spin physics at rhic - kek · 2004. 3. 5. · • origin of the proton spin 1/2 ? – ∆Σ=...

Spin Physics at RHIC

“Particle Physics Phenomenology” at KEKMarch 2, 2004

Yuji Goto (RIKEN/RBRC)

March 2, 2004 Yuji Goto (RIKEN/RBRC) 2

Spin physics at RHIC• Longitudinal polarized proton collision

– helicity structure of the proton• gluon polarization

– parity violating asymmetries• Transverse polarized proton collision

– transverse structure/motion = orbital angular momentum– transversity distribution

• last unmeasured leading-twist distribution

– single transverse-spin asymmetries• transversity, higher twist, T-odd structure and fragmentation

functions, …

• Small-angle pp elastic scattering– unpolarized & polarized measurements


Longitudinal polarized proton collision

• Origin of the proton spin 1/2 ?

– ∆Σ = 0.1-0.3: quark contribution by polarized DIS experiments

– gluon contribution• known poorly from scaling violations in pol. DIS experiments,

spanning a small range of Q2

Lg +∆+∆Σ=21

21

)1GeV(

(th)(sys)(stat)0.1 :SMC22

4.15.0

4.02.0

0.13.0

=

=∆ +−

+−

+−

Q

g

nucleon target

γ*

or

or

quark

lepton beampolarized DIS


Gluon polarization

• Polarized semi-inclusive DIS– COMPASS/SMC/HERMES

• Polarized hadron collision– Fermilab E704 π0/multi-photon– RHIC polarized proton collision

lepton beamor

or nucleon target

γ*

gluonheavy flavor

proton beam

proton beam

or

or

gluon

photon

proton beam

proton beam

or

or gluon

gluonheavy flavor


RHIC (Relativistic Heavy-Ion Collider)


RHIC polarized proton collision

BRAHMS & PP2PP

STARPHENIX

AGS

LINACBOOSTER

Pol. Proton Source500 µA, 300 µs

Spin Rotators Siberian Snakes

200 MeV Polarimeter AGS Quasi-Elastic PolarimeterRf Dipoles

RHIC pC CNI PolarimetersAbsolute Polarimeter (H jet)

PHOBOS

AGS pC CNI Polarimeter

Partial Helical Snake

RHIC√s = 50 - 500 GeV

Partial Solenoid Snake

2001 - 2002

2003

2004 −

√s = 200 GeV transverse polarized proton collisions

√s = 200 GeV transverse+longitudinal polarized proton collisions

√s = 200 GeV longitudinal polarized proton collisions


RHIC polarized proton collision• High √s and high Q2

– √s = 200 GeV and 500 GeV in the future– perturbative QCD applicable

• scale dependence of the NLO pQCD calculation in the cross section measurement

• scale dependence is expected to largely cancel in the asymmetry measurement

M. Stratmann and W. Vogelsang


RHIC polarized proton collision

• Cancellation of systematic uncertainty– flexible combination of spin

direction every crossing

STAR and IP12

PHENIX and PP2PP

IP4 and IP10


RHIC polarized proton runs• Run2: 2001-2002

– transverse polarized collision 150 nb-1

– polarization ~15%• Run3: 2003

– transverse+longitudinal polarized collision 600 nb-1

– polarization ~27%• Run4: 2004 March-April (5 weeks)

– polarized proton commissioning run to develop more luminosity and more polarization

– longitudinal polarized collision data expected• Run5: 2005

– physics run again


Longitudinal polarized proton collision

• Double longitudinal-spin asymmetry

– P: polarization• AGS/RHIC proton-carbon CNI polarimeter• polarized hydrogen gas-jet (absolute polarimeter)• local polarimeters at experiments

– N: yield– R: relative luminosity

++

−+

−+++

−+++

−+++

−+++

=

⋅+⋅−

⋅⋅

=

+−

=

LLR

NRNNRN

PP

ddddALL

21

1σσσσ parallel

anti-parallel


STAR


PHENIX


PHENIX π0 cross section– data covers over 8 orders of

magnitude• pT = 1 – 13 GeV/c

– NLO pQCD calculation is consistent with our data

• within the scale µ = pT/2 - 2pT

– confidence in understanding subprocesses

– input to the fragmentation-function uncertainty

9.6% normalization error not shown

Run2 resulthep-ex/0304038PRL 91, 241803 (2003)


