Spin asymmetry of neutron at zero degree in polarized proton collisions

1
Spin asymmetry of neutron at zero degree in
polarized proton collisions

• International workshop on High-energy scattering
  at zero degree_at_Nagoya Univ.
• Mar. 2, 2013
• Kiyoshi Tanida (Seoul National University)
• for PHENIX collaboration

2
Spin asymmetry of neutron near zero degree in
polarized proton collisions

• International workshop on High-energy scattering
  at zero degree_at_Nagoya Univ.
• Mar. 2, 2013
• Kiyoshi Tanida (Seoul National University)
• for PHENIX collaboration

3
Introduction

• How most forward particles are produced in pp
  collisions?
• High energy, yet non-perturbative (pT lt 1 GeV/c)
• Regge theory?
• Explains total cross sectionin high-energypp
  collisionwith Pomeron
• How about observablesother than totalcross
  section?

4
Forward n production

• Cross section peak around xF 0.8
• Only at pT0, almost independent of vs

5
One-pion exchange model
E.g. N. N. Nikolaev et al., PRD 60, 014004 (1999)
p
r, a2
p?D?n
BG
(xF)
OPE models seem OK
6
Single spin asymmetry AN

• Left-right asymmetry (forward beam
  direction,up spin direction)

 
7
How An is produced?

• Need both helicity flip non-flip amplitudes
• In Regge theory
• Pion exchange givesspin flip
• Non flip? Other reggeons?
• Sensitive to mechanism

8
The Relativistic Heavy Ion Collider accelerator
complex at Brookhaven National Laboratory
9
RHIC pp accelerator complex
RHIC pC CNI polarimeters
absolute pH polarimeter
BRAHMS PP2PP
PHOBOS
RHIC
Siberian Snakes
PHENIX
STAR
Siberian Snakes
Spin Rotators
5 Snake
LINAC
BOOSTER
AGS pC CNI polarimeter
AGS
Pol. Proton Source
Coulomb-Nuclear Interference
200 MeV polarimeter
Rf Dipoles
20 Snake
10
First measurement_at_IP12
20012002_at_vs200 GeV
1800cm
2.8mrad
Dx magnet
10cm
Blue beam
yellow beam
EM Cal
hodoscope
Steel
Charged veto (plastic scinti.)
To measure Collision point
Neutron veto (plastic scinti.)
11
EM calorimeter

• Performance
• ?E/E 10/?E(GeV) for ?
• ?x ?y 0.1 cm for ?
• ?x ?y 0.5 cm for neutron

12
Result
invariant mass of pairs of energy clusters

• Phys. Lett. B 650 (2007) 325.

13
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 gt 20 GeV
• ?x 3 to 4 cm by the post shower counter

14
IP12 experiment summary

• Forward neutron Large asymmetry discovered
• 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

