Overview of spin physics results from PHENIX experiment

Report
Overview of spin physics
results from PHENIX
experiment
The 4th International Workshop of High Energy Physics
in the LHC Era
Valparaiso, Chile
January 4-10, 2012
Kiyoshi Tanida (Seoul National University)
for the PHENIX Collaboration
Overview of spin physics
results from PHENIX
experiment
The 4th International Workshop of High Energy Physics
in the LHC Era
Valparaiso, Chile
January 4-10, 2012
Kiyoshi Tanida (Seoul National University)
for the PHENIX Collaboration
4
What are we aiming at?
• To study proton’s spin structure
• The flagship question:
“Where the proton spin comes from?”
– Proton spin puzzle
– Helicity distribution of partons in longitudinally polarized
protons, especially gluons
– Flavor-decomposed quark helicity distribution using Ws
• What’s there in transversely polarized protons?
– dq ≠ Dq
– Very hot recently
– Needs more than simple
collinear picture to understand
5
The Relativistic Heavy Ion Collider
accelerator complex
at Brookhaven National Laboratory
Brahms
pp2pp
PHENIX
STAR
RHIC p+p accelerator complex
RHIC pC “CNI”
polarimeters
absolute pH
polarimeter
BRAHMS
& PP2PP
PHOBOS
Siberian
Snakes
RHIC
PHENIX
STAR
Siberian Snakes
Spin Rotators
5% Snake
LINAC
Pol. Proton Source
BOOSTER
AGS
200 MeV polarimeter 20% Snake
Rf Dipoles
AGS pC “CNI” polarimeter
Coulomb-Nuclear
Interference
6
PHENIX Experiment
7
Pioneering High Energy Nuclear Interaction EXperiment
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.
9
The PHENIX Detector
• Philosophy
– high resolution & high-rate
at the cost of acceptance
– trigger for rare events
• Central Arms
– |h| < 0.35, Df ~ p
– Momentum, Energy, PID
• Muon Arms
– 1.2 < |h| < 2.4
– Momentum (MuTr)
• Muon piston calorimeter
– 3.1 < |h| < 3.9
PART 1:
Helicity distribution
with longitudinal polarization
Helicity distribution
• Lepton deep inelastic scattering (DIS) experiments
– Quasi-elastic scattering of quark and lepton at high
energies where perturbation is applicable
– Reaction depends on quark spin  spin structure function
Proton spin puzzle
• Quark spin carries only 20-30% of the nucleon spin
 spin puzzle (crisis)
• What carries the rest?
– Gluon spin?
– Orbital angular momentum?
0.2-0.3
1 1
 D  DG  L
2 2
Our Main Goal
What we can’t know from DIS
• Photon mediated  sensitive to charge2
– u:d:s:g=4:1:1:0
– Gluon is invisible!
(c.f., indirect methods: Q2 evolution, photon-gluon fusion)
• Can we see gluons directly?
 Yes, what we need is a
Polarized Proton collider
13
14
What we measure?
 ()   ()
ALL 
 ()   ()
~ (parton pol.)2× (aLL in parton reaction)
15
How can we access gluons?
• Typical parton level diagrams (LO)
gg  gg
Dg Dg