(GeV/c)Tp0 1 2 3 4 5 6

LL

A

-0.15

-0.1

-0.05

0

0.05

0.1=200 GeVs from pp at LL A0π

PHENIX Preliminary

Polarization scaling error~30% is not included

GRSV-max

GRSV-std

GRSV-max:∆G = 1.84

GRSV-std:∆G = 0.42

(at Q2 = 1 GeV2)

PHENIX ALL(π0)

Polarization scaling error δP/P ~30% is not included:

- Analyzing power AN (100 GeV) = AN (22 GeV) is assumed

- δP/P ~ 30%: combined stat. and syst. error for AN (22 GeV) [AGS-E950]

B. Jäger et al.,PRD 67 (2003) 054005NLO pQCD calculations


Gluon polarization

• SMC– semi-inclusive hadron-pair measurement– photon-gluon fusion

• COMPASS– 2004: δ(∆G/G)stat ~ 0.15 ??

lepton beamor

or nucleon target

γ*

gluonheavy flavor


Gluon polarization

• B. Jäger et al., hep-ph/0310197– NLO pQCD calculation– cannot make sizable negative ALL(π0) in this kinematic

range

gg

qq

gq

Fraction of π0s produced


Transversity– last unmeasured leading-twist distribution

• Near future– π+π- interference fragmentation function

• J. Collins, S. Heppelmann, and G. Ladinsky, Nucl.Phys. B420 (1994)565

• R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920

– Collins effect in jets• J.C. Collins, Nucl. Phys. B396, 161(1993)

– inclusive jet production• W. Vogelsang and M. Stratmann, RBRC Workshop on

Transversity (2000)

)( XJetppAT ++→⊥ π

( )XppAT +→ −+⊥ ),( ππ


Transversity at PHENIX

• Transversity throught π+π-

interference FF– non-vanishing “support”

only in the ρ mass region

2P

)( 1xqiδ

)( 2xqi

11Px

22Pxijσ∆

1psv

+π−π

Jet

Jet

ProtonStructure

Hard ScatteringProcess

InterferenceFragmentation

[ ][ ]{ } [ ])(ˆsin)(ˆsin...ˆ)()(

...ˆ)(ˆ)()()cos()sin(sinsin

461

112

002

21

211010 zqzqxGxG

zqxGxqNNNN

PA qq

gg

qgqgI

beam δδσδσδδδ

φδδδδπ+⋅+⋅

+⋅⋅⋅⋅−−=

+−

= ←→

←→

⊥

200 GeV

500 GeV

][GeVp jetT

qqqqqq

m

I ∆+≤=

===

δδ

φη σρ

2,3/ˆˆ4ˆ

1cos83.0,0

102

,

GeV,

Maximum Asymmetry

ρ,σ


Transversity throught π+π- interference FF• Projected asymmetry

pair vs TT pXpA )( +→ −+⊥ ππ

Small aymmetry below5% but good rate!

MeV MeV GeV

GeV

9508004

4

32

22

21

,

1

21

<<

>+

>

=∫ −

mpp

E

pbLdt

TT

ππGeV) Tang 85.0,1(cos == mA φ

)1010Tang sin(sinsincos δδδδφ −⋅⋅⋅⋅A

For 32pb-1 (1 week of running)

5.2 Million events in 32 pb-1

15% with pair after cuts


Fragmentation function at BELLE

• Collins fragmentation function– e+e- → π+

jet1π-jet2X

– reaction plane defined with beam (z-axis) and jet axis

– product (π) plane defined with π and jet axis

– φ: angle between the planes

A ∝ Η1⊥(z1)Η1

⊥(z2)cos(φ1+φ2)– can analyze with/without

using jet axisA ∝ Η1

⊥(z1)Η1⊥(z2)cos(2φ)

S. Lange, A.Ogawa (STAR)K. Hatsuko, M.G-Perdekamp (PHENIX)


Fragmentation function at BELLE

• π+π- interference fragmentation function– e+e- → (π+π-)jet1(π-π+)jet2X– stay in the mass region around ρ−mass– find pion pairs in opposite hemispheres– observe angles φ1+φ2 between the event-plane (beam,

jet-axis) and the two pion planes.A ∝ δqΙ(z1, m1) δqΙ(z2, m2)cos(φ1+φ2)


