Outline:1. Introduction (pol. DIS)2. Goals of the spin program 3. STAR detector at RHIC4. Local polarimetry5. Results (longitudinal pol.)6. Summary and outlook

Joanna Kiryluk (MIT) 17 May 2006, Subatomic Physics Group seminar, LANL

Spin Physics with STAR at RHIC

2

(Spin) Structure of the NucleonInclusive (polarized) Deep Inelastic Scattering

€

~ σ = σ ↑↓ + σ ↑↑

negligible< 10-4

€

rμ +

v N →

rμ ' + X

small

€

~ Δσ||

= σ ↑↓ - σ ↑↑

Cross section for €

Q2 = -q2 = − p - p'( )2

= 2EE' 1- cosθ( )

x =Q2

2P ⋅q =

EE' 1- cosθ( )M E - E'( )

y =P ⋅q

P ⋅ p =

E - E'

E

W 2 = P +q( )2 = M 2 + 2M E − E '( ) − Q2

* square mass (scale)

fraction of * energy

fraction of the proton momentum carried by the struck ‘quark’

final hadronic state mass square

DIS: W2>M2 and v>> M2

F1 and F2 - unpolarized structure functions g1 and g2 - polarized structure functions

Experimentally measured: to determine spin structure function

g1

€

A||=

Δσ||

σ ~

g1

F1

Kinematic variables:

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p = (E,E,0,0)

P = (M,0,0,0)

€

p'= (E ',E 'cosθ,E 'sinθ cosφ,E 'sinθ sinφ)

observed

ij

(Lepton and nucleon - longitudinal polarization)

3

Measurements of g1(x) to determine its first moment

to test spin sum rules:

Description of a nucleon structure in the naïve Quark Parton Model

q(x) -spin independent and q(x) -spin dependent parton distribution functions

€

q2 → ∞ , x = const

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F1(x) =1

2eq

2

q

∑ q+(x) + q−(x)[ ] =1

2eq

2

q

∑ q(x), F2(x) = 2xF1(x)

g1(x) =1

2eq

2

q

∑ q+(x) − q−(x)[ ] =1

2eq

2

q

∑ Δq(x), g2(x) = 0

- Bjorken (1966) derived from current algebra and isospin symmetry; rigorous prediction of QCD€

Γ1 = g1(x)dx0

1

∫ =1

2eq

2

q

∑ Δq Limited x-range of the measurementsextrapolations needed

€

Γ1p - Γ1

n =1

6Δu - Δd( ) =

1

6

gA

gV

⎛

⎝ ⎜

⎞

⎠ ⎟n →p

Ellis-Jaffe (1974) derived by neglecting strange-parton contribution

€

Γ1p(n ) = +(-)

1

12Δu − Δd( ) +

1

36Δu + Δd − 2Δs( ) +

1

9Δu + Δd + Δs( )

€

~gA

gV

⎛

⎝ ⎜

⎞

⎠ ⎟Ξ →Λ

EMC: J.Ashman et al, Nucl. Phys. B328, 1 (1989)

Ellis-Jaffe prediction (1974) ± s= 0 assumed … and thus the rest of Jz arises from orbital motion of its constituents.

EMC results (1989) ± ± s = - ± ±

‘Spin crisis’ : the quarks spins carry only a small fraction of the proton spin Orbital momentum? Gluons?

First measurements of Γ1 of the proton

Spin structure of the proton

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Jz = Szq +L z

q( )

only quarks(assumption)

1 2 4 3 4 where Sz

q =1

2Δu + Δd + Δs[ ]

=ΔΣ1 2 4 4 3 4 4

- total contribution of quarks to the spin of the proton

E80,E130EMCDisagreement between prediction and EMC measurement

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~ 10 years later: SMC, E143, ... - pQCD analysis of the spin structure function:

€

g1(x,Q2) =1

2eq

2dy

yx

1

∫q

∑ Δq(x,Q2) + Δq (x,Q2)[ ]Cq x / y,α s( ) +eq

2

2n f

dy

yΔG(y,Q2)CG x / y,α s( )

=0 LO≠0 NLO

1 2 4 3 4 x

1

∫scale Q2 dependence (caused by quarks interacting with each other by exchange of gluons)

Polarized Deep Inelastic Scattering

Call for alternative methods:Most promising: polarized proton-proton interactions

prompt jets

scale Q2 dependence

Eb = 190 GeVEb = 29 GeV

g1 ~

LO NLO

The singlet and non-singlet quark helicity distributions are well known, The gluon helicity is poorly constrained, but its value is probably not huge

