The total intrinsic k ┴ carried by quarks

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## The total intrinsic k ┴ carried by quarks

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**The total intrinsic k┴carried by quarks**• Extraction of the Sivers function • What do we learn from it? • k┴and orbital angular momentum • Orbiting quarks … ? ? Mauro Anselmino,Parton Orbital Angular Momentum,RBRC-UNM Workshop, Albuquerque,24-26/02/2006**uncertainty principle**gluon radiation k┴ ±1 ± ± l+ Q2 = M2 l– γ* qT p p qL Partonic intrinsic motion Plenty of theoretical and experimental evidence for transverse motion of partons within nucleons qT distribution of lepton pairs in D-Y processes**pT distribution of hadrons in SIDIS**estimates of**S**The Sivers distribution function number density of partons with longitudinal momentum fraction x and transverse momentum k┴, inside a proton with spin S M. Burkardt, PR D69, 091501 (2004)**Transverse single spin asymmetries in SIDIS**y Φπ ΦS x S PT p z X in collinear configurations there cannot be (at LO) any PT needsk┴dependent quark distribution in p↑ (Sivers mechanism)**Sivers mechanism in SIDIS**p┴= PT– zk┴+ O(k┴2/Q2)**Other approaches, with some simplifying assumptions:**J.C. Collins et al. W. Vogelsang, F. Yuan**from Sivers mechanism**M.A., U.D’Alesio, M.Boglione, A.Kotzinian, A Prokudin**M.A, M. Boglione, U. D’Alesio, A. Kotzinian, F. Murgia, A.**Prokudin comparison of different extractions: hep-ph/0511017 first p┴ moments of extracted Sivers functions, compared with models data from HERMES and COMPASS**M. Anselmino, M. Boglione, J.C. Collins, U. D’Alesio, A.V.**Efremov, K. Goeke, A. Kotzinian, S. Menze, A. Metz, F. Murgia, A. Prokudin, P. Schweitzer, W. Vogelsang, F. Yuan The first and 1/2-transverse moments of the Sivers quark distribution functions, defined in Eqs. (3, 9), as extracted in Refs. [20, 21, 23]. The fits were constrained mainly (or solely) by the preliminary HERMES data in the indicated x-range. The curves indicate the 1-σ regions of the various parameterizations.**Q2 > 1 (GeV/c)2 W2 > 25 GeV2**PT > 0.1 GeV/c Eh > 4 GeV 0.2 < zh < 0.9 0.1 < y < 0.9 Predictions for COMPASS, hydrogen target**SSA in p↑p → π X**fit to ANwith Sivers effect U. D’Alesio, F. Murgia E704 data, E = 200 GeV**l+**Q2 = M2 l– γ* qT p p QCD test: qL SSA in p↑p → l+ l- X**SSA in p↑p → D X**only Sivers effect: no transverse spin transfer in dominance of gluonic channel, access to gluon Sivers function assuming saturated Sivers function**What do we learn from Sivers distribution?**total amount of intrinsic momentum carried by partons of flavoura for a proton moving along the+z-axisand polarization vector S**Numerical estimates**from fitting data on Cahn effect from fitting HERMES and COMPASS data on AN M.A., M. Boglione, U. D’Alesio, A. Kotzinian, F. Murgia and A. Prokudin**Sivers functions extracted from ANdata in**give also opposite results, with**k┴and orbital angular momentum (case of 2 quarks)**? Does imply It depends on space distribution …… to be continued ……