20 research outputs found
Collins fragmentation function from gluon rescattering
We estimate the Collins fragmentation function by introducing the effect of
gluon rescattering in a model calculation of the fragmentation process. We
include all necessary diagrams to the one-loop level and compute the nontrivial
phases giving rise to the Collins function. We compare our results to the ones
obtained from pion rescattering. We conclude that three out of four one-loop
diagrams give sizeable contributions to the Collins function, and that the
effect of gluon rescattering has a magnitude comparable to that of pion
rescattering, but has opposite sign.Comment: 6 pages, 5 figures, uses RevTex. Typos corrected and a sentence added
in the conclusions. To be published in PL
Sivers function in a spectator model with axial-vector diquarks
We perform a calculation of the Sivers function in a spectator model of the
nucleon, with scalar and axial-vector diquarks. We make use of gluon
rescattering to produce the nontrivial phases necessary to generate the Sivers
function. The inclusion of axial-vector diquarks enables us to obtain a nonzero
Sivers function for down quarks. Using the results of our model, we discuss the
phenomenology of transvere single spin asymmetries in pi+, pi-, and pi0
production, which are currently analysed by the HERMES and COMPASS
collaborations. We find that the inclusion of axial-vector diquarks
substantially reduces the asymmetries.Comment: 8 pages, 7 figures, uses RevTex, added calculation of h1^perp, final
version accepted for publication in PL
A Monte Carlo for POLarized (semi-inclusive) Deep Inelastic Scattering
POLDIS is a Monte Carlo program for polarized (semi-inclusive) deep inelastic
scattering (DIS). Unpolarized DIS events are generated with the existing
lepto-production event generators LEPTO for DIS and AROMA for Heavy Flavor
production. The relevant spin asymmetries are computed at partonic level to
first order in alpha_s for each generated event, and are then convoluted with
the corresponding ratio between the polarized and unpolarized parton
distribution functions (i.e. parton polarization). This procedure provides a
polarization weight for each event. The average of these polarization weights
gives the polarized cross section spin-asymmetry for the generated sample. The
code consists of a set of subroutines to be linked with LEPTO and/or AROMA.Comment: 18 pages, LaTeX, 6 eps figures included, to be published in Computer
Physics Communication
Transverse Polarisation of Quarks in Hadrons
We review the present state of knowledge regarding the transverse
polarisation (or transversity) distributions of quarks. After some generalities
on transverse polarisation, we formally define the transversity distributions
within the framework of a classification of all leading-twist distribution
functions. We describe the QCD evolution of transversity at leading and
next-to-leading order. A comprehensive treatment of non-perturbative
calculations of transversity distributions (within the framework of quark
models, lattice QCD and QCD sum rules) is presented. The phenomenology of
transversity (in particular, in Drell-Yan processes and semi-inclusive
leptoproduction) is discussed in some detail. Finally, the prospects for future
measurements are outlined.Comment: small changes, references added, as finally published in Physics
Report
Two-particle correlations in azimuthal angle and pseudorapidity in inelastic p + p interactions at the CERN Super Proton Synchrotron
Results on two-particle ΔηΔϕ correlations in inelastic p + p interactions at 20, 31, 40, 80, and 158 GeV/c are presented. The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The data show structures which can be attributed mainly to effects of resonance decays, momentum conservation, and quantum statistics. The results are compared with the Epos and UrQMD models.ISSN:1434-6044ISSN:1434-605
Hadro-production experiments and NA61/SHINE at CERN
The NA61/SHINE detector is a large acceptance hadron spectrometer at the CERN-SPS designed for the study of the hadronic final states produced in interactions of various beam particles at SPS energies. Among other goals, the NA61 experiment aims a t precision hadro-production measurements to characterize the neutrino beam of the T2K experiment at J-PARC. These measurements are performed using a 30 GeV proton beam impinging on carbon targets of different lengths, including a replica of the T2K targe t. Preliminary spectra of @p^+ and @p^- inclusive inelastic cross sections were obtained from data collected in 2007 with a 2 cm thick carbon target
The Mu3e experiment at PSI
Mu3e will search for charged Lepton Flavor Violation in the neutrinoless muon decay with a sensitivity down to (90\% C.L.) using the world most intense continuous muon beam at PSI. This search requires a large acceptance detector capable of coping with rates of up to stopped muons per second with excellent momentum, spatial, and time resolution. The Mu3e detector is based on thin monolithic active silicon pixel sensors for tracking in conjunction with scintillating fibers and tiles for timing measurements. The Mu3e apparatus is under constructions and first data is expected in 2020
A new SPS programme
A new experiemntal program to study hadron production in hadron-nucleus and nucleus-nucleus collisions at the CERN SPS has been recently proposed by the NA49-future collaboration. The physics goals of the program are: -Search for the critical point of strongly interacting matter and a study of the properties of the onset of deconfinemnt in nucleus-nucleus collisions, -Measurements of correlations, fluctuations and hadron spectra at high pT in proton-nucleus collisions needed as for better understanding of nucleus-nucleus results, -Measurements of hadron production in hadron-nucleus interactions needed for neutrino (T2K) and cosmic-ray (Pierre Auger Observatory and KASCADE) expriments. The physics of the nucleus-nucleus program is reviewed in this presentation