Polarized Hadron Collisions Research Articles

How well do we know the gluon polarization in the proton?

We perform the first simultaneous global QCD analysis of spin-averaged and spin-dependent parton distribution functions (PDFs), including single jet production data from unpolarized and polarized hadron collisions. We critically assess the impact of SU(3) flavor symmetry and PDF positivity assumptions on the quark and gluon helicity PDFs, and find strong bias from these, particularly on the gluon polarization. The simultaneous analysis allows for the first time extraction of individual helicity-aligned and antialigned PDFs with a consistent treatment of uncertainties.

Investigating the Transverse Momentum Dependent Gluon Sivers Function in Quarkonium Production at pp Colliders

In this contribution, we will present a short overview of the transverse momentum dependent (TMD) approach as a tool for studying the 3-dimensional structure of hadrons in high-energy (un)polarized hadron collisions. We will then summarize the present status of a running research programme that aims at constraining the poorly known transverse momentum dependent gluon Sivers function, through the study of single spin asymmetries in quarkonium (mainly $J/\psi$), pion, and $D$-meson production in polarized proton-proton collisions at RHIC. Finally, we will shortly discuss perspectives for this field of research, emphasizing in particular its role in the physics programme of LHC in the fixed-target setup and NICA.

Transverse single spin asymmetry in hadronicηc,bproduction

We study the transverse single spin asymmetry in $\eta_{c,b}$ production in polarized hadron collisions, employing the collinear twist-3 approach in combination with the color singlet model. Our main focus lies on the contribution from the twist-3 Efremov-Teryaev-Qiu-Sterman function. By extrapolating the derived spin dependent cross section to the small transverse momentum region, consistency between the collinear twist-3 approach and the transverse momentum dependent factorization approach is confirmed. As a byproduct of this work, we identify a term contributing to the scale evolution of tri-gluon correlations in the flavor-singlet case which was previously missed.

Slepton production in polarized hadron collisions

We calculate cross sections and asymmetries for slepton pair production through neutral and charged electroweak currents in polarized hadron collisions for general slepton masses and including mixing of the left- and right-handed interaction eigenstates relevant for third generation sleptons. Our analytical results confirm and extend a previous calculation. Numerically, we show that measurements of the longitudinal single-spin asymmetry at the existing polarized pp collider RHIC and at possible polarization upgrades of the Tevatron or the LHC would allow for a determination of the tau slepton mixing angle and/or the associated supersymmetry breaking parameters Λ for gauge mediation and A0 for minimal supergravity. Furthermore, the Standard Model background from tau pair production can be clearly distinguished due to the opposite sign of the associated asymmetry.

Parity violation in bottom quark pair production at polarized hadron colliders

Parity violation induced by the chromo-anapole form factor of the bottom quark, generated from weak corrections, is studied in polarized hadron collisions. The forward-backward asymmetry in the bottom quark pair production at polarized pp and p p colliders is evaluated in the Standard Model and in a two Higgs doublet model to examine the effects of parity violation. In the models studied, promising results are found for polarized p p colliders.

Direct photon production in polarized hadron collisions at collider and fixed target energies

Recently determined next-to-leading order sets of polarized parton distributions are used to study large-${p}_{T} p\ensuremath{\rightarrow}p\ensuremath{\rightarrow}\ensuremath{\rightarrow}\ensuremath{\gamma}+X$ at $\sqrt{s}=38$, 100, and 500 GeV. Certain conversion terms, necessary to use the above sets, are determined. It is concluded that, to distinguish between the above sets, planned experiments at BNL RHIC should be successful, in particular, at a c.m. photon pseudorapidity $\ensuremath{\simeq}1$, and that a proposed HERA-$N\ensuremath{\rightarrow}$ fixed target experiment should have a rather large accuracy at relatively large ${x}_{T} {(=2p}_{T}/\sqrt{s})$.

QCD selection rules in polarized hadron collisions

Plans are underway to measure spin asymmetries at large momentum transfer in hadron hadron collisions at RHIC and elsewhere. Proposals have focused on measuring quark transversity and quark and gluon helicity distributions in the nucleon. These experiments will also provide a strong and simple test of perturbative QCD, namely that A TT/ A LL ⪡ 1 in pp → 2 jets + X and several related processes, whereas A TT/ A LL ∼ 1 in Drell-Yan production of muon pairs. The prediction tests the helicity, twist and chirality selection rules of perturbative QCD that form the foundation for the analysis of spin dependent hard processes. We estimate the ratio A TT/ A LL numerically for polarized protons at RHIC.

Unpolarized and polarized structure functions and spin tests at supercollider energies.

We present a simple analytic parametrization for quark and gluon distributions inside a polarized or unpolarized proton. It is valid for small enough x and for very large ${Q}^{2}$, the kinematic domain relevant for supercollider energies. We calculate some helicity hadron asymmetries in polarized-hadron collisions in the multi-TeV energy range and we discuss further possibilities of significant spin effects.