HERMES

• Polarized semi-inclusive DIS

longitudinalpolarized target

transversepolarized target

ULA CollinsUTA

Aπ+~Aπ0>0Aπ-<0 and smaller

Aπ+>0Aπ0~Aπ-<0 and larger


Single transverse-spin asymmetries

• Left-right asymmetry

• Fermilab E704– √s = 20 GeV– unexpected large

asymmetry at large-xF

– 0.2 < pT < 2.0 GeV/c

left

right

Fermilab-E704LRRL

LRRLN NNNN

NNNNP

A↓↑↓↑

↓↑↓↑

⋅+⋅

⋅−⋅⋅=

1

↓

↑

↓↑

↓↑ =⋅+⋅−

⋅=LL

RNRNNRN

PA

LL

LLN 1

square-root formula

luminosity formula


STAR forward π0

• FPD (Forward Pion Detector)– EM calorimeters to cover large-

xF region

FPDEastBBC West BBC East


STAR forward π0

• Cross section– consistent with NLO pQCD calculations

• AN– large spin effects observed for √s = 200 GeV pp

collisionshep-ex/0310058


Neutron asymmetry at IP12• PHENIX local polarimeter R&D

EM Cal Base

PbWO4

Charge Veto

Neutron VetoHadron Cal Base

Pb

Scintillator

W+Fiber Cal

Post-shower


Neutron asymmetry at IP12Hadron Cal EM Cal

AN = −0.126±0.008±0.041AN = −0.116±0.018±0.020

preliminary preliminary

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


PHENIX local polarimeter

• ZDC + SMD– ZDC: Zero-Degree Calorimeter

• hadron calorimeters at the most forward location (~18m from IP)

– SMD: Shower-Maximum Detector• plastic scintillator array• X: 7 array, Y: 8 array

1 ZDC

SMD


Blue Yellow

Blue Yellow

Blue Yellow

PB=35.5% PB=37%

PHENIX local polarimeterSpin Rotators OFF

Spin Rotators ONCorrect Current !

Spin Rotators ONCurrent Reversed

transversely-polarizedproton collisions

radially-polarizedproton collisions

longitudinally-polarizedproton collisions


PHENIX local polarimeter

ST is measured with PHENIX local polarimeter

001.013.009.032.974.)( ++

−−=yellowSL

up-down asymmetryleft-right asymmetry

222 ,1 radialTverticalTTTL SSSSS −− +=−=

000.005.009.014.993.)( ++

−−=blueSL


STAR local polarimeter

• BBC (Beam-Beam Counter)– η = 2 ~ 5– AN ~ +0.5%

Blue beam, BBC West310−×

310−×

Run# Run#Rotators ONOFF

ε CNI (ON-LINE)

εLR BBC = 0.13(2)

εTB BBC = -0.24(2)

Mea

sure

d as

ymm

etry

Yellow beam, BBC Eastε CNI (ON-LINE)

εLR BBC = - 0.07(2)

εTB BBC = - 0.04(2)

drop drop

CNI CNI

BBCBBC

Rotators ONOFF


Summary• We are giving first results of spin physics at RHIC

– gluon polarization in longitudinal polarized proton collisions (ALL)– single transverse-spin asymmetries (AN)

• Many developments have been done and are ongoing– polarimetry

• AGS/RHIC, polarized hydrogen gas-jet• local polarimeter: application of the AN results

– more luminosity and polarization• AGS snakes

– detector upgrades• Many future topics

– more gluon polarization data– transversity (with fragmentation functions)– parity-violating asymmetries– small-angle pp elastic scattering


Backup slides


STAR

RICH: |η|<0.3, ∆φ = π/6

Central Trigger Barrel |η| < 1

Time Projection Chamber |η|< 1.5

Silicon VertexTracker

Forward TPCs2.4 < |η| < 4.0

Barrel EMC0< η< 1 ∆φ =2π/5

Endcap EMC1< η <2 ∆φ = 2π

Forward Pion Detector (FPD) 3.1 < η < 4.4

+ upgradeBeam-Beam Counters

2 .4< |η| < 5.0

+ patch

Magnet Coils

0.5T

4.2 m

2 m

|η| < 1 ∆φ = 2π

Run0Run1Run2 and beyond

B=0.25T

~

Spin2001-2002

2003-


Relative luminosity– achieved relative luminosity precision δR = 2.5×10-4 → δALL =