15
PHENIX Experiment
Pioneering High Energy Nuclear Interaction
EXperiment
16
Universidade de São Paulo, Instituto de Física,
Caixa Postal 66318, São Paulo CEP05315-970,
Brazil Institute of Physics, Academia Sinica,
Taipei 11529, Taiwan China Institute of Atomic
Energy (CIAE), Beijing, People's Republic of
China Peking University, Beijing, People's
Republic of China Charles University, Ovocnytrh
5, Praha 1, 116 36, Prague, Czech Republic Czech
Technical University, Zikova 4, 166 36 Prague 6,
Czech Republic Institute of Physics, Academy of
Sciences of the Czech Republic, Na Slovance 2,
182 21 Prague 8, Czech Republic Helsinki
Institute of Physics and University of Jyväskylä,
P.O.Box 35, FI-40014 Jyväskylä, Finland Dapnia,
CEA Saclay, F-91191, Gif-sur-Yvette,
France Laboratoire Leprince-Ringuet, Ecole
Polytechnique, CNRS-IN2P3, Route de Saclay,
F-91128, Palaiseau, France Laboratoire de
Physique Corpusculaire (LPC), Université Blaise
Pascal, CNRS-IN2P3, Clermont-Fd, 63177 Aubiere
Cedex, France IPN-Orsay, Universite Paris Sud,
CNRS-IN2P3, BP1, F-91406, Orsay, France Debrecen
University, H-4010 Debrecen, Egyetem tér 1,
Hungary ELTE, Eötvös Loránd University, H - 1117
Budapest, Pázmány P. s. 1/A, Hungary KFKI
Research Institute for Particle and Nuclear
Physics of the Hungarian Academy of Sciences (MTA
KFKI RMKI), H-1525 Budapest 114, POBox 49,
Budapest, Hungary Department of Physics, Banaras
Hindu University, Varanasi 221005, India Bhabha
Atomic Research Centre, Bombay 400 085,
India Weizmann Institute, Rehovot 76100,
Israel Center for Nuclear Study, Graduate School
of Science, University of Tokyo, 7-3-1 Hongo,
Bunkyo, Tokyo 113-0033, Japan Hiroshima
University, Kagamiyama, Higashi-Hiroshima
739-8526, Japan KEK, High Energy Accelerator
Research Organization, Tsukuba, Ibaraki 305-0801,
Japan Kyoto University, Kyoto 606-8502,
Japan Nagasaki Institute of Applied Science,
Nagasaki-shi, Nagasaki 851-0193, Japan RIKEN, The
Institute of Physical and Chemical Research,
Wako, Saitama 351-0198, Japan Physics Department,
Rikkyo University, 3-34-1 Nishi-Ikebukuro,
Toshima, Tokyo 171-8501, Japan Department of
Physics, Tokyo Institute of Technology,
Oh-okayama, Meguro, Tokyo 152-8551,
Japan Institute of Physics, University of
Tsukuba, Tsukuba, Ibaraki 305, Japan Chonbuk
National University, Jeonju, Korea Ewha Womans
University, Seoul 120-750, Korea Hanyang
University, Seoul 133-792, Korea KAERI, Cyclotron
Application Laboratory, Seoul, South Korea Korea
University, Seoul, 136-701, Korea Myongji
University, Yongin, Kyonggido 449-728,
Korea Department of Physocs and Astronomy, Seoul
National University, Seoul, South Korea Yonsei
University, IPAP, Seoul 120-749, Korea IHEP
Protvino, State Research Center of Russian
Federation, Institute for High Energy Physics,
Protvino, 142281, Russia INR_RAS, Institute
for Nuclear Research of the Russian Academy of
Sciences, prospekt 60-letiya Oktyabrya 7a,
Moscow 117312, Russia Joint Institute for Nuclear
Research, 141980 Dubna, Moscow Region,
Russia Russian Research Center "Kurchatov
Institute", Moscow, Russia PNPI, Petersburg
Nuclear Physics Institute, Gatchina, Leningrad
region, 188300, Russia Saint Petersburg State
Polytechnic University, St. Petersburg,
Russia Skobeltsyn Institute of Nuclear Physics,
Lomonosov Moscow State University, Vorob'evy
Gory, Moscow 119992, Russia Department of
Physics, Lund University, Box 118, SE-221 00
Lund, Sweden
13 Countries 70 Institutions
Feb 2011
Abilene Christian University, Abilene, TX 79699,
U.S. Baruch College, CUNY, New York City, NY
10010-5518, U.S. Collider-Accelerator Department,
Brookhaven National Laboratory, Upton, NY
11973-5000, U.S. Physics Department, Brookhaven
National Laboratory, Upton, NY 11973-5000,
U.S. University of California - Riverside,
Riverside, CA 92521, U.S. University of Colorado,
Boulder, CO 80309, U.S. Columbia University, New
York, NY 10027 and Nevis Laboratories, Irvington,
NY 10533, U.S. Florida Institute of Technology,
Melbourne, FL 32901, U.S. Florida State
University, Tallahassee, FL 32306, U.S. Georgia
State University, Atlanta, GA 30303,
U.S. University of Illinois at Urbana-Champaign,
Urbana, IL 61801, U.S. Iowa State University,
Ames, IA 50011, U.S. Lawrence Livermore National
Laboratory, Livermore, CA 94550, U.S. Los Alamos
National Laboratory, Los Alamos, NM 87545,
U.S. University of Maryland, College Park, MD
20742, U.S. Department of Physics, University of
Massachusetts, Amherst, MA 01003-9337, U.S.
Morgan State University, Baltimore, MD 21251,
U.S. Muhlenberg College, Allentown, PA
18104-5586, U.S. University of New Mexico,
Albuquerque, NM 87131, U.S. New Mexico State
University, Las Cruces, NM 88003, U.S. Oak Ridge
National Laboratory, Oak Ridge, TN 37831,
U.S. Department of Physics and Astronomy, Ohio
University, Athens, OH 45701, U.S. RIKEN BNL
Research Center, Brookhaven National Laboratory,
Upton, NY 11973-5000, U.S. Chemistry Department,
Stony Brook University,SUNY, Stony Brook, NY
11794-3400, U.S. Department of Physics and
Astronomy, Stony Brook University, SUNY, Stony
Brook, NY 11794, U.S. University of Tennessee,
Knoxville, TN 37996, U.S. Vanderbilt University,
Nashville, TN 37235, U.S.
17
PHENIX Detector

