Transversity – status and what we need in EIC

1. Transversity – status and what we need in EIC EIC Workshop, Hampton, VA May 21 Ralf Seidl (RBRC) R.Seidl: Transversity measurements at EIC

2. Outline • Transversity • Chiral-odd PDF • SIDIS results • Belle results • global analysis • First global analysis • Comparison to Lattice predictions  Evolution of Collins FF(?) • What will be important after these first measurements • Higher scales • kt-Moments , • lower x to get to tensor charge • other measurements (IFF, L) R.Seidl: Transversity measurements at EIC

3. Transversity • In helicity basis: helicity distribution and momentum difference and sum of diagonal amplitudes • Transversity contains helicity flip and is not diagonal • Helicity is conserved quantity for (nearly) massless quarks • All interactions conserve helicity/chirality  Transversity cannot be observed in DIS R.Seidl: Transversity measurements at EIC

4. Transversity and friends Unpol. DF Helicity Transversity q(x) Dq(x) dq(x) Sivers function Boer-Mulders function R.Seidl: Transversity measurements at EIC

5. Transversity properties • Does not couple to gluons adifferent QCD evolution than Dq(x) • Valence dominateda Comparable to Lattice calculations, especially tensor charge: • Test relativistic nature of quarks in the nucleon Positivity bound: Soffer bound: R.Seidl: Transversity measurements at EIC

6. How to access Transversity another chiral-odd function Drell Yan: • Combine two Transversity distributions with each other SIDIS: • Combine Transversity distributions with chiral-odd fragmentation function (FF) • Total process is chiral-even: OK • Possible Partners: • Collins FF • Interference FF • Transverse L FF • Most require single spin asymmetries in the fragmentation R.Seidl: Transversity measurements at EIC

7. First successful attempt at a global analysis for the transverse SIDIS and the BELLE Collins data Tensor charges obtained from this fit (from Alexei Prokudin) at Q2= 2.4 GeV2: • HERMES AUTp data • COMPASS AUT d data • Belle e+ e- Collins data • Kretzer FF  First extraction of transversity (up to a sign) Anselmino et al: hep-ex 0701006 R.Seidl: Transversity measurements at EIC

8. Current problems in the global transversity analysis • Universaliy? Is the Collins function from e+e- the same in SIDIS, how about pp? • According to Bacchetta et al. and Gamberg et al, yes • Evolution? • Is the evolution of transversity understood? Yes • Is the evolution of the Collins function understood? Not really – is this the reason for low transversity in the global fit so far? • Error treatment, first suggestions to start a CTEQ-like transversity global analysis group with contributors from Theory (Torino), COMPASS(Trieste),HERMES(Ferrara), Belle(Illinois, RBRC) R.Seidl: Transversity measurements at EIC

9. Collins measurements II K+ asymmetries compatible withp+ asymmetries (through u quark dominance) K- asymmetries maybe slightly positive R.Seidl: Transversity measurements at EIC

10. In DY: TT Coming additions to global analysis arXiv:0802.2160 COMPASS full d data set, Charged p, K and KS R.Seidl: Transversity measurements at EIC

11. Further additions Belle 547 fb-1 data set (submitted to PRD arXiv:0805.2975) R.Seidl: Transversity measurements at EIC

12. R.Seidl: Transversity measurements at EIC

13. R.Seidl: Transversity measurements at EIC

14. New data to come • HERMES K data not yet used in fits • COMPASS K data not yet used • JLAB 6 and 12 GeV • Low energies and multiplicities • Higher twist an issue? • Very important Test: COMPASS proton data- • Will it be consistent in the overlap with HERMES? • Will they be different R.Seidl: Transversity measurements at EIC

15. DY transversity measurements at RHIC, JPARC and FAIR RHIC @ √s=200GeV Q=15GeV • DY transverse double spin asymmetries golden channel to Transversity: • Requires both (anti)- protons transversely polarized • For mostly sensitive to u-quark transversity • For pp smaller asymmetries due to sea transversity , but for tensor charge absolutely necessary Q= 8GeV Q= 5GeV Q= 3GeV JPARC @ √s=10GeV Kawamura et. al Nucl.Phys.B777:203-225,2007. Assuming Soffer bound R.Seidl: Transversity measurements at EIC

16. Transversity access over DY in single spin asymmetries Transversity over pp DY in double spin asymmetries GSI (collider option) @ √s=15GeV Q=6GeV • Instead of double spin asymmetries measure single spin asymmetries • Advantage: only one proton polarized  better FOM at RHIC, earlier feasible at JPARC and GSI • Disadvantage: first have to measure Boer-Mulders function with good precision • Also planned at COMPASS with pion beam Q=4GeV Q=3GeV Q=2GeV Kawamura et. al Nucl.Phys.B777:203-225,2007. Theory for ATT fairly well understood even at very low scales, if there will be PAX, it will measure mostly du2 – until then already relatively well known only consistency test R.Seidl: Transversity measurements at EIC

17. What is needed at EIC? • Larger x range measured b y existing experiments COMPASS ends at ~ 0.01, go lower by almost one order of magnitude, but asymmetries become small • Have some overlap at intermediate x to test evolution of Collins function and higher twist but at higher Q2 R.Seidl: Transversity measurements at EIC

18. What is needed at EIC II • Detect SIDIS hadrons at z range 0.1 – 0.9 • Have to be able to reject exclusive VMs  nearly hermetic detector, reasonable momentum resolution • Good e/h separation needed everywhere, good hadron PID needed in hadron acceptance • So far: No Ph moments measured yet, why? • Acceptance effects are very difficult to correct • Make sure we have very good and uniform Ph coverage , say cone of Ph < 3 GeV • Need generator capable to produce kT dependent asymmetries  Generalize gmc_trans R.Seidl: Transversity measurements at EIC

19. Other channels: IFF HERMES,COMPASS, pp, BELLE • COMPASS: zero on deuteron target proton date will be interesting • Possibility to measure IFF also at RHIC R.Seidl: Transversity measurements at EIC

20. Other channels II: L polarization • Measurements available from COMPASS on deuteron target, • Plan to measure it at Belle • IFF and L polarimetry can also be probed with great precision at EIC R.Seidl: Transversity measurements at EIC

21. Summary • Transversity: • First global analysis available, errors still huge, • evolution of Collins function? • Newer data not yet included in global analysis from HERMES (K), COMPASS (K, proton data), JLAB • Large Belle Collins data now final • New accesses over IFF, L polarimetry soon • EIC needs to cover intermediate x range, z>0.2, Ph < 3 GeV , good e/h separation and PID R.Seidl: Transversity measurements at EIC

22. Backup slides R.Seidl: Transversity measurements at EIC

23. Quark distributions in spin bases q(x),G(x) Sum of quarks with parallel and antiparallel polarization relative to proton spin (well known from Collider DIS experiments) Unpolarized distribution function q(x) Difference of quarks with parallel and antiparallel polarization relative to longitudinally polarized proton (known from fixed target (SI)DIS experiments) Dq(x), DG(x) Helicity distribution function Dq(x) Difference of quarks with parallel and antiparallel polarization relative to transversely polarized proton (first results from HERMES and COMPASS – with the help of Belle) dq(x) Transversity distribution function dq(x) R.Seidl: Transversity measurements at EIC