SingleSpin Asymmetry at RHICf Collaboration Meeting BNL June

Single-Spin Asymmetry at RHICf Collaboration Meeting @ BNL June 13, 2016 Yuji Goto (RIKEN)

Understanding hadron interaction • Asymmetry measurement of very forward neutron production with polarized proton collisions at RHIC • Measurement at IP 12 in Run 2 (2001 -02) • Very large left-right asymmetry (AN) of very forward neutron was discovered • Used for local polarimeter to monitor polarization direction at the collision point AN = 0. 090 0. 006(stat) 0. 009(syst) Interaction LR definition June 13, 2016 Y. Fukao, et al. , Phys. Lett. B 650 (2007) 325. 2

IP 12 experiment • performed in 2001 -2002 with s = 200 Ge. V polarized proton collisions at the 12 o’clock collision point ～ 1800 cm ± 2. 8 mrad Dx magnet 10 cm Blue beam yellow beam Hadron Cal hodoscope EM Cal Charged veto (plastic scinti. ) Post shower counter Steel To measure Collision point Gamma veto (plastic scinti. ) Lead block June 13, 2016 Neutron veto (plastic scinti. )3

EM calorimeter • Performance • calibrated in the electron beam at SLAC • E/E ~ 10%/ E(Ge. V) for • x ~ y ~ 0. 1 cm for • x ~ y ~ 0. 5 cm for neutron June 13, 2016 4

Forward neutron production • Asymmetry measurement at RHIC-IP 2 • 2001 – 2002 run • Very large asymmetry • Impossible to explain the large asymmetry with one-pion exchange • Kopeliovich et al. , AIP Conf. Proc. 1056 (2008) 199. • e. g. interference between pion and a 1 Interaction LR definition • Polarimeter at IP (local polarimeter) Y. Fukao, et al. , Phys. Lett. B 650 (2007) 325. June 13, 2016 5

Hadron calorimeter • One ZDC prototype module (1/3 length) • Performance • Energy is calibrated by using cosmic-ray data and simulation. • E/E ~ 40 -50% at E > 20 Ge. V • x ~ 3 to 4 cm by the post shower counter June 13, 2016 6

IP 12 experiment results • Forward neutron • EMCal result AN = 0. 090 0. 006 0. 009 • HCal result AN = 0. 135 0. 018 • consistent at the 2 -level • 0 and photon • AN consistent with zero • backward asymmetries • AN consistent with zero June 13, 2016 7

Forward neutron production • Cross section measurement at ISR/FNAL • Forward peak in the x. F distribution • Around x. F 0. 8 • Only a small s dependence • p. T distribution • exp(-a p. T), a 4. 8 Ge. V-1 • OPE (one-pion exchange) model gives a reasonable description p. T = 0 June 13, 2016 8

Forward neutron production • Cross section measurement at HERA(e+p)/NA 49(p+p) • High resolution p. T distribution • a(x. F) exp(-b(x. F) p. T 2), b 8 Ge. V-2 for 0. 3 < x. F < 0. 85 • x. F distribution • Suppression of the forward peak at high s? • feed-down correction? • More data necessary to understand the production mechanism • Asymmetry measurement as a new independent input NA 49 Collaboration, Eur. Phys. J. C 65 (2010) 9. ISR FNAL NA 49 ZEUS June 13, 2016 9

PHENIX local polarimeter • There have existed ZDCs (Zero Degree Calorimeter) to detect neutrons at PHENIX • SMDs (Shower Maximum Detector) were added to measure the hit position of neutrons ZDC @ 18 m away from the IP June 13, 2016 10

ZDC (Zero Degree Calorimeter) PHENIX Collision Point ～ 1800 cm ± 2. 8 mrad 10 cm yellow beam D magnet NORTH ZDC x hadron sampling calorimeter made of Tungsten plate and fibers SOUTH ZDC blue beam 5. 1λT 149 X 0 (3 ZDCs), Energy resolution ~ 20% @ 100 Ge. V 3 modules beam June 13, 2016 beam 11

Shower Maximum Detector • To measure the neutron hit position, SMDs (Shower Maximum Detector) were installed between 1 st and 2 nd modules of ZDC • arrays of plastic scintillators • giving a position by calculating the center of gravity of shower generating in the 1 st ZDC module • position resolution ~1 cm @ 50 Ge. V neutron (simulation study) 100 5 SMD 150 2 nd ZDC module June 13, 2016 x: segmented by 7 y: segmented by 8 Hadron shower Unit : mm 12