• Philosophy
• high resolution high-rate at the cost of
  acceptance
• trigger for rare events
• Central Arms
• h lt 0.35, Df p
• Momentum, Energy, PID
• Muon Arms
• 1.2 lt h lt 2.4
• Momentum (MuTr)
• Muon piston calorimeter
• 3.1 lt h lt 3.9

18
ZDC
1800cm
10cm
blue beam
yellow beam
3 mrad
Dx magnet
SMD
BBC
position measurement with scintillators
5.1?T 149X0 (3 ZDCs), dE/E 20 _at_ 100GeV
19
Shower Maximum Detector

• Arrays of plastic scintillators
• Position given as shower center
• position resolution 1cm _at_ 50GeV neutron

(mm)
100
5
150
Hadron shower
x segmented by 7 y segmented by 8
20
BBC

• Quartz Cherenkov counter
• 2 identical parts (BBC-north and -south)
• 64 segments each.
• Trigger on associated particles

21
Cross section_at_?s 200 GeV

• Consistent withresults at lowerenergy? xF
  scaling works well
• OPE model stillvalid

arXiv1209.3283
22
AN at ?s 200 GeV
ZDC trigger Forward asymmetry AN
?0.061?0.010(stat)?0.004(syst)
ZDC trigger Backward asymmetry AN
?0.006?0.011(stat)?0.004(syst)
ZDC?BBC trigger Forward asymmetry AN
?0.008?0.005(stat)?0.004(syst)
ZDC?BBC trigger Forward asymmetry AN
?0.075?0.004(stat)?0.004(syst)
23
Local Polarimeter
Forward neutron AN is used to know the spin
direction at the PHENIX collision point
PHENIX
Spin Rotators change the direction of spin from
up/downto forward/backward
24
Vertical polarization
at PHENIX
(Raw Asymmetry) / (beam pol.)
ø
ø
BLUE
YELLOW
25
Radial polarization
at PHENIX
(Raw Asymmetry) / (beam pol.)
ø
ø
BLUE
YELLOW
26
Longitudinal polarization
at PHENIX
(Raw Asymmetry) / (beam pol.)
ø
ø
BLUE
YELLOW
27
How about associated particles?

• Asymmetry is 0 when data is selected by BBC only.
• Tag on forward n ? finite AN observed
  
• Backward particles (2.280.550.10)10-2 (4s)
• Forward particles (-4.500.500.22)10-2 (9s)
  (preliminary)

Top view
pion exchange model
Y charged particles
Y
polarized proton
proton
Y
n (neutron)
Y
pol direction
N(D) ? nY ??
AN(Y) lt 0, AN(Y) gt 0
N ???
28
xF Dependence
ZDC trigger
arXiv1209.3283

• No xF dependence observed

ZDC?BBC trigger
29
?s Dependence (1)
Inclusive neutron
30
?s Dependence (2)
Neutron with charged particles
31
pT Dependence (1)
Inclusive neutron
32
pT Dependence (2)
Neutron with charged particles
33
Discussion

• Observed AN is larger for larger ?s
• Can be interpreted as pT dependence pT
  (?s/2)xFq (Note AN 0 at pT
  0)
• On the other hand, xF dependence was not seen.
• Same tendency was observed with and without
  coincident particles in BBC (3.0 lt h lt 3.9),
  though the amplitude is slightly different

34
Comparison with model (1)

• OPE model calculationfailed to reproduce
• No sign change
• There must be somethingbeyond simple OPE
• Other reggeons?

xF 0.60.9
pT (GeV/c)
B.Z. Kopeliovich et al.arXiv0807.1449
35
Comparison with model (2)

• Pion-a1 interference
• Good agreement withdata
• Interference btwspin flip/non-flip? small
  amplitude can make big difference

Kopeliovich et al., PRD 84 (2011) 114012. Also
in Soffers talk in this workshop
36
Summary Perspective

• Neutron AN near 0 degree
• ?s and pT dependence were measured
• Significant ?s and pT dependence was observed,
  while no xF dependence was seen
• ?s dependence can be understood as pT dependence
• One pion exchange model expects AN0 around the
  pT region
• Can be explained by other reggeons, such as a1
• Interference ? sensitive to small amplitudes
• Need data for higher pT
• AN ? pT is inevitable in low pT
• At which pT is AN maximum?

37
Backup slides
38
Cross section
39
Cross section calculation
40
?s dependence

• Neutron with charged particles

backward
forward
41
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