transverse spin and rhic probing transverse spin in p+p collisions

Transverse Spin and RHICProbing Transverse Spin in p+p Collisions

OUTLINE• Features of RHIC for polarized p+p collisions

• Transverse single spin effects in p+p collisions at s=200 GeV

• Towards understanding forward cross sections

• Plans for the future

L.C. BlandBrookhaven National LaboratoryTransverse Polarization in Hard ProcessesComo 7 September 2005

04/19/23 L.C.Bland, Como 2

Developments for runs 2 (1/02), 3 (3/03 5/03) and 4 (4/04 5/03)

• Helical dipole snake magnets• CNI polarimeters in RHIC,AGS fast feedback

• *=1m operataion

• spin rotators longitudinal polarization

• polarized atomic hydrogen jet target

Installed and commissioned during run 4To be commissionedInstalled/commissioned in run 5


RHIC Spin Physics Program

• Direct measurement of polarized gluon distribution using multiple probes

• Direct measurement of anti-quark polarization using parity violating production of W

• Transverse spin: Transversity & transverse spin effects: possible connections to orbital angular momentum?


Calendar Summary for RHICRun-5 p+p Run

• pp commissioning started on March 24, 2005• pp Physics running, for longitudinal polarization, started on April 19, 2005• 410 GeV Collider dev. & data, was May 31st to June 3rd

• Transverse polarization was June 13th to June 16th

• Run ended on June 24, 2005


Total for run

~ 9.2 pb-1 delivered

~ 3.1 pb-1 smpled(nb-1)

(nb-1)

RHIC Run-5 PerformanceRHIC Run-5 Performance

STAR 2005 Longitudinal Goal

Delivered

Sampled


PHENIX DetectorPhilosophy:

High rate capability & granularity Good mass resolution and particle ID

0 reconstruction and high pT photon trigger:

EMCal: ||<0.38, =Granularity = 0.010.01

Minimum Bias trigger and Relative Luminosity:

Beam-Beam Counter (BBC): 3.0<||<3.9, =2


STAR detector layout

• TPC: -1.0 < < 1.0

• FTPC: 2.8 < < 3.8

• BBC : 2.2 < < 5.0

• EEMC:1 < < 2

• BEMC:0 < < 1

• FPD: || ~ 4.0 & ~3.7


First AN Measurement at STARprototype FPD results

STAR collaboration Phys. Rev. Lett. 92 (2004) 171801

Sivers: spin and k correlation in parton distribution functions (initial state)

Collins: spin and k correlation in fragmentation function (final state)

Qiu and Sterman (initial state) / Koike (final state): twist-3 pQCD calculations, multi-parton correlations

Can be described by several models available as predictions:

Similar to result from E704 experiment (√s=20 GeV, 0.5 < pT < 2.0 GeV/c)

√s=200 GeV, <η> = 3.8


Studying pseudorapidity, =-ln(tan/2), dependence of particle production probes parton distributions at different Bjorken x values and involves different admixtures of gg, qg and qq’ subprocesses.

Assume:

1. Initial partons are collinear2. Partonic interaction is elastic

pT, pT,2

Why Consider Forward Physics at a Collider? Kinematics

Can Bjorken x values be selected in hard scattering?

Deep inelastic scattering Hard scattering hadroproduction


Simple Kinematic LimitsMid-rapidity particle detection:

0 and <>0

xq xg xT = 2 pT / s

Large-rapidity particle detection:

>>

xq xT e xF (Feynman x), and

xg xF e(

p+p +X, s = 200 GeV, =01.0

0.8

0.6

0.4

0.2

0.0

frac

tion

0 10 20 30pT,(GeV/c)

qq

qg

gg

Large rapidity particle production and correlations involving large rapidity particle probes low-x parton distributions using valence quarks

NLO pQCD (Vogelsang)


How can one infer the dynamics of particle production?Particle production and correlations near 0 in p+p collisions at s = 200 GeV

Two particle correlations (h)Inclusive 0 cross section

Do they work for forward rapidity?

STARSTAR

At √s = 200GeV and mid-rapidity, both NLO pQCD and PYTHIA explains p+p data well, down to pT~1GeV/c, consistent with partonic origin

STAR, Phys. Rev. Lett. 90 (2003), nucl-ex/0210033

Phys. Rev. Lett. 91, 241803 (2003)hep-ex/0304038


<z>

<xq>

<xg>

• Large rapidity production ~4 probes asymmetric partonic collisions

• Mostly high-x valence quark + low-x gluon

• 0.3 < xq< 0.7

• 0.001< xg < 0.1

• <z> nearly constant and high 0.7 ~ 0.8

• Large-x quark polarization is known to be large from DIS

• Directly couple to gluons = A probe of low x gluons

NLO pQCDJaeger,Stratmann,Vogelsang,Kretzer

p p 0, 3.8, s 200GeV

Forward production in hadron collider

pd

pAu

q

g

Q2 ~ pT2

s 2EN

ln(tan(2

))

xq xF / zEN

xqpxgp

xF 2E

s

z E

Eq

xg pT

se g

EN

(collinear approx.)


