QCD Evolution 2016

Session

Talks

30 May 2016, 11:00

Z011 - Turing room (Nikhef)

11. Quasi-real photon contribution to A_N in lp --> pion X in a TMD approach

Umberto D'Alesio

30/05/2016, 11:00

Within a TMD approach we discuss the impact of quasi-real(Weizsacker-Williams) photon contribution to the transverse single spin asymmetry, A_N, for the inclusive process lp --> pion X. This study extends a previous one where only the leading order contribution was taken into account. The predictions are obtained adopting the Sivers and transversity distributions and the Collins fragmentation...

1. Do fragmentation functions in factorization theorems correctly treat non-perturbative effects?

John Collins

30/05/2016, 11:30

Current all-orders proofs of factorization of hard processes are made by extracting the leading power behavior of Feynman graphs, i.e., by working strictly order-by-order in perturbation theory. The resulting parton densities and fragmentation functions include non-perturbative effects. I discuss how there could be loopholes in the proof such that other non-perturbative and semi-perturbative...

2. Extraction of unpolarized TMDs

Alessandro Bacchetta

30/05/2016, 12:00

We present an extraction of unpolarized TMDs that includes the effects of TMD evolution up to next-to-leading log level. We consider semi-inclusive DIS multiplicites and Drell-Yan cross-sections. Flavor dependence of TMDs is taken into consideration.

4. Transverse phase space and its multipole decomposition

Cedric Lorce

30/05/2016, 14:00

Relativistic phase space distributions are very interesting objects as they allow one to gather the information extracted from various types of experiments into a single coherent picture. Focusing on the 4-dimensional transverse phase space, we identified all the possible angular correlations providing at the same time a clear physical interpretation of all the leading-twist generalized and...

5. Quark Orbital Angular Momentum

Matthias Burkardt

30/05/2016, 14:30

Generalized Parton Distributions (GPDs) provide information on the distribution of quarks in impact parameter space. For transversely polarized nucleons, these impact parameter distributions are transversely distorted and this deviation from axial symmetry leads on average to a net transverse force from the spectators on the active quark in a DIS experiment. This force when acting along the...

6. Structure of the Energy-Momentum Tensor and Applications

Peter Schweitzer

30/05/2016, 15:00

The probably most fundamental information about a particle is contained in the matrix elements of its energy momentum tensor which are accessible via GPDs. The spin decomposition of the nucleon and Ji sum rule is just one example. Less prominent but equally important information is encoded in the stress tensor related to the spatial components of the energy-momentum tensor which shows in...

7. Helicity Evolution at Small-x

Yuri Kovchegov

30/05/2016, 16:30

We construct small-x evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the g1 structure function. These evolution equations resum powers of αs ln2(1/x) in the polarization-dependent evolution: hence our equations collect powers of the parameter excluded in the DGLAP and CSS evolutions. The full non-linear version of our equations also...

8. Resumming large collinear logarithms in the non-linear QCD evolution at high energy

Edmond Iancu

30/05/2016, 17:00

The Balitsky-JIMWLK equations which govern the QCD evolution at high energy and in the presence of unitarity corrections are presently known to next-to-leading order accuracy. However, the NLO approximation turns out to be unstable, due to large radiative corrections enhanced by double, or single, collinear logarithms, i.e. logarithms generated by the transverse phase-space. Via an explicit...

36. Initial state correlations

Alex Kovner

30/05/2016, 17:30

I discuss several mechanisms that result in correlations between gluons in the initial state wave functions. These correlations exhibit themselves as correlated particle production in certain kinematical regime. I also discuss the fate of these correlations under high energy evolution.

10. The RHIC transverse spin physics program: a crucial step to EIC

Elke-Caroline Aschenauer

31/05/2016, 09:00

The most recent results and future possibilities to measure observables to constrain quark and gluon TMDs and their evolution through transverse polarised pp collisions at a center of mass energy of 200 GeV and 500 GeV will be reviewed. Further selective measurements for TMDs at an eRHIC will be discussed

12. Spin asymmetries for vector boson production in polarized p+p collisions

Jin Huang

31/05/2016, 09:30

We investigated the cross section and the associated spin asymmetries for vector boson (W±/Z0/γ∗) production in polarized proton-proton collisions at tree level within the TMD factorization formalism. Besides the well-known Sivers function f1T , the single transverse asymmetry could also probe the transversal helicity distribution g1T via the parity-violating nature of W/Z0 production....