g g
gq  gq
Dq Dg

q g
qq  qq
Dq Dq

q q
• What we actually measure are not partons, but
fragmented hadrons
– Come from different mix of partons
– Parton information (e.g., Bjorken x) is obscured
16
Some examples
• Direct photon: g + q  g + q
– No fragmentation
– Small contamination (e.g.`qq  gg)
• Jet, high-pT hadron production
– Mix of all subprocesses
– LO  highest statistics
 Good measurement with lower luminosity
• Heavy quarks (charm, bottom)
– gg→`qq is the main process at RHIC
• W: sensitive to quark flavors
– e.g., W+ comes from`du
17
Accumulated data
with longitudinal polarization
Year
2003 (Run 3)
2004 (Run 4)
2005 (Run 5)
2006 (Run 6)
2006 (Run 6)
2009 (Run 9)
2009 (Run 9)
2011 (Run 11)
s [GeV]
200
200
200
200
62.4
200
500
500
Recorded L
.35 pb-1
Pol [%]
27
FOM
(P4L)
1.5 nb-1
.12 pb-1
3.4 pb-1
7.5 pb-1
40
49
57
3.3 nb-1
0.2 pb-1
0.69 pb-1
0.08 pb-1
16 pb-1
10 pb-1
48
55
39
5.3 nb-1
1.5 pb-1
0.23 pb-1
17 pb-1
44
0.64 pb-1
Results
18
p0 [email protected] GeV
Run5
Run6
Run9
Precision reaches O(10-3), but still consistent with 0 asymmetry
How to extract Dg(x)? (1)
• p0s come from quarks and gluons of various x
 Deconvolution necessary
• Are we sure that we understand contribution of
partons? YES!
– NLO-pQCD calculation
reproduces  well
p0 @200 GeV, h~0
PRD76:051106,2007
19
How to extract Dg(x)? (2)
20
• Practical analysis
– Assume functional form: e.g., Dg(x)=Cg(x)xa(1-x)b
– Search optimum parameters using data, including DIS.
• Ex: GRSV(M. Gluck et al., PRD 63 (2001) 094005.)
– Assume DG, other parameters are determined from DIS.
– Several versions for various DG(GRSV-std, max, min, ...)
• Several other analyses
– For the same integral, DG, Dg(x) could be very different
– Our measurement mostly constrains DG[0.02,0.3]
DG: Global Fit
RHIC data
21
DSSV analysis
(Run 9 data not taken
into account)
Phys. Rev. Lett.
101, 072001(2008)
Uncertainty
estimation:
D2=1
D2/2=2%
Node in Dg(x)?
Global Fit including Run9
p0
ALL
By S.Taneja et al (DIS2011)
ala DSSV with slightly different uncertainty evaluation approach
DSSV + PHENIX Run9 p0 ALL
DSSV
A node at x~0.1 ?
No node …
Uncertainties decreased
22
Extend x-range  different s
23
p0 at |h|<0.35: xg distribution vs pT bin
s=62 GeV

2-2.5 GeV/c
4-5 GeV/c
9-12 GeV/c
2-2.5 GeV/c
4-5 GeV/c
9-12 GeV/c
s=200 GeV
s=500 GeV
p at s=62 GeV
p0: PHENIX, PRD79, 012003
 Very limited data sample (0.04 pb-1,
compared 2.5 pb-1 from Run2005
s=200 GeV)
 Clear statistical improvement at
larger x; extends the range to
higher x (0.06<x< 0.4)
 Overlap with 200 GeV ALL
provides measurements at the same
x but different scale (pT or Q2)
 s=500 GeV ALL results will be
available soon (from Run2009 with
L~10 pb-1 and P~0.4)
Charged hadrons
25
Forward Calorimetry: MPC
26
Muon Piston Calorimeter (3.1 < |h| < 3.9) : lower x10-3
Fraction of clusters
Cluster (p0 dominant) ALL
Decay photon
π0
Direct photon
PT
W measurement
W
L
A
Du(x1 )d(x 2 )  Dd(x1 )u(x 2 )

u(x1)d(x 2 )  d(x1 )u(x 2 )
W   e  e


Parity Violation Asymmetry
Clean flavor separation

w/o fragmentation uncertainty

W    
W
L
Du ( x1 , M W2 )

, x1  x2 ( yW  0)
2
u ( x1 , M W )
W
L
Dd ( x1 , M W2 )

