvanishing
expectation values of nucleon bilinears. Chiral symmetry is realized
nonlinearly, with a light scalar meson included as a chiral singlet to describe
the mid-range nucleon-nucleon attraction. The low-energy electromagnetic
structure of the nucleon is described within the theory using vector-meson
dominance, so that external form factors are not needed. The effective
lagrangian is expanded in powers of the fields and their derivatives, with the
terms organized using Georgi's ``naive dimensional analysis''. Results are
presented for finite nuclei and nuclear matter at one-baryon-loop order, using
the single-nucleon structure determined within the model. Parameters obtained
from fits to nuclear properties show that naive dimensional analysis is a
useful principle and that a truncation of the effective lagrangian at the first
few powers of the fields and their derivatives is justified.Comment: 43 pages, REVTeX 3.0 with epsf.sty, plus 12 figure
Thermodynamics of pyrope-majorite, Mg3Al2Si3O12-Mg4Si4O12, solid solution from atomistic model calculations
Static lattice energy calculations, based on empirical pair potentials have been performed for a large set of different structures with compositions between pyrope and majorite, and with different states of order of octahedral cations. The energies have been cluster expanded using pair and quaternary terms. The derived ordering constants have been used to constrain Monte Carlo simulations of temperature-dependent properties in the ranges of 1073 3673K and 0 20 GPa. The free energies of mixing have been calculated using the method of thermodynamic integration. At zero pressure the cubic/tetragonal transition is predicted for pure majorite at 3300 K. The transition temperature decreases with the increase of the pyrope mole fraction. A miscibility gap associated with the transition starts to develop at about 2000K and xmaj 0.8, and widens with the decrease in temperature and the increase in pressure. Activity composition relations in the range of 0 20 GPa and 1073 2673K are described with the help of a high-order Redlich Kister polynomial
Next-to-next-to-leading order prediction for the photon-to-pion transition form factor
We evaluate the next-to-next-to-leading order corrections to the
hard-scattering amplitude of the photon-to-pion transition form factor. Our
approach is based on the predictive power of the conformal operator product
expansion, which is valid for a vanishing -function in the so-called
conformal scheme. The Wilson--coefficients appearing in the non-forward
kinematics are then entirely determined from those of the polarized
deep-inelastic scattering known to next-to-next-to-leading accuracy. We propose
different schemes to include explicitly also the conformal symmetry breaking
term proportional to the -function, and discuss numerical predictions
calculated in different kinematical regions. It is demonstrated that the
photon-to-pion transition form factor can provide a fundamental testing ground
for our QCD understanding of exclusive reactions.Comment: 62 pages LaTeX, 2 figures, 9 tables; typos corrected, some references
added, to appear in Phys. Rev.
Electromagnetic probes
We introduce the seminal developments in the theory and experiments of
electromagnetic probes for the study of the dynamics of relativistic heavy ion
collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at
QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200
Electromagnetic Probes
A review is presented of dilepton and real photon measurements in
relativistic heavy ion collisions over a very broad energy range from the low
energies of the BEVALAC up to the highest energies available at RHIC. The
dileptons cover the invariant mass range \mll = 0 - 2.5 GeV/c, i.e. the
continuum at low and intermediate masses and the light vector mesons, . The review includes also measurements of the light vector mesons
in elementary reactions.Comment: To be published in Landolt-Boernstein Volume 1-23A; 40 pages, 24
figures. Final version updated with small changes to the text, updated
references and updated figure
Fast-timing measurements in neutron-rich odd-mass zirconium isotopes using LaBr3:Ce detectors coupled with Gammasphere
A fast-timing experiment was performed at the Argonne National Laboratory to measure the lifetimes of the lowest lying states of nuclei belonging to the deformed regions around mass number A 110 and A 150. These regions were populated via spontaneous fission of 252 Cf and the gamma radiation following the decay of excited states in the fission fragments was measured using 51 Gammasphere detectors coupled with 25 LaBr 3 :Ce detectors. A brief description of the acquisition system and some preliminary results from the fast-timing analysis of the fission fragment 100Zr are presented. The lifetime value of \u3c4 = 840(65) ps was found for the 2 + state in 100 Zr consistent within one standard deviation of the adopted value with 791 +26 -35 ps. This is associated with a quadrupole deformation parameter of 0.36(2) which is within one standard deviation of the literature value of 0.3556 +82 -57
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
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