29. Exploring universality of transversity in p-p collisions

Marco Radici

31/05/2016, 10:00

We consider azimuthal asymmetries of charged pion pairs produced inside the same jet from proton-proton collisions with one transversely polarized proton. A specific asymmetry directly probes the chiral-odd transversity parton distribution in connection with the chiral-odd interference fragmentation function. We present predictions for this observable based on previous extractions of...

13. Double parton scattering in the ultraviolet: addressing the double counting problem

Jonathan Gaunt

31/05/2016, 11:00

At short distance between partons, double parton scattering overlaps with loop contributions to standard single hard scattering. Responsible for this is the splitting of one parton into two, and different choices for the partitioning of these contributions between single and double scattering give rise to different cross section formulae and to different evolution equations for the double...

14. Double parton scattering for perturbative transverse momenta

Maarten Buffing

31/05/2016, 11:30

The cross section for transverse momentum dependent double parton scattering involves transverse momentum dependent double parton distributions (DTMDs). In the region of perturbative transverse momentum the DTMDs can be matched onto collinear double parton distributions. In this talk, we present the framework and results for this matching, as well as the evolution equations for DTMDs in the...

15. Double parton scattering in a multi-scale regime

Markus Diehl

31/05/2016, 12:00

At perturbative transverse momenta, double parton scattering receives contributions from several different regimes, which need to be merged in a consistent way. I show how this can be done by adapting Collins’ subtraction formalism to position space.

16. Generalized Parton Distributions in Deeply Virtual Lepton Scattering Processes

Gary Goldstein

31/05/2016, 14:00

Spin and transverse momentum dependent Generalized Parton Distributions (GPDs) exist at the interface between the non-perturbative regime of QCD hadron structure and observable quantities. The distributions appear as linear superpositions and convolutions within helicity amplitudes for parton-nucleon scattering processes, which, in turn, occur in amplitudes for leptoproduction processes. We...

17. COMPASS results on hard exclusive muoproduction

Andrzej Sandacz

31/05/2016, 14:30

The high energy polarised muon beam available at CERN, with positive or negative charge, makes COMPASS a unique place for studies of General Parton Distributions (GPDs). The first GPD related COMPASS results were obtained for exclusive vector meson production on transversely polarised protons and deuterons. The data were taken in 2003-2010 with solid-state polarised target, although without...

18. Towards three loop evolution equation for GPDs

Alexander Manashov

31/05/2016, 15:00

QCD evolution equations in minimal subtraction schemes have a hidden symmetry: One can construct three operators that commute with the evolution kernel and form an SL(2) algebra. We found explicit expressions for these operators to two-loop accuracy going over to QCD in non-integer d = 4 − 2ǫ space-time dimensions at the intermediate stage. In this way conformal symmetry of QCD is restored on...

19. An EFT for Both Hard and Forward Scattering

Iain Stewart

31/05/2016, 16:00

I will discuss an EFT framework that is valid for both hard scattering and forward scattering processes by including Glauber interactions in the Soft-Collinear Effective Theory. A Lagrangian is constructed that is valid to all orders in alphas. The role of rapidity renormalization and subtractions is highlighted. Applications include understanding factorization violation in hard scattering, as...

20. Multi-differential resummation with SCET+

Wouter Waalewijn

31/05/2016, 16:30

I will discuss how to perform the simultaneous resummation of various series of logarithms using an extension of Soft Collinear Effective Theory, called SCET+. I will discuss this for the simultaneous measurement of the pT of the Z boson and the hadronic beam thrust event shape [arXiv:1410.6483], which was recently measured at the LHC. However, I will also consider other types of logarithms,...

21. Jet fragmentation functions in proton-proton collisions

Felix Ringer

31/05/2016, 17:00

The jet fragmentation function describes the longitudinal momentum distribution of hadrons inside a reconstructed jet. We study the jet fragmentation function in proton-proton collisions in the framework of soft-collinear effective theory (SCET). We find that, up to power corrections, the jet fragmentation function can be expressed as the ratio of the fragmenting jet function and the...

