1. The First Transverse Single Spin Measurement in High Energy Polarized Proton-Nucleus Collision at the PHENIX experiment at RHIC RIKEN/RBRC Itaru Nakagawa 16/03/02WWND 20161

2. Outline Introduction – Forward Neutron Detector – Forward Neutron Single Spin Asymmetry in p+p New measurements of p+A in Run15 – Inclusive Measurement – Semi-exclusive measurements to separate competing effects – Theoretical interpretation Summary 16/03/02WWND 20162 known new

3. Production Mechanism of Forward Neutron PRD88,032006 p p  n Cross Section 16/03/02WWND 20163 Cross Section Neutron Energy ／ Proton Energy Well Explained by One-Pion Exchange Momentum Transfer ~ 100MeV < 2mrad

4. Transverse Single Spin Asymmetry Proton 16/03/02WWND 20164 100GeV

5. Z ero D egree C ounter (ZDC) Neutron Detector 18m 16/03/02WWND 20165 Dipole Magnet Neutron Detector

6. 16/03/02WWND 20166

7. Transverse Single Spin Asymmetry 16/03/02WWND 20167 Published: PRD 88, 032006 (2013) ~6% Observed at PHENIX in Run6

8. Unpolarized Cross Section p ↑ p Forward Neutron A N 8 Spin flip Neutron proton Spin non-flip Neutron proton  : phase shift

9. p ↑ p Forward Neutron A N 9 Spin flip Neutron proton Spin non-flip Neutron proton ++ a1a1  : phase shift a 1 (1260) Reggeon Spin Parity = 1 +

10. Forward Neutron A N in p ↑ p PRD84,114012(2011) p p a1a1 n p ↑ Data are well reproduced by the interference between  and a 1 Reggeon 16/03/02WWND 201610 Neutron P T (GeV/c)

11. Atomic Mass Dependence of A N p A a1a1 n A/p/n ↑ Can it be explained by the existing  and  a 1 Reggeon frame work? 16/03/02WWND 201611

12. The First Time Ever High Energy Collisions 16/03/02WWND 201612 100GeV Au, Al Run15 (2015) Porarized Proton 100GeV/nucleon

13. A-Dependent A N (inclusive) 16/03/02WWND 201613 Analysis by Minjung Kim (SNU/RIKEN) No A-dependence  Stronger gluonic field  Vanishing 

14. A-Dependent A N (inclusive) 16/03/02WWND 201614 ! Absolutely Unexpected! Analysis by Minjung Kim (SNU/RIKEN)

15. What is going on  Isospin Symmetry Surface Structure of Nucleus QED Process Gluon Saturation Else… # of proton# of neutron p10 Al1314 Au79118 15

16. Electro-Magnetic Ultra Peripheral Collision (UPC) neutron t → 0 A A 16/03/02WWND 201616 Peripheral p A   ↑  n p A  n  ↑ In pAu case  

17. Full Description of A N (For pp)   : relative phase of amplitudes

18. 16/03/02WWND 201618

19. Neutral Particle @ 200GeV UPC Monte Carlo 19 ZDC Predicts comparable yields between QCD and UPC processes QCD(DPMJET) UPC (SOPHIA)

20. PHENIX Detector 16/03/02WWND 201620

21. Beam-Beam Counter 16/03/02WWND 201621 PHENIX Detector Quartz Cherenkov radiator ZDC Dipole Bending Magnet BBC

22. Can we identify UPC events? 22 BBC    ZDC Dipole n  + Most of decayed pions go through BBC hole and will be swept away by the dipole magnet (DX). Very little coincidence measurements of final state from resonance. BBC  + Rapidity   distribution of n+  + events UPC (SOPHIA)

23. BBC Tagging and Vetoing 23 Inclusive

24. BBC Tagging and Vetoing 24 BBC Tagging Large A N vanished in p+Au No sign flip in A N A N for p+p and p+Al are comparable EM surpressed

25. BBC Tagging and Vetoing 25 BBC Vetoing Even larger A N ~ 0.28 in p+Au Sign flip occurs between p+p and p+Al A N for p+p gets even smaller ~ 0.02 EM enhanced

26. BBC Tagging and Vetoing 26 BBC Vetoing p A  ↑  n BBC Tagging p A  ↑ n BBC

27. Coulomb-Nuclear Interference  p A n  A t → 0 p A    A  P n Same Final State Diffractive Process Required?

28. Non-Diffractive Events  p A n  X t → 0 p A    X  P n Little chance to be same final state Suppressed 

29. Diffractiveness Dependence 16/03/02WWND 201629 p A  ↑ n n p A  ↑ A-going veto p-going veto n p A  ↑ Both BBC veto BBC p A  ↑ n Both BBC Fired BBC Only doubly diffractive diagram causes large positive A N. Likely indication of CNI

30. Asymmetry Induced by  30 p e    EM e' Transversely polarized fixed proton target Polarized Delta Asymmetric neutron decay from polarized  So far, I haven’t heard such an experiment in electron facilities  Pseudo-vector n

31. Summary The first attempt to explore asymmetries in high energy p+A colliding experiment. Absolutely unexpected strong A-dependence was observed. Diffractive EM and hadronic interference drives large positive A N in large A. Hadronic Interaction likely to keeps negative A N between p+p and p+A. Further measurements in different are necessary to disentangle. 16/03/02WWND 201631

32. BACKUP 16/03/02WWND 201632

33. Surface Effect of Nucleus 33 neutron # of proton# of neutron p10 Al1314 Au79118 Neutron skin protons

34. PHENIX New Forward Neutron A N Results ! 34 Analysis by Minjung Kim (SNU/RIKEN) 16/03/02WWND 2016

35. 35

36. A N at Coulomb Nuclear Interference (CNI) Region Pomeron Pomerion/Reggeon Exchange zero hadronic spin-flip With hadronic spin-flip (E950) Phys.Rev.Lett.,89,052302(2002) pC Analyzing Power E beam = 21.7GeV ( High energy & small t limit ) E beam = 100 GeV unpublished 36

37. Diffractiveness Dependence 16/03/02WWND 201637 n p A  ↑ A-going veto BBC p A  ↑  n EM contribution should be small Hadronic amplitude still flip the sign  Statistically significant!

38. EM Contribution 16/03/02WWND 201638 p A  ↑ n p-going veto n p A  ↑ Both BBC veto BBC Isn’t this easier to interfere with hadronic interaction? Better check A- going behavior of A- going in MC