TMDe2015 - A path towards TMD extraction

2 Sept 2015, 08:00 → 4 Sept 2015, 19:30 Europe/Rome

Giambiagi Lecture Hall (Trieste)

Andrea Bressan (Universita e INFN, Trieste (IT)), Anna Martin (Trieste University and INFN (IT)), Franco Bradamante (Universita e INFN, Trieste (IT))

Transverse momentum dependent parton distribution functions (TMD PDFs) are crucial elements for the understanding of the nucleon structure in terms of the quark and gluon degrees of freedom in QCD, beyond the collinear approximation. The recent findings in the theoretical and experimental fields have allowed remarkable progress. The knowledge of these functions, however, is still in its infancy. 

This mini-workshop is focused on transversity and TMD extraction from semi-inclusive deep inelastic scattering (SIDIS) data. It is structured as a working group meeting, gathering people directly involved in the field, with the goal of tracking the road towards further progress using the existing data and planning new measurements in the near future. 

The aim of the Italian community involved in the organization is to create an opportunity for deep, open and constructive discussions to review the state of the art and the near future perspectives on

• TMD evolution and higher twist effects
• analysis of unpolarised SIDIS data, pT distributions, azimuthal dependences
• azimuthal asymmetries in transversely and longitudinally polarized SIDIS
• TMD fragmentation functions in e+e- and SIDIS processes
• new data analysis methods

with focus on TMD extraction.

The participants, all physicists working on TMD phenomenology and on related experiments, are expected to share their experience, discuss methodologies and propose new ideas with a collaborative attitude in a relaxing environment.
The mini-workshop will mainly consist of round table discussions with a few introductory presentations.

The proceedings will be replaced by a short written report on the outcome of the meeting.

The Workshop is supported by ECSAC, the European Centre for Science Arts and Culture which organizes conferences and meetings in Losinj or Trieste each year since 2001, and it is a hosted activity of the Abdul Salam International Centre for Theoretical Physics.

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For any information please contact the Organizing Committee:    e-mail: ecsac@ictp.it

TMDe2015 Summary

Scientific Programme http://ecsac.ictp.it/ecsac15/programma.php

Wednesday, 2 September

08:45 → 09:15 Welcome

ICTP and organizers

09:15 → 12:00 TMD evolution

Conveners: Barbara Pasquini (University of Pavia), Mauro Anselmino (Torino University and INFN)

09:20 TMD evolution -The next stage in the 3D imaging of the nucleon

Speaker: Mauro Anselmino (Torino University and INFN)

TMDe2015Anselmino.pdf

09:50 TMD evolution: an overview

In this talk I will present an overview of TMD evolution and of its recent tests and developments

Speaker: Ignazio Scimemi (U)

TMDe2015Scimemi.pdf

10:25 Phenomenological implementations of TMD evolution

abstract ....

Speaker: Stefano Melis (University of Torino and INFN)

TMDe2015Melis.pdf

11:35 Effects of TMD evolution and partonic flavor on e+e- annihilation into hadrons

abstract ....

Speaker: Andrea Signori (VU University Amsterdam - Nikhef)

TMDe2015Signori.pdf

11:00 → 11:30 coffee

12:00 → 15:15 Higher twist and target fragmentation effects

Conveners: Marco Mirazita (Istituto Nazionale Fisica Nucleare (IT)), Vincenzo Barone (University of Piemonte Orientale)

12:00 Disentangling different effects, from higher twist to target fragmentation

abstract ...

Speaker: Harut Avakian

avakian-triese-tmd2015.pdf

avakian-triese-tmd2015.ppt

12:45 The Target Fragmentation Region of SIDIS: A Few Remarks

Speaker: Vincenzo Barone (University of Piemonte Orientale)

TMDe2015Barone.pdf

14:45 Lambda production in the DIS target-fragmentation region

We briefly discuss motivations and physical assumptions of a recently proposed set of Lambda fracture functions obtained by a combined QCD a fit to a variety of semi-inclusive DIS data. We then specialise to CLAS12 kinematics and present predictions for a number of observables sensitive to the assumptions made in the model and which could be used to further improve and/or constrain it.

Speaker: Federico Alberto Ceccopieri (Universita & INFN, Milano-Bicocca (IT))

TMDe2015Ceccopieri.pdf

15:00 Lambda production in the DIS target-fragmentation region: the CLAS12 program

Speaker: Marco Mirazita (Istituto Nazionale Fisica Nucleare (IT))

TMDe2015mirazita.pdf

13:15 → 14:30 lunch

15:15 → 19:00 TMDs from unpolarised SIDIS data (pT distributions, azimuthal asymmetries)

Conveners: Alessandro Bacchetta (University of Pavia), Patrizia Rossi (Laboratori Nazionali di Frascati (LNF)-Istituto Nazionale Fisic), Silvia Pisano (LNF)

15:15 TMDs from unpolarised SIDIS data - Experimental Overview

abstract ....

