Douglas Fields University of New Mexico. Direct vs. Indirect Measurement Width of room Tape measure...

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Douglas Fields University of New Mexico Experimental Evidence for Partonic Orbital Angular Momentum at RHIC

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  • Douglas Fields University of New Mexico
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  • Direct vs. Indirect Measurement Width of room Tape measure Spin of proton Stern-Gerlach experiment DIS G DIS Q 2 dependence, RHIC But, definition is unclear L g, L q, L g+q Can one simply say L = - - G? No! Other methods Temperature of room Tape measure? 6/21/2011 2 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • Directly measured quantity Theory basis for implying indirect measurement Limits on indirect measurement from experimental and theoretical uncertainties 6/21/2011 3 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • 6/21/2011 4 Douglas Fields PacSPIN2011, Cairns, QLD, Australia BRAHMS & PP2PP (p) STAR (p) PHENIX (p) AGS LINAC BOOSTER Pol. Proton Source 500 A, 300 s Spin Rotators Partial Siberian Snake Siberian Snakes 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipoles RHIC pC Polarimeters Absolute Polarimeter (H jet) 2 10 11 Pol. Protons / Bunch = 20 mm mrad
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  • Spin transport in Snake Magnets Burkardt & Schnell Phys. Rev. D 74, 013002 (2006) Toy model for u-quarks in the valence region yields: I.e., very weak (but nonzero) constraint on contributions of nonzero orbital angular momentum states to each quark flavor. But the sum over flavors is not necessarily nonzero! 6/21/2011 5 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • 6/21/2011 6 Douglas Fields PacSPIN2011, Cairns, QLD, Australia left right Fixed target pion SSAs (E704) QCD prediction -> zero
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  • 6/21/2011 7 Douglas Fields PacSPIN2011, Cairns, QLD, Australia There is a long history of trying to explain SSAs with orbital motion. C.Boros, et al., PRL 70 p1751 (1993). Interaction with orbiting valence quarks.
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  • 6/21/2011 8 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Sivers Effect Collins Effect Sivers Function (angular momentum) Transversity (structure) Collins Function (Fragmentation)
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  • Nice conceptual picture from D. Sivers (talk given at UNM/RBRC Workshop on Parton Orbital Angular Momentum). Summary: Sivers effect requires orbital motion. Is process dependent. 6/21/2011 9 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • 6/21/2011 10 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Leads to Asymmetric parton densities. Which leads to preferential left-right interaction depending upon direction of OAM relative to spin direction. Which leads to left-right scattering depending upon the initial/final state interactions.
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  • 6/21/2011 11 Douglas Fields PacSPIN2011, Cairns, QLD, Australia So what do we see at RHIC?
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  • x F scaling Larger asymmetries at larger x F Valence quark effects? 6/21/2011 14 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • Charged mesons in muon arms. 6/21/2011 15 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • Seen as a limit on Gluon Sivers 6/21/2011 18 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • 6/21/2011 19 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Have extracted Sivers functions for DIS. Can extend to include RHIC data? What does it mean for OAM?
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  • 6/21/2011 20 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Preliminary Re r 5 =0, Im r 5 =0 no hadron spin-flip p+p CNI (jet) p+C CNI
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  • 6/21/2011 21 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • 6/21/2011 22 Douglas Fields PacSPIN2011, Cairns, QLD, Australia 1800cm 10cm 3 mrad D x magnet blue beamyellow beam
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  • 6/21/2011 23 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Inclusive neutron
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  • OPE fails to predict both the cross section and the asymmetry. Also possible relation to OAM? 6/21/2011 24 Douglas Fields PacSPIN2011, Cairns, QLD, Australia B.Z. Kopeliovich et al. arXiv: 0807:1449
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  • 6/21/2011 25 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Boer & Vogelsang, PRD 69 (2004) 094025 jet A N p beam ( k T S T ) p beam into page Idea: directly measure k T by observing momentum imbalance of a pair of jets produced in p+p collision and attempt to measure if k T is correlated with incoming proton spin
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  • 6/21/2011 26 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • 6/21/2011 Douglas Fields PacSPIN2011, Cairns, QLD, Australia 27 Intrinsic (Confinement) k T 200 MeV/c Breaks collinear factorization Soft QCD radiation. An example - J/ production. Extra gluon kick p T J/ =1.8 0.23 0.16 GeV/c Phys. Rev. Lett. 92, 051802, (2004).
