DIS 2014 - XXII. International Workshop on Deep-Inelastic Scattering and Related Subjects

Session

WG6: Spin Physics

29 Apr 2014, 08:30

Warsaw

Conveners

WG6: Spin Physics

• Ernst Sichtermann (Lawrence Berkeley National Laboratory)
• Yann Bedfer (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))
• Barbara Pasquini (University of Pavia)

WG6: Spin Physics

• Ernst Sichtermann (Lawrence Berkeley National Laboratory)
• Barbara Pasquini (University of Pavia)
• Yann Bedfer (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))

WG6: Spin Physics: WG6: Spin Physics

• Barbara Pasquini (University of Pavia)
• Yann Bedfer (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))
• Ernst Sichtermann (Lawrence Berkeley National Laboratory)

WG6: Spin Physics

• Yann Bedfer (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))
• Ernst Sichtermann (Lawrence Berkeley National Laboratory)
• Barbara Pasquini (University of Pavia)

270. Measuring the gluon spin contribution to the proton spin in polarized p+p collisions with the PHENIX experiment

Dr Itaru Nakagawa (RIKEN/RBRC)

29/04/2014, 08:30

WG6: Spin Physics

Oral presentation

A primary goal of the RHIC Spin program has been to measure $Deltag$, the gluon spin contribution to the proton spin, through the double helicity asymmetry, $A_{LL}$. The PHENIX detector is designed with very good electromagnetic calorimetery, allowing for a high statistics ${\pi }^0$ $A_{LL}$ measurement. PHENIX results from 2005 and 2006 at $\sqrt{s}=200$ GeV have been used in the DSSV...

224. Probing Sea Quark and Gluon Polarization at STAR

Justin Stevens (Massachusetts Institute of Technology)

29/04/2014, 09:00

WG6: Spin Physics

Oral presentation

One of the primary goals of the spin program at the Relativistic Heavy Ion Collider (RHIC) is to determine the sea quark and gluon polarization distributions of the proton. The polarization of the sea quarks is probed through the production of $W^{-(+)}$ bosons via the annihilation of $\overline{u}+d(\overline{d}+u)$, at leading order. Measurements of the single-spin asymmetry, $A_L$, for $W$ and...

229. Measurements of parity violating spin asymmetries of the W boson, $W^{\pm }\to e^{\pm }$, at mid-rapidity with the PHENIX Detector at RHIC

Mr Ciprian Gal (Stony Brook University)

29/04/2014, 09:30

WG6: Spin Physics

Oral presentation

Precision measurements of polarized parton distributions (PDFs) lie at the heart of unraveling the nucleon spin puzzle. The $u$ and $d$ quark distributions are significantly better constrained than the anti-quark $\bar{u}$ and $\bar{d}$ distributions. A clean way to measure the anti-quark distributions directly, without the dilution of poorly known polarized fragmentation functions,...

165. PHENIX W to mu measurements in polarized proton-proton collisions

Dr Ralf Seidl (RIKEN)

29/04/2014, 09:50

WG6: Spin Physics

Oral presentation

The Parity violation of the weak interaction allows to use real W production in polarized proton-proton collisions as a tool to select both helicity and flavor of the participating quarks and antiquarks. With W+ production one is mostly sensitive to u and dbar quarks while W- production selects d and ubar quarks. The PHENIX experiment at RHIC has been taking data over the past several years...

228. Hermes reevaluation of the Parton Distribution of Strange Quarks in the Nucleon

Francesca Giordano (UIUC)

29/04/2014, 10:10

WG6: Spin Physics

Oral presentation

An earlier extraction from the HERMES experiment of the polarization-averaged parton distri- bution of strange quarks in the nucleon has been reevaluated using final data on the multiplicities of charged kaons in semi-inclusive deep-inelastic scattering obtained with a kinematically more com- prehensive method of correcting for experimental effects. General features of the distribution are...

