Single spin asymmetry in πp\pi p Drell-Yan process

We study the single spin asymmetries for the $\pi p^\uparrow\rightarrow\mu^+\mu^-X$ process. We consider the asymmetries contributed by the coupling of the Boer-Mulders function with the transversity distribution and the pretzelosity distribution, characterized by the $\sin(\phi+\phi_S)$ and $\sin(3\phi-\phi_S)$ azimuthal angular dependence, respectively. We estimate the magnitude of these asymmetries at COMPASS by using proper weighting functions. We find that the $\sin(\phi+\phi_S)$ asymmetry is of the size of a few percent and can be measured through the experiment. The $\sin(3\phi-\phi_S)$ asymmetry is smaller than the $\sin(\phi+\phi_S)$ asymmetry. After a cut on $q_T$, we succeed in enhancing the asymmetry.Comment: 11 pages, 2 figures, final version to appear in PL

Azimuthal asymmetry in unpolarized πN\pi N Drell-Yan process

Taking into account the effect of final state interaction, we calculate the non-zero (na\"{i}ve) $T$-odd transverse momentum dependent distribution h_1^{\perp}(x,\kp^2) of the pion in a quark-spectator-antiquark model with effective pion-quark-antiquark coupling as a dipole form factor. Using the model result we estimate the $\cos 2\phi$ asymmetries in the unpolarized $\pi^- N$ Drell-Yan process which can be expressed as $h_1^{\perp}\times\bar{h}_1^{\perp}$. We find that the resulting h_{1\pi}^\p(x,\kp^2) has the advantage to reproduce the asymmetry that agrees with the experimental data measured by NA10 Collaboration. We estimate the $\cos2\phi$ asymmetries averaged over the kinematics of NA10 experiments for 140, 194 and 286 GeV $\pi^-$ beam and compare them with relevant experimental data.Comment: 11 pages, 4 figures, to appear in PL

Flavor separation of the Boer-Mulders function from unpolarized π−p\pi^- p and π−D\pi^- D Drell-Yan processes

We show that measuring the $\cos 2\phi$ angular dependence in unpolarized Drell-Yan processes with $\pi^-$ beams colliding on proton and deuteron targets can determine the ratio of the Boer-Mulders functions for $d$ and $u$ quarks inside the proton $h_1^{\perp,d}/h_1^{\perp,u}$, which is still lack of theoretical constraint. The comparison of the $\cos 2 \phi$ asymmetries measured in unpolarized $\pi^- p$ and $\pi^- D$ Drell-Yan processes, which are accessible at CERN by the COMPASS collaboration, can help to discriminate whether $h_1^\perp$ effects or QCD vacuum effects are preferred by data.Comment: 10 pages, 2 figures, published in Physics Letters

Lorentz invariance relations between parton distributions and the Wandzura-Wilczek approximation

The violation of the so-called Lorentz invariance relations between parton distribution functions is considered in a model independent way. It is shown that these relations are not violated in a generalized Wandzura-Wilczek approximation, indicating that numerically their violation may be small.Comment: 13 pages, added references, minor changes, to appear in Phys. Lett.

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 $pp$ and $pd$ 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 $\sqrt{s}=115$ GeV. We calculate and estimate the $\cos2\phi$ azimuthal asymmetries of unpolarized $pp$ and $pd$ dilepton production processes in the Drell--Yan continuum region and at the $Z$-pole. We also calculate the $\sin(2\phi-\phi_S)$, $\sin(2\phi+\phi_S)$ and $\sin2\phi$ azimuthal asymmetries of $pp$ and $pd$ dilepton production processes with the target proton and deuteron longitudinally or transversally polarized in the Drell--Yan continuum region and around $Z$ 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 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

Azimuthal and Single Spin Asymmetries in Hard Scattering Processes

In this article we review the present understanding of azimuthal and single spin asymmetries for inclusive and semi-inclusive particle production in unpolarized and polarized hadronic collisions at high energy and moderately large transverse momentum. After summarizing the experimental information available, we discuss and compare the main theoretical approaches formulated in the framework of perturbative QCD. We then present in some detail a generalization of the parton model with inclusion of spin and intrinsic transverse momentum effects. In this context, we extensively discuss the phenomenology of azimuthal and single spin asymmetries for several processes in different kinematical configurations. A comparison with the predictions of other approaches, when available, is also given. We finally emphasize some relevant open points and challenges for future theoretical and experimental investigation.Comment: 70 pages, 34 ps figures. Invited review paper to be published in Progress in Particle and Nuclear Physic

Measurement of the Atmospheric Muon Spectrum from 20 to 3000 GeV

The absolute muon flux between 20 GeV and 3000 GeV is measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0 degree to 58 degree. Due to the large exposure of about 150 m2 sr d, and the excellent momentum resolution of the L3 muon chambers, a precision of 2.3 % at 150 GeV in the vertical direction is achieved. The ratio of positive to negative muons is studied between 20 GeV and 500 GeV, and the average vertical muon charge ratio is found to be 1.285 +- 0.003 (stat.) +- 0.019 (syst.).Comment: Total 32 pages, 9Figure

The cos 2 phi asymmetry of Drell-Yan and J/psi production in unpolarized ppbar scattering

We investigate the cos 2 phi azimuthal asymmetry in Drell--Yan and J/psi production from unpolarized ppbar scattering at GSI-HESR energies. The contribution to this asymmetry arising from the leading-twist Boer-Mulders function h_1^perp(x, k_T^2), which describes a correlation between the transverse momentum and the transverse spin of quarks in an unpolarized hadron, is explicitly evaluated, and predictions for the GSI-HESR kinematic regime are presented. We show that the cos 2 phi asymmetry is quite sizable both on the J/psi peak and in the Drell-Yan continuum region. Therefore these processes may offer an experimentally viable access to the Boer-Mulders function in the early unpolarized stage of GSI experiments.Comment: 5 pages, 3 figures, to be published in Eur. Phys.

Search for Charged Higgs Bosons in e+e- Collisions at \sqrt{s} = 189 GeV

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.4 pb^-1. Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed events are consistent with the expectations from Standard Model background processes. A lower limit of 65.5 GeV on the charged Higgs mass is derived at 95 % confidence level, independent of the decay branching ratio Br(H^{+/-} -> tau nu)