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In Quest of Nucleon Spin Vernon W. Hughes The Last Decade: 1993-2003. Abhay Deshpande RIKEN-BNL Research Center SYMMETRIES & SPIN PRAGUE, JULY 2003. Parton Distributions. (well known). Nucleon. (moderately well known). (unknown). (moderately well known). (unknown). - PowerPoint PPT Presentation
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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+ ….