Theoretical Interpretation of Forward Neutron AN RIKENRBRC Itaru
Theoretical Interpretation of Forward Neutron AN RIKEN/RBRC Itaru Nakagawa 1
PP AN 2
p↑p Forward Neutron AN Spin flip Spin non-flip Neutron 3
p↑p Forward Neutron AN Spin flip Spin non-flip Neutron p+ a 1 n + p+ component of proton GS contributes d a 1 Reggeon Spin Parity = 1+ 4
p↑p Forward Neutron AN PRD 84, 114012(2011) p ↑ p p p+, a 1 n Well explained by the interference between p and a 1 Reggion 5
p+ p S ing le Sp in A sym me tr y A N ATOMIC MASS DEPENDENCE Atomic Ma ss Numbe PRD 84, 114012 (2011) r 6
Atomic Mass Number Dependence p Al Au # of proton # of neutron 1 13 79 0 14 118 • Isospin Symmetry • Surface Structure of Nucleus • QED Process • Gluon Saturation • else 7
Surface Effect of Nucleus neutron p Al Au # of proton # of neutron 1 13 79 0 14 118 Neutron skin protons 8
QED Process Ultra Peripheral Collision (UPC) neutron A A In p. Au case t → 0 p ↑ p p A p+ n p a. EM Z 2 g* ↑ D p+ n 9
Ultra Peripheral Collision UPC 10
11
12
Forward Neutron Angular Distributions PHENIX ZDC LHCf Dx ~ a few mm Dx ~ 1 cm The ZDC acceptance doesn’t reach QCD dominant region. 13
UPC : SOPHIA QCD : DPMJET 14
Rapidity Distributions by MC UPC Process QCD Process Minjung’s cut@ZDC 6. 8 < ZDC acceptance < 8. 2 Neutral particle yields are in the similar order between QCD and UPC 15
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.
UPC p+ (b>0. 7) kinematics p+ n BBC • Most of UPC events decay into two bodies (n+p+ from D) • Very little make it to BBC acceptance. • Most of pions will escaped through BBC hole. psudo rapidity
Can we identify UPC events? . 9 D h=3 Dipole h = 3. 1 BBC 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. p+ n ZDC hp distribution of n+p+ events BBC p+ Rapidity Simulation by Gaku Mitsuka 18
Asymmetry Induced by D e e' a. EM p Transversely polarized fixed proton target g* D Polarized Delta p+ n Asymmetric neutron decay from polarized D So far, I haven’t heard such an experiment in electron facilities 19
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). • Don’t aware of experimental evidence of large A_N induced by UPC alone. 20
Full Description d : relative phase of amplitudes Elastic (polarimeter) For pp:
Full Description d : relative phase of amplitudes Elastic (polarimeter) For pp:
Coulomb-Nuclear Interference(CNI) p+ p+ t → 0 More terms to be considered. Possibly leads to large asymmetry. Each EM amplitude would be proportional to Z. 23
CNI 24
RHIC CNI Polarimeter (Undetected) Carbon target 90º in Lab frame Polarized proton Recoil carbon (Detected) Elastic polarized proton-Carbon/proton scattering 25
Analyzing Power AN for polarimeter p. C Analyzing Power zero hadronic spin-flip With hadronic spin-flip (E 950) t->0 Phys. Rev. Lett. , 89, 052302(2002) Pomeron QED: Calculable 26
AN at Coulomb Nuclear Interference (CNI) Region Pomeron (High energy & small t limit) Pomerion/Reggeon Exchange p. C Analyzing Power zero hadronic spin-flip With hadronic spin-flip (E 950) Phys. Rev. Lett. , 89, 052302(2002) Ebeam = 21. 7 Ge. V unpublished Ebeam = 100 Ge. V 27
ZDC t range runs further out t~0. 02 - 0. 5 (Ge. V/c) 2 peaked at ~0. 07 (Ge. V/c) 2. Slide from Oleg Eyser (The 2015 PSTP workshop) Run 15 HJet results
29
Underlying Mechanism Comparison Forward n Polarimeter p, A p+, a 1, . . n Pomeron p p DI =1 DI = 0 Inelastic Elastic √s = 200 Ge. V √s = 14 Ge. V 30
Coulomb-Nuclear Interference (0) p+ p+ A p elastic p+ t → 0 p+ A n A Z 2 p Pion cloud Same Final State g* D A p+ n
Coulomb-Nuclear Interference (1) p+ p+ t → 0 Huge rapidity interval, not the case for UPC? A P p A A Z 2 p+ n p Pion cloud Same Final State g* D A p+ n
Coulomb-Nuclear Interference (2) p+ p+ t → 0 Huge rapidity interval, not the case for UPC? A p P A A p+ n p Not same intermediate State Z 2 g* D A p+ n