48. Factorization and Resummation for Massive Quark Effects in Exclusive Drell-Yan

Daniel Samitz

31/05/2016, 17:30

Within the framework of Soft-Collinear Effective Theory we discuss how to incorporate massive bottom quark effects in the resummed cross section for exclusive 0-jet Drell-Yan, where as a specific example for a measured exclusive observables we consider the transverse momentum of the electroweak boson. At NNLL’ order, i.e. including matrix elements at O(α2 s) and NNLL resummation, one has to...

25. Gluon TMD in the Loop Space Formalism

Igor Cherednikov

01/06/2016, 09:00

We discuss a method to derive the gauge-invariant gluon transverse-momentum dependent distribution function (gTMD) within the Wilson loop space framework. The basic ingredient of this approach is a set of hadronic matrix elements of arbitrary Wilson loops. We compare this approach with other definitions of the gTMD at small- and large-x existing in the literature.

22. TMD factorization from small to large transverse momentum

Ted Rogers

01/06/2016, 09:30

I will discuss issues that arise when TMD factorization theorems are combined with descriptions of large transverse momentum. The importance of accurate treatments of large transverse momentum in processes with lower hard scales, like semi-inclusive deep inelastic scattering, will be emphasized. I will also discuss the relationship between TMD factorization and collinear factorization.

23. SIDIS cross sections: perturbative and non-perturbative aspects

Mariaelena Boglione

01/06/2016, 10:00

I will address the study of semi-inclusive deep inelastic scattering cross sections over a wide range of transverse momenta, and in particular in the region of low to moderate $q_T$, when the interplay between perturbative and non-perturbative effects becomes more relevant. Some realistic SIDIS kinematical configuration will be considered where the commonly used prescription of “matching”...

24. PDF from Hadronic Tensor on the Lattice and Connected Sea Evolution

Keh-Fei Liu

01/06/2016, 11:00

A path-integral formulation of the hadronic tensor is reviewed where the connected and disconnected sea parsons are separated. I shall discuss how to calculate them on the lattice and will discuss how the evolution equations should be modified to accommodate both the connected and disconnected sea partons.

42. Probing Gluon TMDs at a future EIC

Cristian Pisano

01/06/2016, 11:30

We show how the study of azimuthal asymmetries for heavy quark pair and dijet production in electron-proton collisions could provide detailed information on gluon distributions, including their transverse momentum dependence. In particular, in the case of transversely polarized protons, the gluon Sivers effect is examined. Moreover, we discuss the strong analogies between the gluon single spin...

27. Twist-3 asymmetries in proton-proton collisions

Yuji Koike

01/06/2016, 12:00

In this talk, I will discuss twist-3 spin asymmetries in proton-proton collisions based on the collinear twist-3 factorization. We discuss the characteristic features of the relevant twist-3 cross sections for the double spin asymmetries ALT for the hadron production in the collision between longitudinally and transversely polarized protons, and the transverse spin polarization for the...

49. Structure of transverse momentum dependent (TMD) distributions at NNLO

Alexey Vladimirov

01/06/2016, 12:30

In this work we perform the detailed analyses of TMD operators and provide a complete calculation at next-to-next-to leading order of unpolarized transverse momentum dependent parton distribution functions (TMDPDF) and fragmentation functions (TMDFF) for all flavor combinations. Our analysis is made in general framework without any reference to a specific process. We recover the known results...

28. Improved theoretical description of Mueller-Navelet jets at LHC

Dimitri Colferai

02/06/2016, 09:00

Mueller-Navelet jets (MNJ) are one of the most sensitive observables to QCD dynamics in the high-energy (low-x) regime. In this talk I describe two aspects that are important in order to provide accurate predictions for MNJ: 1) the matching of BFKL NLL dynamics with fixed NLO calculations; 2) a modified selection of the final state particles in order to be consistent with experimental...

56. Evolution of sum rules and positivity constraints

Oleg Teryaev

02/06/2016, 09:30

The stability of sum rules and preservation of positivity constraints under the different versions of QCD evolution are considered. It is shown that the crucial role belongs to the kinetic interpretation of evolution equations as a gain-loss ones. The cases of DGLAP, BFKL and ERBL evolutions are considered. The various approaches to TMD evolution are compared and the role of transverse degrees...

