quest for nucleon spin: past, present & future

Quest for Nucleon Spin: Past, Present & Future

Abhay DeshpandeRIKEN BNL Research Center

Stony Brook UniversityApril 2nd, 2003

RIKEN BNL Research Center

2

OverviewOverviewNUCLEON SPIN (Quick review of the Past)• Present status and open questions

RHIC SPIN (Present)• Relativistic Heavy Ion Collider at BNL• Status of RHIC as polarized proton collider • Recent results with polarized protons at RHIC • Long term perspective for RHIC Spin (pp)

Electron Ion Collider (EIC) at RHIC (Future)• Electron ring at RHIC• Physics at the EIC (mostly pol. e-p and some e-A)• Status & Plans

April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

3

Parton Distributions

q

q

g

Nucleon

u u

d

averagehelicity quark)Qq(x 2,

differencehelicity quark )Qq(x 2,

fliphelicty )Qq(x 2,

(well known)

(moderately well known)

(unknown)

onDistributi Gluon)QxG 2,(

(moderately well known)

onPolarizati Gluon )QxG 2,((unknown)


4

Our knowledge of spin structure Our knowledge of spin structure functionfunction

F2

g1

Q2 (GeV2) Q2 (GeV2)10510 1021 10103


5

Global NLO pQCD

fit:SMC, B. Adeva et al. Phys. Rev. D 112002 (1998)

6

Nucleon Spin: Status & Open Nucleon Spin: Status & Open QuestionsQuestions

1/2=(1/2)+G+Lq+Lg

Proton Spin Puzzle remains unsolved!

constrained, need to measure G

SMC, B. Adeva et al. Phys. Rev. D 112002 (1998)

07.023.0)1,( 22

dxQx GeV

5.10.1

1

0

22 0.1)GeV 1,( dxQxgG

Gluon Spin Contribution:

Quark Spin Contribution:

1/2=(1/2)+G+Lq+Lg

Extensive uncertainty studies


7

Low x behavior of g1(p)!

Clear need for low x measurements!

HERMES

8

Semi-inclusive DIS…Semi-inclusive DIS…

• In addition to the scattered electron, one measures in addition, the hadronic final state(s)

• Access to flavor separated parton distributions

• HERMES has the most significant data on these


9

RHIC Accelerator ComplexRHIC Accelerator Complex

BRAHMS & PP2PP (p)

STAR (p)

PHENIX (p)

AGS

LINACBOOSTER

Pol. Proton Source500 A, 300 s

GeVs

L

50050

onPolarizati%70

cms102 2132max

Spin Rotators

Partial Siberian Snake

Siberian Snakes

200 MeV Polarimeter AGS Internal PolarimeterRf Dipoles

RHIC pC Polarimeters

Absolute Polarimeter (H jet)

2 1011 Pol. Protons / Bunch = 20 mm mrad

RHIC accelerates heavy ions to 100 GeV/A and polarized protons to 250 GeV


10

RHIC PolarimetryRHIC Polarimetry

Beam’s View

Si #1

Si #2

Si #4Si #3

left right

down

up

Si #5

Si #6

Carbon filament target (5g/cm2) in the RHIC beam

Measure recoil carbon ions at q~90º

100 keV < Ecarbon< 1 MeVWave-Form Digitizer +FPGA high counting rates (~0.5

MHz) scaler measurement A ~ 310-4 in ~1 minute.

Carbon

ADC values

Arr

ival

tim

e (n

s)

E950 Experiment at AGS (1999) RHIC Polarimetry Now

ANL, BNL, Kyoto, RIKEN/RBRC & Yale Collaboration


11

Siberian SnakesSiberian Snakes

STARPHENIX

AGSLINAC

RHIC

Depolarizing Resonance:Spin tune = no. of spin kicksImperfection resonances: --magnet errors & misalignements Intrinsic resonances: --vertical focusing fields

Effect of depolarizing resonances averaged out by rotating spin by large angles on each turn

4 helical dipoles S. snake2 snakes in each ring -- axes orthogonal to each other


RIKEN/BNL

12

Successful Operation of the Successful Operation of the SnakeSnake

• Injection with Spin Flipped: Asymmetry Flipped

• Adiabatically Snake on: Horizontal polarization

• Accelerate equivalent to 180o rotation: 180o rotated

Successful SingleSnake Operation !

Blue Ring, Run 1 (2000-2001)


13

Polarization in Run 2 (2001-2002)Polarization in Run 2 (2001-2002)

Yellow Ring Blue Ring

First polarized collisions ever at Sqrt(s)=200 GeV


14

Why low polarization?Why low polarization?

10% 20% 30%

PAGS

PRHIC SourceImprovement

AGS power generator failure½ ramp up speed2x resonance effect

New AGSSNAKE2004-5

Ramp upSpead

Injection1st Year

Hot News:20th March 2003: ~42% and growing


15

Machine Performance Machine Performance ExpectationsExpectations

RUN #proton/bunch

[x109]#bunch Beta*

(m)

Emittance

(m)

Luminosity

1030 cm-2s-1

Pol.

