1 Future of Transverse Spin at RSC Meeting, Ames, Iowa, May 15th Anselm Vossen

2 What contributes most of the visible mass in the universe? –Not Higgs: The QCD interaction! SPIN is fundamental quantity: What role does it play in strong interactions?  Interesting transverse spin effects help us understand QCD  Transverse Spin allows to probe Matrix elements via Interference  RHIC is the only place with polarized proton collisions in the foreseeable future  Test Factorization  Explore role of soft interactions  How and why is pp->hadrons different from SIDIS & DY Motivation for Transverse Spin Physics

3 Still not understood… Several orders of magnitude in sqrt(s) Several theoretical frameworks… Effects strong in forward direction Valence quark effect in parton picture A N (%)

4 HCAL EM CAL Preshower Next decadal Plan: Full Forward Spectrometer Coverage in 2 <  < 4 (2 o <  < 30 o ) Needs Open Geometry replace current central detector with a new one covering |  | =< 1 replace South muon arm by a endcap spectrometer able to do all the physics on the next slides 60cm 2T Solenoid EMCAL HCAL Silicon Tracker VTX + 1 layer Silicon Tracker FVTX 1.2 <  < o <  < 37 o North Muon Arm 68cm IP 80cm 145cm

5 Subsystems Charged Particle Tracking RICH allows PID up to high momenta: Flavor decomposition EM Cal: Neutral particles HCAL: Hadrons and jet reconstruction Dedicated Magnet? Jets! EM CAL HCAL Tracking

6 Mechanisms for A N (An Outline) Spin dependent quark distributions –TMD picture: Sivers –Collinear Picture: Twist3 pdfs →Tests of Factorization Spin dependent Fragmentation –Collins Effect –Interference Fragmentation Function Flavor separation for all of the above More forward physics –Charm A N –Lambda –… M. Boglione at DIS09

7 Collinear, Unpolarized Factorization is valid in the forward region

8 Spin Dependent Quark Distributions Twist 3 –One hard scale (p t ) Sivers TMD + soft gluon interaction One hard, one soft scale TMD factorization not proven for pp->hX (counterexample) DY should work twist-3 PRD 74, STST P xPxP

9 Shape like Hermes Sivers measurement In SIDIS turnover seems to be at around 1 GeV in p T Scale Dependence PheniX A N in MPC: Turnaround At p T ~ 3GeV??

10 Sivers in Different Configurations Open Questions –Factorization: Does it break, how much? –How does PP compare to DY and DIS (Kinematics similar) DIS: attractive Drell-Yan: repulsiveProton-Proton ? (Werner Vogelsang)

11 Flavor Decomposition can answer differences between pp and SIDIS Role of Strange Quarks Additional interesting Channels –Vector Mesons

12 Sivers Channels Crucial: Jet Measurements to get initial parton kinematics Back To Back Jets Photon-Jet Possible Correlations –Forward – Forward –Forward – Central –Forward – Backward (isolated photons in MPC)

13 Kinematic Coverage of New Arm Min Energy of 20GeV (inclusive pions) One jet forward, EJet>20GeV, One jet in central arm xFxF PTPT xFxF PTPT Q2Q2 pTpT Q2Q2 pTpT Pythia, Tune100, sqrt(s)=200GeV, only hard processes, all units in GeV

14 Compass observed possible W dependence One mechanism to explain Discrepancy to HERMES More Input required W in DIS: Mass of hadronic system pp equivalent:

15 Kinematics Q2Q2 Q2Q2 x Bj COMPASS HERMES Jets Inclusive Pions

16 W is not large Jet energy > 20GeV W can be reconstructed in di-jet events->Test of COMPASS observation  xFxF Jets Inclusive pions  W W W W xFxF xFxF

17 Shape of Expected Sivers Asymmetries Gauss around 0.3, width 0.4, Amp. 0.3 Not taking into account the partial cancellation between u and d  A Siv PTPT