Speaker: Rolf Ent (Jefferson Lab)

TMDe2015Ent.pdf

16:00 Phenomenology: status and perspectives - POSTPONED

abstract ...

Speaker: Alessandro Bacchetta (University of Pavia)

16:30 Unraveling hadron transverse momentum in SIDIS: Dynamics, present data, future measurements

The transverse momentum of hadrons observed in the current fragmentation region of SIDIS is generally compounded of several parts: the intrinsic transverse momentum of partons in the target, the effects of QCD radiation, and the broadening due to the fragmentation process. Unraveling the different contributions is a major challenge that needs to be addressed before one can reliably apply QCD factorization formulas and extract information about TMD distributions. Recent pion/kaon multiplicity data from HERMES and COMPASS indicate that non-perturbative dynamics plays an essential role in the measured P_T distributions, particularly at z >~ 0.5. In this talk I briefly summarize (a) what our present knowledge of non-perturbative dynamics suggests regarding the magnitude of the different contributions to hadron transverse momentum; (b) what SIDIS measurements could/should be done to unravel the different contributions; (c) what could be learned from measurements of particle correlations between the current and target fragmentation regions. The talk will be a concise summary and aim to provide input to the discussions. It relates mainly to the topics of Sessions 1 and 2 of the program.

Speaker: Christian Weiss (Jefferson Lab)

17:30 Multiplicities, azimuthal asymmetries, ...

see presentation on Thursday morning

Speaker: Mariaelena Boglione (University of Turin)

18:30 pT multiplicities at COMPASS

Speaker: Giulio Sbrizzai (Universita e INFN, Trieste (IT))

TMDe2015Sbrizzai.pdf

16:00 → 16:30 coffee

19:00 → 19:20 summary -- POSTPONED

Thursday, 3 September

10:00 → 15:00 TMDs from azimuthal asymmetries in transversely and longitudinally polarized SIDIS

Conveners: Marco Contalbrigo (Dipartimento di Fisica), Mauro Anselmino (Torino University and INFN)

10:00 Experimental overview: status and perspectives

abstract ....

Speaker: Andrea Bressan (Universita e INFN, Trieste (IT))

TMDe2015Bressan.pdf

11:00 Phenomenology: status and perspectives

abstract ....

Speaker: Mariaelena Boglione (University of Turin)

TMDe2015Boglione.pdf

12:00 Point by point extraction of the transversity distribution

The transversity distributions have been recently extracted in a point to point analysis using the Collins and di-hadron asymmetries for p and d, and the corresponding e+e- asymmetries. This alternative method to access transversity (and the other TMD PDFs) has some advantages which are proposed for discussion.

Speaker: Anna Martin (Trieste University and INFN (IT))

TMDe2015Martin.pdf

12:25 An update on the extraction of neutron SSAs from 3He data

The time reversal-odd parton transverse momentum distributions (TMDs) [1] in the neutron will be studied through polarized SIDIS experiments off 3He, where a high-energy pion is detected in coincidence with the scattered electron (see for example [2]). To disentangle the nuclear and the partonic degrees of freedom an accurate theoretical description of the process is needed. In Ref. [3] the plane wave impulse approximation (IA) was adopted. It was found that the nuclear effects described in IA can be taken into account in a simple effective way, and a procedure to safely extract the neutron SSAs was proposed. In a recent paper [4] the spectator SIDIS process off 3He was studied, and the final state interaction (FSI) between the hadronizing quark and a recoiling deuteron was taken into account through a distorted spin-dependent spectral function. We are now studying the standard SIDIS process, where the FSI between the observed pion and the remnant is again taken into account through a distorted spin-dependent spectral function [5]. The result, very interesting in particular for the experiments planned at the 12 GeV upgrade of JLab [2], is that in the nuclear SSA the effect of FSI cancels to a large extent and the ususal extraction appears to be safe. An extension of the approach to a relativistic treatment will be addressed [6]. REFERENCES [1] V. Barone, F. Bradamante, a. Martin Prog. Part. Nucl. Phys. 65, 267, 2010. [2] G. Cates et al., E12-09-018, JLAB approved experiment, hallaweb.jlab.org/collab/PAC/PAC38//E12-09-018-SIDIS.pdf [3] S. Scopetta, Phys. Rev. D 75, 054005 (2007). [4] L.P. Kaptari, A. Del Dotto, E. Pace, G. Salme` and S. Scopetta, Phys. Rev. C 89, 035206 (2014). [5] A. Del Dotto, L. Kaptari, E. Pace, G. Salme` and S. Scopetta, in preparation. [6] E. Pace, G. Salme`, S. Scopetta, A. Del Dotto and M. Rinaldi, Few Body Syst. 54, 1079 (2013); A. Del Dotto, L.P. Kaptari, E. Pace, G., Sergio Scopetta, Few-Body Syst. 55, 877 (2014).

