Spin Physics with High Energy Polarized pp Collisions Junji Tojo - - PowerPoint PPT Presentation

Spin Physics with High Energy Polarized pp Collisions

Junji Tojo RIKEN Spin and Quantum Structure in Hadrons, Nuclei and Atoms (SQS04)

Tokyo Institute of Technology February 20th, 2004

Junji Tojo (RIKEN)

Physics with Polarized pp Collisions

• Spin structure of the proton

– Understanding the proton spin 1/2 on the basis of quarks and gluons – Determination of polarized parton distribution functions with hard scattering processes

• Spin effects in the fundamental reactions

– Search for new phenomena caused by unexpected mechanisms

• Physics beyond the standard model

– Polarized partons as a tool to search for new physics

Junji Tojo (RIKEN)

Spin Structure of the Proton

• Understanding the proton spin 1/2 on the basis of quarks

and gluons

• Proton spin sum rule
• Polarized DIS experiments at SLAC/CERN/DESY from

1970’s showed

• Looking for missing contributors to the proton spin

– Measuring with polarized pp collisions at RHIC

: quark polarizaion :gluon polarization :orbitalangular momentum

z

g L ∆Σ ∆

0.1 0.2 ∆Σ − ฀

1 1 2 2

z

g L = ∆Σ + ∆ +

, , g q q ∆ ∆ ∆

Junji Tojo (RIKEN)

Tool : Hard Scattering Processes

• Emitting Partons : f(x)
• Hard interaction of

partons : σ

• Parton fragments into

hadron : D(z)

• Universality of f(x), σ ,

D(z)

3 1 2 3 ,

ˆ ( ) ( ) ( )

i j i j

d d E f x f x D z dP dp dt σ σ =∑∫

Junji Tojo (RIKEN)

Asymmetries

• ALL: Double longitudinal spin asymmetry

– Useful in extracting quark/gluon helicity distributions

) ( ) ( ) ( ) ( +− + ++ +− − ++ = σ σ σ σ

LL

A

AN:Twist-3 or T ATT: Transversity AL:Parity Violation

Junji Tojo (RIKEN)

Wide Variety of Reactions Available in pp Collisions

Our Bible : “Prospects for Spin Physics at RHIC”

• G. Bunce, N. Saito, J. Soffer and W. Vogelsang
• Ann. Rev. of Nucl. And Part. Science 2000, 50 : 525

Junji Tojo (RIKEN)

Prompt photon production

The Golden Channel for ∆g Determination

• Gluon Compton Dominates

– At LO LO no fragmentation function – Small contamination from annihilation

2 i i 2 i u,d,s 2 i i 2 i u,d,s LL 1 1 LL

e f (x g( ) e f ( A x ) ˆ a (gq x ) g(x ) q )

= =

= ⊗ ⊗ ∆ → γ ∆

∑ ∑

A1

Junji Tojo (RIKEN)

∆g Measurement by Prompt Photon

prompt photon GS95

x

( )

G x ∆

Junji Tojo (RIKEN)

W Production in Polarized pp Collisions

• W is produced through pure V-A

– Chirality is fixed ideal for spin structure studies

• W couples to weak charge ~ flavor

– Flavor is (almost) fixed ideal for flavor structure studies

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

W a b a b L a b a b

u x d x d x u x A u x d x d x u x

+

∆ −∆ = +

Junji Tojo (RIKEN)

Physics beyond the Standard Model

One of Expectations

• Anomalous Parity Violation

in Jet Production

– Contact Interaction (Scale L)

• CDF L>1.8 TeV
• D0 L>2.4 TeV
• RHIC Spin Reach L~3.3 TeV

– New Gauge Boson Z’

Junji Tojo (RIKEN)

Relativistic Heavy Ion Collider at Brookhaven National Laboratory

Junji Tojo (RIKEN)

RHIC Spin Collider Complex

Junji Tojo (RIKEN) EMCAL

MuID MuTr RICH PCs TEC/TRD DC TOF BBC MVD ZDC

The PHENIX Detector

Junji Tojo (RIKEN)