(%)

2001-

2002

70 55 3 25 1.8 15-25

2002-2003

100 112 1 25 16 45-55

2005- ? 112 1 ? ? 70-80

Design 200 112 1 20 80 70


16

G :onPolarizati Gluon

RHIC spin programRHIC spin program

Production

),( 0 XgqggALL

Heavy Flavors

),( XbbccggALL

Direct Photon

)( XgqALL

Jet Photon )( XJetgqALL

STA

R +

P

HEN

IX

Spin Transversed

d

d

d

u

u

u

u , , ,

W Production

)( lL lWduA

STAR +PHENIX

STAR +PHENIX

:)Qq(x,ty Transversi 2

:A sAsymmetrie Single N

BRAHMS, STAR, PHENIX, Local Polarimeter

) () (

) (1reaction parton a A

x G

x GALL

pLL


17

PHENIX Detector Run 2 PHENIX Detector Run 2 Electrons & photons

( || < 0.35)

Charged tracks(Beam-Beam, Drift Chamber,

Pad Chambers)+

RICH rings+

EM Calorimeter clusters

Muons(1.2 < < 2.2)

Muon Identifier+

Muon TrackerApril 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

18

PHENIX Preliminary

Normalization error of 30% not shown.

On the way to On the way to G… G… 00 spectrum spectrum

PT spectrum over 8 orders of magnitudeComparison with NLO pQCD calculation--CTEQ5M PDFs--Potter, Knielh, Kramer (PKK) fragmentation functions--Uncertainty shown: = pT/2, 2pT

Consistent with data within scaledependence

PHENIX 0 cross section (Preliminary)From RHIC Run 2 (2001-2002)


19

PHENIX PreliminaryPHENIX Preliminary

µ+µ-e+e-

Br(J/l+l-) (total) = 226 36 (stat.) 79 (syst.) nb

(p+pJ/X) = 3.8 0.6 (stat.) 1.3 (syst.) µb

Total Cross section vs. the Total Cross section vs. the Color-Evaporation Model predictionColor-Evaporation Model prediction

• CEM Parameters are fixed by fitting low energy data• The result agrees with the CEM prediction at s=200GeV

Rapidity distribution compared Rapidity distribution compared with PHITHIA simulationwith PHITHIA simulation


20

STAR Performance

• Time Projection Chamber worked beautifully!

Au-Au Collision at STAR


21April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

Single spin asymmetries: L-RSingle spin asymmetries: L-R

Essential for proton spin orientation information at IPs

0 1 2 3 4 5Rapidity

STARFPD

0o CAL

BBC

PHE

NIX

MU

ON

PHE

NIX

CE

NT

RA

L

STA

R T

PC

pp2pp

E704 at Fermilab at s=20 GeV, pT=0.5-2.0 GeV/c: XF 0.2 0.4 0.6 0.8PT

Possible Origins: Transversity, Higher Twist,Fragmentation, kT, Orbital. Etc.

22

12 o’clock 12 o’clock PHENIX test setup PHENIX test setup

Hadron Cal Base

Pb

Scintillator

W+Fiber Cal

Post-shower

EM Cal Base

PbWO4

Charge Veto

Neutron Veto

0

RIKEN-BNL Research Center + Kyoto + PHENIX


23

AsymmetriesAsymmetriesEMCal ZDC

EMCal EMCal


24

STAR Forward rapidity high xSTAR Forward rapidity high xFF 00 AANN

STAR FPD Preliminary DataAssuming AN(CNI)= 0.013pT=1.1 - 2.5 GeV/c

0.0

0.2

0.4

-0.20 0.2 0.4 0.6 0.8 1.0

AN

Systematic uncertainty + － 0.05

0 at s 200p p X GeV 0 at s 20p p X GeV Theory predictions

at pT = 1.5 GeV/c

Anselmino, et al.PRD 60 (1999) 054027.

Anselmino, et al.Phys. Lett. B442 (1998) 470.

Twist 3 effectQiu and Sterman,Phys. Rev. D59 (1998) 014004.

Y.KoikePaNic02

xF ~ E / 100 GeVApril 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

25

Asymmetries seen at RHIC so Asymmetries seen at RHIC so far…far…

0 1 2 3 4 5Rapidity

STARFPD

0o CAL

BBC

PHE

NIX

MU

ON

PHE

NIX

CE

NT

RA

L

STA

R T

PC

pp2pp

XF 0.2 0.4 0.6 0.8PT

0

+10 ~ +20%

Charged+1%

Neutron -10%

~0 %

0 ~0%

… will be used to tune the spin rotators in Run 3!


26

Upcoming Run FY03Upcoming Run FY03

3 pb-1 and 50%Expectation

G will be probed

STAR JET

PHENIX Charged


27

RHIC vs. DIS Kinematic CoverageRHIC vs. DIS Kinematic Coverage

GeVs 200 :RHIC

prompt photon

Xecc

Xebb


28

W

Z

) , ( ) , ( ) , ( ) , (

) , ( ) , ( ) , ( ) , (2

22

12

22

1

22

21

22

21

W W W W

W W W W WL

M x u M x d M x d M x u

M x u M x d M x d M x uA

W Production in Polarized

pp Collisions Single Spin Asymmetry

GeV for dominates 20TpWImprovements in muon trigger under Study factor of 50 seems possible and sufficient

Backgrounds from decays of other hadrons produced in pp scattering constitutes the main background.1) Different energies of muons2) Different event topologies


29

1. Statistical errors for 800 pb800 pb-1-1

2. Flavor decomposition will reduce the uncertainty in current pol-PDF models.

GS95LO(A): Gehrmann and Stering (Z.Phys.C65(1995)461) BS: pol-PDF set by Bourrely and Soffer (PLB314(1993)132)

Flavor Decomposition


30

RHIC Spin Luminosity

Year CM Energy Weeks Int. Lum. Remarks

FY2002 200 GeV 5 5 pb-1(1/15) Single spin asymmetries and CommissioningFY2003 200 GeV 8(3) 9 pb-1 Gluon pol. with 0s & jets(?)