Inclusive cross section at s = 200 Ge. V • x. F distribution measurement • With hadron calorimeter • p. T range & resolution limited • 0 < p. T < 0. 11 x. F Ge. V/c • Limited by ZDC acceptance • Limited by SMD position resolution • p. T shape assumed • gaussian form (HERA form) • exponential form (ISR form) • Comparison of p. T distribution from experimental data and two simulations including p. T resolution June 13, 2016 Difference between data and two simulations are not large 13

Inclusive cross section at s = 200 Ge. V • Systematic uncertainties • p. T distribution form • Beam center shift • Possible 1 cm shift • Proton background • Scattered forward proton could hit the DX magnet or beam pipe • Multiple hit • Absolute normalization • 9. 7% (22. 9 2. 2 mb for the BBC trigger cross section) • Energy unfolding • ref. V. Blobel, ar. Xiv: hep-ex/0208022 Consistent with x. F scaling from ISR results June 13, 2016 14

Single transverse-spin asymmetry at s = 200 Ge. V • Square-root formula • P: polarization, C : smearing correction • sine fit AN • Systematic uncertainties • p. T correlated • Beam center shift • Scale uncertainties • Proton background • Multiple hit • Smearing by position resolution • Polarization scale uncertainties from RHIC polarimeters • 6. 2% for the Yellow beam • 5. 9% for the Blue beam June 13, 2016 15

Single transverse-spin asymmetry at s = 200 Ge. V Inclusive neutron trigger (ZDC trigger) Forward asymmetry Backward asymmetry AN = 0. 061 0. 010(stat) 0. 004(syst) AN = 0. 006 0. 011(stat) 0. 004(syst) neutron charged particles neutron Interaction trigger with charged particles in beam-beam counter (ZDC BBC trigger) Forward asymmetry Backward asymmetry AN = 0. 075 0. 004(stat) 0. 004(syst) AN = 0. 008 0. 005(stat) 0. 004(syst) June 13, 2016 16

Single transverse-spin asymmetry at s = 200 Ge. V • Comparison to IP 12 experiment • ZDC BBC trigger results • PHENIX ZDC trigger • AN = 0. 075 0. 004(stat) 0. 004(syst) • IP 12 • AN = 0. 090 0. 006(stat) 0. 009(syst) • Consistent within the errors • Higher precision • x. F dependence • Significant negative AN in the forward ZDC BBC trigger region • No x. F dependence within the uncertainties • No significant backward asymmetry June 13, 2016 17

s dependence • distribution • Inclusive neutron q ZDC/ SMD forward backward s = 62 Ge. V s = 200 Ge. V s = 500 Ge. V • Neutron with charged particles (in beam-beam counter) s = 200 Ge. V s = 500 Ge. V June 13, 2016 18

s dependence • p. T distribution • p. T x. F s / 2 • Assuming p. T shape of ISR • No smearing correction (no-unfolding) • wide p. T deviation for each bin Inclusive neutron Neutron with charged particles • AN(62 Ge. V) < AN (200 Ge. V) < AN (500 Ge. V) • s dependence or p. T dependence? June 13, 2016 19

Forward neutron production • Interference between spin-flip and non-flip with a relative phase f : spin non-flip amplitude g : spin flip amplitude • Pion exchange • Kopeliovich, Potashnikova, Schmidt, Soffer: Phys. Rev. D 78 (2008) 014031. • Spin-flip amplitude and non-flip amplitude have the same phase • No single transverse-spin asymmetry can appear • Absorption correction for a relative phase • Initial/final state interaction • Also important for cross section calculation • Gained shift between spin-flip and non-flip amplitudes is too small to explain the large asymmetry • Interference with other Reggeons • Kopeliovich, Potashnikova, Schmidt, Soffer: Phys. Rev. D 84 (2011) 114012. • a 1 axial-vector meson • Pion-a 1 interference • - in 1+S state instead of a 1 June 13, 2016 20

Forward neutron production • Interference with other Reggeons • Kopeliovich, Potashnikova, Schmidt: ar. Xiv: 1109. 2500 • a 1 axial-vector meson • Pion-a 1 interference • B. Kopeliovich, Veli Losinj, Aug. 28 -Sep. 3, 2011 • - in 1+S state instead of a 1 June 13, 2016 21

Forward neutron production • Pion-a 1 interference: results • The data agree well with independence of energy • The asymmetry has a sensitivity to presence of different mechanisms, e. g. Reggeon exchanges with spin -non-flip amplitude, even if they are small amplitudes June 13, 2016 22