Coulomb-Nuclear Interference (3) p+ p+ t → 0 A p p 0 D A p+ n A Z 2 p Same Final State g* D A p+ n
AN at Coulomb Nuclear Interference (CNI) Region Pomeron (High energy & small t limit) f emflip f hadnon-flip f emnon-flip Elastic neutron Elastic pp/p. A f hadflip Pomeron a 1 p+ 35
Coulomb-Nuclear Interfarence p+ p+ A p elastic p+ t → 0 p+ A n A Z 2 a. EM p Pion cloud Same Final State A p+ D n 36
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. 37
Trigger Dependent AN As soon as BBC is required, the A-Dependence becomes moderate. 38
Can we identify UPC events? . 9 D h=3 Dipole h = 3. 1 BBC Counterpart pions barely landed in BBC acceptance p+ n ZDC hp distribution of n+p+ events BBC MC: SOPHIA UPC (QED) contribution is suppressed in ZDCx. BBC trigger where p+ Rapidity 39
Trigger Dependence Summary • ZDCx. BBC suppresses UPC contribution • Contribution from EM term becomes small. • AN is dominated by interference between strong force • The difference in AN between ZDC and ZDCx. BBC should be rather substational in large A (Z) nuclei. 40
ZDCx. BBC AN and STAR pi 0
ZDC x BBC AN. 9 p n h=3 Dipole h = 3. 1 p+ BBC n ZDC • The most simple final state will be n+p+ • BBCx. ZDC 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 BBCx. ZDC BBC ZDC
Forward p 0 AN • Another iso-spin alternative final state p+p 0 can be described in similar framework (assumption). • MPC pi 0 are similar rapidity with BBC. • AN gets larger at higher x. F, but may be ~0. 05 if statistically averaged becomes similar to BBCx. ZDC AN
Diffractive process in pion cloud model The proton ground state can be described as a super position of n+p+ and p+p 0 states. I forgot relative strength between two states though. p+ p p BBC X p+ Pion cloud n p 0 p ZDC p EMCal X p 0 p Pion cloud Not sure if pi 0 interfare with a 1 reggion. May be different reggion. Roman Pot
STAR AN BEMC EEMC FMS η = 2. 6 -4. 2 η = -1. 0, 1. 0 η = 1. 09, 2. 0 central EMJets forward EMJets Midrapidity EM Jets Jet algorithm : anti-k. T, R = 0. 7 p. TEM-Jet > 2. 0 Ge. V/c, -1. 0<ηEM-Jet<2. 0 Inputs for central EMJets : towers from BEMC and EEMC Leading central EM-Jets : Jet with highest p. T • • Case-I : having no central jet Case-II : having a central jet DIS 2014, Warsaw, Apr. 28 -May 2, 2014 45
AN vs. EM-Jet Energy C B B o t ar Simil ptance acce <3. 9 ta 3. 1<e π0 -Jets – 2γ-EM-Jets with mγγ <0. 3 Zγγ <0. 8 EM-Jets – with no. photons >2 ² Isolated π0’s have large asymmetries consistent with previous observation (CIPANP-2012 Steven Heppelmann) https: //indico. triumf. ca/contribution. Display. pycontrib. Id=349&session. Id=44&conf. Id=1383 ² Asymmetries for jettier events are much smaller DIS 2014, Warsaw, Apr. 28 -May 2, 2014 46
AN for different # photons in EM-Jets ² 1 -photon events, which include a large π0 contribution in this analysis, are similar to 2 photon events ² Three-photon jet-like events have a clear nonzero asymmetry, but substantially smaller than that for isolated π0’s ² AN decreases as the event complexity increases (i. e. , the "jettiness” ² AN for #photons >5 is similar to that for #photons = 5 Jettier events DIS 2014, Warsaw, Apr. 28 -May 2, 2014 47
STAR’s Run 15 Attempt Trying to tag diffractive pi 0 by taking coincidence with forward proton which stayed intact through collision.
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
Run 16 • 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 50
BACKUP 51
Proton Spin +1/2 52
Proton Spin +1/2 53
Proton Spin +1/2 P-wave 54
Proton Spin +1/2 55
Proton Spin +1/2 56
Proton Spin +1/2 57
Proton Spin +1/2 P-wave 58
Proton Spin +1/2 d
60
UPC Final States forward neutron in ZDC Dominated by two body decay Dominated by neutron + p+ system
p↑p Forward Neutron AN Spin flip Spin non-flip Neutron p+ a 1 OPE : One Pion Exchange 62
- Slides: 62