2,347 research outputs found
Identified hadron production at high transverse momenta in p+p collisions at sqrt(NN) = 200 GeV in STAR
We report the transverse momentum (pT) distributions for identified charged
pions, protons and anti-protons using events triggered by high deposit energy
in the Barrel Electro-Magnetic Calorimeter (BEMC) from p + p collisions at psNN
= 200 GeV. The spectra are measured around mid-rapidity (|y|<0.5) over the
range of 3<pT<15 GeV/c with particle identification (PID) by the relativistic
ionization energy loss (rdE/dx) in the Time Projection Chamber (TPC) in the
Solenoidal Tracker at RHIC (STAR). The charged pion, proton and anti-proton
spectra at high pT are compared with published results from minimum bias
triggered events and the Next-Leading-Order perturbative quantum chromodynamic
(NLO pQCD) calculations (DSS, KKP and AKK 2008). In addition, we present the
particle ratios of pi-/pi+, pbar/p, p/pi+ and pbar/pi- in p + p collisions.Comment: 4 pages, 4 figures, Hot Quark 2008 proceedin
Chiral Dirac fermions on the lattice using Geometric Discretisation
A new approach to the problem of doubling is presented with the Dirac-Kahler
(DK) theory as a starting point and using Geometric Discretisation providing us
with a new way of extracting the Dirac field in the discrete setting of a
hyper-cubic complex.Comment: Lattice2003(Chiral), 3 page
Double transverse spin asymmetries in vector boson production
We investigate a helicity non-flip double transverse spin asymmetry in vector
boson production in hadron-hadron scattering, which was first considered by
Ralston and Soper at the tree level. It does not involve transversity functions
and in principle also arises in W-boson production for which we present the
expressions. The asymmetry requires observing the transverse momentum of the
vector boson, but it is not suppressed by explicit inverse powers of a large
energy scale. However, as we will show, inclusion of Sudakov factors causes
suppression of the asymmetry, which increases with energy. Moreover, the
asymmetry is shown to be approximately proportional to x_1 g_1(x_1) x_2 \bar
g_1(x_2), which gives rise to additional suppression at small values of the
light cone momentum fractions. This implies that it is negligible for Z or W
production and is mainly of interest for \gamma^* at low energies. We also
compare the asymmetry with other types of double transverse spin asymmetries
and discuss how to disentangle them.Comment: 12 pages, Revtex, 2 Postscript figures, uses aps.sty, epsf.sty;
figures replaced, a few minor other correction
Open Heavy Flavor Production in Heavy Ion Collisions
The interaction of heavy partons, charm and beauty, with the matter created
in heavy ion collisions has been of great interest in recent years. Heavy
partons were predicted to interact less strongly with the matter than light
partons. In apparent contrast to these predictions, unexpectedly strong
suppression of non-photonic electrons from heavy flavor decays has been seen.