RHICf experiment @ STAR • RHICf detector will be installed in front of the ZDC+SMD of the STAR experiment • Wide p. T region will be covered by changing the position of the RHICf detector vertically movable ZDC IP • up to 1. 4 Ge. V/c • RHICf detector has much higher position resolution than ZDC+SMD so that enable us higher resolution p. T measurement • Position resolution 1 cm 1 mm • Kinematic region (x. F, p. T) of RHICf at s = 510 Ge. V is similar to that of LHCf at s = 7 Te. V June 13, 2016 23

Neutron asymmetry at RHICf (projection) • Much enough statistics will be obtained in 12 -hour measurement • 1% neutron asymmetry measurement possible up to p. T = 1 Ge. V/c • Existing data covers up to 0. 4 Ge. V/c June 13, 2016 24

Neutron asymmetry at RHICf • Common measurement with the cross section measurement of the cosmic-ray program • Position 1: • TS: 3 mm < r < 8 mm ring region, p. T = 0. 05 Ge. V/c in average • 0. 3% precision for 3% asymmetry • TL: p. T = 0. 3 Ge. V/c in average • Position 2: highest p. T achieved • Radial polarization is essential to have sensitivity and precision in the asymmetry measurement at high p. T measurement Position 1 June 13, 2016 Position 2 25

Summary • Zero-degree forward neutron • Large asymmetry found and used for local polarimeter at RHIC • Production mechanism? • Cross section • Asymmetry measurement • Pion-a 1 interference • New physics from p +A collisions • Ultra-peripheral collision • RHICf experiment @ STAR • High p. T resolution and wide p. T coverage • Radial polarization • More physics by combining with STAR detectors June 13, 2016 26

Backup Slides

RHIC-Spin physics • Origin of the nucleon spin in quark-gluon picture • Quark spin • Gluon spin • Orbital angular momenta of quarks and gluons • Quark-spin contribution is only 20%-30% of the nucleon spin • Longitudinal-spin asymmetry measurement • Gluon polarization • Anti-quark polarization with W boson • Transverse-spin asymmetry measurement • Understanding of orbital motion inside the nucleon and orbital angular momenta of quarks and gluons from large transverse single-spin asymmetry in the forward kinematic region June 13, 2016 28

RHIC (Relativistic Heavy-Ion Collider) June 13, 2016 29

RHIC polarized proton collider BRAHMS & PP 2 PP PHOBOS Absolute Polarimeter (H jet) Full Helical Siberian Snakes RHIC p. C Polarimeters PHENIX STAR Spin Rotators Pol. H- Source LINAC BOOSTER rf Dipole AGS 200 Me. V Polarimeter Partial Solenoidal Snake Warm Partial Helical Siberian Snake AGS Internal Polarimeter Cold Partial Helical Siberian Snake June 13, 2016 AGS p. C Polarimeters 30

PHENIX detector • Philosophy • high resolution at the cost of acceptance • high rate capable DAQ • excellent trigger capability for rare events • Central Arms • Global detectors • beam-beam counter (BBC), zerodegree calorimeter (ZDC) • Minimum-bias trigger • Luminosity measurement • Local polarimeter June 13, 2016 • | | < 0. 35, f = /2× 2 • Momentum and energy measurement, particle-ID • Detecting electron, photon, hadron • Small amount of material to reduce conversion background • Muon Arms • 1. 2 < | | < 2. 4 • Momentum measurement and muon-ID • Hadron absorber (muon piston) 31

Gluon polarization ２０１４．７．１１ • Positive gluon polarization has been finally obtained at RHIC ２０１４．７．２１ ２０１４．７．２ June 13, 2016 32

Gluon polarization: 0 asymmetry measurement 2=1 2=9 or 2/ 2=2% G[x 1 -x 2] NNPDFpol 1. 1 [0. 05 -0. 2] DSSV++ [0. 05 -0. 2] 2005+06+09 [0. 05 -0. 2] DSSV 08 [0. 05 -0. 2] 2005+06 [0. 02 -0. 3] 2005 data [0. 02 -0. 3] Measurement of positive gluon polarization by QCD global analysis PRD 76 (2007) 051106 PRL 103 (2009) 012003 PRD 90 (2014) 012007 June 13, 2016 Y. Fukao (Kyoto/RIKEN) K. Boyle (SBU/RBRC) A. Manion (SBU) 33

