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16–21 Aug 2019
Guilin Bravo Hotel, Guilin, China
Asia/Shanghai timezone

TDA measurements based on hard excusive pion electroproduction with CLAS at JLAB

20 Aug 2019, 09:35
20m
Guihu Room (Guilin Bravo Hotel, Guilin, China)

Guihu Room

Guilin Bravo Hotel, Guilin, China

14 South Ronghu Road, Xiangshan, Guilin 541002, Guangxi, China
Parallel Session 6: QCD and hadron structure Session 6: QCD and hadron structure

Speaker

Dr Stefan Diehl (stefan.diehl@exp2.physik.uni-gessen.de)

Description

For the first time, we have measured single beam spin asymmetries to extract $A_{LU}^{sin(\phi)}$ moments from the hard exclusive π$^{+}$ channel off the unpolarized hydrogen target in a wide range of kinematics from forward angles to backward angles in the center of mass frame. While many experiments showed the QCD factorization mechanism in the "nearly forward region" (large Q² and small |t|) can be divided into a hard part, described by perturbative QCD (pQCD) and in two general structure functions, the GPDs for the nucleon and the pion distribution amplitudes (DAs), describing the complex non perturbative structure of these particles. The recent measurement from CLAS in the "nearly backward" kinematic region (large Q² and small |u|) provided the potentially applicable collinear factorized description in terms of a convolution of the non-perturbative nucleonto-pion transitions (TDAs), the nucleon DAs and the hard interaction amplitude from pQCD. The measured moment in forward angles is known to be sensitive to generalized parton distributions (GPDs), while in backward angles, it is known to be sensitive to transition distribution amplitudes (TDAs). Our results clearly show that the sign of forward beam spin asymmetry measurements is positive whereas that of backward BSA measurements is negative, with the sign transition taking place around 90 degrees. By performing accurate measurements over a wide range of Q², x$_{B}$ and -t, we can explore the transition from hadronic to partonic reaction mechanisms.

Primary author

Dr Stefan Diehl (stefan.diehl@exp2.physik.uni-gessen.de)

Presentation materials