3. Selected Results and Future Perspectives for TMD Observables at CERN with COMPASS

Matthias Grosse Perdekamp

02/06/2016, 10:00

9. Hadronic matrix elements in three dimensions

Ahmad Idilbi

02/06/2016, 11:00

I will review some basic features of hadronic matrix elements describing the three dimensional hadronic structure. I will focus on generalized transverse momentum dependent parton distributions (GTMDs) which, in many ways, are considered as the most fundamental objects in hadronic physics, and how they should be properly defined. I will also discuss some open questions regarding another...

31. Definition and evolution of GTMDs

Miguel Echevarria

02/06/2016, 11:30

Three-dimensional hadronic matrix elements are fundamental objects needed to explore hadronic structure. Among them, the most basic quantities are the “generalized transverse momentum dependent parton distribution functions” (GTMDs). In my talk I will argue that, currently, they are improperly defined and will propose a new definition which is in accordance with QCD fundamentals. Using it, I...

32. Evolution equations for light-cone distribution amplitudes of heavy-light hadrons

Vladimir Braun

02/06/2016, 12:00

QCD factorization approach for heavy hadron decays introduces light-cone distribution amplitudes for heavy mesons and baryons as the main nonperturbative input. The scale dependence of these distributions is nontrivial and was understood only recently. I review these results and their relation to more familiar DGLAP-and ERBL-type evolution for light hadrons.

34. Gluon TMD in particle production from low to moderate $x$

Ian Balitsky

02/06/2016, 14:00

I discuss the rapidity evolution of gluon transverse momentum dependent distributions appearing in processes of particle production and show how this evolution changes from small to moderate Bjorken $x$.

35. Sub-gauge Conditions for the Gluon Propagator Singularities in the Light-Cone Gauge and Temporal Gauge

Giovanni Antonio Chirilli

02/06/2016, 14:30

Perturbative QCD calculations in the light-cone gauge have long suffered from the ambiguity associated with the regularization of the poles in the gluon propagator. Using the functional integral method, we re-derive the known sub-gauge conditions for the θ-function gauges and identify the sub-gauge condition for the principal value regularization of the gluon propagator’s light-cone poles....

33. Selected topics on QCD evolution

Jian Zhou

02/06/2016, 15:00

In this talk, I am going to disscuss various topics on QCD evolution, including the scale evolution of the collinear twist-3 correlation functions relevant for the single spin asymmtries phenomenology and the evolution of the small x gluon TMD. It is shown that the Burkardt sum rule can be used to check the consistency of the derived evolution equations for the twist-3 functions. In addition,...

37. Pion structure function and SU(2) flavor asymmetry

Chueng-Ryong Ji

02/06/2016, 16:00

We refine the computation of the ¯ d − ¯u flavor asymmetry in the proton sea with a complementary effort to reveal the dynamics of pion exchange in high-energy processes. In particular, we discuss the efficacy of pion exchange models to simultaneously describe leading neutron electroproduction at HERA along with the ¯ d−¯u flavor asymmetry in the proton.The analysis disfavors several models of...

38. Tagged spectator DIS off a polarized spin-1 target

Wim Cosyn

02/06/2016, 16:30

We introduce the theoretical framework for deep-inelastic electron scattering (DIS) on the polarized deuteron with detection of a nucleon in the nuclear fragmentation region (“spectator tagging”). Such experiments enable measurements of neutron spin structure and nuclear modifications with full control of the nuclear configuration. We discuss the general expressions of the cross section of...

39. Cos (2φ) azimuthal asymmetry in virtual photon-jet production in pA collisions

Yajin Zhou

02/06/2016, 17:00

We numerically investigate the cos(2phi) azimuthal asymmetry in virtual photon-jet production in pA collisions, which provides the direct access to the linearly polarized gluon distribution. Our analysis incorporates both the saturation effect and the Sudakov suppression effect. The preliminary numerical result suggests that the asymmetry could be sizeable in the kinematical region accessible...

50. Gluon TMDs in the small-x limit

Tom van Daal

02/06/2016, 17:20

We investigate the gluon transverse momentum dependent (TMD) correlators as Fourier transforms of matrix elements of nonlocal operator combinations. At the operator level these correlators include both field strength operators and gauge links bridging the nonlocality. In contrast to the collinear PDFs, the gauge links are no longer unique for TMD PDFs (TMDs) and also Wilson loops lead to...

