Studies on nucleon spin at PHENIX

3rd International Conference on New Frontiers in Physics

Kolymbari, Greece

August 2, 2014

Kiyoshi Tanida (Seoul National University) for the PHENIX Collaboration

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

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PART 1: Helicity distributions

with longitudinal polarization

Helicity distributions

• 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?

LG 2

1

2

1

Our Main Goal

0.2-0.3

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

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RHIC p+p accelerator complex

BRAHMS & PP2PP

STARPHENIX

AGS

LINACBOOSTER

Pol. Proton Source

Spin Rotators

20% Snake

Siberian Snakes

200 MeV polarimeter Rf Dipoles

RHIC pC “CNI” polarimeters

PHOBOS

RHIC

absolute pHpolarimeter

SiberianSnakes

AGS pC “CNI” polarimeter

5% Snake

Coulomb-Nuclear Interference

What do we measure?

~ (parton pol.)2× (aLL in parton reaction)

)()(

)()(

LLA

8

How can we access gluons?• Typical parton level diagrams （ LO ）

• What we actually measure are not partons, but fragmented hadrons– Come from different mix of partons– Parton information （ e.g., Bjorken x ） is obscured

qqqq gggg

g g

g g

gqgq

q g

q g

q

q

q

q

9

Result -- p0 ALL@200 GeV10

PRD90 (2014) 012007

Impact on Global Analysis• Including DIS and other data as well as RHIC data

– Based on DSSV [PRL101 (2008) 072001, PRD 80 (2009) 034030]

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Strong constraint on DG in 0.05 < x < 0.2:

ALW

u(x1)d(x2) d(x1)u(x2)

u(x1)d(x2) d(x1)u(x2)

Parity Violation AsymmetryClean flavor separationw/o fragmentation uncertainty

)0( , ),(

),(

)0( , ),(

),(

2121

21

2121

21

WW

WWL

WW

WWL

yxxMxd

MxdA

yxxMxu

MxuA

W e e

W

W measurement

W asymmetries@500-510 GeV13

ye

Central arm (e) – 2011-13 Muon arm – 2011,12

• Consistent with theories• Will be finalized soon

Part 2:Transverse spin physics

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Transverse spin physics• Transversity dq: Due to Einstein’s relativity, not the

same as Dq – Unexplored leading twist PDF

• AN ： left-right asymmetry wrt transverse polarization

xF<0 xF>0

R

L

Left

Right

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RL

RLNA

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

particles. WHY??

We need somethingmore

hot topic

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PRD90 (2014) 012006

(ii) Collins mechanism: Transversity (quark polarization) × jet fragmentation asymmetry

(i) Sivers mechanism:

correlation between proton spin & parton kT SP

p

p

Sq kT,π

Possible mechanisms (ex.)

SP

kT,qp

p

Sq

Phys Rev D41 (1990) 83; 43 (1991) 261 Nucl Phys B396 (1993) 161

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(iii) Twist 3: quark-gluon/gluon-gluon correlation A source for Sivers function Expectation: at large pT, AN ~ 1/pT

Recent results -- forward 19

• No √s dependence – scaling effect?• Same behavior for p0 & h

PRD90 (2014) 012006arXiv:1406.3541

Forward – pT dependence 20

• Twist-3 calculation (by Kanazawa & Koike): quite good– Though naïve 1/pT dependence not seen

arXiv:1406.3541

Midrapidity p0 and h

• Exceeds precision of previous result by factor of 20, extends pT range [PRL 95 (2005) 202001]

• AN is zero within 0.1% contrast with forward hadrons

• Theories must be able to explain those features at the same time.

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PRD90 (2014) 012006

Summary & Outlook• Gluon helicity distribution

– gluon spin in this x range is not enough to explain proton helicity.

– √s=500 GeV data will come soon for lower x.

• Flavor decomposed quark distribution via W– AL are consistent with predictions from existing PDFs

– 2013 muon data will be available soon

• Transverse spin physics– Large AN seen only in forward region, independent of

collision energy– Twist-3 calculation gives a rather good agreement,

though naïve 1/pT dependence is not seen

• More results are there and still to come

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Backups

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The Relativistic Heavy Ion Collideraccelerator complex

at Brookhaven National Laboratory

PHENIXSTAR

Brahmspp2pp

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RHIC p+p accelerator complex

BRAHMS & PP2PP

STARPHENIX

AGS

LINACBOOSTER

Pol. Proton Source

Spin Rotators

20% Snake

Siberian Snakes

200 MeV polarimeter Rf Dipoles

RHIC pC “CNI” polarimeters

PHOBOS

RHIC

absolute pHpolarimeter

SiberianSnakes

AGS pC “CNI” polarimeter

5% Snake

Coulomb-Nuclear Interference

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PHENIX Experiment

Pioneering High Energy Nuclear Interaction EXperiment

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13 Countries; 70 Institutions

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.