Eb = 190 GeVEb = 29 GeV

statistical errors only

NLO pQCD

SMC - PRD 58 112002 (1998).

singlet quark pol.x

gluon polarizationxg

6

Brookhaven National Laboratory, Upton NY, USA

542 collaborators from51 institutions and 12 countries

The STAR Collaboration

PHENIX

BRAHMS &PP2PPPHOBOS

STAR1.2 km

RHIC

STAR = Solenoid Tracker at RHICRHIC = Relativistic Heavy Ion Collider

Polarized proton-proton collisions with STAR

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are to determine:• gluon polarization

• (anti-)quark polarization (u,d)

• anti-strange quark polarization (model dependent, Xu et. al. hep-ph/0511061)

In addition: spin program with transversly polarized beams (not covered here)

€

r p +

r p → jet + X

r p +

r p → π 0 + X

r p +

r p → γ + (jet +) X

r p + p → W± + X → e± + X

€

s = 200 - 500 GeV

s = 500 GeV

The goals of STAR spin program at RHIC(longitudinal polarization)

Rhic-Spin program review article: G.Bunce et.al., hep-ph/0007218

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r p + p → ( anti− )

r Λ + X s = 200 − 500 GeV

8

€

s = 200 (500) GeV

Known NLO corrections (all cases)

Determination of gluon polarization - a major emphasis at STAR-Spin program at RHIC

Inclusiveproduction

High production rate

Classic ‘tool’ to access gluon distribution function - but rare probes

How are we going to access information about pol. gluon distribution function?

9

€

pT3

d Δ( )σ pp →FX

dpT dη= dxa

xamin

1

∫ dxbxb

min

1

∫ Δ( ) fa xa,μ( ) Δ( ) fb xb,μ( ) abc

∑

× pT3

d Δ( ) ˆ σ ab →FX '

dpT dηxaPa , xbPb,PF ,μ( ) + P.C.

€

ˆ σ (0) + α sˆ σ (1) + ...... perturbative series

measure unknown pdf calculate

€

σ =σ ±σ

ALL =Δσ

σ =

σ ++ −σ +−

σ ++ + σ +−

σ - very small (difficult to measure) We measure asymmetries instead, where most of systematic effects cancel outRequired knowledge of unpolarized pdf’s in the measured kinematic region

• Cross section for inclusive (single) particle production

• Asymmetries

€

xamin = xTeη 2 − xTe−η( )

xbmin = xa xTe−η 2xa − xTeη( )

xT = 2pT s

Inclusive particle/jet production in pp interactions (1)

for jets - no fragmentation functions are needed (systematics!)

€

σ ∝ pdf⊗ pdf⊗ hard scattering⊗ fragmentation( )

10

Inclusive particle/jet production in pp interactions (2)

• Convolutions “pdf pdf cross section” relatively complicated and inversion is not straightforward

• At the moment emphasis is on NLO predictions of ALL in terms of “model” g, to study the sensitivity of the observable

• Future: CTEQ-style global analysis of variety of ALL data (should include NLO)

• Alternative approach: “correlations” (+jet, di-jets, +) that probe kinematics in more detail

€

ALL =σ σ → g(x)

Sensitivity to the gluon polarization

Similar

Jager et.al, PRD70(2004)034010 =0

V. Guzey et al., Phys.Lett.B603 (2004)

W.Vogelsang RBRC/BNL, RHIC-AGS User’s Mtg talk

g=g inputGRSV-std

g=0 input

g=-g input

scale ~ pT2 of

Gluon polarization from Prompt Photon Production (1)

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ALL =σ ++ −σ +−

σ ++ +σ +−

≈ Δg(xg )

g (xg ) ×

e i2Δqi xq( )∑

e i2qi xq( )∑

× ˆ a LL gq → qγ( )

The cross section asymmetry ALL for ( description at Leading Order):

€

r p +

r p → + jet + X

Direct measurement of gluon polarization

Quark-Gluon Compton scattering dominates

(~75%) direct production

calculable in pQCD,=A1p

known from pol. DIS

LO pQCD

€

x1(2) =pT

γ

sexp(±η γ ) + exp(±η jet )[ ]

€

cosθ * = tanh ± η jet −η γ( ) 2( )[ ]

€

where xg = min x1, x2[ ]

and xq = max x1,x2[ ]

DIS results

x

A1p

Parton kinematics reconstruction from pT,, and jet measurements:

direct production

A1p

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Gluon polarization from Prompt Photon Production (2)G

/G

Two beam energies - large range of xg - needed to minimize extrapolation errors

€

G (Q2) = ΔG(x, Q2) dx0

1

∫ Sim

ula

ted A

LL

We expect it will be determined to a precision of 0.5

Reconstructed xg (Leading Order)

hep-ex/9907058

The best determination of G will result from a global analysis of the data from: RHIC (other channels, e.g. inclusive jet production), pDIS (HERMES, COMPASS), and possibly eRHIC through g1(x,Q2)

measurements over a wide range Compass DIS06

Deep Inelastic Scattering experiments

STAR xG range from future -jet channel

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Flavor Decomposition of the proton’s spin

Are the light-quark polarizations in the proton sea is large and asymmetric?

