Conveners
TMDs: Parallel I
- Andreas Metz (Temple University, Philadelphia)
TMDs: Parallel II
- Yoshitaka Hatta (University of Tsukuba)
TMDs: Parallel III
- Marco Contalbrigo (INFN - National Institute for Nuclear Physics)
TMDs: Parallel IV
- Akio Ogawa (BNL)
TMDs: Parallel V
- Jen-Chieh Peng (University of Illinois at Urbana-Champaign)
TMDs: Parallel VI
- Franco Bradamante (Universita e INFN, Trieste (IT))
TMDs: Parallel VII
- Marco Radici
TMDs: Parallel VIII
- Gunar Schnell
Description
3D structure of the nucleon: TMDs
The Transverse Momentum Dependent Partonic Distributions (TMD-PDFs) and Fragmentation Functions (TMD-FFs) should reveal new properties of the 3-dimensional structure of nucleons and of the quark hadronization process. Many experimental data are now available, much progress has been made in their phenomenological interpretation, future facilities and experiments are being planned. A short...
In this talk I will present an overview of recent developements on gluon transverse momentum dependent (TMD) parton distributions. Such non-perturbative objects might be feasible in high-energy proton collisions at the LHC, but also at a future Electron-Ion Collider (EIC). Most interestingly, due to the gluon’s transverse momentum the gluon can have a linear polarization which is encoded in a...
The COMPASS experiment (SPS, CERN) covers a broad range of physics aspects in the field of hadron structure and spectroscopy. Particular focus is given to the exploration of the transverse spin structure of the nucleon via the study of spin (in)dependent azimuthal asymmetries measured in semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan
(DY). Within QCD parton model approach,...
Studies of the Transverse Momentum Dependent parton distributions (TMDs) of the nucleon in the valence quark region have emerged as one of the flagship physics programs of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. The TMDs of the nucleon describe the spin-dependent, three-dimensional distributions of its constituent partons in momentum space. The simplest and...
I examine some of the complications involved when combining (matching) TMD factorization with collinear factorization to allow accurate predictions over the whole range of measured transverse momentum in a process like Drell-Yan. Then I propose some improved methods for combining the two types of factorization. (This talk is based on work reported in arXiv:1605.00671.)
Precision measurements on the transverse momentum dependent hadron multiplicities in semi-inclusive deep inelastic scattering is, with unpolarised azimuthal asymmetries, crucial in the determination of the quark intrinsic transverse momentum and in TMD evolution studies. COMPASS has measured differential multiplicities of hadrons using a deuteron target in a four-dimensional space. This data...
We discuss a new hard pole contribution to the transverse- momentum weighted single-transverse spin asymmetry in semi inclusive deep inelastic scattering. We perform a complete next-to-leading order calculation of the Ph⊥-weighted cross section and show that the new hard pole contribution is required in order to obtain the complete evolution equation for the Qiu-Sterman function.
We present a point-by-point determination of the Sivers parton distribution function. The extraction is similar to the one already performed for the transversity distribution, namely it is based on the simultaneous use of proton and deuteron semi-inclusive deeply inelastic scattering data. Since the Sivers asymmetries involve the ordinary unpolarized fragmentation functions, SIDIS data are...
In the context of the nucleon spin structure the Sivers effect, which describes the correlation between the nucleon spin and the orbital motion of partons, may give information on the gluon orbital angular momentum, one of the missing elements in th nucleon spin sum rule. The gluon Sivers function can be accessed via the photon-gluon fusion process. To enhance the fraction of photon-gluon...
In recent years, measuring azimuthal asymmetries in semi -inclusive deep-inelastic scattering (SIDIS) off polarized targets emerged as a powerful tool to investigate the nucleon spin structure, one of the main objectives of the COMPASS physics program. The two-stage COMPASS spectrometer at the CERN SPS is characterized by a large acceptance and a broad kinematic coverage. It makes use of a...
The transversity distribution was recently extracted from deep inelastic scattering processes producing hadron pairs in the final state because it is involved, together with a specific chiral-odd di-hadron fragmentation function, in the elementary mechanism that generates a transverse-spin asymmetry in the azimuthal distribution of the detected hadron pairs. The same elementary mechanism was...
Over the last decade, theoretical and experimental engagement of the oft challenging phenomena of nucleon transverse-spin has unlocked tantalizing opportunities for new insight into nucleon structure and more expansive formulations of QCD, e.g. with higher dimensions in momentum space. The RHIC experiments continue this exploration through an array of measurements from high-energy...
Two-particle angular correlations have long been used as an observable for measuring the initial-state partonic transverse momentum kT . Sensitivity to this small transverse momentum scale allows nonperturbative transverse momentum dependent (TMD) effects to be probed in high pT dihadron and direct photon-hadron correlations. The observable pout, the out-of plane transverse momentum component...
The transversity distribution is a fundamental component of the spin structure of the nucleon, and is only loosely constrained by existing semi-inclusive deep inelastic scattering data. The di hadron interference fragmentation function (IFF), which describes the fragmentation of transversely polarized quarks, is expected to give rise to spin-dependent di-hadron correlations in p↑+p collisions....
A Monte-Carlo code of jet generation by a transversely polarized quark is proposed. It is based on the recursive splitting of a string, like in the symmetric Lund fragmentation model, together with the 3P0 model of quark-antiquark pair creation. The code involves a complex mass parameter, in addition to the usual Lund parameters. The Collins effect is obtained and the related asymmetries,...