STARSTAR

xF and pT range of FPD data


The error bars are point-to-point systematic and statistical errors added in quadrature

The inclusive differential cross section for 0 production is consistent with NLO pQCD calculations at 3.3 < η < 4.0

The data at low pT are more consistent with the Kretzer set of fragmentation functions, similar to what was observed by PHENIX for production at midrapidity.

ppX cross sections at 200 GeV

D. Morozov (IHEP), XXXXth Rencontres de Moriond - QCD,March 12 - 19, 2005

NLO pQCD calculations by Vogelsang, et al.


STAR -FPD STAR -FPD PreliminaryPreliminaryCross SectionsCross Sections

Similar to ISR analysisJ. Singh, et al Nucl. Phys. B140 (1978) 189.

6

5

13

3

B

N

pxdp

dE B

TN

F


• PYTHIA prediction agrees well with the inclusive 0 cross section at 3-4• Dominant sources of large xF production from:

● q + g q + g (22) + X

● q + g q + g + g (23) + X

g+g andq+g q+g+g

q+g

Soft processes

PYTHIA: a guide to the physicsForward Inclusive Cross-Section: Subprocesses involved:

q

gg

q g

STAR FPD


Single Spin AsymmetryDefinitions

• Definition:

• dσ↑(↓) – differential cross section of then incoming proton has spin up(down)

Two measurements:• Single arm calorimeter:

R – relative luminosity (by BBC)

Pbeam – beam polarization

• Two arms (left-right) calorimeter:

No relative luminosity needed

dd

ddAN

L

LR

RNN

RNN

PA

BeamN

1

LRRL

LRRL

BeamN

NNNN

NNNN

PA

1π0, xF<0

π0, xF>0

Left

Right

p p

positive AN: more 0 going

left to polarized beam


Caveats:Caveats: -RHIC CNI Absolute polarization -RHIC CNI Absolute polarization still preliminary. still preliminary. -Result Averaged over azimuthal -Result Averaged over azimuthal acceptance of detectors.acceptance of detectors. -Positive XF (small angle -Positive XF (small angle scattering of the scattering of the polarized proton). polarized proton).

Run 2 Published Result.Run 2 Published Result. Run 3 Preliminary Result.Run 3 Preliminary Result. -More Forward angles.-More Forward angles. -FPD Detectors.-FPD Detectors. - ~0.25 pb- ~0.25 pb-1-1 with P with Pbeambeam~27%~27%

Run 3 Preliminary Run 3 Preliminary Backward Angle Data.Backward Angle Data. -No significant Asymmetry -No significant Asymmetry seen.seen. (Presented at Spin 2004: hep-ex/0502040)


Figure 3 Diagram showing the boundary Figure 3 Diagram showing the boundary between possible “phase” regions in the between possible “phase” regions in the =ln(1/x) vs ln Q=ln(1/x) vs ln Q22 planeplane

.. Edmond Iancu and Raju Venugopalan, review for Quark Gluon Plasma 3,Edmond Iancu and Raju Venugopalan, review for Quark Gluon Plasma 3, R.C. Hwa and X.-N. Wang (eds.), World Scientific, 2003 [hep-ph/0303204].R.C. Hwa and X.-N. Wang (eds.), World Scientific, 2003 [hep-ph/0303204].

New Physics at high gluon densityNew Physics at high gluon density

1. Shadowing. Gluons hidingbehind other gluons. Modificationof g(x) in nuclei. Modified distributionsneeded by codes that hope to calculateenergy density after heavy ion collision.