500 GeV ?? Machine Studies, identify Ws.

FY2004 200 GeV 8 160 pb-1 Gluon pol. with g + jet/ TT500 GeV 2 120 pb-1 First ubar,dbar pol. meas..

FY2005 500 GeV 8 480 pb-1 Gluon pol. with g+jet, g,jet+jet, heavy flavor, ubar, dbar pol.

200 GeV 2 48 pb-1 Gluon pol. with g, g+jet, heavy

flavor/TT

FY2006 500 GeV 5 300 pb-1 More statistics200 GeV 5(?) 120 pb-1

FY2007 (?) GeV 10 ?? More statistics

Collider Accelerator Department’s Projections (early ’02)


31

Global Analysis for nucleon Spin Structure Functions:

In near future we will have data from:-- Fixed target polarized DIS experiments (l-p scattering) NLO pQCD analysis exists (SMC, SLAC Exp.s & theoretical groups) Constrain polarized quark distributions well, polarized gluons largely

unconstrained. ( See detailed analysis: SMC, PRD 112002 (1998)) Adding eRHIC/EIC data is trivial and possible-- RHIC Spin data on various polarized pp interactions Additional constraints on polarized gluon distributions-- Should use all available data to get the best possible constraints on all

polarized parton distributions.-- Something like CTEQ/GRSV groups but for a global data set to

understand polarized parton distributions-- A. D., W. Vogelsang & M. Stratmann towards a “Global Analysis” See tremendous opportunity for a completely new venture. Will develop

this summer with many others joining us.


32

Summary & OutlookSummary & Outlook

• RHIC spin program has begun very successfully! -- Polarized protons were injected, accelerated, stored -- CNI polarimeters have measured non zero asymmetries

indicating polarization at 100 GeV proton beam energies -- Detectors operating - will be 100% completed in 2003-5 -- Single spin asymmetries (1% to 20%) have been measured

• Next run (Apr.03) promises: a first glimpse of G and

-- First trials of 500 GeV CM collisions and W’s produced

• A ~5 year run plan exists for the RHIC spin physics -- to explore G, transversity, q & qbar -- and also perhaps physics beyond SM(?)


33

The Electron Ion ColliderThe Electron Ion Collider

A high energy, high intensity polarized electron beam facility at BNL to collide

with the existing RHIC heavy ion and polarized proton beam

would significantly enhance RHIC’s ability to

probe fundamental and universal aspects of QCD


34

Deep Inelastic ScatteringDeep Inelastic Scattering

•Observe scattered electron/muon & hadrons in current jets•Observe spectator or remnant jet


35

Why Collider in the Future?Why Collider in the Future?

• Past polarized DIS experiments: FIXED TARGET• Collider has distinct advantages

• Better angular separation between scattered lepton & nuclear fragments

Better resolution of electromagnetic probe Recognition of rapidity gap events (recent diffractive physics)• Better measurement of nuclear fragments• Higher center of mass (CoM) energies reachable• Tricky integration of beam pipe – interaction region -- detector


36

EIC vs. DIS Facilities (I)EIC vs. DIS Facilities (I)

• New kinematic region

• Ee = 5-10 GeV

• Ep = 30 – 250 GeV

• Sqrt(s) = 20 – 100 GeV

• Kinematic reach of EIC x = 10-4 0.6 Q2 = 0 104 GeV

• High Luminosity L ~1033 cm-2 sec-1


37

EIC vs. Other DIS Facilities (II)EIC vs. Other DIS Facilities (II)

Variable beam energy

Variable hadron species

Hadron beam polarization

Large luminosity

TESLA-N


38

Scientific Frontiers Open to EICScientific Frontiers Open to EIC

• Nucleon Structure: polarized & unpolarized e-p/n scattering -- Role of quarks and gluons in the nucleon -- Spin structure: polarized quark & gluon distributions -- Unpolarized quark & gluon distributions -- Correlation between partons hard exclusive processes leading to

Generalized Parton Distributions (GPD’s)

• Nuclear structure: unpolarized e-A scattering -- Role of quarks and gluons in nuclei -- e-p vs. e-A physics in comparison

• Hadronization in nucleons and nuclei & effect of nuclear media

-- How do partons knocked out of nucleon in DIS evolve in to colorless hadrons?

