1. Theoretical Interpretation of Forward Neutron AN
RIKEN/RBRC
Itaru Nakagawa

2. Pion Cloud Model

3. Proton Spin +1/2

4. Proton Spin +1/2

5. Proton Spin +1/2
P-wave

6. Proton Spin +1/2

7. Proton Spin +1/2

8. Proton Spin +1/2

9. Proton Spin +1/2
P-wave
P-wave

10. Proton Spin +1/2 d

11. p↑p Forward Neutron AN
Spin flip
Spin non-flip
Neutron
Neutron

12. p↑p Forward Neutron AN p+ a1 a1 Reggeon Spin Parity = 1+ Spin flip
Spin non-flip
Neutron
Neutron p+ a1 n
a1 Reggeon
Spin Parity = 1+ d +
n + p+ component of proton GS contributes

13. p↑p Forward Neutron AN p+ a1 Spin flip Spin non-flip
OPE : One Pion Exchange

14. p↑p Forward Neutron AN n p p+,a1
PRD84,114012(2011) p
p+,a1 n ↑
Well explained by the interference between p and a1 Reggion

15. Does the existing framework works for p↑A Forward Neutron AN?
A/p/n ↑
p+p Single Spin Asymmetry AN
Atomic Mass Number
PRD 84, (2011)
Search for the Totally Unexplored Dimension!!

16. pp Summary Forward neutron production is well described by OPE
The interference between p and a1 gives decent asymmetry

17. Atomic Mass Dependence

18. Atomic Mass Number Dependence
# of proton
# of neutron p 1 Al 13 14 Au 79
118
Isospin Symmetry
Surface Structure of Nucleus
QED Process
Gluon Saturation
else

19. Surface Effect of Nucleus
# of proton
# of neutron p 1 Al 13 14 Au 79
118
neutron
Neutron skin
protons

20. QED Process Ultra Peripheral Collision (UPC)
neutron A A
In Au case
t　→ 0 Z2 p p+ n p A n p+ D
aEM

21. UPC

25. Forward Neutron Angular Distributions
LHCf
PHENIX ZDC
The ZDC acceptance doesn’t reach QCD dominant region.
Dx ~ a few mm
Dx ~ 1cm

26. UPC : SOPHIA
QCD : DPMJET

27. Rapidity Distributions by MC
UPC Process
QCD Process
Minjung’s
6.8 < ZDC acceptance < 8.2
Neutral particle yields are in the similar order between QCD and UPC

28. UPC Neutron Raw Spectrum
ZDC
Energy profile is biased towards higher energy side than QCD one as Boris predicted.
Rapidity distribution looks skinner than Gaku’s draft.

29. UPC Final States for forward neutron in ZDC
Dominated by two body decay
Dominated by neutron + p+ system

30. UPC p+ (b>0.7) kinematics
Very little make it to BBC acceptance.
Most of pions will escaped through BBC hole.
BBC
psudo rapidity

31. Can we identify UPC events?
Dipole p +
h = 3.9
h = 3.1
ZDC D
BBC n
hp distribution of n+p+ events
Most of decayed pions go through BBC hole and will be swept away by the dipole magnet (DX).
BBC
p+ Rapidity
Very little coincidence measurements of final state from resonance.
Simulation by Gaku Mitsuka

32. UPC Summary
LHCf claims there is distinctively large forward neutron production near zero degree in p-Pb
Neutrons are mostly decayed from D excitation of forward going proton
About ½ of photon yields of LHCf is expected in RHIC p-Au.
Majority of decayed counterpart p flies through BBC beam hole (undetected)

33. CNI

34. RHIC CNI Polarimeter Elastic polarized proton-Carbon/proton scattering
(Undetected)
Carbon target
90º in Lab frame
Polarized proton
Recoil carbon
(Detected)
Elastic polarized proton-Carbon/proton scattering

35. Analyzing Power AN for polarimeter
zero hadronic
spin-flip
With hadronic
spin-flip (E950)
Phys.Rev.Lett.,89,052302(2002)
pC Analyzing Power
t->0
Pomeron
QED: Calculable

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

37. Run15 HJet results ZDC t range runs further out t~0.02 - 0.5 (GeV/c) 2
peaked at ~0.07 (GeV/c) 2.
Run15 HJet results
Slide from Oleg Eyser (The 2015 PSTP workshop)

38. Underlying Mechanism Comparison
Forward n
Polarimeter
p,A
p,A
p,A
p+,a1, ..
Pomeron p p n p
DI =1
DI = 0
Inelastic
Elastic
√s = 200 GeV
√s = 14 GeV