The STAR Detector

Junji Tojo (RIKEN)

RHIC Spin Run Since 2000

• Run1 : Sep. 2000

– The first polarized proton beam acceleration in one RHIC ring – One Siberian Snake, One pC CNI polarimeter

• Run2 : Dec. 2001 - Jan. 2002

– The first spin run with transverse polarization – 4 Siberian Snakes, Two pC CNI polarimeters –

• Run3 : Apr. – May 2003

– The first spin run with longitudinal polarization – 4 Spin rotators, AGS pC CNI polarimeter –

• Run4 : Apr. 2004, very soon !

– Commissioning for high PB and L – AGS warm snake, Absolute polarimeter, Spin flipper

• 1

200GeV, 0.15, 0.15pb (PHENIX)

B

s P dt L = = =

∫

• 1

200GeV, 0.25, 0.35pb (PHENIX)

B

s P dt L = = =

∫

Run2 and Run3 Results Highlight

Junji Tojo (RIKEN)

AN in Forward Neutron Production (Run2)

• Exp. for PHENIX Local

Polarimeter at 12 O’clock

• Unexpected observation !
• This neutron results used

for PHENIX Local Polarimeter in Run3

Junji Tojo (RIKEN)

R F T

p µ µ = =

NLO pQCD CTEQ6M PDF KKP FF Kretzer FF

π0 Cross Section (Run2)

• π0 measurement by PHENIX
• Results consistent with

NLO pQCD calculation

– Within the scale dependence (µ = pT/2, pT, 2pT) – Favors a larger gluon-to-pion fragmentation function (KKP)

• Important confirmation of

theoretical foundations for spin physics measurements

– Applicability of pQCD

PHENIX, PRL91, 241803 (2003)

Junji Tojo (RIKEN)

AN in Forward π0 Production (Run2)

• Forward π0 detection by STAR
• Large spin effects observed,

qualitatively consistent with models extrapolating from FNAL E704 data at √s = 20 GeV. – Collins effect : Transversity – Sivers effect : Orbital motion – Twist-3 : quark-gluon correlation

STAR, hep-ex/0310058 Submitted to PRL FNAL E704, √s = 20 GeV

Junji Tojo (RIKEN)

J/ψ Cross Section (Run2)

• J/ψ detection in both ee and

μμ channels by PHENIX

• Cross sections are sensitive

to the production mechanism – Color Octet Model (COM) describes cross sections with the present statistical precision.

• Future high statistical

measurement of J/ψ polarization allows us to test the production mechanism.

Junji Tojo (RIKEN)

ALL (pp→ π0X) (Run3)

• π0 measurement by PHENIX
• Double long. asym. ALL sensitive to

∆g(x) : Mixture of qq, qg and gg scattering

• Assumption : Analyzing Power of

RHIC CNI polarimeter To be calibrated with the Absolute Polarimeter installed in Run4

• The first measurement of nonzero

ALL in the RHIC Spin Collider

) ( ) ( ) ( ) ( +− + ++ +− − ++ = σ σ σ σ

LL

A

(GeV/c)

T

p

1 2 3 4 5 6

LL

A

• 0.15
• 0.1
• 0.05

0.05 0.1

=200 GeV s from pp at

LL

A π PHENIX Preliminary

Polarization scaling error ~30% is not included

GRSV-max GRSV-std

Solid line : B.Jagger et al., PRD67, 054005 (2003)

(100GeV) (24GeV)

N N

A A =

Junji Tojo (RIKEN)

Summary

• Spin physics run in RHIC has started since Dec.

2001.

• In two physics runs (Run2 and Run3), we obtained

the results of

– AN in Forward Neutron Production – π0 Cross Section – AN in Forward π0 Production – J/ψ Cross Section – ALL (pp→ π0X)

– And more

• Performance of RHIC as the Spin Collider will be

enhanced by new accelerator hardware installed in 2004-2005.