• Partonic matter under extreme conditions -- e-A vs. e-p scattering; study as a function of A


39

Unpolarized DIS e-p at EICUnpolarized DIS e-p at EIC

• Large(r) kinematic region already covered at HERA but additional studies at EIC are possible & desirable

• Uniqueness of EIC: high luminosity, variable Sqrt(s), He3 beam, improved detector & interaction region

• Will enable precision physics: -- He3 beams neutron structure d/u as x0, dbar(x)-ubar(x)

-- precision measurement of S(Q2)

-- flavor separation (charm and strangeness) -- precision gluon distribution in x=0.001 to x=0.6 -- slopes in dF2/dlnQ2

-- precision photo-production physics -- exclusive reaction measurements -- nuclear fragmentation region measurements

http://www.bnl.gov/eic


40

Polarized DIS at EICPolarized DIS at EIC• Spin structure functions g1 (p,n) at low x, high precision

-- g1(p-n): Bjorken Spin sum rule better than 1% accuracy• Polarized gluon distribution function G(x,Q2) -- at least three different experimental methods

• Precision measurement of S(Q2) from g1 scaling violations• Polarized structure function of the photon from photo-

production• Electroweak structure function g5 via W+/- production• Flavor separation of PDFs through semi-inclusive DIS• Deeply Virtual Compton Scattering (DVCS) Gerneralized

Parton Distributions (GPDs)• Transversity• Drell-Hern-Gerasimov spin sum rule test at high • Target/Current fragmentation studies• … etc….

http://www.bnl.gov/eic


41

Spin structure function gSpin structure function g1 1 at low at low xx

~5-7 days of data3 years of data

A. Deshpande & V. W. Hughes EIC WS at Yale ‘00

Studies included statistical error & detector smearing to confirm that asymmetries are measurable. No present or future approved experiment will be able to make this measurement

At HERA At EIC/eRHIC


42

Low x measurement of gLow x measurement of g11 of of NeutronNeutron

• With polarized He3 or deuteron

• ~ 2 weeks of data at EIC w.r.t. ~ 3 yrs of HERA data

• Compared with SMC(past) & possible HERA data

• If combined with g1 of proton results in Bjorken sum rule test of better than 1% within a couple of months of running (G.Igo & T. Sloan, AD & V. Hughes)

EIC 1 fb-1

A. Deshpande & V. W. Hughes EIC WS at Yale ‘00


43

Polarized Gluon Measurement at Polarized Gluon Measurement at EICEIC

• This is the hottest of the experimental measurements being pursued at various experimental facilities:

-- HERMES/DESY, COMPASS/CERN, RHIC-Spin/BNL & E159/E160 at SLAC

• Large kinematic range of EIC allows measurements using:

-- Scaling violations (pQCD analysis at NLO) of g1

-- (2+1) jet production in photon-gluon-fusion (PGF) process -- 2-high pT hadro production in PGF

• Photo-production (real photon) kinematics at EIC -- Single and di-jet production in PGF

-- Open charm production in PGF


44

Photon Gluon Fusion at EICPhoton Gluon Fusion at EIC

• “Direct” determination of G -- Di-Jet events -- High pT leading hadrons • High Sqrt(s) at EIC -- no theoretical ambiguities• Both methods tried at HERA

for un-polarized gluon determination & both are successful!

-- NLO calculations exist -- H1 and ZEUS published

results -- Consistent with G

determined from scaling violation F2

Signal: PGF

BackgroundQCD Compton


45

G from Scaling Violations of gG from Scaling Violations of g11

• World data (today) allows a NLO pQCD fit to the scaling violations in g1 resulting in the polarized gluon distribution and its first moment.

• SM collaboration, B. Adeva et al. PRD (1998) 112002 G = 1.0 +/- 1.0 (stat) +/- 0.4 (exp. Syst.) +/- 1.4 (theory)• Theory uncertainty dominated by the lack of knowledge of

the shape of the PDFs in unmeasured low x region where EIC data will play a crucial role.

• With approx. 1 week of EIC data, statistical and theoretical uncertainties on G will be reduced by a factor of 3-5

-- coupled to better low x knowledge of spin structure -- less freedom for fits to depend on factorization & re-

normalization scale uncertainty

A. Deshpande, V. W. Hughes & J. Lichtenstadt EIC WS @ Yale’00


46

Di-Jet events at EIC: Analysis at Di-Jet events at EIC: Analysis at NLONLO

• Stat. Accuracy for two luminosities

• Detector smearing effects considered

• NLO analysis

A. De Roeck, A. Deshpande, V. W. Hughes & J. Lichtenstadt,G. Radel EIC WS, Yale’00

• Easy to differentiate different G scenarios: factor 3 improvements in ~2 weeks of data• If combined with scaling violations of g1: factors of 5 improvements in uncertainties observed in the same time.• Better than 3-5% uncertainty on G can be expected from EIC


47

Polarized PDFs of the PhotonsPolarized PDFs of the Photons

• Photo-production studies with single and di-jet

• Photon Gluon Fusion or Gluon Gluon Fusion (Photon resolves in to its partonic contents)

• Resolved photon asymmetries result in measurements of spin structure of the photon

• Asymmetries sensitive to gluon polarization as well… but we will consider the gluon polarization “a known” quantity!