2. Saturation Physics. New phenomena associated with large gluon density.• Coherent gluon contributions. • Macroscopic gluon fields.• Higher twist effects.• “Color Glass Condensate”


Dependence of RdAu

pp

dAuR

1972

1dAu

• From isospin considerations, p + p h is expected to be suppressed relative to d + nucleon h at large [Guzey, Strikman and Vogelsang, Phys. Lett. B 603, 173 (2004)]

• Observe significant rapidity dependence similar to expectations from a “toy model” of RpA within the Color Glass Condensate framework.

y=0

As y grows

Kharzeev, Kovchegov, and Tuchin, Phys. Rev. D 68 , 094013 (2003)

See also J. Jalilian-Marian, Nucl. Phys. A739, 319 (2004)

G. Rakness (Penn State/BNL), XXXXth Rencontres de Moriond - QCD,March 12 - 19, 2005

pp

dAu

pp

dAuinelasticdAubinary

inelasticpp

dAu

dpEd

dpEd

NR

1972

1

3

3

3

3


Constraining the x-values probed in hadronic scattering

Guzey, Strikman, and Vogelsang, Phys. Lett. B 603, 173 (2004).

CONCLUSION: Measure two particles in the final state to constrain the x-values probed

Log

10(x

Glu

on)

Gluon

TPC

Barrel EMC

FTPC FTPC

FPDFPD

For 22 processes

• FPD: || 4.0

• TPC and Barrel EMC: || < 1.0

• Endcap EMC: 1.0 < < 2.0

• FTPC: 2.8 < < 3.8

Collinear partons: ● x+ = p

T/s (e+1 + e+2)

● x = pT/s (e1 + e2)

Log10(xGluon)


Back-to-back Azimuthal Correlationswith large

Midrapidity h tracks in TPC

• -0.75 < < +0.75

Leading Charged Particle(LCP)

• pT > 0.5 GeV/c LCP

Coi

cide

nce

Prob

abil

ity

[1/

radi

an]

S = Probability of “correlated” event under Gaussian

B = Probability of “un-correlated” event under constant

s = Width of Gaussian

Fit LCP normalized distributions and with

Gaussian+constant

Beam View Top View

Trigger by forward

• E > 25 GeV

• 4

]

]


PYTHIA (with detector effects) predicts

• “S” grows with <xF>

and <pT,>

• “s” decrease with

<xF> and <pT,>

PYTHIA prediction agrees with p+p data

Larger intrinsic kT

required to fit data

Statistical errors only

25<E<35GeV

45<E<55GeV

STARSTAR

STAR Preliminary

STAR Preliminary


Plans for the Future


NSF Major Research Initiative (MRI) ProposalNSF Major Research Initiative (MRI) Proposal-submitted January 2005submitted January 2005

[hep-ex/0502040][hep-ex/0502040]

STAR Forward Meson Spectrometer


STAR detector layout with FMS

TPC: -1.0 < < 1.0

FTPC: 2.8 < < 3.8

BBC : 2.2 < < 5.0

EEMC:1 < < 2

BEMC:-1 < < 1

FPD: || ~ 4.0 & ~3.7FMS: 2.5<< 4.0


Three Highlighted Objectives In FMS Proposal(not exclusive)

1. A d(p)+Aud(p)+Au+X+X measurement of the parton model gluon density distributions xg(x) in gold nucleigold nuclei for 0.001< 0.001< xx <0.1 <0.1. For 0.01<x<0.1, this measurement tests the universality of the gluon distribution.

2. Characterization of correlated pion cross sections as a function of Q2 (pT

2) to search for the onset of gluon saturation effects associated with macroscopic gluon fields. macroscopic gluon fields. (again d-Au)(again d-Au)

3. Measurements with transversely polarized transversely polarized protonsprotons that are expected to resolve the origin resolve the origin of the large transverse spin asymmetriesof the large transverse spin asymmetries in reactions for forward forward production. production. (polarized pp)(polarized pp)


Frankfurt, Guzey and Strikman, Frankfurt, Guzey and Strikman, J. Phys. G27 (2001) R23 [hep-ph/0010248].J. Phys. G27 (2001) R23 [hep-ph/0010248].

Pythia Simulation Pythia Simulation

• constrain x value of gluon probed by high-x quark by detection of second hadron serving as jet surrogate.

• span broad pseudorapidity range (-1<<+4) for second hadron span broad range of xgluon

• provide sensitivity to higher pT for forward reduce 23 (inelastic) parton process contributions thereby reducing uncorrelated background in correlation.


Disentangling Dynamics of Single Spin Asymmetries

Spin-dependent particle correlations

Collins/Hepplemann mechanism requires transversity and spin-

dependent fragmentation

Sivers mechanism asymmetry is present for forward jet or

Large acceptance of FMS will enable disentangling dynamics of spin asymmetries


New FMS CalorimeterLead Glass From FNAL E831804 cells of 5.8cm5.8cm60cmSchott F2 lead glass

Loaded On a Rental Truck for Trip To BNL


Run-5 FPDRun-6 FPD++Run-7 FMS

FPD++ Physics for Run6

We intend to stage a large version of the FPD to prove our ability to detect direct photons.