Speaker: Sergio Scopetta (Perugia University)

TMDe2015Scopetta.pdf

12:55 The pretzelosity of the nucleon

Speaker: Bo-Qiang Ma (Peking University)

TMDe2015Ma.pdf

13:20 Transversity from GPDs

Speaker: Gary Goldstein (Tufts University)

TMDe2015Goldstein.pdf

13:45 Collins asymmetries in p p → jet pion X

We study the azimuthal asymmetries for the distributions of leading pions inside a jet produced inclusively in high-energy proton-proton collisions within the framework of the transverse momentum dependent generalized parton model. We present results for the Collins effect at the RHIC center-of-mass energies $\sqrt{s}$ = 200 and 500 GeV and compare our predictions with very recent, preliminary data from the STAR Collaboration.

Speaker: Cristian Pisano (Vrije Universiteit Amsterdam)

TMDe2015Pisano.pdf

10:30 → 11:00 coffee

13:00 → 13:30 lunch

15:00 → 19:30 TMD fragmentation functions in e+e- and SIDIS processes

Conveners: Andrea Bressan (Universita e INFN, Trieste (IT)), Franco Bradamante (Universita e INFN, Trieste (IT)), Marco Radici (INFN)

15:00 Phenomenology: status and perspectives

abstract ....

Speaker: Marco Radici (INFN)

TMDe2015Radici.pdf

15:40 Asymmetry measurements in e+e-: methods, open points and perspectives

some points which I think wold be valuable to discuss -The correct frame to extract azimuthal correlations in e+e-: The theory is mostly worked out for back-to-back hadrons. However, for experimental and theoretical reasons, two other methods are used: The 'thrust' method and lately modulations in jets. What are the consequences for fits? E.g. are evolution effects different for jets? Will it be possible to use measurements with two soft scales (as thrust or jet method) in global fits? -Extraction of the multidimensional dependence of fragmentation functions: I saw that you plan to have an extensive discussion at of this point. From the e+e- POV the question is probably which kinematic region is in particular important for SIDIS, p+p. There is also a specific IFF question about the importance to extract the different partial wave contributions separately. -Can we formulate observables that are sensitive to Twist3 fragmentation functions in e+e-? I am thinking here about the recently proposed framework by Kanazawa, Koike, Metz and Pitonyak and the twist3 FF that doesn't have a counterpart in the TMD framework. I think it might be difficult to observe in e+e- but maybe worth a discussion. -We use double ratios to cancel acceptance effects and effects from radiative gluons. The effects from radiative gluons are small in simulation. How useful are complicated double ratios in global analysis, e.g. for pi0 we use (pi0pi++pi0pi-)/(pi+p++pi-pi-)

Speaker: Anselm Vossen

TMDe2015Vossen.pdf

16:30 Collins asymmetries in e+e- annihilation

Inclusive hadron production cross section and angular distributions in $e^+e^-$ collisions shed light on fundamental questions of hadronization and fragmentation processes. We present measurements of the so called Collins azimuthal asymmetries in inclusive production of hadron pairs in $e^+e^- \rightarrow h_1h_2X$ annihilation process, where the two hadrons are produced in opposite hemispheres. In particular, we show BaBar preliminary results for $KK$, and $K\pi$ hadron pair combinations, as well as the Collins asymmetries for pion pairs. We also report the preliminary results from the BESIII experiment, which studies pion pairs azimuthal asymmetries using a data set collected at the center-of-mass energy $\sqrt{s}=3.65$ GeV. The comparison between asymmetries measured at B factories ($\sqrt{s}~10.6$ GeV) and those measured at BESIII can be used as a tool to understand the evolution of the Collins fragmentation function.

Speaker: Isabella Garzia (INFN)

TMDe2015-Garzia.pdf

17:05 Interplay between the Collins and the di-hadron asymmetries

The recent COMPASS results on the interplay between the Collins asymmetry and the di-hadron asymmetry are briefly presented. Their possible implications on the transversity extraction are discussed. The feasibility of the same studies in e+e- annihilation should also be addressed during the round tables.

Speaker: Franco Bradamante (Universita e INFN, Trieste (IT))

TMDe2015Bradamante.pdf

17:40 Dependence of 2h SIDIS structure functions on DeltaPhi

The general formalism to study the dependence of 2h SIDIS structure functions on DeltaPhi. Examples: 1) Sivers effect in 2h production in CFR. a) General formula and convolution expressions for SFs b) Results based on mLEPTO and comparison with released COMPASS data 2) A_LU^sin(DeltaPhi) asymmetry in b2b SIDIS (one hadron produced in the CFR and the second -- in the TFR). Leading order expression based on fracture and fragmentation functions. Preliminary data from JLab CLASS experiment.