Direct Photon Resolved Photon


48

Will measure the photon PDFs…Will measure the photon PDFs…• Stat. Accuracy

estimated for 1 fb-1 running (2 weeks at EIC)

• Single and double jet asymmetries

• ZEUS acceptance

• Will resolve photon’s partonic spin contents

Direct Photon Resolved Photon

M. Stratmann & W. Vogelsang EIC WS at Yale’01


49

A Case for EIC A Case for EIC • The polarized e-N facility at the EIC will enable the polarized DIS

studies of nucleons in a completely new x-Q2 that no other present or future facility will be able to access

• The measurements with variable Sqrt(s) & light polarized nuclei will include:

-- inclusive physics in DIS as well as photo-production regime -- semi-inclusive physics -- exclusive physics leading to DVCS, DES GPDs

• In addition a lot of spin measurements which would study target and current fragmentation for the first time in polarized DIS will be possible…

• And then there is an exciting un-polarized e-A physics program which proposes to measure partonic matter under extreme conditions….


50

A Case for EIC … for e-AA Case for EIC … for e-A

• Through its large luminosity, beam energy & beam species variability, the EIC will explore a new universal and fundamental aspects of QCD including looking for the new states of matter at high gluon densities….

• It is natural to assume that these measurements probe the initial conditions in the nuclei for parton distributions… as such this knowledge would be essential to fully understand the QGP which is being pursued at RHIC

• The e-A physics at RHIC will allow for the first time a large number of measurements which have never been performed beyond the fixed target regime… They will be at high energies where pQCD could be used reliably to understand the nuclear structure


51

Moving Towards EIC….Moving Towards EIC….• September 2001: EIC grew out of joining of two communities: 1) polarized eRHIC (ep and eA at RHIC) BNL, UCLA, YALE and people from DESY & CERN 2) Electron Poliarized Ion Collider (EPIC) 3-5 GeV e X 30-50 GeV polarized light ions Colorado, IUCF, MIT/Bates, HERMES collaborators

• February 2002: White paper submitted to NSAC Long Range Planning Review Received enthusiastic support as a next R&D project (see: US/DoE Nuclear Report on the Web)

• Steering Committee: 7 members, one each from BNL, IUCF, LANL, LBL, MIT, UIUC, Yale + Contact person

• February 2003: NSAC Subcommittee Recommendation!• ~20 (~13 US + ~7 non-US) Institutes, ~100 physicists + ~40

accelerator physicists• See for more details: EIC Web-page at “http://www.bnl.gov/eic”

(under construction)• Subgroups: Accelerator WG, Physics WG, Detector WG


52

Present Collider LayoutPresent Collider Layout• Proposed by BINP & MIT/Bates

presently being studied at BNL• E-ring is ¼ of RHIC ring• Collisions in ONE interaction region• Collision energies 5-10 GeV• Injection linac 2-5 GeV• Lattice based on “superbend”

magnets• Self polarization using Sokolov

Ternov Effect: (14-16 min pol. Time)

• IP12, IP2 and IP4 are possible candidates for collision points

p

e2GeV (5GeV)

2-10 GeV

IP12

IP2

IP4

IP6

IP8

IP10

RHIC

OTHER DESIGNS: Ring with 6 IPS, Linac-Ring, Linac-Re-circulating ring


53

A Detector for EICA Detector for EIC A 4 A 4 DetectorDetector

• Scattered electrons to measure kinematics of DIS• Scattered electrons at small (~zero degrees) to tag photo

production• Central hadronic final state for kinematics, jet measurements,

quark flavor tagging, fragmentation studies, particle ID• Central hard photon and particle/vector detection (DVCS)• ~Zero angle photon measurement to control radiative

corrections and in e-A physics to tag nuclear de-excitations

• Missing ET for neutrino final states (W decays)

• Forward tagging for 1) nuclear fragments, 2) diffractive physics

• The e-ring & the IR design The e-ring & the IR design Detector Design Detector DesignApril 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

54

Interaction Region Design….Interaction Region Design….

B. Parker’s (BNL) ProposalBudker/MIT Proposal


55

A time line for EIC…A time line for EIC…

“Predictions are very difficult to make, especially when they are about the future” --- A very wise man….

• Proposal/CDR0 by 2005• Expected formal approval 2005-6 Long Range Review• R&D money could start for hardware 2007• Construction of IR and Detector begin 2008• 3-5 years for staged detector and IR construction

without interfering with the RHIC running• First collisions (2010-2011)???

If any one knows how to do this earlier… -- I am listening.


56

Detector Design (I)… others Detector Design (I)… others expectedexpected

J. Chwastowski & W. Krasny EIC WS at Yale ‘00


57

Detector Design (I)… others Detector Design (I)… others expectedexpected

J. Chwastowski & W. Krasny

Integration with e-ring & IR design is crucial


58

Di-Jet at EIC vs. World Data for Di-Jet at EIC vs. World Data for G/G G/G

Good precisionClean measurement in x

range 0.01< x < 0.3Constrains shape of G(x)

Polarization in HERA much more difficult than RHIC.

G. Radel & A. De Roeck

EIC Di-Jet DATA 2fb-1


59

Parity Violating Structure Parity Violating Structure Function gFunction g55

For EIC kinematics

• Experimental signature: huge asymmetry in detector (neutrino)• Unique measurement• Unpolarized xF3 measurements at HERA in progress• Will access heavy quark distribution in polarized DIS

March 20th, 2003 Quest for Nucleon Spin: Past, Present & Future

60

Measurement Accuracy PV gMeasurement Accuracy PV g55 at at EICEIC

Assumes:1. Input GS Pol.