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  • 6/21/2011 28 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Di-hadron p T kTkT Net transverse momentum of a di-hadron pair in a factorization ansatz I = initial fermi motion of the confined partons, initial-state gluon radiation S = soft one or several soft gluons emitted H = hard final-state radiation (three-jet) Another Possibility: Spin-correlated transverse momentum partonic orbital angular momentum Can examine the helicity dependence of each term:
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  • 6/21/2011 29 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Peripheral Collisions Larger Jet 1 Jet 2 w/ =0 Jet 2 Integrate over b, left with some residual k T Net p T kick Central Collisions Smaller Jet 2 Jet 1 Jet 2 w/ =0 Like helicities : Beam momenta Partonic orbital angular momentum leads to rotation of partons correlated with the proton spin vector This leads to different p T imbalances (p T -kicks) of jet pairs in semiclassical models Can be measured by measuring helicity dependence of For details on jets see: Phys. Rev. D 74, 072002 (2006)
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  • 6/21/2011 30 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Partonic orbital angular momentum leads to rotation of partons correlated with the proton spin vector This leads to different p T imbalances (p T -kicks) of jet pairs in semiclassical models Can be measured by measuring helicity dependence of Integrate over b, left with different residual k T Net p T kick Central Collisions Larger Jet 2 Jet 1 Jet 2 w/ =0 Peripheral Collisions Smaller Jet 1 Jet 2 w/ =0 Jet 2 Unlike helicities : Beam momenta For details see: Phys. Rev. D 74, 072002 (2006)
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  • 6/21/2011 31 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Drell-Yan pair production in polarized p+p collisions. (Meng Ta-Chung et al. Phys. Rev. D 1989) k PR k TR k PR Like Helicity Un-like Helicity k TR Averaging over D(b): Integrating over impact parameter b:
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  • 6/21/2011 32 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Intra-jet pairs angular width : near j T Inter-jet pairs angular width : far j T j Ty p Tt p Ta ^ p Tt ^ Zero k T
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  • 6/21/2011 33 Douglas Fields PacSPIN2011, Cairns, QLD, Australia Non-Zero k T kT kT Intra-jet pairs angular width : near j T Inter-jet pairs angular width : far j T j Ty p Tt p Ta ^ p Tt ^ k Ty
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  • 6/21/2011 34 Douglas Fields PacSPIN2011, Cairns, QLD, Australia j Ty p Tt p Ta ^ p Tt ^ k Ty p Tt p out For details, see PRD 74, 072002 (2006)
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  • 6/21/2011 35 Douglas Fields PacSPIN2011, Cairns, QLD, Australia o - h azimuthal correlation Trigger on a particle, e.g. o, with transverse momentum p Tt. Measure azimuthal angular distribution w.r.t. the azimuth of associated (charged) particle with transverse momentum p Ta. The strong same and away side peaks in p-p collisions indicate di-jet origin from hard scattering partons.
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  • Both j T and k T consistent with zero. We now have higher statistics data which we will soon analyze. 6/21/2011 36 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • The first term can be related in the Meng conjecture to partonic transverse momentum: where c ij give the initial state weights and W ij give the impact parameter weighting. 6/21/2011 37 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • Since PYTHIA studies show that the final state studied here is dominated by gg scattering (~50%), We can interpret this as a (rather weak) constraint on the gluon orbital angular momentum. Consistent with previous (Sivers) measurements, and complimentary, since one navely needs no initial or final state interactions (although Sivers measures orbital in transversely polarized proton). 6/21/2011 39 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • We have an analysis tool di-hadron azimuthal correlations - that allows us to measure k T. We are studying this in helicity-sorted collisions to see if there is a spin-dependent, coherent component of k T. In our kinematic range, we find j T RMS = -3 8(stat) 5(syst) MeV, and k T RMS = -37 88 14(syst) MeV. While this is consistent with other measurements related to gluon OAM, the connection to parton OAM needs theoretical guidance! 6/21/2011 40 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • Drell Yan: Plans to look at intermediate mass range. Is that sufficient? 6/21/2011 41 Douglas Fields PacSPIN2011, Cairns, QLD, Australia -states J/ Drell Yan charm bottom
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  • For the non-zero DIS result, Q 2 =1GeV. 6/21/2011 42 Douglas Fields PacSPIN2011, Cairns, QLD, Australia 0.1 0.2 0.3 x Sivers Amplitude 0 HERMES Sivers Results Markus Diefenthaler DIS Workshop Mnchen, April 2007
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  • There are many direct measurements that have been/will be made at RHIC that have a connection to Partonic Orbital Angular Momentum. Theoretical work is needed to relate these measurements to OAM on a more quantitative footing. 6/21/2011 43 Douglas Fields PacSPIN2011, Cairns, QLD, Australia
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  • Blue real (raw ) Red Fit from above equation 11/11/2009 45 Douglas Fields - OAM'09
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  • 11/11/2009 46 Douglas Fields - OAM'09 asymmetry results are not sensitive to this x h and values only needed to set the scale. ^ x h and are determined through a combined analysis of the inclusive cross section and using jet fragmentation function measured in e + e - collisions. Ref. PRD 74, 072002 (2006) ^
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