243. First results on A₁^p and g₁^p at low x and low Q² from COMPASS

Ana Sofia Nunes (LIP Laboratorio de Instrumentacao e Fisica Experimental de Part)

29/04/2014, 11:00

WG6: Spin Physics

Oral presentation

The COMPASS experiment at CERN has collected a large sample of about 700 million events of quasi-real photoproduction in polarised μ⁺-p scattering using a beam momentum of 160 (GeV/c)² in 2007 and 200 (GeV/c)² in 2011. The events have a Bjorken scaling variable in the range 0.00004<x<0.04 and a four-momentum transfer squared in the...

198. A new LO extraction of gluon polarisation from COMPASS DIS data

Marcin Stolarski (LIP)

29/04/2014, 11:30

WG6: Spin Physics

Oral presentation

A new COMPASS LO evaluation of the gluon polarization in the nucleon is presented. The events in DIS region were re-analyzed and gluon polarization was extracted using the so called all-pT method. In this new method gluon polarization and leading process asymmetry are extracted simultaneously from the same data set using Neural Network approach. The gluon polarization was extracted in...

245. Single hadron double longitudinal spin asymmetries at $p_T<1$ GeV/c measured at COMPASS

Maxime Levillain (CEA/IRFU, Centre d'Etude de Saclay, Gif-sur-Yvette (FR))

29/04/2014, 12:00

WG6: Spin Physics

Oral presentation

In order to understand why quarks only share about a third of the nucleon spin, quite a few recent experiments have focussed on the measurement of the gluon polarization in the nucleon. To access the gluon polarization, reactions where the Photon Gluon Fusion sensibly contributes are necessary. A way to enhance the PGF contribution in lepton-nucleon or nucleon-nucleon scattering is to study...

170. New COMPASS results on the spin structure function $g_1^p$, and QCD fit

Malte Christian Wilfert (Johannes-Gutenberg-Universitaet Mainz (DE))

29/04/2014, 14:00

WG6: Spin Physics

Oral presentation

The COMPASS experiment at CERN SPS has taken data with a polarised muon beam scattering off a polarised NH${}_3$ target in 2011. The beam energy has been increased to 200 GeV compared to 160 GeV in 2007 and thus, higher values of $Q^2$ and lower values of $x$ are reached. We will present our results on the longitudinal double spin asymmetry $A_1^p$ and the spin-dependent structure function...

209. The JAM fit of spin-dependent PDFs

Alberto Accardi (Hampton U. and Jefferson Lab)

29/04/2014, 14:30

WG6: Spin Physics

Oral presentation

We present results of a new next-to-leading order fit of spin-dependent parton distribution functions from the most recent world data on inclusive polarized deep-inelastic scattering, focusing in particular on the large-x and low-Q² regions. By directly fitting polarization asymmetries we eliminate biases introduced by using polarized structure function data extracted...

161. Unbiased helicity-dependent parton distributions with polarized collider data

Emanuele Roberto Nocera (Università degli Studi di Milano & INFN Milano,Italy)

29/04/2014, 15:00

WG6: Spin Physics

Oral presentation

We present an unbiased global determination of spin-dependent parton distribution functions and their uncertainties using the NNPDF methodology: NNPDFpol1.1. As compared to our previous determination, NNPDFpol1.0, longitudinally polarized deep-inelastic scattering data are now supplemented with the most recent polarized hadron collider data for inclusive jet and W boson production from STAR...

250. Phenomenological aspects of evolution in transverse momentum dependent PDF's and fragmentation

Prof. Ignazio Scimemi (Departamento de Fısica Teorica II, Universidad Complute nse de Madrid)

29/04/2014, 15:30

WG6: Spin Physics

Oral presentation

In this talk I will review and update several characteristic of TMD evolution for PDF's and extend the formalism to include fragmentation. I will present also a phenomenological data analisis for unpolarized TMDPDF using evolution at NNLL.