PDfs2. xF3 measured by

then3. 4 fb-1 luminosity

Positrons & Electrons in EIC g5(+)

>> Issues for linac vs. ring design of EIC

J. Contreras, A. Deshpande & A. De Roeck EIC WS at Yale ‘00


61

Strange Quark Distributions at Strange Quark Distributions at EICEIC

• After measuring u & d quark polarized distributions…. Turn to s quark (polarized & otherwise)

• Detector with good Particle ID: pion/kaon separation

• Upper Left: statistical errors for kaon related asymmetries shown with A1 inclusive

• Left: Accuracy of strange quark distribution function measurements possible with EIC and HERMES (2003-05) and some theoretical curves on expectations.

E. Kinney & U. Stoesslein EPIC WS at MIT’01


62

Highlights of e-A Physics at EICHighlights of e-A Physics at EIC

• Study of e-A physics in Collider mode for the first time• QCD in a different environment

• Clarify & reinforce physics studied so far in fixed target e-A & -A experiments including target fragmentation

QCD in: x > [1/(2mNRN) ] ~ 0.1 (high x)

QCD in: [1/(2mNRA)] < x < [1/(2mNRN)] ~ 0.1 (medium x)

• …. And extend in to a very low x region to explore: saturation effects or high density partonic matter also called

by some as the Color Glass Condensate (CGC) QCD in: x < [1/(2mNRA)] ~ 0.01 (low x)


63

DIS in Nuclei is Different! DIS in Nuclei is Different!

Regions of:• Fermi smearing• EMC effect• Enhancement• Shadowing• Saturation?

Regions of shadowing and saturation mostly around Q2 ~1 GeV2

An e-A collision at EIC can be at significantly higher Q2

F2D/F2A

Low Q2!

E665, NMC, SLAC Experiments


64

Statistical Precision at EIC for e-Statistical Precision at EIC for e-AA

• High precision at EIC shown statistical errors for 1 pb-1

• Recall: EIC will deliver ~85 pb-1 per day

• NMC data F2(Sn/D)

• EIC’s Q2 range between 1 and 10 GeV2

• Will explore saturation region!

T. Sloan, EIC WS at Yale’00


65

Problems & Possible Solutions…Problems & Possible Solutions…• The “low x” problem: High energy behavior of hadronic

cross sections is one of the most intriguing of the problems… Intimately related to the high energy behavior of the parton densities.

• GDLAP & BFKL evolution of PDFs predict a rapid growth at high energies that violates the unitarity constraints.

• Perturbative QCD also provides a way out… the above evolutions exclude the interactions amongst the

partons themselves, which are argued to help keep the rapid rise of cross sections finite resulting in the saturation phenomenon

• These effects however have to be included explicitly (“by hand”) in the calculations (as the evolution prescriptions are linear and explicitly ignore these “cascades”)


66

The Saturation Region…The Saturation Region…

• As parton densities grow, standard pQCD break down.

• Even though coupling is weak, physics may be non-perturbative due to high field strengths generated by large number of partons.

• A new state of matter???

An e-A collider/detector experiment with high luminosity and capability to have different species of nuclei in the same detector would be ideal… Need the Electron Ion Collider at BNL

Signatures of the CGS/Saturation: F2s of nuclei, gluon densities….


67

Search for new physics:Search for new physics:

• Anomalous parity violation in jet production – Contact Interaction (Scale )

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

– New gauge boson Z’

P. Taxil & J-M. Virey, Phys. Rev. D(55) 2457 (1999)


68

RHIC Spin Physics ProgramRHIC Spin Physics Program

• Spin Structure of Nucleon

>1/2=(1/2)+G+Lq+Lg G: gluon polarization q: Anti-quark polarization

> New Structure Functions• h1: transversity

•NEW tool to study hadronic processes•W,Z @500GeV

•flavor sensitive studies on the structure functions

•cc/bb•Production mechanism

•Spin in fragmentation•Parity,CP violating interaction?

•Test of pQCD •Use asymmetries sensitive ONLY to the higher orders (AN at high PT etc.)

?QCD triumph? or

?beyond ?


69

ProductionFlavor Heavy in G

a

AQQgg

LL

XQQpp

LL

xG

xG

xG

xG

xx

)(

2

2

1

1

21

)(

)(

)(

)(

)(

),(

charm

0 Dalitz

pT in GeV/c

Example: Single Electrons

1p

2p


70

Transversity Measurements at RHIC

)δq(x,Q

) (x,QgQxq

)(x,QFQxq ,

2

21

2

221

2

2

1

2

1

2

1

2

1

,(

,(

2

1

2

1

2

1

2

12

1

2

1

2

1

2

1

- -

diff.)(helicity ),

av.)(helicity , )

- -

(helicity flip!)