18 With FVTX: Measure F, D type Sivers and Tri-Gluon Functions model trigluon correlation functions using ordinary unpolarized gluon distribution function : A rough estimate PRD 78, quark-gluon negligible T (f) = T (d) = 0 T (f) = T (d) T (f) = -T (d) trigluon Charm A N with FVTX: Vast improvement

19 Spin Dependent Fragmentation Needs one reconstructed jet Coupling to transversity Collins effect (also Twist3 analogues) Interference Fragmentation Function

20 Chiral odd FFs + _ + _   + _ Collins effect q N : Collins FF

21 The Collins effect in the Artru fragmentation model π + picks up L=1 to compensate for the pair S=1 and is emitted to the right. String breaks and a dd-pair with spin -1 is inserted. A simple model to illustrate that spin-orbital angular momentum coupling can lead to left right asymmetries in spin-dependent fragmentation: In Artru Model: favored (ie u    ) and disfavored (ie u    ) Collins function naturally of opposite sign Jet direction

22 Observables: Azimuthal Asymmetries of Hadrons around Jet Axis  pTpT Tests Transversity at high x, high z –High x: Tensor Charge  Connection to Lattice Again: what does u, d quark sign difference mean for us? A Col ptpt z Mean z: 0.64 PTPT

23 Chiral odd FFs + _ + _   + q N _ L z -1LzLz Interference Fragmentation Function

24 Advantages of IFF Independent Measurement Favorable in pp: no Sivers Transverse momentum is integrated – Collinear factorization – No assumption about k t in evolution – Universal function – Evolution known, collinear scheme can be used – Directly applicable to semi-inclusive DIS and pp First experimental results from HERMES, COMPASS, PHENIX

25 IFF as Measured by BELLE Charm contributions unaccounted RHIC could shed light on flavor composition etc… M Inv Invariant mass in new Arm

26 Combined Analysis: Extract Transversity Distributions Transversity, δq(x) Tensor Charge Lattice QCD: Tensor Charge Factorization + Universality ?! Theory SIDIS ~ δq(x) x CFF(z) ~ δq(x) x IFF(z) e + e - ~ CFF(z 1 ) x CFF(z 2 ) ~ IFF(z 1 ) x IFF(z 2 ) pp  jets ~ G(x 1 ) x δq(x 2 ) x CFF(z) pp  h + + h - + X ~ G(x 1 ) x δq(x 2 ) x IFF(z) pp  l + + l - + X ~ δq(x 1 ) x δq(x 2 )

27 A N for He 3 Predictions by Umberto D’Alesio, with DSS FF Sign Flip due to isospin Measurement would test Universality, moderate & high x for u, d quarks

28 First Measurement of Forward Lambda’s Lambda Kinematics with , proton in Forward Arm ptpt xfxf ptpt 

29 Summary: What we will learn from Proton Proton Transverse Spin essential! Test QCD Measure Sivers, Collins & IFF –Asymmetries expected to be large in forward direction –Cancellation between different flavors still unclear Asymmetries should be smaller than SIDIS, but A N large Color charges in initial and final states –Factorization –TMD, Collinear –Attractive, repulsive forces (color ‘anti-color’) Transversity at high X (should be faster than JLab..) Lambdas Local Parity Violation, other TMDs… RHIC is the only place… for a long time!! ….and finally we will understand A n and can lay it to its well deserved rest..

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31 Backup

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33 DCA R Shape μ decay from D, B and hadrons have different DCA R shapes in a given μ p T bin. DCA R shape also depends on the parent particle and the decay μ p T. Distributions are normalized according to PHENIX cross sections. Single particle shapes can be evaluated using MC. They can be fitted together to the merged event shape, to get B, D and BG contributions.

34 c and b Separation -- Results Limitations: Same p T spectra for B and D and same background sample are used in training sample and mixed sample. Systematic error need to be quantified. With 10 pb -1 statistics With achieved statistics

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37 DCA R DCA R = impact parameter projected onto μ p T.

38 Collins Fragmentation at Belle First extraction of transversity quark distribution Together with HERMES, COMPASS First, still model dependent transversity Extraction : Alexei Prokudin, DIS2008, update of Anselmino et al: hep-ex Belle 547 fb -1 data set (Phys.Rev.D78:032011,2008.)

