Search

We present a detailed simulation study of the signatures from the sequential decays of the triple-strange pbar p -> {\Omega}+{\Omega}- -> K+{\Lambda}barK- {\Lambda} -> K+pbar{\pi}+K-p{\pi}- process in the PANDA central tracking system with focus on hit patterns and precise time measurement. We present a systematic approach for studying physics channels at the detector level and develop input criteria for tracking algorithms and trigger lines. Finally, we study the beam momentum dependence on the reconstruction efficiency for the PANDA detector.

The transverse polarization of a quark is a degree of freedom that is not taken into account in the most commonly used Monte Carlo generators. For the case "e^+e^- -> hadrons" I show that it is possible to use these generators to simulate processes where the parent quark and antiquark are transversely polarized and the fragmentation process is affected by this polarization. The key point is that it is possible to obtain this without touching the generator code at all. One only works on the parton-level and hadron-level outputs that the Monte Carlo code has produced, modifying them in a correlated way. A group of techniques is presented to obtain this, matching the most obvious needs of a user (in particular: reproducing a pre-assigned final distribution). As an example these methods are applied to modify Pythia-generated events to obtain a nonzero Collins function and a consequent cos(Phi1+Phi2)-asymmetry of pion pairs., 22 pages, 9 figures

T-odd distributions like Sivers and Boer-Mulders functions are normally modeled using few-body models. In the present work I want to follow the completely opposite point of view, and study a high-energy proton-proton Drell-Yan where both the annihilating partons are wee, and one (at least) comes from a high-order Fok state of the parent proton, i.e. a state where a large number N of partons is present. I show that rescattering between active and spectator partons is modified, with suppression of those terms that are needed to build T-odd parton distributions., 12 pages, 2 figures

I study hard collisions between unpolarized protons and antiprotons where a lepton-antilepton pair is detected in coincidence with a final proton-antiproton pair, and no more particles are produced, in the regime 10 GeV^2 << s << 1000 GeV^2, M > 4 GeV, q_T < 3 GeV/c. The present work is centered on azimuthal asymmetries. Because of momentum conservation, a Boer-Mulders term in the momentum distribution of a quark implies a balancing effect in the momentum distribution of some spectators. This produces azimuthal asymmetries of the final hadrons. To analyze this, I have organized a parton-level MonteCarlo generator where a standard cos(2phi)-asymmetry of the dilepton distribution is produced, thanks to a soft rescattering process between an active quark coming from a hadron and a spectator anti-diquark coming from the other hadron. This produces cos(2phi)-asymmetries of the final hadron pair. Hadron and lepton asymmetries have the same size., final version

In this note I report and discuss the physical scheme and the main approximations used by the event generator code DY\_AB. This Monte Carlo code is aimed at preliminary simulation, during the stage of apparatus planning, of Drell-Yan events characterized by azimuthal asymmetries, in experiments with moderate center of mass energy $\sqrt{s}$ $<, Comment: 26 pages, 10 figures. In print on Nuncl. Instr. and Methods in Phys. Res. A

Recent works have discussed the violation of factorization and universality in hadronic hard scattering processes aimed at measurements of T-odd distributions. We use simple arguments to show that it is possible to restore an approximate factorization involving T-odd contributions if the factorization breaking interactions present a frequency spectrum dominated by by a narrow and regular peak whose maximum value corresponds to a respected factorization., 5 pages, no figures

I study the effect of scalar and spin-orbit absorption potentials, in the production of a nonzero Sivers-like asymmetry in hadron-hadron high energy collisions (Drell-Yan and single spin asymmetries). A basic model is built for the intrinsic state of a quark in the projectile hadron. S-wave and P-wave 2-component states are considered. Before the hard event, this quark is subject to absorbing scalar and spin-orbit local mean fields simulating interactions with a composite target. The relevant interaction terms are found to be the imaginary diagonal spin-orbit ones. Spin rotating terms, and scalar absorption, are not decisive. For $x$ $=$ 0 the found Sivers asymmetry vanishes, while at larger $x$ its qualitative dependence on $x$, $K_T$ follows the usual trends met in available models and parameterizations. Given the present-day knowledge of the considered phenomenological interactions, it is not possible to establish whether the related Sivers-like asymmetry is a leading twist one., 11 printed pages, 6 figures