, x1  x2 ( yW  0)
2
d ( x1 , M W )
A
A
We in mid-rapidity
Phys. Rev. Lett. 106, 062001 (2011)
W asymmetry
e+
Uncertainty is still large
More data in 2011 and from now
29
Run 9 data
e-
Forward ー New Trigger System
Resistive Plate Counter
(RPC) (Φ segmented)
30
Trigger events with straight track
(e.g. Dstrip <= 1) SG1
Level 1
Trigger
Board
RPC
FEE
Trigger
MuTRG
Amp/Discri.
Transmit
5%
MuTRG
ADTX
B
Optical
1.2Gbps
Trigger
MuTRG
MRG
Trigger
2 planes
95%
Data
Merge
MuTr
FEE
Interaction Region
RPC / MuTRG data are
also recorded on disk.
Rack Room
Trigger efficiency
OK: plateau
eff. 92%
Run11 data under analysis ー results coming soon
More results ... no time to show them all
31
32
Part 2:
Transverse spin physics
Transverse spin physics
33
• Transversity dq: Due to Einstein’s relativity, not the
same as Dq
– Unexplored leading twist PDF
• AN: left-right asymmetry wrt transverse polarization
Left
xF<0
xF>0
L


Right
R
 L  R
AN 
 L  R
Requirements for AN
• Helicity flip amplitude & relative phase
• In QCD, helicity is conserved if mq=0.
 AN ~ asmq/pT ~ O(10-3)
in naive collinear picture
Reality
However, large AN
observed in forward
pions. WHY??
We need something
more
 hot topic
35
36
Possible mechanisms (ex.)
(i) Sivers mechanism:
(ii) Collins mechanism:
correlation between proton
spin & parton kT
Transversity (quark polarization)
× jet fragmentation asymmetry
SP
SP
p
kT,q
Sq
p
p
p
Sq
Phys Rev D41 (1990) 83; 43 (1991) 261
kT,π
Nucl Phys B396 (1993) 161
(iii) Twist 3: quark-gluon/gluon-gluon correlation
 A source for Sivers function
Expectation: at large pT, AN ~ 1/pT – not observed so far
Forward -- MPC
p0 AN
37
MPC @ 200 GeV
Cluster (p0 dominant) AN
Same tendency with other energies and experiments
38
Forward h AN
39
Forward h AN
same tendency with p0
40
Comparison with STAR
Quite different
at high xF
Due to slightly
different kinematic
conditions?
Need confirmation/
deconfirmation
41
Midrapidity hadrons AN
• AN is zero within 0.1%  contrast with forward hadrons
42
43
IFF and Collins FF

Interference fragmentation function H1 ( z, Mpp
)
J. Collins, S.Heppelmann, G. Ladinsky, Nuclear Physics B, 420 (1994) 565
AUT  dq  H1□
h1
Quark spin

_ 
quark
quark
h2
h1
h2
Collins fragmentation function H1
J. C. Collins, Nucl. Phys. B396, (1993) 161
AUT  dq  H1
h
_ 

quark
quark
(courtesy A. Bacchetta)
h
FF measurements are ongoing at KEK-BELLE
Asymmetry result
Still need more data...
• More results ... again, no time to show them all
44
45
Part 3:
Future measurements
46
More data!
• Goal:
> 50 pb-1 @ 200 GeV, > 300 pb-1 @ 500 GeV
mid rapidity p0
forward p0
MPC p0 500 GeV
300 pb-1 P=0.55
W in forward
47
More detectors – (F)VTX
• VTX (from 2011)
• FVTX (from 2012)
• Study of c & b
Gluon polarization via
 → ,  
• Larger acceptance
 Jet tagging
VTX barrel |h|<1.2
– q+g  g+jet
– Theoretically clean channel
– Luminosity hungry
FVTX
More will be discussed by J. Seele this afternoon
48
Even further upgrade -- sPHENIX
49
Compact, hermetic, EM + hadron calorimetry
Forward region is important for
spin physics
- AN in forward regions
- Dg(x) in small x region
Details will be discussed by J. Seele this afternoon
Summary
• Gluon polarization
– Significant constraints on Dg(x) for 0.02<x<0.3
– Extension toward lower x is important
 higher energy, forward region
• Flavor decomposed quark distribution via W
– W e observed in central arm, muon arm follows
• Transverse spin physics
– Trying to find the mechanism to produce large AN in
forward region
– Access transversity
• More data are still to come
50

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