39 vs Invariant Mass of the Pair First measurement of IFF in pp beijing

40 Comparison to theory predictions Leading order, experimental results might contain effects from gluon radiation not contained in the model Mass dependence : Magnitude at low masses comparable, high masses significantly larger (some contribution possibly from charm ) Z dependence : Rising behavior steeper However: Theory contains parameters based on HERMES data. Initial model description by Bacchetta,Checcopieri, Mukherjee, Radici : Phys.Rev.D79:034029,2009.

41 Subprocess contributions (MC) 41 8x8 m 1 m 2 binning charged B(<5%, mostly at higher mass) Neutral B (<2%) charm( 20-60%, mostly at highest masses) uds (main contribution) Charm Asymmetries in simulated data consistent with zero! To be checked with charm enhanced sample Data not corrected for Charm contributions

42 Simulations: ~ 10(nb)-1

43 Other Lambda Local P viol

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45 vs invariant mass of the pair Added statistics from 2008 running NEW No significant asymmetries seen at mid-rapidity.

46 Di-Hadron SSA in SIDIS (both on proton target, sign convention different)

47 Motivation: Transversity Quark Distributions δq(x) from Transverse Single Spin Asymmetries in Semi Inclusive Deep Inelastic Scattering Collins- and IFF- asymmetries in semi-inclusive deep inelastic scattering (SIDIS) and pp measure ~ δq(x) x CFF(z)  combined analysis with CFF from e + e - annihilation Example: COMPASS results for Collins Asymmetries on proton target (see talk by H. Wollny)

48 Definition of Vectors and Angles Bacchetta and Radici, PRD70, (2004)

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55 What plots? X1, x2 Eta, x1 (or greater x1) eta, pt X1, pt Collins, eta & (tagged) (eta, pt??)

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57 Outline Jets sivers, photons, Wernder, daniel back to back sivers (quark sivers sehr grosse x) Transversity > x ->Tensor charge Collins in jets DY Lambda ip2

58 PRD 74, (2006) twist-3

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60 Collins Fragmentation at Belle First extraction of transversity quark distribution Together with HERMES, COMPASS First, still model dependent transversity Extraction : Alexei Prokudin, DIS2008, update of Anselmino et al: hep-ex Belle 547 fb -1 data set (Phys.Rev.D78:032011,2008.)

61 Collins Extraction of Transversity: model dependence from Transverse Momentum Dependences! Anselmino, Boglione, D’Alesio, Kotzinian, Murgia, Prokudin, Turk Phys. Rev. D75:05032,2007 k ┴ transverse quark momentum in nucleon p ┴ transverse hadron momentum in fragmentation transversity Collins FF hadron FF quark pdf The transverse momentum dependencies are unknown and difficult to obtain experimentally!

62 Transversity Quark Distribution Why is this so difficult to measure? –

63 Handbag Diagrams γ*γ*γ*γ* u,d, s e-e-e-e- Optical Theorem:  =-I m( A forward scattering ) + ++   +

64 Transversity is Chiral Odd _ + _   + ↑ ↑↑   ↑ ↓ ↑↑   ↓  _ Helicity base: chiral odd Need chiral odd partner => Fragmentation function Difference in densities for ↑, ↓ quarks in ↑ nucleon Transversity base:

65 QED and QCD interactions (and SM weak interactions) conserve helicity: Cannot measure h 1 inclusively _ + _   + QED, QCD Preserve Helicity Helicity base: chiral odd Need chiral odd partner => Fragmentation function

66 Chiral odd FFs + _ + _   + _ Collins effect q N : Collins FF

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68 Kinematics Put pics at 200 and 500 Gev here…  

69 XfXf W W ptpt

70   xFxF W W 

71 in P T & Q 2 Min Energy of 20GeV (incl. pions)  Q2Q2 pTpT

72 Jet Kinematics One jet forward, E Jet >20GeV, One jet in central arm  pTpT