Unpolarized experiments, like e.g. NMC, E866/NuSea, have shown a strong breaking of SU(2) symmetry in the antiquark sea, with: (strong x-dependence)

Where?

Semi-inclusive polarized DIS - sensitivity reduced by fragmentation functions and eq

2 weighting

x

Q2=2.5GeV2

€

d (x) /u (x) ≠1

B. Dressler et al. Predictions

13

14

Polarized Quark Densities (HERMES data)

Good agreement with NLO-QCD

First complete separation of pol. PDFs without assumption on sea polarization u(x) > 0 and d(x) < 0

u(x), d(x) ~ 0

No indication for s(x) < 0< 0 in measured range 0.02 < x < 0.6€

u ∫ (x)dx = −0.002 ± 0.043

Δd ∫ (x)dx = −0.054 ± 0.035

€

s∫ (x)dx = +0.006 ± 0.029 ± 0.007

Earlier HERMES conclusions of unpolarised strange sea confirmed (factor 2 smaller error bars)

E. Auschenauer (HERMES), Workshop on Hardron Structure at J-PARC, November-December 2005 14

15

€

σ = max :

θ∗ = π θ∗ = 0

- angle between lepton and proton momenta in W rest frameyW - rapidity of W boson

€

x(2 ) =MW

sexp (±yW )

Cross section for W production at Leading Order at Q2=M2W and pT

W

neglected

€

dσ H1,H 2

dyW dΩ∗ =3

16πi, j

∑ 1± cosθ∗( )

2f H1

i x1( ) f H 2j x2( ) ˆ σ ij

€

yelab

=

ln

+ cos∗

−cos∗

⎡

⎣ ⎢

⎤

⎦ ⎥+ yW cosθ

∗= ± 1 −

4p2T,e

MW2

yW (not observable) can be reconstructed from lepton pT and rapidity Additional cuts required!

€

for example c.s . for W+ production dσ H1,H 2

dyW dΩ∗ ~ uH1− x1( )d H 2

+ x2( ) 1− cosθ∗( )

2+ d H1

+ x1( )uH 2− x2( ) 1+ cosθ∗

( )2 ⎡

⎣ ⎢ ⎤ ⎦ ⎥

W+

€

u H− x( ) d H2

+ x2( )

€

e+ ν e

z+

W+

€

d H+ x( ) uH2

− x2( )

€

νe e+

z

yW<0yW>0

Flavor Decomposition of the proton’s spin

from W boson production at RHIC

€

ˆ σ ij = πGF 2MW

2

3sVij where i,j=u,d (approx)

W produced through weak interactionHelicity of the quark and antiquark (u and d flavors dominate) are fixed.

Ideal tool to study spin flavor structure of the proton!

sign=pL,e,/| pL,e | in ~ 70% cases 15

16

€

ALPV(yW ) =

σ − −σ +

σ − + σ +

= Δu(x1 )d (x2 ) − Δd (x1 )u(x2 )

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

= Δd(x1 )u (x2 ) − Δu (x1 )d(x2 )

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

€

AL ≈Δq

q for y

W≥1

AL ≈ −Δq

q for y

W≤ -1

)yexp(s

Mx W

W1(2) ±=

yW - rapidity of the W boson

Forward e detection gives direct probe of quark (anti-quark) polarization:

Single spin asymmetry with W production

W+ W-

Electron(positron) detected in ElectroMagnetic Calorimeter: Barrel+Endcap -1 < e < 2 Barrel only -1 < e <1

0.035 0.7 x

Pythia generator

ll0.035 0.7 x

l l

Q2=M2W

Assumption:no cuts on lepton

17

€

− d

d

€

− u

u

€

d

d

0.035 0.7 x

0.035 0.7 x

Polarized pdf GRSV2000M.Gluck et al, PRD 63 094005,

Standard Scenario: flavor symmetric light sea (antiquark) distributions

Valence Scenario: completely SU(3)f broken scenario with flavor asymmetric light sea densities:

€

u≠d≠s

STAR will distinguish

between the two scenarios

Unpolarized pdf GRV98M.Gluck et al., Eur.Phys.JC5 461

€

u

u

NLO calculations: P.Nadolsky, C.Yuan hep-ph/0304002

18

Rich program with high energy polarized pp colliderMany measurements proposed by theorists over a decade ago

Experimental difficulties: How to get and accelerate polarized proton beams

19

Difficulties in the acceleration of polarized protons (1)

Assumption: protons are being accelerated in a planar circular accelerator: thus the equilibrium orbit lies in the XY-plane

The spin precession and the motion of the proton:

€

d

r s

dt= −

q

mcγγG +1( )

r B 0 ×

r s Thomas - BMT

d

r β

dt= −

q

mcγ

r B 0 ×

r β Lorentz

mean spin vector in the canonical rest frame reached from the frame, where the particle of spin s has velocity by the boost

€

where gyromagnetic anomaly G =g - 2

2 = 1.7928 for protons( )

and γ =E

mc 2

€

rB ≡

r B 0 = B0

ˆ e z and

r E = 0

€

rβ ⊥

r B 0( )

€

∗)

€

∗) r s

€

rv

Since G > 0 both and rotate about with angular frequencies c (relativistic cyclotron freq.) and s

for equilibrium orbit (R=const): |c|=v/R , i.e. c increases as the particle accelerates

€

rβ r s

r B 0

€

Ωc = −q

γmcB0 and Ωs = γG +1( )Ωc

Source: W.MacKay (BNL)

20

Difficulties in the acceleration of polarized protons (2)

In a perfect machine with uniform field :-all particles moving along the equilibrium orbit of radius R and mean spin precesses about the z-axis

In a real hadron machine there are 2 effects which disturb ideal situation and lead to appearance of so called depolarizing resonance conditions (number of spin rotations per turn = number of spin kicks per turn )

€

rB = B0

ˆ e z

€

rB • the quadrupole fields that focus the beam have a component of in the horizontal

plane and Bz=Bz(r)

• there are imperfections in the fields due to misaligment of magnets and field errors(equilibrium orbit is not the idealized circle)Imperfection resonance condition: G = νspin = n E (spacing between resonances) ~ 523 MeV

Resonance condition depends on the energy of the particle and the number of resonances of varying strenght will grow with increasing energy.

The intrinsic resonance condition due to vertical focusing fields:G = νspin = Pn ± νy P: superperiodicity (AGS: 12) νy: betatron tune (AGS: 8.75) n = integer

Source: W.MacKay (BNL)

In reality s will pick up a net non-zero precession around horizontal axes along and perp. to the beam

21

€

ˆ x

€

ˆ y

€

ˆ z

€

ˆ x

€

ˆ y

€

ˆ z

€

ˆ x €

ˆ y

€

ˆ x €

ˆ y

€

ˆ z = 0

€

ˆ x

€

ˆ y

€

ˆ x €

ˆ y

€

ˆ z

€

ˆ x €

ˆ y

€

ˆ x €

ˆ y €

ˆ z = 0

€

ˆ x

€

ˆ y

The unwanted precession which happens to the spin in one half of the ring

is unwound the other halfResult: Stable spin direction - vertical (z-direction) Spin is up in one half of the ring and down in the other halfSiberian snake built and first tested at Indiana (Krish et al, 1989)

At RHIC: two snakes in each ring - spin rotation around y-axis and x-axis

€

ˆ x

€

ˆ y €

ˆ z

€

ˆ x

€

ˆ y

€

ˆ x

€

ˆ y

Difficulties in the acceleration of polarized protons (3)Solution: Siberian Snakes

Siberian snake - proposed by Derbenev and Kondratenko in 1976 -magnet system that rotates particle’s spin s through 180o around a horizontal axis each revolution to cancel out depolarizing effects

A

A A

22

pp Run 2002 2003 2004 2005-ongoing

analysis

2006 run started in March > 2006 LongTermGoals

CM Energy 200 GeV 500 GeVBeam polarization/direction at STAR 0.15 T 0.30 T/L 0.40

L0.45 L/T 0.7 T/L 0.7 T/L

Lmax [ 1030 s-1cm-2 ] 2 6 6 16 80 200

Lint [pb-1 ] (STAR,delivered) 0.3 0.5/0.4 0.4 9 /0.4 320 800

200 GeV

YB

Helicity +Helicity -Polarization pattern at STAR(2004)

