Download ppt - Spin of the proton and its transverse spin structure at RHIC

Spin of the protonand its transverse spin structure

at RHIC

HERMES seminar at Tokyo Tech

November 9, 2005

Yuji Goto (RIKEN)

November 9, 2005 Yuji Goto (RIKEN) 2

RHIC – QCD collider


RHIC polarized-proton collision

• Luminosity 11031 cm-2sec-1 at s = 200 GeV achieved– 81031 cm-2sec-1 at 200 GeV and 21032 cm-2sec-1 at 500 Ge

V in the future• Polarization 50% achieved – 70% in the future

BRAHMS & PP2PP

STAR

PHENIX

AGS

LINAC BOOSTERPol. H- Source

Spin Rotators(longitudinal polarization)

Solenoid Partial Siberian Snake

Siberian Snakes

200 MeV Polarimeter AGS Internal Polarimeter

Rf Dipole

RHIC pC PolarimetersAbsolute Polarimeter (H jet)

AGS pC PolarimetersStrong AGS Snake

Helical Partial Siberian Snake

PHOBOS

Spin Rotators(longitudinal polarization)

Spin flipper

Siberian Snakes

installed and commissioned during in 2004 runinstalled in 2005 and to be commissionedto be commissioned


STAR and PHENIX

• STAR detector• 2 coverage for

jet measurement• barrel TPC and EMC• endcap EMC

• PHENIX detector• limited acceptance• high resolution central EMCal• high-rate trigger and DAQ• forward muon detectors


RHIC/PHENIX polarized-proton runs

s = 200 GeV P recorded L recorded LP4 data volume2001-2002 transverse-spin run 15% 0.15 pb-1 20 TB first polarized proton collisions2003 longitudinal-spin run 27% 0.35 pb-1 1.5 nb-1 35 TB spin rotators commissioned, AGS p-C CNI polarimeter2004 commissioning run (longitudinal spin) 40% 0.12 pb-1 3.3 nb-1 35 TB AGS warm snake commissioned, gas-jet absolute polarimeter2005 longitudinal-spin run 49.5/44.5% 3.8 pb-1 205 nb-1 262 TB AGS cold snake installed

2005 – First long longitudinal-spin polarized-proton runFigure of merit (LP4) more than 40 times larger thanthat of previous runs


Where is the proton spin ?

• Origin of the nucleon spin 1/2– polarized DIS experiments showed the quark contribution is only 10-30%– gluon contribution ?

• Scaling violation in polarized DIS

• Semi-inclusive DIS– high-pT hadron pairs– open charm production

(th)(syst)(stat)99.0)GeV 1( :SMC 43.145.0

42.022.0

17.131.0

22

Qg

1.1(syst)(stat)8.06.1)GeV 5( :E155 22 QgB. Adeva et al., PRD 58, 112002 (1998).

P.L. Anthony et al., PLB 493, 19 (2000).

lepton beam or

or nucleon target

*

gluon

heavy flavor


Gluon contribution ?

• Polarized hadron collision– leading-order gluon measurement

• ALL of 0

][][][ qqgqgg

dd

ddA

qqgqgg

LL

proton beam

proton beam

or

or

gluon

photon

proton beam

proton beam

or

or gluon

gluonheavy flavor

direct photon production heavy-flavor production

gg + qg dominantsensitive to the gluon reaction


PHENIX ALL of 0

Theory model C.L. (%)

GRSV-std 17.1-21.7

*GRSV-max (g=g) 0.0-0.0

*GRSV g=0 16.7-18.4

*GRSV g=−g 0.0-0.7

* at input scale Q2 = 0.4 GeV

- Run5 conclusively excludes GRSV maximal scenarios.- Data consistent with GRSV standard and GRSV G = 0.

GRSV-max: g = 1.84

GRSV-std: g = 0.42at Q2=1(GeV/c)2

best fit to DIS data


Single transverse-spin asymmetry

• Left-right asymmetry

• Forward-rapidity– Fermilab-E704

• fixed-target experiment at s = 19.4 GeV

left

rightRightLeft

RightLeftN dd

ddA


STAR forward pion

• Run2 results– In agreement with several model

s including different dynamics:

Sivers: spin and k correlation in initial state (related to orbital angular momentum?)