However, significant experimental uncertainties remain, both in the
measurements themselves and in the separation of the contribution from charm
and beauty, which have complicated the interpretation of these results. The
current experimental situation is critically reviewed and prospects for making
these measurements more easily interpretable discussed.Comment: 8 pages, 5 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee v2: typos
correcte
Monopoles and clusters
We define and study certain hyperkaehler manifolds which capture the
asymptotic behaviour of the SU(2)-monopole metric in regions where monopoles
break down into monopoles of lower charges. The rate at which these new metrics
approximate the monopole metric is exponential, as for the Gibbons-Manton
metric.Comment: v2.: relation to calorons mentioned; added explanation
Left-right asymmetry for pion and kaon production in the semi-inclusive deep inelastic scattering process
We analyze the left-right asymmetry in the semi-inclusive deep inelastic
scattering (SIDIS) process without introducing any weighting functions. With
the current theoretical understanding, we find that the Sivers effect plays a
key role in our analysis. We use the latest parametrization of the Sivers and
fragmentation functions to reanalyze the production process and find
that the results are sensitive to the parametrization. We also extend our
calculation on the production, which can help us know more about the
Sivers distribution of the sea quarks and the unfavored fragmentation
processes. HERMES kinematics with a proton target, COMPASS kinematics with a
proton, deuteron, and neutron target (the information on the neutron target can
be effectively extracted from the He target), and JLab kinematics (both 6
GeV and 12 GeV) with a proton and neutron target are considered in our paper.Comment: 7 latex pages, 11 figures, final version for publication, with
references update
Shielding Calculations on Waste Packages – The Limits and Possibilities of different Calculation Methods by the example of homogeneous and inhomogeneous Waste Packages
For nuclear waste packages the expected dose rates and nuclide inventory are beforehand calculated. Depending on the package of the nuclear waste deterministic programs like MicroShield® provide a range of results for each type of packaging. Stochastic programs like “Monte-Carlo N-Particle Transport Code System” (MCNP®) on the other hand provide reliable results for complex geometries. However this type of program requires a fully trained operator and calculations are time consuming. The problem here is to choose an appropriate program for a specific geometry. Therefore we compared the results of deterministic programs like MicroShield® and stochastic programs like MCNP®. These comparisons enable us to make a statement about the applicability of the various programs for chosen types of containers. As a conclusion we found that for thin-walled geometries deterministic programs like MicroShield® are well suited to calculate the dose rate. For cylindrical containers with inner shielding however, deterministic programs hit their limits. Furthermore we investigate the effect of an inhomogeneous material and activity distribution on the results. The calculations are still ongoing. Results will be presented in the final abstract
A three dimensional investigation of two dimensional orbits
Orbits in the principal planes of triaxial potentials are known to be prone
to unstable motion normal to those planes, so that three dimensional
investigations of those orbits are needed even though they are two dimensional.
We present here an investigation of such orbits in the well known logarithmic
potential which shows that the third dimension must be taken into account when
studying them and that the instability worsens for lower values of the forces
normal to the plane. Partially chaotic orbits are present around resonances,
but also in other regions. The action normal to the plane seems to be related
to the isolating integral that distinguishes regular form partially chaotic
orbits, but not to the integral that distinguishes partially from fully chaotic
orbits.Comment: Accepted for publication in CMD
Azimuthal asymmetries in lepton-pair production at a fixed-target experiment using the LHC beams (AFTER)
A multi-purpose fixed-target experiment using the proton and lead-ion beams
of the LHC was recently proposed by Brodsky, Fleuret, Hadjidakis and Lansberg,
and here we concentrate our study on some issues related to the spin physics
part of this project (referred to as AFTER). We study the nucleon spin
structure through and processes with a fixed-target experiment using
the LHC proton beams, for the kinematical region with 7 TeV proton beams at the
energy in center-of-mass frame of two nucleons GeV. We calculate
and estimate the azimuthal asymmetries of unpolarized and
dilepton production processes in the Drell--Yan continuum region and at the
-pole. We also calculate the , and
azimuthal asymmetries of and dilepton production
processes with the target proton and deuteron longitudinally or transversally
polarized in the Drell--Yan continuum region and around resonances region.
We conclude that it is feasible to measure these azimuthal asymmetries,
consequently the three-dimensional or transverse momentum dependent parton
distribution functions (3dPDFs or TMDs), at this new AFTER facility.Comment: 15 pages, 40 figures. Version accepted for publication in EPJ
Transverse momentum dependence in gluon distribution and fragmentation functions
We investigate the twist two gluon distribution functions for spin 1/2
hadrons, emphasizing intrinsic transverse momentum of the gluons. These
functions are relevant in leading order in the inverse hard scale in scattering
processes such as inclusive leptoproduction or Drell-Yan scattering, or more
general in hard processes in which at least two hadrons are involved. They show
up in azimuthal asymmetries. For future estimates of such observables, we
discuss specific bounds on these functions.Comment: 14 pages, revtex, 7 Postscript figure
- …