RHIC ( Relativistic Heavy Ion Collider ) - polarized pp

collider

stable polarization direction at RHIC - vertical

beam polarization measured by RHIC polarimeters

longitudinal polarization at STAR and Phenix

STAR local polarimeter - to (continuously) monitor beam polarization direction

23

Solenoidal Magnet• B = 0.5 T

Tracking Detectors• Time Projection Chamber ||<1.6 • Forward TPC 2.5<||<4.0 • Silicon Vertex Tracker ||<1

Trigger Detectors• Beam-Beam Counters 3.4<||<5 • Zero-Degree Calorimeter ||~6

+ E-M Calorimeters - installation in stagesto be completed before 2006• Barrel EMC ||<1 • Endcap EMC 1.0< <2.0 • Forward Pion Detector 3.3<|<4.1

STAR continues to add EM calorimetry to detect high-energy , e, 0 ( wide region ) TPC+EMC for jet reconstruction

BBC + scaler board system for relative luminosity and polarization monitoring

STAR detector

CTB

ZDCZDC

(BBC)

Cutway side view of the detector

where pseudorapidity ln tan

Yellow(proton) beam

Blue(proton) beam

24

Beam Beam Counters at STAR

~7.5m

Forward Pion Detector

(FPD)

STAR Magnet and

Time Projection Chamber

BBC (East) BBC (West)

Schematic side view of the STAR detector

beam

pip

e

A coincidence condition between BBC East and West (3.4 < || < 5) suppresses beam-gas background and used for: triggering in pp (minimum bias, jet

triggers) (relative) luminosity measurements for

ALL

local polarimetery

7.5m

- scintillator annulus installed around the beam pipe,

on the east and west poletips of STAR magnet at ±3.74m

from IR for detection of charged particles in 2 < || < 5

25

The BBC East and West data sets sorted by beam polarization states: 1. Polarized Yellow beam (sum over Blue beam polarization states) + heads towards the East2. Polarized Blue beam (sum over Yellow beam polarization states) + heads towards the West

Beam Beam Counters - Transverse Single Spin Asymmetries

for charged hadron production in forward region

BBC West

BBC East

Left Right

Top

BottomXTop

Right Left

Bottom 3.4<||< 5.0 (small tiles only)

Interaction

Vertex

Single spin asymmetries measured for p+p -> A + X, where A – hit(s) in the BBC

€

εLR

= NL↑NR

↓ − NL↓NR

↑

NL↑NR

↓ + NL↓NR

↑~

€

Pbeamvert × AN × cos(φ)

Pbeamrad × AN × sin(φ)

Left-Right

Top-Bottom

NL(R) – number of counts in BBC (East or West - small annuli )counted every bunch crossing by the scaler system

26

Unexpected AN of unknown origin measured with the BBC Strong pseudorapidity dependence of AN for xF>0 and AN = 0 for xF<0 Use for local polarimetry

AN BBC <cos > = p1 AN

CNI +p0

AN BBC ~0.7 AN CNI ~ 1% 3.9 < < 5.0

AN BBC = 0 3.4 < < 3.9

Transverse Single Spin AsymmetriesBBC Preliminary Results

ε(CNI) (x10-3) CNI Asymmetry (x10-3)

ε(B

BC

) (x1

0-3)

BB

C A

sym

metr

y (

x1

0-3)

€

ε BBC = Pbeamvert × A N

BBC × cos(φ)

Pbeamvert = εCNI /A N

CNI

27

BBC - Local Polarimeter at STAR

- Stable spin direction at RHIC is vertical- Spin Rotator brings to almost radial- D0/DX magnet causes spin precession- Longitudinal at IR- DX/D0/Spin Rotator put back to vertical

Measured asymmetryi ~ AN Pi Left-Right asym - sensitive to verical polarizationTop-Bottom asym - sensitive to radial polarization

Longitudinal polarization at STAR (Pvert and Prad< 5%) - first step to ALL

measurement

Pvert Prad

Rotators OFF Rotators ON Rotators OFF Rotators ON

CNI polarimeter

BBCBBC

DROP

Rotators OFF

ON

CNI polarimeter non-zero non-

zero

BBC Left-Right ( vertical ) NON_ZERO

ZERO

BBC Top-Bottom ( radial ) zero zero

STAR Electromagnetic Calorimeter at mid-rapidity

0 (pT > 5.5 GeV/c)

BEMC module

Invariant Mass (GeV/c2 )

Barrel EMC (BEMC) - a lead-scintillator sampling calorimeter, used to detect and trigger on high pT photons and jets (completed in 2005)