147. COMPASS results on the transverse spin asymmetry in identified dihadron production in SIDIS

Christopher Braun (Friedrich-Alexander-Univ. Erlangen (DE))

29/04/2014, 16:00

WG6: Spin Physics

Oral presentation

The parton distribution function $h_1^q(x)$ of a transversely polarized quark $q$ inside a transversely polarized nucleon, is chiral-odd and therefore not accessible in inclusive deep-inelastic scattering. It can however be observed in semi-inclusive deep-inelastic scattering (SIDIS) in combination with another chiral-odd function, for instance the dihadron interference...

186. HERMES results on transverse target single-spin asymmetries in inclusive electroproduction of charged pions and kaons

Klaus Rith (University of Eralngen-Nürnberg)

29/04/2014, 17:00

WG6: Spin Physics

Oral presentation

Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the HERMES experiment. The asymmetries were studied as a function of the azimuthal angle $\psi$ about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum $p_T$ relative to the direction...

265. Transverse-spin gluon distribution function

Kazuhiro Tanaka

29/04/2014, 17:25

WG6: Spin Physics

Oral presentation

We define the novel polarized PDF, the transverse-spin gluon distribution function $G_T(x)$, as the nucleon matrix element of the gauge-invariant bilocal light-cone operator in QCD, and discuss their properties. $G_T(x)$ is the gluonic analogue of the transverse-spin quark distribution function $g_T(x)$ that contributes to the transverse-spin structure function $g_2(x,Q^2)$ in the DIS of a...

14. Orbital angular momentum in the nucleon

Dr Cédric Lorcé (IPN Orsay and IFPA Liège)

29/04/2014, 17:50

WG6: Spin Physics

Oral presentation

In the last decade, it has been realized that the orbital angular momentum of partons inside the nucleon plays a major role. It contributes significantly to nucleon properties and is at the origin of many asymmetries observed in spin physics. It is therefore of paramount importance to determine this quantity if we want to understand the nucleon internal structure and experimental observables....

263. A_N in inclusive lepton-proton collisions

Dr Umberto D'Alesio (University of Cagliari and INFN, Italy)

30/04/2014, 08:30

WG6: Spin Physics

Oral presentation

Some estimates for the transverse Single Spin Asymmetry, $A_N$, in the inclusive processes $\ell p^{\uparrow }\to hX$ are compared with new experimental data. The predictions are based on the Sivers and Collins functions as extracted from SIDIS azimuthal asymmetries, within a transverse momentum dependent factorization approach. The values of $A_N$ thus obtained agree in sign and...

216. Measurement of the Transverse Single-Spin Asymmetries for ${\pi }^0$ and Jet-like Events at Forward Rapidities at STAR in $p+p$ Collisions at $\sqrt{s}$ = 500 GeV

Dr Mriganka Mouli Mondal (Texas A&M University)

30/04/2014, 09:00

WG6: Spin Physics

Oral presentation

Large transverse single-spin asymmetries ($A_N$) have been observed for forward inclusive hadron production in $p+p$ collisions at various experiments. In the collinear perturbative scattering picture, twist-3 multi-parton correlations can give rise to such an asymmetry. A transversely polarized quark can also give rise to a spin-dependent distribution of its hadron fragments via the...

244. Results on Transverse Spin Asymmetries in Polarized Proton - Proton Elastic Scattering at sqrt(s) = 200 GeV

Wlodek Guryn (BNL)

30/04/2014, 09:30

WG6: Spin Physics

Oral presentation

We present a preliminary result on a precision measurement of the transverse double spin asymmetries ANN and ASS in polarized proton-proton elastic scattering at sqrt(s) = 200 GeV in the small four momentum transferred (t) region 0.005 < -t < 0.035 (GeV/c)2, the Coulomb Nuclear Interference (CNI) region, which were obtained with the STAR experiment at RHIC. The result is based on about 20...