How do we detect direct photons?

Isolate photons by having sensitivity to partner in decay of known particles:

π0 M=0.135 GeV BR=98.8%

K0 π0π0 0.497 31%

0.547 39%

π0 0.782 8.9%

Detailed simulations underway


Where do decay partners go?

• Gain sensitivity to direct photons by making sure we have high probability to catch decay partners• This means we need dynamic range, because photon energies get low (~0.25 GeV), and sufficient area (typical opening angles few degrees at our ranges).

m = di-photon parameters

z = |E1-E2|/(E1+E2)

= opening angle

Mm = 0.135 GeV/c2 ()

Mm=0.548 GeV/c2 ()

mesonfor factor Lorentz of in terms angle opening minimum gives ,1

2sin

yprobabilit with angle opening maximum gives ,1

1

22sin

photon second ofenergy gives ,1

1,Eh photon wit candidatefor

21

2min

2max

2

1

m

m

m

EE

cM

zz

z

E

cM

Ez

zE

E


Sample decays on FPD++

With FPD++ module size and electronic dynamic range, have >95% probability of detecting second photon from decay.


Timeline for the Baseline RHIC Spin ProgramOngoing progress on developing luminosity and polarization

Program divides into 2 phases:

s=200 GeV with present detectors for gluon polarization (g) at higher x & transverse asymmetries;

s=500 GeV with detector upgrades for g at lower x & W production

Research Plan for Spin Physics at RHIC (2/05)


Summary / Outlook

• Large transverse single spin asymmetries are observed for large rapidity production for polarized p+p collisions at s = 200 GeV

AN grows with increasing xF for xF>0.35

AN is zero for negative xF

• Large rapidity cross sections for p+p collisions at s = 200 GeV is in agreement with NLO pQCD, unlike at lower s. Particle correlations are consistent with expectations of LO pQCD (+ parton showers).

• Large rapidity cross sections and particle correlations are suppressed in d+Au collisions at sNN=200 GeV, qualitatively consistent with parton saturation models.

• Plan partial mapping of AN in xFpT plane in RHIC run-5

• Propose increase in forward calorimetry in STAR to probe low-x gluon densities and establish dynamical origin of AN (complete upgrade by 10/06).


Backups


Towards establishing consistency between FPD ()/BRAHMS(h)

Extrapolate xF dependence at pT=2.5 GeV/c to compare with BRAHMS h data. Issues to consider:

• of BRAHMS data for 2.3<pT<2.9 GeV/c bin. From Fig. 1 of PRL 94 (2005) 032301 take =3.07 xF=0.27

• /h ratio?

Results appear consistent but have insufficient accuracy to establish p+p isospin effects


SystematicsMeasurements utilizing independent calorimeters consistent within uncertainties

Systematics:

Normalization uncertainty = 16%: position uncertainty (dominant)

Energy dependent uncertainty = 13% - 27%: energy calibration to 1% (dominant) background/bin migration correction kinematical constraints


FPD Detector and FPD Detector and º reconstructionº reconstruction

• robust di-photon reconstructions with FPD in d+Au collisions on deuteron beam side.

• average number of photons reconstructed increases by 0.5 compared to p+p data.


d+Au d+Au +++X, pseudorapidity correlations with forward +X, pseudorapidity correlations with forward

HIJIING 1.381 Simulations HIJIING 1.381 Simulations

• increased pT for forward over run-3 results is expected to reduce the background in correlation

• detection of in interval -1<<+1 correlated with forward (3<<4) is expected to probe 0.01<xgluon<0.1 provides a universality test of nuclear gluon distribution determined from DIS

• detection of in interval 1<<4 correlated with forward (3<<4) is expected to probe 0.001<xgluon<0.01 smallest x range until eRHIC

• at d+Au interaction rates achieved at the end of run-3 (Rint~30 kHz), expect 9,700200 (5,600140) coincident events that probe 0.001<xgluon<0.01 for “no shadowing” (“shadowing”) scenarios.


STAR Forward Calorimetry Recent History and Plans

• Prototype FPD proposal Dec 2000 – Approved March 2001 – Run 2 polarized proton data (published

2004 spin asymmetry and cross section)

• FPD proposal June 2002– Review July 2002

– Run 3 data pp dAu (Preliminary An Results)

• FMS Proposal: Complete Forward EM Coverage(hep-ex/0502040).


Students prepare cells at test Lab at BNL

transverse spin and rhic probing transverse spin in p+p collisions

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