39. Coulomb-Nuclear Interferencep+ p+
t　→ 0 p+ Z2 A
elastic A p A n p+ D A p+ p n
Pion cloud
Same Final State

40. AN at Coulomb Nuclear Interference (CNI) Region
Pomeron
Elastic pp/pA
(High energy & small t limit)
f emflip
f hadnon-flip
f emnon-flip
f hadflip
Elastic
Pomeron
neutron
+D ? a1
+ D ? p+

41. Coulomb-Nuclear Interfarencep+ p+
t　→ 0 p+ Z2 A
elastic A p A n p+ D A
aEM p+ p n
Pion cloud
Same Final State

42. Full Description d : relative phase of amplitudes
Elastic (polarimeter)
For pp:

43. Full Description d : relative phase of amplitudes
Elastic (polarimeter)
For pp:

44. Coulomb-Nuclear干渉(CNI)p+ p+
t　→ 0
More terms to be considered. Possibly leads to large asymmetry. Each EM amplitude would be proportional to Z.

45. CNI Summary
The interference between QED process and strong force could open up possibility to larger asymmetry
Similar behavior between CNI polarimeters may indicates the interference, but yet conclusive.

46. Trigger Dependent AN
As soon as BBC is required, the A-Dependence becomes moderate.

47. Can we identify UPC events?
Dipole p +
h = 3.9
h = 3.1
ZDC D
BBC n
BBC requires this minor pion to be detected
hp distribution of n+p+ events
BBC
UPC (QED) contribution becomes small
p+ Rapidity
where

48. ZDCxBBC AN and STAR pi0

49. ZDC x BBC AN ZDC BBC The most simple final state will be n+p+
Dipole
h = 3.9
h = 3.1
ZDC p n
BBC n p +
The most simple final state will be n+p+
BBCxZDC is the subset of BBC inclusive event.
It is possible to have finite AN by only detecting p+ in BBC. If inclusive BBC is dominated by n+p+, then BBC AN will be similar to BBCxZDC
BBC
ZDC

50. Forward p0 AN
Another iso-spin alternative final state p+p0 can be described in similar framework (assumption).
MPC pi0 are similar rapidity with BBC.
AN gets larger at higher xF, but may be ~0.05 if statistically averaged becomes similar to BBCxZDC AN

51. Diffractive process in pion cloud model
The proton ground state can be described as a super position of n+p+ and p+p0 states. I forgot relative strength between two states though.
BBC p+
EMCal p0 p X p X p+ p0 p n p p
Roman Pot
ZDC
Pion cloud
Pion cloud
Not sure if pi0 interfare with a1 reggion. May be different reggion.

52. STAR AN BEMC EEMC FMS η = 2.6-4.2 η = 1.09,2.0 η = -1.0,1.0
central EMJets
forward EMJets
Midrapidity EM Jets
Jet algorithm : anti-kT, R = 0.7
pTEM-Jet > 2.0 GeV/c, -1.0<ηEM-Jet<2.0
Inputs for central EMJets : towers from BEMC and EEMC
Leading central EM-Jets : Jet with highest pT
Case-I : having no central jet
Case-II : having a central jet
DIS 2014, Warsaw, Apr. 28-May 2, 2014

53. Similar to BBC acceptance 3.1<eta<3.9
AN vs. EM-Jet Energy
Similar to BBC acceptance 3.1<eta<3.9
π0-Jets –
2γ-EM-Jets with
mγγ <0.3
Zγγ <0.8
EM-Jets –
with no. photons >2
Isolated π0’s have large asymmetries consistent with previous observation (CIPANP Steven Heppelmann)
Asymmetries for jettier events are much smaller
DIS 2014, Warsaw, Apr. 28-May 2, 2014

54. AN for different # photons in EM-Jets
1-photon events, which include a large π0 contribution in this analysis, are similar to 2-photon events
Three-photon jet-like events have a clear non-zero asymmetry, but substantially smaller than that for isolated π0’s
AN decreases as the event complexity increases (i.e., the "jettiness”
AN for #photons >5 is similar to that for #photons = 5
Jettier events
DIS 2014, Warsaw, Apr. 28-May 2, 2014

55. STAR’s Run15 Attempt
Trying to tag diffractive pi0 by taking coincidence with forward proton which stayed intact through collision.

56. Something similar to STAR Study
See AN dependence on BBC charge as Sasha suggested
This more like seeing “diffractiveness”. Smaller the BBC charge, the charged particle is isolated-> diffractive process.
If this attempt is really similar to what STAR did, then the asymmetry will get smaller as BBC charge gets larger at least in pp. AN
BBC charge

57. Run16 No pp No plan to run H-Jet due to lack of man power
Need to estimate if 1.5 week is sufficient to accumulate statistics

58. backup