0.2%• pessimistic estimation limited by ZDC statistics (30 times less than

BBC statistics used in relative luminocity measurements)– ALL of BBC relative to ZDC consistent with zero (<0.2%)

• strong indication that both ALLs are zero (very different kinematical regions, different physics signals)

BBC

ZDC


Zero-Degree Calorimeter (ZDC)– tungsten + scintillating fiber hadron calorimeter– 5.1 λI, 149 X0 (3 modules)

beam

beam


High-pT trigger

• √s=200 GeV data collected with high-pT photon trigger– Based on EMCal; Threshold

~1.4 GeV/c– Rejection factor ~110– Analyzed data sample: – 42.7M events (~0.215 pb-1)– √⟨PbPy⟩ ~ 26%

• Minimum Bias data – To obtain “unbiased” π0 cross

section at low pT

– For high-pT photon trigger efficiency study

Pi0 efficiency plateaus for pT>4 GeV/cLimited efficiency at pT<4 GeV/c:

1-2 GeV/c: 6%2-3 GeV/c: 60%3-4 GeV/c: 90%4-5 GeV/c: 95%

Monte Carlo reproduces Data well

Trigger efficiency for π0


π0 reconstruction

– results obtained for four pT bins from 1 to 5 GeV/c

– π0 peak width varies from 12 to 9.5 MeV/c2

from lowest to highest pT bins

– background contribution under π0

peak for ±25 MeV/c2

mass cut varies from 45% to 5% from lowest to highest pTbins

2-3 GeV/cBckgr=17%

3-4 GeV/cBckgr=7%

4-5 GeV/cBckgr=5%

1-2 GeV/cBckgr=45%


π0 counting for ALL

Nπ0: ±25 MeV/c2 around π0 peak (and also ±15 and ±35 MeV/c2 for cross checks)