In order to illustrate the capabilities of COMPASS using a hadronic beam, I review some of the azimuthal asymmetries in hadronic collisions, that allow for the extraction of transversity, Sivers and Boer-Mulders functions, necessary to explore the partonic spin structure of the nucleon. I also report on some Monte Carlo simulations of such asymmetries for the production of Drell-Yan lepton pairs from the collision of high-energy pions on a transversely polarized proton target., Comment: talk delivered to the "International Workshop on Structure and Spectroscopy", Freiburg, March 19-21, 2007; 18 pages, RevTeX4 style, 8 figures with 10 .eps files

We have performed numerical simulations of the single-polarized e+ e- --> \vec p anti p process in kinematic conditions under discussion for a possible upgrade of the existing DAFNE facility. By fitting the cross section and spin asymmetry angular distributions with typical Born expressions, we can study the conditions for extracting information on moduli and phases of the proton electromagnetic form factors in the timelike region, which are poorly known and whose preliminary data show puzzling features. We have explored also non-Born contributions by introducing a further component in the angular fit, which is related to two-photon exchange diagrams. Using a dipole parametrization, we show that these corrections can be identified if larger than 5% of the Born contribution; we also explore the conditions for extracting information on the phase and, consequently, on the relative weight between their real and imaginary parts, which are presently unknown., 17 pages, 6 figures, version to appear in Phys. Rev. D

We present Monte Carlo simulations of both the Sivers and the Boer-Mulders effects in the polarized Drell-Yan $��^\pm p^\uparrow \to ��^+ ��^- X$ process at the center-of-mass energy $\sqrt{s} \sim 14$ GeV reachable at COMPASS with pion beams of energy 100 GeV. For the Sivers effect, we adopt two different parametrizations for the Sivers function to explore the statistical accuracy required to extract unambiguous information on this parton density. In particular, we verify the possibility of checking its predicted sign change between Semi-Inclusive Deep-Inelastic Scattering (SIDIS) and Drell-Yan processes, a crucial test of nonperturbative QCD. For the Boer-Mulders effect, because of the lack of parametrizations we can make only guesses. The goal is to explore the possibility of extracting information on the transversity distribution, the missing piece necessary to complete the knowledge of the nucleon spin structure at leading twist, and the Boer-Mulders function, which is related to the long-standing problem of the violation of the Lam-Tung sum rule in the unpolarized Drell-Yan cross section., RevTeX, 13 pages, 7 figures included in .eps format

Recently, a reconsideration of Drell-Yan cross sections at moderate energies and masses has suggested the possibility of relevant enhancements of the cross sections in some kinematical regions. If confirmed, these predictions could largely affect the planning of Drell-Yan experiments aimed at transverse spin measurements after 2010. More in general, the problem is present of a precision measurement of the $��$ dependence of Drell-Yan cross sections. Here we discuss the feasibility of such a measurement within short time at the COMPASS apparatus, and its relevance for the PANDA experiment., 4 pages, 4 figures, in print on Physical Review D

We present Monte Carlo simulations of the Sivers effect in the polarized Drell-Yan $pp^\uparrow \to ��^+ ��^- X$ process at the center-of-mass energy $\sqrt{s}=200$ GeV reachable at the Relativistic Heavy-Ion Collider (RHIC) of BNL. We use two different parametrizations for the Sivers function, one deduced from the analysis of Semi-Inclusive Deep-Inelastic Scattering (SIDIS) data at much lower energies, and another one constrained by the RHIC data for the $pp^\uparrow \to ��X$ process at the same energy. For a given luminosity of $10^{32}$ cm$^{-2}$ sec$^{-1}$, we explore the necessary conditions to reach a statistical accuracy that allows to extract unambiguous information on the structure of the Sivers function. In particular, we consider the feasibility of the test on its predicted universality property of changing sign when switching from SIDIS to Drell-Yan processes., 17 pages in RevTeX; 7 figures in eps format; improved text, added reference

We present a systematic study of the final-state interaction (FSI) effects in $D(e,e'p)$ scattering in the CEBAF energy range with particular emphasis on the phenomenon of the angular anisotropy of the missing momentum distribution. We find that FSI effects dominate at missing momentum $p_m \gsim 1.5 $fm$^{-1}$. FSI effects in the excitation of the $S$-wave state are much stronger than in the excitation of the $D$-wave., Comment: LATEX, 11 pages, 5 figures available from the authors on request, KFA-IKP(TH)-1994-34