Universidade de São Paulo, Instituto de Física, Caixa Postal 66318, São Paulo CEP05315-970, BrazilInstitute of Physics, Academia Sinica, Taipei 11529, TaiwanChina Institute of Atomic Energy (CIAE), Beijing, People's Republic of ChinaPeking University, Beijing, People's Republic of ChinaCharles University, Ovocnytrh 5, Praha 1, 116 36, Prague, Czech RepublicCzech Technical University, Zikova 4, 166 36 Prague 6, Czech RepublicInstitute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech RepublicHelsinki Institute of Physics and University of Jyväskylä, P.O.Box 35, FI-40014 Jyväskylä, FinlandDapnia, CEA Saclay, F-91191, Gif-sur-Yvette, FranceLaboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS-IN2P3, Route de Saclay, F-91128, Palaiseau, FranceLaboratoire de Physique Corpusculaire (LPC), Université Blaise Pascal, CNRS-IN2P3, Clermont-Fd, 63177 Aubiere Cedex, FranceIPN-Orsay, Universite Paris Sud, CNRS-IN2P3, BP1, F-91406, Orsay, FranceDebrecen University, H-4010 Debrecen, Egyetem tér 1, HungaryELTE, Eötvös Loránd University, H - 1117 Budapest, Pázmány P. s. 1/A, HungaryKFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences (MTA KFKI RMKI), H-1525 Budapest 114, POBox 49, Budapest, HungaryDepartment of Physics, Banaras Hindu University, Varanasi 221005, IndiaBhabha Atomic Research Centre, Bombay 400 085, IndiaWeizmann Institute, Rehovot 76100, IsraelCenter for Nuclear Study, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, JapanHiroshima University, Kagamiyama, Higashi-Hiroshima 739-8526, JapanKEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, JapanKyoto University, Kyoto 606-8502, JapanNagasaki Institute of Applied Science, Nagasaki-shi, Nagasaki 851-0193, JapanRIKEN, The Institute of Physical and Chemical Research, Wako, Saitama 351-0198, JapanPhysics Department, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima, Tokyo 171-8501, JapanDepartment of Physics, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152-8551, JapanInstitute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305, JapanChonbuk National University, Jeonju, KoreaEwha Womans University, Seoul 120-750, KoreaHanyang University, Seoul 133-792, KoreaKAERI, Cyclotron Application Laboratory, Seoul, South KoreaKorea University, Seoul, 136-701, KoreaMyongji University, Yongin, Kyonggido 449-728, KoreaDepartment of Physocs and Astronomy, Seoul National University, Seoul, South KoreaYonsei University, IPAP, Seoul 120-749, KoreaIHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, 142281, RussiaINR_RAS, Institute for Nuclear Research of the Russian Academy of Sciences, prospekt 60-letiya Oktyabrya 7a, Moscow 117312, RussiaJoint Institute for Nuclear Research, 141980 Dubna, Moscow Region, RussiaRussian Research Center "Kurchatov Institute", Moscow, RussiaPNPI, Petersburg Nuclear Physics Institute, Gatchina, Leningrad region, 188300, RussiaSaint Petersburg State Polytechnic University, St. Petersburg, RussiaSkobeltsyn 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

Feb 2011

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

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Forward Calorimetry: MPCMuon Piston Calorimeter (3.1 < |h| < 3.9) : lower x10-3

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Cluster (p0 dominant) ALLDecay photon

π0

Direct photon

PT

Fra

ctio

n of

clu

ster

s

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 s well

p0@200 GeV, h~0

PRD76:051106,2007

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How to extract Dg(x)? (2)• 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]

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Global Fit including Run9 0 ALL By S.Taneja et al (DIS2011)

ala DSSV with slightly different uncertainty evaluation approach

DSSV DSSV + PHENIX Run9 0 ALL

No node …Uncertainties decreased

A node at x~0.1 ?

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