),( 2Qxq

helicity proton HH H

h h

On Transversity:

helicity quark h

H h H h

For non-relativistic quarks: ),(),( 22 QxqQxq

Differences provides information on rela-tivistic nature of quarks inside the proton

Soffer’s bound: ),(),(),(2 222 QxqQxqQxq iii

Not small! Possibly !ii qq

),( 2Qxq does not mix with gluons under evolution

First lattice QCD result: 09.056.0 sdu

S. Aoki, M. Doui, T. Hatsuda and Y. Kuramashi Phys.Rev. D56 (1997)433More recently: S. Capitani et.al. Nucl. Phys. B (Proc. Suppl.) 79 (1999) 548

Hard Scattering Amplitudes

Transversity distributions remain last unmeasured leading twist distributions

Incoming proton

probe


71

Present and Near Future Upgrades

XppAT

),(

,

:ionFragmentat

ceInterferen

STA

RP

HEN

IX

qqllppATT )( : YanDrell

ionFragmentat ceInterferen Jets, in Collins

: Photon Direct

func.) ionfragmentat func.-ondistributi O (

sObservable

Hq34 103105 TTA

production jet Inclusive

)( XJetppAT

: Jets in Effect Collins

EIC

GeVpb 200,320 1 sLdt EIC fb ,8 1 Ldt

PH

EN

IX

ionFragmentat ceInterferen

Jets in Effect Collins


72

Projected Asymmetry

pair vs TT pXpA )(

Small aymmetry below5% but good rate!

MeV MeV

GeV

GeV

950800

4

4

32

22

21

,

1

21

m

pp

E

pbLdt

TT

GeV) Tang 85.0,1(cos mA

)1010Tang sin(sinsincos A

(For 1 week of running)


73

Why e-A at a Collider?Why e-A at a Collider?

• Highest fixed target experiments in past: NMC & E665 used secondary muon beams & achieved Sqrt(s) ~ 30 GeV

• HERMES at DESY uses electron beam in gaseous targets but achieves very low Sqrt(s) ~7 GeV

• Solid state fixed targets… target fragments hard to measure Only inclusive measurements

• EIC with large luminosity 1033 cm-2 sec-1 Nucleon-1

~85 pb-1 /day• EIC with variable beam energies can provide:

Sqrt(s)~2060 GeV• EIC with variable species will allow any nucleus from D

to Gold to Uranium…! A detail study of A dependence is possible.


74

Hints of the Unusual in NucleiHints of the Unusual in Nuclei

• E866 at FNAL

• 800 GeV protons on fixed target A collisions

• Comparison of Drell-Yan di-muon production vs. production and then decay of J/and

• Nuclear medium clearly plays a role…


75

Recent results from RHIC….!Recent results from RHIC….!

Numerous interesting results from:

PHENIXPHOBOSSTAR

All pointing to the significant role the nuclear medium seems to play in nuclear collisions.

We are sure to see more dramatic results in the up coming d-A run…


76

Importance of high QImportance of high Q2 2 at low xat low x

• Before HERA for x ~10-4 Q2 << 2QCD

-- Strong coupling constant S(Q2) too large to make reliable pQCD predictions and comparisons with data

• Lack of data with sufficiently high Q2 a significant stumbling block for interpretation of the results from this region.

• At HERA Sqrt(s) ~300 GeV x~10-4 Q2 ~1-10 GeV2

• At HERA S(Q2) << 1 a good approximation… pQCD applicable


77

Experimental Hints of the Experimental Hints of the Unusual…Unusual…

• At high Q2 the gluon distribution is well behaved and understood (pQCD framework)

• Intermediate and low Q2 however things are different: Although fits accommodate data, interpretation is problematic

• Relation between sea quarks and gluons seems to break down

)/1ln())/ln(ln(exp~

),(ln/),(ln

22

2222

xQ

QxGQdQxFd

QCD

Is the pQCD approach breaking down? If so why?


78

High Parton Density Matter (I)High Parton Density Matter (I)

• For a fixed external probe the number of partons per unit area grows rapidly with increasing energy (decreasing x)

• QCD field strengths grow as (F)2 ~ 1/S

Small coupling large field strengths Non-linearities of theory manifest and significantly

change the effective properties of distributions at high energies

• Calculations indicate that the rapid rise of structure functions due to gluons will saturate (the rise will be tamed!) due to the collective properties of the medium

Perhaps as slowly as ln(1/x)


79

A Color Glass Condensate??A Color Glass Condensate??• At small x, partons are rapidly fluctuating gluons interacting

weakly with each other, but still strongly coupled to the high x parton color charges which act as random static sources of COLOR charge

Analogous to spin GLASS systems in condensed matter: a disordered spin state coupled to random magnetic impurities

• Gluon occupation number large, being bosons they can occupy the same state to form a CONDENSATE

Bose Einstein condensate leads to a huge over population of ground states

• A new “state of matter”(??): Color Glass Condensate (CGC) at high energy density would display dramatically different, yet simple properties of glassy condensates

E. Iancu, J.J-MarianL. McLerran,R. Venugopalan, et al.


80

Signatures of Saturation/CGC (I)Signatures of Saturation/CGC (I)• Structure functions F2(x,Q2), dF2/dlnQ2, dF2/dlnx

- dF2/dlnQ2 at fixed x at high Q2 is the gluon distribution - CGC vs. conventional pQCD predict very different - Gluon measurements using semi-inclusive… di-jet final states - EIC will differentiate them easily for protons and heavy nuclei

• Longitudinal structure function FL = F2 – 2xF1

- Provide independent gluon distribution measurement - Needs variable electron beam energy Possible at EIC

• Measurement of nuclear shadowing - Quark shadowing (F2

A/A*F2N) in fixed target experiments observed

- Gluon shadowing (GA/A*GN) indirect evidence only… pQCD at NLO - This is expected to be severe at low x and high Q2

- Ideal measurement for EIC


81

Signatures of CGC (II)Signatures of CGC (II)• Shadowing and diffraction: Relation between nuclear shadowing and diffraction will be

very different at high parton density media… EIC will study this systematically as a function of A of the nuclei.

