Single spin asymmetries in the Drell-Yan process

We discuss single transverse spin asymmetries in the Drell-Yan process originating from so-called gluonic poles in twist-three hadronic matrix elements, as first considered by Qiu and Sterman. Even though time-reversal invariance is not broken, the effects of such poles cannot be distinguished from those of time-reversal odd distribution functions. We show the connection between gluonic poles and large distance gluon fields, in particular we focus on boundary conditions. We identify the possible single spin asymmetries in the Drell-Yan process.Comment: 10 pages, Latex, 4 Postscript figure, uses epsfig.sty. Invited talk presented at the workshop 'Deep inelastic scattering off polarized targets: theory meets experiment', DESY-Zeuthen, September 1-5, 199

Spectral analysis of gluonic pole matrix elements for fragmentation

The non-vanishing of gluonic pole matrix elements can explain the appearance of single spin asymmetries in high-energy scattering processes. We use a spectator framework approach to investigate the spectral properties of quark-quark-gluon correlators and use this to study gluonic pole matrix elements. Such matrix elements appear in principle both for distribution functions such as the Sivers function and fragmentation functions such as the Collins function. We find that for a large class of spectator models, the contribution of the gluonic pole matrix element in fragmentation functions vanishes. This outcome is important in the study of universality for fragmentation functions and confirms findings using a different approach.Comment: 9 pages, 4 figures, added reference

A model independent analysis of gluonic pole matrix elements and universality of TMD fragmentation functions

Gluonic pole matrix elements explain the appearance of single spin asymmetries (SSA) in high-energy scattering processes. They involve a combination of operators which are odd under time reversal (T-odd). Such matrix elements appear in principle both for parton distribution functions and parton fragmentation functions. We show that for parton fragmentation functions these gluonic pole matrix elements vanish as a consequence of the analytic structure of scattering amplitudes in Quantum Chromodynamics. This result is important in the study of the universality of transverse momentum dependent (TMD) fragmentation functions.Comment: 5 pages, 5 figures, version to appear in Phys. Rev.

Single transverse-spin asymmetry for DD-meson production in semi-inclusive deep inelastic scattering

We study the single-transverse spin asymmetry for open charm production in the semi-inclusive lepton-hadron deep inelastic scattering. We calculate the asymmetry in terms of the QCD collinear factorization approach for $D$ mesons at high enough $P_{h\perp}$, and find that the asymmetry is proportional to the twist-three tri-gluon correlation function in the proton. With a simple model for the tri-gluon correlation function, we estimate the asymmetry for both COMPASS and eRHIC kinematics, and discuss the possibilities of extracting the tri-gluon correlation function in these experiments.Comment: 13 pages, 7 figure

Beam Single-Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering

We calculate, in a model, the beam spin asymmetry in semi-inclusive jet production in deep inelastic scattering. This twist-3, $T$-odd observable is non-zero due to final state strong interactions. With reasonable choices for the parameters, one finds an asymmetry of several percent, about the size seen experimentally. We present the result both as an explicit asymmetry calculation and as a model calculation of the new transverse-momentum dependent distribution function $g^\perp$.Comment: 10 pages, 6 figures; minor changes made in the discussion; version accepted for publicatio

Quark-gluon correlation functions relevant to single transverse spin asymmetries

We investigate the relative size of various twist-3 quark-gluon correlation functions relevant to single transverse spin asymmetries (SSAs) in a quark-diquark model of the nucleon. We calculate the quark-gluon correlation function $T_{q,F}(x, x)$ that is responsible for the gluonic pole contribution to the SSAs, as well as $T_{q,F}(0, x)$ and $T_{\Delta{q}, F}(0, x)$ responsible for the fermionic pole contributions. We find in both cases of a scalar diquark and an axial-vector diquark that at the first nontrivial order only the \tq(x, x) is finite while all other quark-gluon correlation functions vanish. Using the same model, we evaluate quark Sivers function and discuss its relation to the \tq(x, x). We also discuss the implication of our finding to the phenomenological studies of the SSAs.Comment: 12 pages, 5 figure

Single-Transverse Spin Asymmetry in Dijet Correlations at Hadron Colliders

We present a phenomenological study of the single-transverse spin asymmetry in azimuthal correlations of two jets produced nearly "back-to-back" in pp collisions at RHIC. We properly take into account the initial- and final-state interactions of partons that can generate this asymmetry in QCD hard-scattering. Using distribution functions fitted to the existing single-spin data, we make predictions for various weighted single-spin asymmetries in dijet correlations that are now readily testable at RHIC.Comment: 14 pages, 2 figure

Accessing tri-gluon correlations in the nucleon via the single spin asymmetry in open charm production

We calculate the single transverse-spin asymmetry for open charm production in $pp$ collisions within the QCD collinear factorization approach. We include contributions from both twist-three quark-gluon and tri-gluon correlation functions. We find that the quark-gluon correlation functions alone generate only a very small asymmetry for open charm production in the kinematic region of current interest at RHIC, so that the observation of any significant single-spin asymmetry would be a clear indication of the presence of tri-gluon correlations inside a polarized proton. We furthermore demonstrate that the tri-gluon contribution could be very different for the production of $D$ and $\bar{D}$ mesons. These features make the single spin asymmetry in open charm production in polarized $pp$ collisions at RHIC an excellent probe of tri-gluon correlation functions.Comment: 10 pages, 7 figure

First measurement of the cross section for top-quark pair production in proton–proton collisions at √s = 7 TeV

20 páginas, 3 figuras, 1 tabla.-- This article is published Open Access at sciencedirect.com. It is distributed under the terms of the Creative Commons Attribution License 3.0.-- CMS Collaboration: et al.The first measurement of the cross section for top-quark pair production in pp collisions at the Large Hadron Collider at center-of-mass energy √s = 7 TeV has been performed using a data sample corresponding to an integrated luminosity of 3.1 ± 0.3 pb−1 recorded by the CMS detector. This result utilizes the final state with two isolated, highly energetic charged leptons, large missing transverse energy, and two or more jets. Backgrounds from Drell–Yan and non-W/Z boson production are estimated from data. Eleven events are observed in the data with 2.1 ± 1.0 events expected from background. The measured cross section is 194±72(stat.)±24(syst.)±21(lumi.) pb, consistent with next-to-leading order predictions.Acknowledge support from: FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); Academy of Finland, ME, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLPFAI (Mexico); PAEC (Pakistan); SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA).Peer reviewe

Single Transverse Spin Asymmetries at Parton Level

Two factorization approaches have been proposed for single transverse spin asymmetries. One is the collinear factorization, another is the transverse-momentum-dependent factorization. They have been previously derived in a formal way by using diagram expansion at hadron level. If the two factorizations hold or can be proven, they should also hold when we replace hadrons with parton states. We examine these two factorizations at parton level with massless partons. It is nontrivial to generate these asymmetries at parton level with massless partons because the asymmetries require helicity-flip and nonzero absorptive parts in scattering amplitudes. By constructing suitable parton states with massless partons we derive the two factorizations for the asymmetry in Drell-Yan processes. It is found from our results that the collinear factorization derived at parton level is not the same as that derived at hadron level. Our results with massless partons confirm those derived with single massive parton state in our previous works.Comment: shortened version to match published versio