Speaker: Aram Kotzinian (ANSL (Yerevan Physics Institute) (AM))

TMDe2015Kotzinian.pdf

18:15 Transverse Spin Effects in Two Hadron Electroproduction

The measurement of various angular single spin asymmetries (SSA) in a single hadron production off a transversely polarized target in semi-inclusive deep inelastic scattering (SIDIS) process allows to access both the Sivers and Collins effects describing the correlations of the the transverse spin and transverse momenta in both parton distribution and fragmentation functions. In our recent work we have explored both Sivers and Collins effects in the two-hadron SIDIS process. We showed that non-vanishing Sivers-effect-induced SSAs exist for modulations involving sines of the azimuthal angles of both the total and the relative transverse momenta of the hadron pair with respect to the the azimuthal angle of the nucleon's transverse spin. We have made projections for the sizes of these SSAs for the kinematics of the CLAS12 and EIC experiments. Similarly, in the fragmentation of a transversely polarized quark we used the NJL-jet model to demonstrate that Collins effect generates modulations of the polarized fragmentation function involving the sines of the same azimuthal angles of the hadron pair's transverse momenta, now with respect to the transverse quark spin. Moreover, our results for the Collins effect modulations are consistent with the recent experimental measurements by the COMPASS collaboration. These results help to demonstrate that the experimental measurements in two hadron SIDIS process can provide additional information for precise extractions of Sivers and Collins functions.

Speaker: Hrayr Matevosyan (University of Adelaide)

TMDe2015Matevosyan.pdf

16:00 → 16:30 coffee

20:00 → 20:30 dinner

Friday, 4 September

09:00 → 12:31 New data analysis methods (multiD and "4pi" measurements, weighted asymmetries, use of generators ...)

Conveners: Alessandro Bacchetta (University of Pavia), Anna Martin (Trieste University and INFN (IT)), Marco Radici (INFN)

09:00 Bessel and p_T weighted asymmetries

abstract ...

Speaker: Leonard Gamberg

TMDe_gamberg.pdf

09:45 PDF extraction with neural network

and extension to TMDs

Speaker: Simonetta Liuti (University of Virginia)

TMDe2015_Liuti.pdf

11:10 "4pi" and multiD measurements

abstract ...

Speaker: Marco Contalbrigo (Dipartimento di Fisica)

TMDe2015_Contalbrigo.pdf

12:05 Adaptation of a generator to TMD analysis

abstract ...

Speaker: Andrea Bianconi (Brascia University)

TMDe2015_bianconi.pdf

10:30 → 11:00 coffee

12:30 → 13:00 lunch

14:00 → 15:31 New channels: Λ, J/Ψ, high pT pairs … production in SIDIS

Conveners: Andrea Bressan (Universita e INFN, Trieste (IT)), Franco Bradamante (Universita e INFN, Trieste (IT)), Marco Radici (INFN)

14:00 The Gluon Sivers effect measurement at COMPASS from high-pt hadron pairs.

The COMPASS collaboration has recently released results of the gluon contribution to the Sivers effect measurement from high-pt hadron pairs both for proton and deuteron targets. The analysis method is based on the assumption that in the high Q2 range three processes contribute to the cross section: Leading Process, QCD Compton and Photon Gluon Fusion. The selection of high-pt hadron pairs enhances the fraction of PGF events in the sample and assures weak kinematic dependence of the asymmetries for each process. A novel approach of event-by-event weighting based on Monte Carlo simulations and with the use of Neural Networks is applied to extract all three asymmetries from the same data sample.

Speaker: Adam Szabelski (National Centre for Nuclear Research (PL))

TMDe2015_szabelski.pdf

14:25 Estimating the gluon Sivers function from A_N data in polarized pp collisions at RHIC

Within a generalized TMD parton model we use the latest highly precise mid-rapidity data on A_N for inclusive neutral pion production in polarized pp collisions by the PHENIX Collaboration to get a first estimate of the still poorly known gluon Sivers distribution. To this end we adopt present information on the quark Sivers functions as extracted from SIDIS data. These results, together with the recent preliminary analysis on the extraction of gluon Sivers asymmetry in SIDIS by the COMPASS Collaboration can help in clarifying the role of the gluon contribution to the Sivers effect.

Speaker: Francesco Murgia (INFN - Sezione di Cagliari)

TMDe2015_fmurgia.pdf

14:50 Sivers asymmetry of the J/ in COMPASS 2010 proton data

Speaker: Jan Matousek (Charles University (CZ))

TMDe2015Matousek.pdf

15:30 → 16:00 coffee

16:00 → 18:00 summary of the Workshop and preparation of the written report