Transverse distributions of polarized quarks Harut Avakian JLab
Transverse distributions of polarized quarks Harut Avakian (JLab) January 22 -24, 2015 Thomas Jefferson National Accelerator Facility H. Avakian, JLab, Jan 23 1
3 D structure of the nucleon Semi-Inclusive processes and transverse momentum distributions up h TMDs down Hard exclusive processes and spatial distributions of partons Pasquini & Yuan g, h GPDs Combination of polarized and unpolarized targets and large acceptance coverage of CLAS 12 allows studies of GPDs in a wide kinematic range. H. Avakian, JLab, Jan 23 (QCDSF) 2
Quark distributions at large k. T: lattice B. Musch et al ar. Xiv: 1011. 1213 g 1 q=Dq=(q+-q-)/2 B. Pasquini et al ar. Xiv: 0705. 4345 distributions of PDFs may depend on flavor and spin (lower fraction aligned with proton spin at large k. T, b. T) Avakian, Jlab May 28 3
Flavor separation of form factors G. Cates et al. PRL 106 (2011) 252003 Q 4 F 1 q Q 4 F 2 q/k Quark transverse charge densities inside an unpolarized proton ar. Xiv: 1304. 5926 space distributions depend on flavor and spin (modify in medium) G. Miller et al (2011 ) • H. Avakian, JLab, Jan 23 form factors of the nucleon fell off faster in nuclear matter 4
3 D structure: GPDs ep e’pp 0 CLAS e 1 dvcs DVCS asymmetries measured at HERMES & JLAB More measurements at JLab, Compass Transverse photon dominates the xsection for exclusive p 0 production Lattice (QCDSF) Spin-azimuthal asymmetries in hard exclusive production of photons and pions give access to underlying GPDs H. Avakian, JLab, Jan 23 5
~ t-dependence of H Unpolarized beam, longitudinal target (TSA) : Ds. UL ~ sinf. Im{F 1 H~+x(F 1+F 2)(H + x. B/2 E) –xk. F 2 E+…}df H. Avakian, JLab, Jan 23 ~ Im{Hp, Hp} 6
t-dependences of HT ep e’pp 0 Goldstein, Liuti et al P. Kroll & S. Goloskokov • The production amplitude at large Q 2 factorizes into the hard subprocess and GPDs • Within the handbag approach g*T p transitions are related to transversity (helicity-flip) GPDs accompanied by a twist-3 pion wave function Hard partonic subprocess A. Kim’s talk • CLAS 12 can measure Q 2 dependence of HT SSAs significantly extending the range of CLAS H. Avakian, JLab, Jan 23 7
Studies of Chiral-Odd GPDs in Hard Exclusive Pseudoscalar Meson Production Using the CLAS 12 Detector PAC 42 Lo. I H. Avakian, JLab, Jan 23 8
Outline We propose a combination of measurements of cross sections, spin and azimuthal asymmetries with a longitudinally polarized beam and both unpolarized and longitudinally polarized proton target providing a flavor decomposition of underlying chiral-odd GPDs. • Exclusive production of pseudoscalar mesons • Chiral-Odd GPDs and transverse _photon • Studies of Transversity and GPD ET • Exclusive kaon production and separation of different channels H. Avakian, JLab, Jan 23 9
Exclusive kaon production Unlike p+ the K+ x-section is totally dominated by the transverse photon pole contribution negligible Exclusive production of KL and KS provide access to different combinations of chiral-odd GPDs H. Avakian, JLab, Jan 23 10
SSAs in exclusive kaon production Goloskokov&Kroll KS asymmetries are predicted to be large and with opposite sign to KL Goldstein, Hernandez, & Liuti Beam and target asymmetries in exclusive production of KL and KS are very sensitive to chiral-odd GPDs. H. Avakian, JLab, Jan 23 11
K/K* and L/S separation L S Due to detector resolution clean separation of different channels (L, S, K*) will require detection of 4 particles H. Avakian, JLab, Jan 23 12
K+ L/S separation K+ q L Detection of K+ p and p- would allow to separate of different final states (L, S, K*) H. Avakian, JLab, Jan 23 13
Exclusive L/S separation L S Detection of the complete final sate allow separation of exclusive Ss H. Avakian, JLab, Jan 23 14
GPDs from cross section ratios M. Diehl et al. hep-ph/0506171 K*+ K+ • Study ratio observables: K/K*/r+, polarization transfer • Different final state mesons filter out different combinations of unpolarized (H, E) and polarized (H, E) GPDs. H. Avakian, Glasgow, May 13 15
Summary • Understanding of transverse space distributions of polarized quarks is crucial for interpretation of exclusive production of photons and pions • Identification of Kaons will significantly enhance CLAS 12 capabilities to study exclusive processes involving kaons. • Combination of DVCS measurements from CLAS 12 with unpolarized, longitudinally and transversely polarized targets would allow studies of chiral-odd GPDs • Measurements of hard-exclusive production of photons and pseudoscalar mesons will help to accomplish the CLAS 12 program of studies of the 3 D structure of the nucleon Nead GPD/CFF extraction framework with controlled systematics. H. Avakian, JLab, Jan 23 16
Support slides…. H. Avakian, JLab, Jan 23 17
Exclusive p 0 rates higher for small W s. T – dominates for p 0. ds. T /dt ds. L /dt K 2⊥/Q 2 corrections in the propagators of the hard subprocess amplitude are essential in the description of the cross section at low Q 2. They decrease s by a factor of about 10 at Q 2 ∼ 3 Ge. V 2 M 0+, ++ amplitude is important in s T. H. Avakian, JLab, Jan 23 18
Exclusive p+ cross sections in modified perturbative approach • For π+ production the p → n transition GPDs are required which are given by the isovector combination of proton GPDs F(3) = Fu − Fd. • The γ∗q → πq subprocess amplitudes within the modified perturbative approach is defined Fourier transform to b space momentum fraction of the quark defined with respect to the meson momentum transverse cross section for large t (−t>∼ 0. 2 Ge. V 2) is larger than the longitudinal one H. Avakian, JLab, Jan 23 19
Transverse densities in the nucleon in nuclear matter Quark transverse charge densities inside an unpolarized proton ar. Xiv: 1304. 5926 Skyrme model proton • • medium form factors of the nucleon fell off faster in nuclear matter the size of the nucleon tends to bulge out in nuclear matter. H. Avakian, JLab, Jan 23 20
Exclusive p+/p 0 ar. Xiv: 0906. 0460 Different transverse moments will give access to different combinations of GPDs H. Avakian, JLab, Feb 24 21
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