In Quest of Nucleon SpinIn Quest of Nucleon Spin Vernon W. HughesVernon W. Hughes

The Last Decade: 1993-2003The Last Decade: 1993-2003

Abhay Deshpande

RIKEN-BNL Research Center

SYMMETRIES & SPIN

PRAGUE, JULY 2003

Parton Distributions

q

q

g

Nucleon

u u

d

averagehelicity quark)Qq(x 2,

differencehelicity quark )Qq(x 2,

fliphelicity , 2 )Qq(x

(well known)

(moderately well known)

(unknown)

onDistributi Gluon)QxG 2,(

(moderately well known)

onPolarizati Gluon )QxG 2,((unknown)

•Late 50s and early 60s V.W.HughesV.W.Hughes develops polarized electron source at Yale : Why?… I once asked… “… it seemed it would provide an interesting tool for atomic and high energy physics experiments…”•1966 Bjorken Sum Rule (published) “… of little consequence since no measurement techniquesare presently or foreseen in future…” – J.D. Bjorken • 1969 Proton substructure presented by Panofsky at Vienna • V.W.HughesV.W.Hughes et al. try to develop polarized nuclear targets - Collaboration with J. Kuti to calculate spin effects in nucleons – effort abandoned after observation that they may be small in nuclei• 1974 Ellis-Jaffe Spin Rule• 1980s V.W.HughesV.W.Hughes leaves SLAC to join EMC @ CERN -- SLAC decides to emphasize Linear Collider Development• SLAC Experiments: Talk by E. Hughes in this meeting•1989 EMC Spin Puzzle/Crisis

• E142/143 Proposed at SLAC, SMC Proposed at CERNE142/143 Proposed at SLAC, SMC Proposed at CERN

1993: Background and times….1993: Background and times….

First moments & Spin Sum RulesFirst moments & Spin Sum Rules

NA47 Experiment at CERNSpin Muon Collaboration (SMC)

Polarized Target:• 2.5 T longitudinal field• 0.5 T transverse field Polarization reversal every 5hrs• Dynamic Nuclear Polarization • Polarization measurement with ~10 Polarization measurement with ~10 coils embedded in the target volumecoils embedded in the target volume

Polarized -N inclusive & semi-inclusive scatteringPolarized muon beam, polarized twin target setuppolarized twin target setup, spectrometer

Polarized beam from weak decays of • Shape of Michel Spectrum of positron from decays in flight• e e scattering• Pbeam~ 0.79 +/- 0.03

SMC SpectrometerSMC Spectrometer

A1 Q2 dependent?

Global NLO pQCD

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

*Based on: Ball et al. Phy. Lett. B378 255 (1996)

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

Low x behavior of g1(p)!

Clear need for low x measurements!

SMC, PRD58, 112001 &112002, 1998 SMC, PRD58, 112001 &112002, 1998

E154 NeutronE154 NeutronSMC NeutronSMC Neutron

Bjorken Sum Rule

HERMES

Kinematic Coverage from Fixed Target ExperimentsKinematic Coverage from Fixed Target Experiments

Some spin surprises…Some spin 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 (??)

Some Low x SurprisesSome Low x Surprises

• 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(??)

Our knowledge of structure functionsOur knowledge of structure functions

F2

g1

Q2 (GeV2) Q2 (GeV2)10510 1021 10103

Extended Kinematic CoverageOf HERA

Accelerator Issues:Accelerator Issues: PolarizedBeams in HERA non-trivialStudies initiated with VWHVWH’s efforts

AT DESY:AT DESY:

A strong physics motivation to go to low x and high Q2 with spin variables was developed

HERA Existed…..Polarized electrons existed….Accelerator Physicists working on e and p beams existed…

H1 and ZEUS detector existed along with collaborators…HERMES polarized DIS community existed…

“Polarized Proton Beam” was the ONLY missing item…!

A linear collider seems to comes in again (!) for V.W.Hughes…

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

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

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

RIKEN/BNL

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

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)

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

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 25-35

2005- ? 112 1 ? ? 70-80

Design 200 112 1 20 80 70

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

Deep Inelastic ScatteringDeep Inelastic Scattering

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

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

eRHIC vs. other DIS Facilities (I)eRHIC vs. other DIS Facilities (I)

• New kinematic region

• Ee = 5-10 GeV

• Ep = 30 – 250 GeV

• Sqrt(s) = 20 – 100 GeV

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

• High Luminosity L ~1033 cm-2 sec-1

eRHIC

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

Variable beam energy

Variable hadron species

Hadron beam polarization

Large luminosity

TESLA-N

eRHIC

Scientific Frontiers Open to Scientific Frontiers Open to eRHICeRHIC

• 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

Polarized DIS at eRHICPolarized DIS at eRHIC• 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

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

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

• With polarized He3 or deuteron

• ~ 2 weeks of data at eRHIC vs. ~ 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)

eRHIC 1 fb-1

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

Polarized Gluon Measurement at Polarized Gluon Measurement at eRHICeRHIC

• 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 eRHIC 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 eRHIC -- Single and di-jet production in PGF

-- Open charm production in PGF

Photon Gluon Fusion at eRHICPhoton Gluon Fusion at eRHIC

• “Direct” determination of G -- Di-Jet events -- High pT leading hadrons • High Sqrt(s) at eRHIC -- 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

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

Di-Jet events at eRHIC: Analysis Di-Jet events at eRHIC: Analysis at NLOat NLO

• 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 eRHIC

Di-Jet at eRHIC vs. World Data for Di-Jet at eRHIC 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

eRHIC Di-Jet DATA 2fb-1

Moving Towards eRHIC….Moving Towards eRHIC….• September 2001: eRHIC 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 (Abhay Deshpande)

• 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

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 (10 GeV)

2-10 GeV

IP12

IP2

IP4

IP6

IP8

IP10

RHIC

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

A Detector for eRHICA Detector for eRHIC 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 Design

A time line for eRHIC…A time line for eRHIC…

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

• Accelerator R&D started 2003 as part of “RHIC II and eRHIC”

• ZDR Requested by January 2004 for machine design• Proposal/CDR0 by 2005• Expected formal approval 2005-6 Long Range Review• Detector R&D money could start 2007• Construction of IR and Detector begin 2009/10• 3-5 years for staged detector and IR construction

without interfering with the RHIC running• First collisions??? If any one knows how to do this earlier…

-- I am listening.

1990-1998 Spin Muon Collaboration at CERN SpokespersonPolarized targetAnalysis…

1995-2003Polarized HERADevelopment on physics case/motivationPolarized proton beam development at HERADevelopment of high energy proton beam polarimetry

1997-2003 Polarimetry for proton

beams at RHIC

2000-2003eRHIC at BNL

Steering CommitteeWorkshop on eRHIC physics motivation

+ (g-2) of m at BNL+ muonium exp. LANL+ Lambshift of Hydrogen+ ….