256. Gluon TMDs and Higgs boson production

Marc Schlegel (University of Tuebingen)

30/04/2014, 09:50

WG6: Spin Physics

Oral presentation

Recent activities on the determination of Transverse-Momentum Dependent Gluon Distributions (gluon TMDs) are reviewed. Several processes in lepton-proton and proton-proton collisions have been identified which give a clean access to gluon TMDS, in particular the back-to-back production of photon pairs, photon + Heavy Quarkonium pairs, ZZ-pairs, etc. It is also argued that gluon TMDs can be...

277. Di-hadron production at Jefferson Laboratory

Dr Sergio Anefalos Pereira (INFN-Frascati)

30/04/2014, 10:10

WG6: Spin Physics

Oral presentation

Semi-inclusive deep inelastic scattering (SIDIS) has been used extensively in recent years as an important testing ground for QCD. Studies so far have concentrated on better determination of parton distribution functions, distinguishing between the quark and antiquark contributions, and understanding the fragmentation of quarks into hadrons. Pair of hadrons (di-hadron) SIDIS provides...

200. Precise spin-averaged and spin-dependent fragmentation function measurements at Belle

Francesca Giordano (UIUC)

30/04/2014, 11:00

WG6: Spin Physics

Oral presentation

Fragmentation functions (FFs) describe the formation of final state particles from a partonic initial state and are directly related to the intriguing QCD phenomenon of confinement. Precise knowledge of these functions is a key ingredient in accessing quantities such as the nucleon spin structure in semi-inclusive deep inelastic scattering and proton-proton collisions. However,...

184. Hadron multiplicities at COMPASS

Mr Nicolas du Fresne von Hohenesche (Uni Mainz)

30/04/2014, 11:30

WG6: Spin Physics

Oral presentation

Quark fragmentation functions (FF) $D_q^h(z,Q^2)$ describe final-state hadronisation of quarks $q$ into hadrons $h$. The FFs can be extracted from hadron multiplicities produced in semi-inclusive deep inelastic scattering. The COMPASS collaboration has recently measured charged hadron multiplicities for identified pions and kaons using a 160\,GeV/c muon beam impinging on an isoscalar LiD...

135. Phenomenology of unpolarized TMDs from Semi-Inclusive DIS data

Mr Andrea Signori (VU University Amsterdam - Nikhef)

30/04/2014, 11:50

WG6: Spin Physics

Oral presentation

The analysis of experimental data on unpolarized Semi-Inclusive Deep-Inelastic Scattering (SIDIS) allows the extraction of information on the unpolarized transverse-momentum-dependent distribution functions (TMD PDFs) and fragmentation functions (TMD FFs). For the first time we investigate the flavor dependence of the partonic transverse momentum. Assuming Gaussian behavior in the transverse...

74. Unpolarized TMD extraction from HERMES and COMPASS SIDIS data

J. Osvaldo Gonzalez H. (INFN Torino)

30/04/2014, 12:10

WG6: Spin Physics

Oral presentation

We present results from our study of the unpolarized SIDIS cross sections. The analysis is based on the multiplicities of charged particles from HERMES and COMPASS experiments and of their corresponding azimuthal moments .

252. Deeply Virtual Compton Scattering to the twist-four accuracy: Impact of finite-t and target mass corrections

Vladimir Braun (University of Regensburg)

30/04/2014, 14:00

WG6: Spin Physics

Oral presentation

We carry out the first complete calculation of kinematic power corrections $\sim t/Q^2$ and $\sim m^2/Q^2$ to several key observables in Deeply Virtual Compton Scattering. The issue of convention dependence of the leading twist approximation is discussed in detail. In addition we work out representations for the higher twist corrections in terms of double distributions, Mellin-Barnes...