Coverage |<1 and = 2 [ TPC covarage |<1.6 and = 2 120 modules, total 4800 towers ( x )tower = 0.05 X 0.05 Depth ~ 21 X0 Energy resolution dE/E~16%/√E

Shower Maximum Detector (SMD) – located at ~ 5 X0 in BEMC, a detector with high spatial resolution ( x )tower = 0.007 X 0.007, used for /0

29

EMC on-line event displaydi-jet event

- via TPC pT for charged hadrons+EMC ET for e-m showers

2) Trigger used in this analysis - High Tower:

ET > 2.4 GeV deposited in one tower ( x = (0.05 x 0.05)

+ additional requirement of BBC coincidence.

1) Jets reconstruction - midpoint cone algorithm (Tevatron II)seed energy = 0.5 GeV, cone angle R = 0.4 in splitting/merging fraction f=0.5

Jet reconstruction at STAR

pa

rton

pa

rticled

ete

ctor

etcp

e

,,

,

ν ,,

gq,

4) Selections: charged tracks | | < 1.6 and pT >0.1 GeV/c

jets: pT jet > 5 GeV/c , 0.2< jet (det) <0.8 beam-background: Ejet(neutral)/Ejet(total)< 0.8(0.9) for 2003

(2004) |z-vertex| < 60cm

3) Data set: 0.4 pb-1 (2003 and 2004) recorded luminosity <Pb> =0.3 (2003) and <Pb> = 0.4 (2004)

5) Final statistics (after cuts) ~ 300k jets for ALL and ~ 40k jets for cross section (ET>3.5 GeV)

30

Data/Monte Carlo comparison• Pythia 6.203 (CDF Tune A) + GEANT3 +

reconstruction

(r) = fraction of jet pT in sub-cone r

(common jet shape variable)

• HT trigger bias at low pT

• Bias decreases with increasing jet pT, well described by MC

31

Cross section for inclusive jet production

acceptedeventsMB

MBvertBBC

NdtL −

⋅=

⋅∫εσ

generated

measured

N

Npurity :

trueT

measT

trueT

p

ppresolution

− : ~25% ± 5%

From simulations. Consistent result obtained from di-jet evts

€

1

2π

1

dη

dσ

dpT

=1

2π ⋅0.6⋅

1

ΔpT

⋅1

L ⋅dt∫⋅

1

c pT( )⋅

dN

dpT

(MC)

• Bins of width 1-sigma (resolution) “purity” of ~35% over range on the diagonal.• Motivates application of bin-by-bin correction factors (dominated by trigger eff.)

€

1

NMB-eventsaccepted

MB( ) →1

NMB-eventsaccepted ⋅ psMB

trigHighTower( )

( ) ( )( )pythia

Tpythia

geantTgeant

T pN

pMpc =

“measured”

“true”

32

• Good agreement between MB and HT data

• Good agreement with NLO over 7 orders of magnitude

• Leading systematic uncertainty– 10% E-scale uncertainty 50%

uncertainty on yield• Other sources of systematic

uncertainties (smaller, not shown): normalization, BBC trigger efficiency, background contribution

• Agree with NLO calculation within systematic uncertainty

Preliminary results for the cross section in inclusive jet production in p+p at sqrt(s)=200 GeV vs NLO

Calculation

33

Double Longitudinal Spin Asymmetry Measurements

Require concurrent measurements:• magnitude of beam polarization, P1(2) RHIC polarimeters

• direction of polarization vector at interaction point

• relative luminosity of bunch crossings with different

spin directions: STAR experiment

• spin dependent yields of process of interest Nij

€

P12P2

2 ⋅ Ldt∫Statistical significance:

€

R =L

++

L+−

€

ALL =σ ++ −σ +−

σ ++ + σ +−

=1

P1P2

×N++ − RN+−

N++ + RN+−

BBC +scalers

34

Results limited by statistical precision Total systematic uncertainty ~0.01 (STAR) + beam pol. (RHIC) GRSV-max gluon polarization scenario disfavored

jet cone=0.4B.Jager et.al, Phys.Rev.D70(2004) 034010

Double spin asymmetry ALL(preliminary) resultsin inclusive jet production in p+p collisions at

sqrt(s)=200GeV

Sources of sys. uncertainties: background contribution, trigger bias, relative luminosity, residual (non-longitudinal) asymmetries, bunch to bunch systematic variations (random pattern analysis)+ beam pol.ALL(Pb)/ALL= 2Pb/Pb ~25%