41. Interpretation of Angular Distributions of Z-boson Production

Jen-Chieh Peng

03/06/2016, 09:00

High precision data of dilepton angular distributions in γ∗/Z production were reported recently by the CMS Collaboration covering a broad range of the dilepton transverse momentum, qT , up to _ 300 GeV. Pronounced qT dependencies of the λ and ν parameters, characterizing the cos2 θ and cos 2φ angular distributions, were found. Violation of the Lam-Tung relation was also clearly observed. We...

40. Drell-Yan lepton angular distributions in perturbative QCD

Werner Vogelsang

03/06/2016, 09:30

We present a comprehensive comparison of the available experimental data for the Drell-Yan lepton angular coefficients $\lambda$ and $\nu$ to calculations at leading and next-to-leading order of perturbative QCD. Our comparisons reveal that perturbative QCD is able to describe the experimental data overall rather well, especially at colliders, but also in the fixed-target regime.

26. Accessing gluon TMDs with quarkonium production

Jean-Philippe Lansberg

03/06/2016, 10:00

I will discuss the opportunities offered by the study of single, double and associated quarkonium production in hadronic collisions in order to access gluon TMDs. I will argue that, at the LHC, with unpolarised nucleons, the distributions of linearly polarised gluons, h_1^perp,g, is already accessible with various data on tape. I will the discuss the case of low pT C=+1 quarkonia which can be...

43. Probing TMDs in heavy quarkonium production

Asmita Mukherjee

03/06/2016, 11:00

We investigate the effect of unpolarized transverse momentum dependent gluon parton distributions as well as the effect of linearly polarized gluons on transverse momentum and rapidity distributions of J/ψ and _ production within the framework of transverse momentum dependent factorization employing color evaporation model (CEM) in unpolarized proton-proton collision. We estimate the...

44. Differential cross section for Higgs boson production in 4 lepton channel at LHC and kT factorisation approach

Vaibhav Rawoot

03/06/2016, 11:30

We study the inclusive Higgs boson production cross section within the QCD kT factorization approach where the intrinsic transverse momentum effect of gluons is taken in to account. Differential cross section for the process pp ! H ! ZZ∗ ! ¯ll′¯l is estimated considering gluon to be off-shell and compared with the usual QCD results obtained within collinear factorization approach. Unintegrated...

45. Off-shell amplitudes and 4-jet production in kt-factorization

Mirko Serino

03/06/2016, 12:00

We present a framework for the evaluation of tree-level amplitudes with off-shell legs for kt-factorization, based on the BCFW recursion relation, and discuss its recent application to 4-jet production. We evaluate both single and double parton scattering contributions to the cross section and discuss the differences between the results of collinear and kt-factorization, comparing them to the...

51. Azimuthal asymmetries as the probe of nuclear matter at EIC

Yu-kun Song

03/06/2016, 14:00

Nuclear dependence of transverse momentum dependent parton distributions and azimuthal asymmetries in SIDIS off polarized nuclear targets are studied. Multiple gluon interaction, which is responsible for gauge link, contain information of nuclear dependence of parton distributions. We show the suppression of azimuthal asymmetries for eA SIDIS relative to that of eN case, and the suppression...

52. On the high-energy evolution of the jet quenching parameter

Pieter Taels

03/06/2016, 14:30

We present ongoing work concerning the high-energy evolution of the jet quenching parameter (the transport coefficient which characterizes the transverse momentum broadening of an energetic jet propagating through a dense partonic medium, such as the quark-gluon plasma created in the intermediate stages of nucleus-nucleus collisions at the LHC). Within the framework developed in Iancu (2014)...

53. Heavy flavour corrections to polarised and unpolarised deep-inelastic scattering at 3-loop order

Arnd Behring

03/06/2016, 14:50

We report on progress in the calculation of 3-loop corrections to the deep-inelastic structure functions from massive quarks in the asymptotic region of large momentum transfer Q2. Recently completed results allow us to obtain the O(a3 s) contributions to several heavy flavour Wilson coefficients which enter both polarised and unpolarised structure functions for lepton-nucleon scattering. In...

54. Transverse Single Spin Asymmetries in Hard Processes

Leonard Gamberg

03/06/2016, 15:10

The results of a combined TMD and twist-3 formalism analysis of single spin asymmetries in SIDIS, e+e- annihilation into hadron pairs, and proton-proton scattering are presented.