261. Crossed channel analysis of quark and gluon generalized parton distributions with helicity flip

Dr Kirill Semenov-Tian-Shansky (University of Liege)

30/04/2014, 14:25

WG6: Spin Physics

Oral presentation

Quark and gluon helicity flip generalized parton distributions (GPDs) are seen to be a convenient tool to address the transversity quark and gluon structure of the nucleon. In order to construct a theoretically consistent parametrization of these hadronic matrix elements, we work out the set of combinations of those GPDs suitable for the SO(3) partial wave (PW) expansion in the...

278. A classification of chiral-odd pion generalized parton distributions beyond leading twist

Samuel Wallon

30/04/2014, 14:50

WG6: Spin Physics

Oral presentation

We define in a systematic way, based on the light-cone collinear factorization method, the chiral-odd generalized parton distributions (GPDs) of a pseudoscalar hadron (such as the ${\pi }^0$) up to twist 6. For that, we introduce the relevant matrix elements for 2-parton non-local operators, as well as matrix elements for 3-parton non-local correlators. Their detailed parametrization is fixed...

174. Transverse densities in the nucleon's chiral periphery

Carlos Granados (Uppsala University)

30/04/2014, 15:15

WG6: Spin Physics

Oral presentation

Transverse densities describe the nucleon's spatial structure in the parton picture and correspond to a projection of the GPDs in the impact parameter representation. We use chiral effective field theory to calculate the transverse charge and current densities in the nucleon's chiral periphery (transverse distances b ~ 1/m_pi) and study their properties [1]. The peripheral densities...

288. DVCS measurements at HERMES

Klaus Rith (University of Eralngen-Nürnberg)

30/04/2014, 15:40

WG6: Spin Physics

Oral presentation

Deeply Virtual Compton Scattering is currently one of the most promising processes that provides information about the structure of the nucleon in the framework of Generalized Parton Distributions. During its last years the Deeply Virtual Compton Scattering process was extensively studied at HERMES experiment through measurement of cross section asymmetries. To the virtue of unique...

212. The $g_2$ Spin Structure Function

Ms Melissa Cummings (College of William and Mary)

30/04/2014, 16:30

WG6: Spin Physics

Oral presentation

Jefferson Lab has been at the forefront of a program to study the polarized structure of nucleons. Measurements of the spin-dependent structure functions, $g_1$ and $g_2$, have proven to be powerful tools in testing and understanding Quantum Chromodynamics. To measure $g_2$ a transversely polarized target is needed, which proves to be challenging experimentally. Prior to JLab, the only...

179. Single and double polarization asymmetries from deeply virtual exclusive ${\pi }^0$ electroproduction

Andrey Kim (University of Connecticut)

30/04/2014, 17:00

WG6: Spin Physics

Oral presentation

The target and double spin asymmetry measurements of exclusive ${\pi }^0$ electroproduction were performed for the first time in DIS region at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS) and longitudinally polarized proton target. The wide kinematic coverage and good resolution of CLAS allowed measurements in full azimuthal range providing an opportunity to extract single...

208. New JLab/Hall A Deeply Virtual Compton Scattering results

Franck Sabatié (CEA Saclay)

30/04/2014, 17:30

WG6: Spin Physics

Oral presentation

Due to new information obtained during the 2010 DVCS experiment in JLab/Hall A, we have performed a re-analysis of the 2004 JLab/Hall A E00-110 DVCS experiment. In addition to the extraction of helicity-dependent and unpolarized cross sections at fixed $x_B=0.36$ for three different $Q^2$ (as the original analysis), we have used the same data set to extract the same quantities at fixed...

231. Exclusive meson production at COMPASS

Pawel Sznajder (National Centre for Nuclear Research (PL))

30/04/2014, 18:00

WG6: Spin Physics

Oral presentation

Hard exclusive leptoproduction of mesons on nucleons has played an important role in studies of the hadron structure and recently gained renewed interest as it allows access to generalised parton distributions (GPDs). GPDs provide a novel and comprehensive description of the partonic structure of the nucleon and contain a wealth of new information. For instance GPDs give a description of the...