Collins: Transversity distribution function & spin-dependent fragmentation function

suppressed? (hep-ph/0408356)

Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations

STAR collaboration, hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801

STARSTAR


STAR forward pion

• Run3 results– Positive AN at large positive x

F has been confirmed

• Larger significance to be non-zero & positive than published data

– The first measurement of negative xF AN has been done, and is consistent with zero

• Sensitive to twist-3 gluon-gluon correlation

Statistical error only for <>=4.1


STAR outlook

• Disentangling the dynamics of AN via

– Higher precision AN measurement vs xF and pT

– AN with mid rapidity correlation

– Forward jet

• Proposal for forward calorimeter upgrade– Heavy mesons and direct photons – Low x gluons in nuclei

• Mid rapidity jets– Di-jet kT balance gluon Sivers function

– Inside jet particle correlation Collins function * Transversity

~2.4m square~1500 cells

=4.2

=3.2

=2.5

Current FPD


Mid-rapidity at PHENIX

• Different kinematic region– forward-rapidity at STAR (xF > 0.3)

• quark-gluon reaction dominant

• large contribution from x ~ 0.6 quark polarization/transversity

– mid-rapidity at PHENIX (xF ~ 0)

• contribution from both gluon-gluon and quark-gluon reactions

• x = 0.03 – 0.1

• small quark polarization/transversity

• no gluon transversity in leading twist

• negligible transversity & Collins effect contribution


Mid-rapidity at PHENIX

• Run2 results– AN for both 0 and charged hadrons consistent with zero at mid-

rapidity– ~5 times smaller asymmetry than STAR forward-rapidity data

(~10%)– comparable data with Fermilab-E704 for 0 and charged hadrons

Fermilab-E704


Forward neutron asymmetry

• PHENIX local polarimeter R&D at IP12

EM Cal Base

PbWO4

Charge Veto

Neutron VetoHadron Cal Base

Pb

Scintillator

W+Fiber Cal

Post-shower


Forward neutron asymmetry

Hadron Cal EM Cal

AN = 0.1260.0080.041AN = 0.1160.0180.020

preliminary preliminary

preliminaryvery forward neutronAN ~ -12%xF > 0.2pT < 0.3 GeV/c


Local polarimeter at PHENIX

• Longitudinal component of the proton polarization at PHENIX

• 410 GeV run in 2005– analyzing power of local polarime

ter roughly the same despite doubling of energy

2005 run

%04.021.094.98/

%02.012.048.99 /

YellowL

BlueL

pp

pp


Back-to-back jet at PHENIX

• Boer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the distribution of back-to-back jets

• Should also be able to see this effect with fragments of jets, and not just with fully reconstructed jets

ST

j1

j2

0

2

h

Boer and Vogelsang, Phys.Rev.D69:094025,2004

Ng = Nd (E704)


Back-to-back jet at PHENIX

• Measurement of the gluon Sivers function via AN for di-hadron angular correlations– Sivers distribution is a transverse parton momentum

distribution correlated with the nucleon’s spin axis, which could arise from orbital angular momentum

– Error bars: Expected sensitivity with P=60% and 7 pb-1


Back-to-back jet at STAR


Spin dependence of kT of jets

• Possible helicity effect– We may observe net effec

t (after averaging over impact factor)

kT larger kT smaller

Same helicity

Opposite helicity



• Run3 result: hint of helicity dependence ?– not yet sure

• Run5 data should yield a definite answer.


Summary

• RHIC data began to provide restriction to the gluon-spin contribution to the proton spin– We need to know contribution of the orbital angular moment

um as the final piece

• RHIC has potential measurements of the orbital angular momentum and/or transverse spin structure of the proton– single transverse-spin asymmetries– Sivers effect/function measurements– …

• We will have some transverse-spin run in 2006

Backup slides


Naohito’s analysis


Vertical vs radial run in 2006

Boer and Vogelsang, PRD69:094025,2004

STST

1 = 01 = /2

)sin(||)sin(|| 22,1, TTN ppA

1 = 0 : )sin(|| 2, TN pA 1 = /2 : )cos(|||| 2,1, TTN ppA

21 ~

)(

TT pp

sin(

cos(1~

private communication, Boer and Vogelsang



• Back-to-back nature of jets is broken by initial/final state transverse momentum kT （ e.g., intrinsic kT, soft gluon radiation ）

• Orbital angular momentum: kT× rintroduces intrinsic kT in the initial state

measurement of jet kT gives an access to parton orbital angular momentum


Transversity at PHENIX

• Transversity throught +- interference FF– non-vanishing “support” only in

the mass region

2P

)( 1xqi

)( 2xqi

11Px

22Pxij

1ps ,

Jet

Jet

Proton Structure

Hard Scattering Process

InterferenceFragmentation

)(ˆsin)(ˆsin...ˆ)()(

...ˆ)(ˆ)()()cos()sin(sinsin

4

61

112

002

21

211010 zqzqxGxG

zqxGxq

NN

NN

PA

qqgg

qgqgI

beam

,

200 GeV

500 GeV

][GeVp jetT

qqqqqq

m

I

2,3/ˆˆ4ˆ

1cos83.0,0

102

,

GeV,

Maximum Asymmetry


Transversity throught +- interference FF

• Projected asymmetrypair vs TT pXpA )(

GeV) Tang 85.0,1(cos mA

)1010Tang sin(sinsincos A

Small aymmetry below5% but good rate!

MeV MeV

GeV

GeV

950800

4

4

32

22

21

,

1

21

m

pp

E

pbLdt

TT

For 32pb-1 (1 week of running)

5.2 Million events in 32 pb-1

15% with pair after cuts