• Hard Diffraction Large rapidity gap between current and target fragmentation

region. At HERA 7% cross section diffractive. In e-A at EIC, diffractive processes may contribute 30-40% to

the total cross section.

• Coherent & Inclusive vector meson production: For light vector mesons diff. Cross section. = 0.5 (inclusive) Heavy vector mesons this decreases…finally reaching 1/lnQ2

EIC will measure for different nuclei, Jcross sections

22 ;'*' QCDXMAXeAeAe


82

EICEIC AA & dA Physics at RHIC AA & dA Physics at RHIC

• Goal of RHIC is to discover & study the properties of QGP

• CGC has been dubbed as the “initial condition” for gluon distributions in nuclei

• A possible scenario: “QGP is formed when CGC shatters!”

• d-A physics is indeed complementary to e-A physics Differences here would come from experimental

differences and difficulties when one uses “e”, a better structure less probe, compared to “deuteron” as a probe to explore the high density nuclear matter…


83

Motivation: Past ExperienceMotivation: Past Experience

Historically, “spin” and “low-x/high-Q2” measurements have had high discovery potential.

Experimental surprises related to both of them have opened unexpected fields of physics and have led us in towards understanding nature that would have not been possible otherwise.


84

Motivation: Some spin Motivation: Some spin surprises…surprises…

• Stern & Gehrlach (1921) Space quantization associated with direction

• Goudschmidt & Ulhenbeck (1926): Atomic fine structure & electron spin magnetic moment

• Stern (1933) Proton anomalous magnetic moment 2.79 N

• Kusch(1947) Electron anomalous magnetic moment 1.001190

• Prescott & Yale-SLAC Collaboration (1978) EW interference in polarized e-d DIS, parity non-conservation

• European Muon Collaboration (1989) Spin Crisis/Puzzle• E704, AGS pp scattering, HERMES (1990s) Transverse spin

asymmetries (??)• RHIC Spin (2001) Transverse spin asymmetries (??)


85

Motivation: Some Low x Motivation: Some Low x SurprisesSurprises

• Elastic e-p scattering at SLAC (1950s) Q2 ~ 1 GeV2 Finite size of the proton

• Inelastic e-p scattering at SLAC (1960s) Q2 > 1 GeV2 Parton structure of the proton

• Inelastic mu-p scattering off p/d/N at CERN (1980s) Q2 > 1 GeV2 Unpolarized EMC effect, nuclear shadowing?

• Inelastic e-p scattering at HERA/DESY (1990s) Q2 > 1 GeV2 Unexpected rise of F2 at low x Diffraction in e-p

Saturation(??)


86

Drell Hern Gerasimov Spin Sum Drell Hern Gerasimov Spin Sum RuleRule

• DHG Sum rule:

• At EIC range: GeV few TeV

• Although contribution from to the

this sum rule is small, the high behavior is completely unknown and hence theoretically biased in any present measurements at:

Jefferson Lab., MAMI, BNL

S. Bass, A. De Roeck & A. Deshpande EIC/HERA WS Erice’01

• Inclusive Photo-production measurement

• Using electron tagger in RHIC ring Q2 ~ 10-6 10-2 GeV2

Sqrt(s) ~ 25 85 GeV


87

DVCS/Vector Meson ProductionDVCS/Vector Meson Production

• Hard Exclusive DIS process

• (default) but also vector mesons possible

• Remove a parton & put another back in!

Microsurgery of Baryons!

•Claim: Possible access to skewed or off forward PDFs? Polarized structure: Access to quark orbital angular momentum?

On going theoretical debate… experimental effort just beginning…


88

DVCS at EICDVCS at EIC

• DVCS recently observed at ZEUS, H1 & HERMES and Jlab.

• Experimental difficulties being understood

• Potential to get to partonic angular momentum

• Initial studies for EIC begun• Variable beam energy of e

and p beam at EIC will be of great help to explore all aspects of generalized parton distributions!

D. Hasell & R. Milner

5 GeV e X 50 GeV p at EIC


89

Relativistic Heavy Ion ColliderRelativistic Heavy Ion Collider

this is testRHIC accelerates heavy ion beams upto and polarized proton

beams to 250 GeV

Two large detectors PHENIX and STAR

have extensive Spin Physics Programs

PHENIX

STAR

GeVA 100


90

Cheers!Cheers!


91

RHIC Luminosity FY02RHIC Luminosity FY02

PHENIX 150 nb-1

0

50

100

150

200

250

300

350

1 3 5 7 9 111315171921232527293133

Days into run (from 12/20/01)

STAR 300 nb-1

Machine Luminosity300 nb-1 /week

Peak 1.8x1030 cm-2s-1


92

Scale Dependence vs. Pt

quest for nucleon spin: past, present & future

Documents