Uncertainties - statistical only25% scale uncertainty (from beam polarization) not included

35

High-tower trigger Jet patch trigger

Statistical precision achieved for inclusive jet prod’n @ STAR in 2005

AL

L(j

et)

Prospects for Run5 (first long pp run) and Run6(ongoing)

0.2 < < 0.8

Potential to discriminate between several ALL predictions based on DIS parametrizations

Jet patch trigger

• Pb~45% (~40% in Run4) L= 3/pb (0.3/pb in Run4) FoM (Run5)/FoM(Run4) = 16 • Acceptance: 3/4 BEMC complete (1/2 in Run4)

• Two complementary jet triggers permit assessment of trigger bias due to q vs. g jet differences in shape, multiplicity, hardness in z.

Run5 improvements:

36

Summary and Outlook

• First longitudinal spin results from STAR - inclusive jets Gluon polarization is not likely saturated

• 10 times the statistics from run-5, with better polarizations(ongoing analysis)

• a new run started on March 1, 2006

• stay tuned for new probes and sqrt(s) = 500 GeV!

37

Spin Structure of the NucleonSummary: past, present and future

1980s E80,130 - SLAC

EMC - CERN

1990s consolidation SMC - CERN

E142… - SLAC HERMES - DESY

2000s COMPASS - CERN HERMES - DESY RHIC-SPIN - BNL and continuing measurements

2010s planned J-PARC - KEK, eRHIC - BNL

Spin Crisis

Tim

e

G

Lz??

38

Backup

39

Beam Beam Counters Instrumentation- 1 cm thick scintillator- 4 optical fibers for light collection - 1,2 or 3 tiles connected to a PMT- 15 photoelectron/MIP

~2m

T

BL R~0.5

m

Large hexagonal annulus: - inner (outer) diameter 38cm (193cm); - of 18 pixels, covering 2.1 < || < 3.3 and 0< <2 ;- 8 PMT, no timing information

Small hexagonal annulus: - inner (outer) diameter 9.6cm (48cm); - of 18 pixels, covering 3.3<||< 5.0 and 0< <2- 16 PMT - feasible segmentation (i) two bins in h and (ii) azimuthal Top/Bottom/Left/Right, timing information

tiles triplet

40

Monte Carlo (MC) = Pythia+Geant for STAR

BBC response simulator: Light yield: dE/dE(MIP)x15 photoelectrons(MIP)= N photoel. Single photoelecton resolution = 30% PMT gain = 0.30 pC/photoelectron ADC bin = 0.25 pC Time resolution = 900 ps

Data and MC agree

Beam Beam Counters - trigger data

pp minbias trigger condition = BBC East and West coincidence (3.4 < || < 5) Cross section: σBBC= σtot(pp) x acc(BBC) = 51 mb x 0.53 ~ 27 mb ( 87% of ) from MC In agreement with RHIC luminosity measurements (van der Meer scans)

L=Rate(BBC)/σBBC e.g. at L=1030 cm-2 s-1 the Rate(BBC) ~ 27 kHz DAQ limitations - cannot take data at this rate Solution: deadtimeless scaler boards - - very useful when ‘details’ such as ADC information not needed, but statistics is an issue

€

σ inelastic−s.diffraction

41

STAR Scaler Boards B

BC

E.W

coin

cidence

co

unts

bunch crossing#

Run 4150010

Bit# Input 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 BBC E.W (Luminosity bit) 18 BX1 19 BX2 20 BX3 21 BX4 22 BX5 23 BX6 24 BX7 …and same for BBC West

Bunch crossing number

Example of the BBC scaler bits

BBC East PMT#i, i=1-16

The scaler board - 24 bit and 10 MHz VME memory module It has 224 cells, each cell 40-bit deep to keep continuous (deadtimeless) record for up to 24 hours operation at 10 MHz (10 MHz clock corresponds to bunch crossing frequency at RHIC, 107 ns)

24 input bits = 7(bunch crossing) + 17(physics inputs) 217=105 combinations Physics input bits = data from fast detectors e.g. BBC, which consists of discriminator outputs from individual PMTs as well as logic levels produced by the STAR Level 0 trigger electronics

Lum

inosi

ty ~

42

bunch crossing#

Time [Run Number]

Relative Luminosity R=L++/L+-

R = 1 and time dependent!