Anti-quark polarization with W boson • Muon trigger upgrade for W boson measurement • Trigger FEE of Muon Tracker • RPC (Resistive Plate Chamber) K. Shoji (Kyoto/RBRC) K. Karatsu (Kyoto/JRA) K. Nakamura (Kyoto/JSPS) H. Oide (Tokyo/JRA) S. Park (Seoul/IPA) I. Yoon (Seoul/IPA) M. Kim (Seoul/IPA) S. Han (Ewha/IPA) June 13, 2016 34

Anti-quark polarization with W boson • RHIC W-boson run performed until 2013 STAR 2012 Results PHENIX 2013 (Preliminary) Results K. Karatsu (Kyoto/JRA) H. Oide (Tokyo/JRA) S. Park (Seoul/IPA) C. Kim (Korea/IPA) June 13, 2016 35

Transverse-spin asymmetry measurement • Transverse single spin asymmetry (SSA) • Expected to be small in hard scattering at high energies • FNAL-E 704 • Unexpected large asymmetry found in the forward-rapidity region • Development of many models based on perturbative QCD June 13, 2016 36

Transverse-polarization runs • Muon arm 2001 • MPC 2006 • EM calorimeter • FVTX 2012 - • Silicon detector • MPC-EX 2015 - • Preshower detector Year Energy Recorded Luminosity Polarization Fo. M (P 2 L) 2001 -2 200 Ge. V 0. 15 pb-1 15% 0. 0034 pb-1 2005 200 Ge. V 0. 16 pb-1 47% 0. 035 pb-1 2006 200 Ge. V 2. 7 pb-1 57% 0. 88 pb-1 2006 62. 4 Ge. V 0. 02 pb-1 53% 0. 0056 pb-1 2008 200 Ge. V 5. 2 pb-1 45% 1. 1 pb-1 2012 200 Ge. V 9. 2 pb-1 59% 3. 3 pb-1 2015 200 Ge. V 110 pb-1 57% 35 pb-1 June 13, 2016 37

High-p. T measurements • Forward EM cluster at s = 200 Ge. V • 0 and June 13, 2016 38

Heavy-flavor measurements • Gluon contribution • Quark sector good knowledge • Twist-3 quark-gluon correlation functions • Gluon sector largely unknown • Twist-3 tri-gluon correlation functions • Heavy-flavor from gluon-gluon process • No final state effect • Single muon SSA • 2012 run preliminary result June 13, 2016 39

3 D structure of the nucleon • Conclusive understanding of the nucleon spin • orbital motion inside the nucleon and orbital angular momenta of quarks and gluons • TMD (Transverse-Momentum Dependent) distribution function • Correlation between transverse-momentum distribution, spin and orbital motion • GPD (Generalized Parton Distribution) • Spatial distribution or tomography June 13, 2016 40

Single muon SSA • Much improved results expected from 2015 run with VTX and FVTX June 13, 2016 41

Forward J/ SSA • 2012 run preliminary result • Asymmetry consistent with zero • More from 2015 run June 13, 2016 42

RHIC schedule • PHENIX will end data taking after 2016 run • Polarized proton runs have already ended in 2015 • “s. PHENIX” in 2021 -22 • Starting as a new collaboration • There will be polarized proton runs June 13, 2016 43

“s. PHENIX” • A new large-acceptance jet and Upsilon detector around the Ba. Bar megnet • Probe QGP with precision measurements of jet quenching and Upsilon suppression • Spin physics and initial conditions at forward rapidities with p+p and p+A collisions June 13, 2016 44

Forward “s. PHENIX” s. PHENIX baseline (barrel only) s. PHENIX + fs. PHENIX • Transverse spin physics • Transverse spin “puzzle” • Large single spin asymmetry (SSA) in the forward region • Understanding of the orbital motion • p+A and p +A physics • Cold Nuclear Matter (CNM) effects • Polarization for probe to the gluon saturation June 13, 2016 45

Direct photon • Distinguish predicted higher-twist quark-gluon correlation functions • No final state effect Kang, Qiu, Vogelsang and Yuan, PRD 83 094001 (2011) Gamberg and Kang, ar. Xiv 1208. 1962 v 1 (2012) June 13, 2016 Kanazawa, Koike, Metz and Pitonyak, PRD 83 094001 (2015) 46

p + A • Unique capability of RHIC • Polarization for probe to the gluon saturation (CGC) • Measurement of Qs • Projection for 2015 run Z. -B. Kan and F. Yuan PRD 84, 034019 (2011) June 13, 2016 Odderon mechanism (Kovchegov and Sievert) predicts 0 47