We investigated the cross section and the associated spin asymmetries for vector boson (W^\pm/Z_0/γ*) production in polarized proton-proton collisions at tree level within the TMD factorization formalism. Besides the well-known Sivers function f_1T, the single transverse asymmetry could also probe the transversal helicity distribution g_1T via the parity-violating nature of W/Z_0 production....
Measurements of single single spin asymmetries (AN ) in spin-polarized proton-proton collisions are a relatively straightforward experimental measurement that offers insight into the structure of the proton. However, AN integrates over both initial and final state effects, making the interpretation of a single measurement in terms of the underlying physical processes difficult. The RHIC...
In 2015 the first collisions between polarized protons and nuclei occurred at the Brookhaven Relativistic Heavy Ion Collider (RHIC). This talk will present preliminary measurements of the forward transverse single spin asymmetries AN in p+p and p+A collisions with CM energy of √sNN = 200 GeV. Photons from π0 decays were measured with the STAR FMS electromagnetic calorimeter that had been...
The first high energy polarized proton-nuclei collisions at RHIC in 2015 give us opportunities to study unexplored reaction mechanisms of hadron production in the forward region. In PHENIX, single transverse spin asymmetries (AN s) of forward (6.8 < η < 8.8) neutron production in √sNN = 200 GeV p+Al, and p+Au collisions are measured, and an unexpected strong A dependence in AN is found. The...
Historically, large transverse single spin asymmetries (SSA) have been measured in protonproton collisions which are nearly independent of the collision energy. At RHIC, both PHENIX and STAR experiments measured SSA’s in neutral pion and η meson production from p + p collisions, in central and forward pseudo rapidity regions (η). The central η measurements were found to be consistent with zero...
In two π + W induced Drell-Yan experiments at CERN and Fermilab, angular distributions of the resultant dimuons showed a violation of the Lam-Tung relation, a perturbative QCD, “Callan-Gross-like” relationship between the polar and azimuthal angles made by the initial hadronic plane and final state dimuon plane in the Collins-Soper frame. At these energies, the violation manifests itself as a...
Pion-Induced reactions offer an unique opportunity to test the Quantum ChromoDynamics improved quark-parton model using angular distributions of unpolarised Drell-Yan process. Early experiments clearly showed a strong violation of the Lam-Tung relation from their angular distributions. This violation may indicate that the QCD mechanism needs to go beyond collinear by including the intrinsic...
Transverse single spin asymmetries (SSAs) quantify the asymmetry of particle production relative to the transverse spin axis of a polarized hadron. SSAs have come to be recognized as a means of accessing QCD dynamics, both within initial-state hadrons and in the process of hadronization from partons. At √s = 200 GeV, heavy flavor single-spin asymmetries in proton proton collisions provide...
It has been recently pointed out that gluons can be linearly polarized even inside an unpolarized hadron provided that gluons should have non-zero transverse momentum with respect to the parent hadron. The effect of linearly polarized gluons on transverse momentum (PT ) and rapidity (y) distributions of J/ψ and Υ production is studied within the framework of transverse momentum dependent (TMD)...
We investigate the spin structure of gluon transverse momentum dependent (TMD) correlators defined as Fourier transforms of matrix elements of nonlocal operator combinations. At the operator level these correlators include gauge links that bridge the nonlocality. In contrast to the collinear PDFs, the gauge links are no longer unique for TMD PDFs (TMDs). The single Wilson loop operator is...
We study the contribution of the twist-3 fragmentation function to the production of transversely polarized hyperons in unpolarized proton-proton collisions in the framework of the collinear factorization. Taking into account the constraint relations among twist-3 fragmentation functions which follow from the QCD equation-of-motion and the Lorentz invariance property of the correlation...
Spontaneous hyperon polarization has been a long standing issue for about 40 years. The so called polarizing Fragmentation Function(FF), D⊥ 1T(z, p2⊥), describes the production of a transversely polarized hadron from an unpolarized quark, where z denotes the fractional energy of the hadron and p⊥ the transverse momentum with respect to the fragmenting quark. The polarizing FF can be determined...
The transverse spin transfer to Λ hyperon can provide insights into the polarized fragmentation function and the transversity distribution which play important roles in understanding the spin structure of the nucleon. In 1997, significant spin transfer along the normal direction of the Λ production plane was observed at large xF by Fermilab E704 Collaboration. In this contribution we report an...
Semi-inclusive vector and pseudoscalar meson production in e
+e− annihilation at high energies is an ideal place to study three dimensional fragmentation functions, especially for the tensor polarization dependent part. We present the complete general kinematic analysis of this process and show that the cross section should be expressed by 81 independent structure functions, and give the...
Fragmentation functions describe the transition from asymptotically free, high energetic partons into final state hadrons. Since fragmentation functions are non-perturbative objects, they need to be measured experimentally. In particular electron-positron annihilation provides very clean input into fragmentation functions as no hadrons are involved in the initial state. The Belle experiment...
Inclusive hadron production cross sections and angular distributions in e+e− collisions shed light on fundamental questions of hadronization and fragmentation processes. We present measurements of the Collins azimuthal asymmetries in inclusive production of hadron pairs, in the e+e− → h1h2X annihilation process, where the hadrons h1,2 (either kaons or pions) are produced in opposite...
We present a framework to study the quark Orbital Angular Momentum OAM component of the proton spin, including the spin orbit interaction term. As shown recently in [1], quark OAM can be described in terms of either a Generalized Transverse Momentum Distribution (GTMD), or a twist three GPD, the two distributions being connected through a Lorentz Invariance Relation. A similar relation exists...