05/16/03 05/30/03

1.0

Relative Luminosity Measurement from Beam Beam Counters

Precision of relative luminosity monitoring critical: for ALL ~1% ALL/ALL ~5% if R/R~10-3

Luminosity ~ BBC coincidence rate ( large cross section of ~27mb) counted every 107ns

RHIC stores up to 120 bunches per ring - different bunches injected with different spin orientation

- collision luminosity can vary with spin combination

Relative luminosities uncertainties: Rstat~ 10-4 – 10-3 and Rsyst < 10-3

beam-1beam-2

YB

Helicity +Helicity -

Polarization pattern at STAR

43

BBC Event Selection for Asymmetry Measurement

Right scattering

3.4 < < 3.9

3.9 < < 4.9Mean=2.3RMS =1.2

Mean=2.3RMS =1.2

Number of hits PMT number

Number of hits PMT number

Monte Carlo simulation• Data

44

Local polarimetry -online monitoringfeadback within minutes

left-right

Time

TimeTime

BB

C R

aw A

sym

met

ry (

x F>

0)

Rot

ator

s’ c

urre

nts

(A)

Bea

m P

olar

izat

ion

3 hours

RHIC CNI

45

Anti-Lambda at RHIC: The measurement of hyperon polarization at RHIC can give insights into polarized fragmentation and parton distribution functions

)!(xs

Pythia s-bar

gluon€

PΛ +(η ) =

σ p + p−>Λ + (η )X −σ p + p−>Λ − (η )X

σ p + p−>Λ + (η )X + σ p + p−>Λ − (η )X

≡ DLL (η )

DIS, set II

SU(6), set II (GRSV00_std)

Xu, Liang, Sichtermann, hep-ph/0511061

€

PΛ

+

STAR acceptance

€

pT > GeV/c and s = 200 GeV

- D. de Florian et al, PRL81(1988)530 - C. Boros et al, PRD62(2000)014021

- B.Q. Ma et al, NPA703(2002)346- Q.H. Xu et al, PRD65(2002)114008

€

s

DIS, set I

SU(6), set I(GRSV00_val)

Lambda-bar polarization (p+p) is sensitive (in a model dependent way) to

Lambda polarization (p+p) less sensitive to s, because of u,d fragmentation, e.g.

€

s

46

• reconstruction at STAR via decay channel: p+(Br=64%)

- combining TPC tracks with opposite charges- cuts for tracks and decay vertex topology- |<xF>|~0.008 <pT> ~1.5 GeV/c • Data sample (after all cuts) 2003+2004 ~30k Lambda and ~27k anti-Lambda

Lambda and anti-lambda reconstruction in p+p collisions at STAR

MΛ=1.1157 GeV(PDG)

Invariant mass

Podolanski-Armenteros plot

€

α = pL+ − pL

−( ) pL+ + pL

−( )

€

pv GeV( )

- momentum of positive (negative) tracks parallel to the V0 momenta- momentum of tracks perpendicular to the V0 momentum

€

pL+( pL

− )pv

47

• Standard Method: Angular distribution of decay proton in the rest frame

relies on knowledge of the Acceptance Function (usually from simulation).

Measuring Longitudinal polarization without Acceptance Function

€

dN

d cosθ=

N tot

2A(cosθ)(1+ α

r P Λ • ˆ p p ),

• The four combinations (++, --, +-, and -+) of beam helicities at RHIC, and

symmetries (parity, proton indistinguishability) in the production process

allow one to determine the longitudinal polarization (spin transfer) from

measured asymmetries in (narrow) intervals in ,

where α decay parameter (empirical) = 0.642(PDG)

A(cos) acceptance

€

ε =N + − RN−

N + + RN−≈ α cosθ Pbeam PΛ

+

in which the Acceptance Function largely cancels.

N+=N+++ N+-

N-=N-- + N-+

R- relative luminosity

Number of Lambdas

48

Lambda polarization from 2003 and 2004 pp data with longitudinal polarization - Preliminary

Results

€

DLL

€

PΛ+(η ) =

σ p + p−>Λ+ (η )X −σ p + p−>Λ− (η )X

σ p + p−>Λ+ (η )X + σ p + p−>Λ− (η )X

≡ DLL

P small ( |xF|~0.01, pT~1.5GeV )

Gluon fragmentation at such low pT

should be important

Results limited by statistical precision

Prospects for Run5 (first long pp run), Run6 (on-going) and beyond Jet-Patch trigger 160k High-Tower trigger 80k MinBias 36k

Run5

Run6 (10pb-1) DLL~0.04 for pT> 6 GeV/c

>100 pb-1 needed for DLL~0.01 for pT> 8 GeV/cTrigger on anti-Lambda ?

-0.5 0.5

pT[GeV/c]

Q. Xu, hep-ex/051205