Forward neutron asymmetry ～ 1800 cm PHENIX Collision Point SOUTH ZDC blue beam • ZDC + SMD ± 2. 8 mrad 10 cm yellow beam D magnet NORTH ZDC x PRD 88, 032006 (2013) • ZDC (Zero-Degree Calorimeter) • Hadron sampling calorimeter • SMD (Shower Maximum Detector) • Position measurement • x. F distribution • Significant negative AN in the forward region • No x. F dependence within the uncertainties • No significant backward asymmetry • s dependence or p. T dependence June 13, 2016 48

Forward neutron production • Cross section measurement • Forward peak in the x. F distribution around x. F 0. 8 • OPE (one-pion exchange) model gives a reasonable description • Asymmetry measurement • Interference between spin-flip and non-flip with a relative phase • Kopeliovich, Potashnikova, Schmidt, Soffer: Phys. Rev. D 84 (2011) 114012 • Pion-a 1 interference: the data agree well with independence of energy • The asymmetry has a sensitivity to presence of different mechanisms, e. g. Reggeon exchanges with spinnon-flip amplitude, even if they are small amplitudes June 13, 2016 49

Introduction • Longitudinal-spin is monitored by the local polarimeter by using physics processes with leftright asymmetry (AN) • AN of forward 0 found at FNAL-E 704 • Only very forward region was available at PHENIX • But, there was no measurement at very forward • Measurement at IP 12 in Run 2 (2001 -02) • With EM calorimeter to measure AN of photons mainly from 0 decay too small to measure • Very large asymmetry of very forward neutron was found AN = 0. 090 0. 006(stat) 0. 009(syst) Interaction LR definition June 13, 2016 Y. Fukao, et al. , Phys. Lett. B 650 (2007) 325. 50

Forward neutron production • Cross section measurement at ISR/FNAL • Forward peak in the x. F distribution • around x. F 0. 8 • Only a small s dependence • OPE (one-pion exchange) model gives a reasonable description • Cross section measurement at HERA(e+p)/NA 49(p+p) • s dependence indicated • Suppression of the forward x. F peak at high s? • More data necessary to understand the production mechanism • Asymmetry measurement as a new independent input June 13, 2016 p. T = 0 No cross section measurement performed at IP 12 experiment measurement at PHENIX 51

What’s new • 100 Ge. V/nucleon 100 Ge. V Au, Al Porarized Proton June 13, 2016 52

Result • Surprise ― huge dependence on A • Even sign changes • Simple -a 1 interference predicts small dependence • Mechanism? Why? p Al Au # of proton # of neutron 1 13 79 0 14 118 June 13, 2016 53

BBC (Beam-Beam Counter) • Quartz Cherenkov counter • 2 identical parts (BBC-north and south) • 64 segments each. • Trigger on associated particles South North ⊿φ = 2π June 13, 2016 144. 35 cm 54

BBC tagging • AN changes with BBC tagging • AN is still negative with BBC hits • p & A are not (badly) broken • Large positive AN is seen only when there is no hit on BBC • Diffraction? (common to p+p) • Ultra-Peripheral Collision? Both BBC veto A ↑ p ? n Both BBC Fired A ↑ p June 13, 2016 ? BBC n BBC 55

Coulomb-Nuclear Interference (CNI) • * exchange and Reggeon exchange can interfere • may give positive AN • * amplitude is proportional to Z • significant for large Z A A *, 0, P, . . . p June 13, 2016 + , N* n 56

Neutron asymmetry at RHICf • Asymmetry at position 1 • TS: 3 mm < r < 8 mm ring region • p. T = 0. 05 Ge. V/c in average • 0. 3% precision for 3% asymmetry • TL: p. T = 0. 3 Ge. V/c in average • Statistics and precision June 13, 2016 57

Summary • RHIC-spin physics • Origin of the nucleon spin in quark-gluon picture • Longitudinal-spin asymmetry measurement • Gluon polarization • Anti-quark polarization with W boson • Transverse-spin asymmetry measurement • Orbital motion inside the nucleon? • Zero-degree forward neutron • Large asymmetry found and used for local polarimeter at RHIC • Production mechanism? • Cross section • Asymmetry measurement • Pion-a 1 interference • New physics from p +A collisions • Ultra-peripheral collision • RHICf experiment @ STAR • high p. T resolution and wide p. T coverage • More physics by combining with STAR detectors June 13, 2016 58