Nbck1: Two 50 MeV/c2 wide areas adjacent to π0 peak

Nbck2: 250 MeV/c2 wide area between π0 and η peaks

12k3.9k39k38k34k4-5

83k27k208k201k176k3-4

989k335k1146k1059k874k2-3

3478k1470k2129k1777k1278k1-2

Nbck2Nbck1Nπ035 MeV/c2

Nπ025 MeV/c2

Nπ015 MeV/c2

ptGeV/c

Nπ0 and Nbck accumulated statistics


ALL Calculations

ALL averaged over fills

3-4 GeV/c

1-2 GeV/c

4-5 GeV/c

2-3 GeV/c 1-2 GeV/cALL= -2.8%±1.2%χ2/ndf = 64/48

2-3 GeV/cALL= -2.2%±1.5%χ2/ndf = 34/48

3-4 GeV/cALL= -0.2%±3.3%χ2/ndf = 49/48

4-5 GeV/cALL= -2.3%±7.4%χ2/ndf = 39/48


Bunch shuffling

• Systematic error evaluation– randomly shuffle the bunch

combination to calculate false asymmetries

-0.2 -0.1 0 0.1 0.20

20

40

60

80

100

120

140

hasym_set0_pt0Nent = 1000 Mean = 0.000224RMS = 0.01168

hasym_set0_pt0Nent = 1000 Mean = 0.000224RMS = 0.01168

-0.2 -0.1 0 0.1 0.20

20

40

60

80

100

120

hasym_set0_pt1

Nent = 1000 Mean = 0.000916RMS = 0.01407

hasym_set0_pt1

Nent = 1000 Mean = 0.000916RMS = 0.01407

-0.2 -0.1 0 0.1 0.20

20

40

60

80

100

hasym_set0_pt2

Nent = 1000

Mean = 0.000248

RMS = 0.03221

hasym_set0_pt2

Nent = 1000

Mean = 0.000248

RMS = 0.03221

-0.3 -0.2 -0.1 0 0.1 0.2 0.30

20

40

60

80

100

hasym_set0_pt3

Nent = 1000

Mean = -0.004048

RMS = 0.06958

hasym_set0_pt3

Nent = 1000

Mean = -0.004048

RMS = 0.06958

2-3 GeV/c

3-4 GeV/c 4-5 GeV/c

1-2 GeV/c

0 0.5 1 1.5 2 2.50

10

20

30

40

50

60

70

80

90

hchi2_set0_pt0Nent = 1000 Mean = 1.043RMS = 0.2103


0.5 1 1.5 2 2.50

10

20

30

40

50

60

70

80

90



0 0.5 1 1.5 2 2.50

10

20

30

40

50

60

70

80



0.5 1 1.5 2 2.50

10

20

30

40

50

60

70

80

90



2-3 GeV/c

3-4 GeV/c 4-5 GeV/c

1-2 GeV/c

⟨χ2/ndf⟩ ~ 1 ALL: consistent with statistical error


ALL results

0.10±0.140.38±0.24-0.013±0.073-0.023±0.074-0.014±0.0794-5

0.019±0.0550.094±0.092-0.001±0.032-0.002±0.033-0.017±0.0353-4

-0.022±0.017-0.035±0.027-0.022±0.014-0.022±0.015-0.027±0.0162-3

0.004±0.010-0.006±0.014-0.024±0.011-0.028±0.012-0.023±0.0141-2

35 MeV/c225 MeV/c215 MeV/c2

ptGeV/c

bckLLA +0π bck

LLA +0π 1bckLLA 2bck

LLAbckLLA +0π


ALL results: plots

π0+bck 35 MeV/c2

π0+bck15 MeV/c2

Bck2

π0+bck 25 MeV/c2

Bck1


Gluon polarization

• Fermilab E704– fixed target experiment– √s = 19.4 GeV

ALL(π0) PLB 261 (1991) 197. ALL(multi-γ) PLB 336 (1994) 269.

… also shows negative ALL …


Gluon polarization• Direct photon production

– Gluon Compton process dominant• factorization

LLqp

g

gTLL axA

xgxg

pA ˆ)()()(

)( 1 ⋅⋅∆

=

)(/)( gg xgxg∆)(1 q

p xALLa

GS95 NLO (A)

√s=200GeV320pb-1

√s=500GeV800pb-1

inclusive photon measurementphoton + jet measurement

: gluon polarization: measured in pol. DIS: calculable


PP2PP

to IR2

Roman Pot Station with Detectors ( used in 2002 )

RP Station not used in 2002

Roman Pot above beam

Roman Pot below beam

RHIC Intersection Region with PP2PP Basic CB Setup

0. 100. m -100. m

D0

RP Stations

IRDXD0

RP Stations

-50. m 50. m

Inelastic Detectors

Accelerator magnets ensure that scattered protons have beam momentum

• Spin physics at PP2PP– single transverse-spin

asymmetry measurement in CNI region

• Setup– silicon microstrip detectors

to measure (x,y) coordinates with 100 µm pitch

– Need special tune of accelerator and detectors to approach the proton beams


PP2PP

• 2002 engineering run– collected ~300,000 elastic

scattering events– expected results of 2002 data

analysis• extraction of diffraction cone slope b• calculation of single spin asymmetry

AN

– preliminary |t |-distribution for elastically scattered protons with

• for all azimuthal angles and• for a limited range of azimuth,

resulting in full acceptance in |t |0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-t [ GeV2/c2 ]

Arm A

Full φ Acceptance

45° < φ < 135°

Preliminary


Quark polarization flavor decomposition

• W production– parity-violating asymmetry AL

– PHENIX Muon Arms– AL~∆u/u(x)~0.7-0.9 at large-x– no fragmentation ambiguity– x-range limited– complementary to HERMES

semi-inclusive DIS• wide x-range• limited sensitivity to sea flavors

)()()()()()()()(

baba

babaWL xuxdxdxu

xuxdxdxuA+

∆−∆=

+


Transversity throught π+π- interference FF• Invariant mass resolution at PHENIX

accep. into GeV, 0.3

accep. into GeV,

1

2

21 >>

>

,ppz

Eγ

RMS=12 MeVrecpythia mm −

mmm recpythia vs −

GeV GeV

40.21.0

5.0

><<

>

Tpm

z


Parity violating asymmetries

• Jet production• W/Z production

J. -M. Virey, hep-ph/9707470ALL(jet)

J. Murata

spin physics at rhic - kek · 2004. 3. 5. · • origin of the proton spin 1/2 ? – ∆Σ=...

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