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Kazutaka NakaharaKEK
for the G0 Collaboration:Caltech, Carnegie-Mellon, William&Mary, Grinnell
College, Hampton, IPN-Orsay, LPSN-Grenoble, JLab, Kentucky, LaTech, NMSU, TRIUMF, UIUC, U
Manitoba, U Maryland, UNBC, U Winnipeg, VPI, Yerevan
The G0 ExperimentStrange quark contribution to proton structure
SPIN2006 Kyoto 10/6/2006
s quark contributionGGGG
ps
ME
pd
ME
pu
ME
p
ME
,
,
,
,
,
,
,
, 3
1
3
1
3
2
GGGGps
ME
pd
ME
pu
ME
n
ME
,
,
,
,
,
,
,
, 3
1
3
2
3
1
Proton and neutron EM form factors (assuming charge symmetry):
GGGGps
MEw
pd
MEw
pu
MEw
pZ
ME
,
,
2,
,
2,
,
2,
, sinsinsin 3
41
3
41
3
81
Neutral Weak form factor:
Measure GZ,p !!!
Flavor Decomposition of Nucleon Form Factors
Spin2006 Kyoto 10/6/06
Determine s quark contribution to the charge and magnetization distribution of the proton
Parity Conserving Parity Violating
GG
GGGGGGQGAp
Mp
E
eA
pMW
pZM
pM
pZE
pEF
,2
,2
,'2,,,,2sin41
24
Measure at forward angles (elastic e-p)
Measure at backward angles (elastic e-p andquasi-elastic e-d)
Q2
4M 2
1 2(1 )tan2 2 1
(1 2) (1 )
GG
GGG
AAA
ps
M
ps
E
e
A
pZ
M
pZ
E
backwardD
backwardH
forward
,
,
,
,
,
,
Parity Violating Electron-Proton Scattering
Spin2006 Kyoto 10/6/06
Jefferson Laboratory
A B CInjector/Source
linacs
Forward Angle ApparatusForward angle mode:
• Q2 = 0.12 ~ 1.0
•40A longitudinally polarized beam. 32MHz repetition rate for TOF.
• Helicity flip at 30 Hz (macro-pulse, MPS), arranged into quartet pattern.
• High power LH2 target. Capable of maintaining stable temperature/density with high power deposit.
• 8 octant superconducting toroidal magnet, array of 16 scintillator pairs per octant.
• Different scintillator Different Q2. Distinguish elastic protons from background through TOF separation.
• Fast electronics counting individual particle.
lead collimators
elastic protons
detectors
targetbeam
Electron Beam
LH2 Target
SuperconductingCoils
Particle Detectors
Spin2006 Kyoto 10/6/06
Backward angle mode:
• Q2 = 0.23 and 0.62
• 80A longitudinally polarized beam. 499MHz repetition rate no TOF
• Helicity flip at 30 Hz (macro-pulse, MPS), arranged into quartet pattern.
• High power LH2 & LD target. 8 octant superconducting toroidal magnet.
• 8 octant, array of 16 scintillator pairs per octant. Additional detectors (Cerenkov, CED) for background (pion) rejection.
• FPD-CED matrix electronic/detector package separate elastics from background.
TargetScintillator Detector
SuperconductingCoils
Backward Angle Apparatus
G0 beammonitoring
Superconducting Magnet (SMS)
Detectors (Ferris wheel)
FPD
Spokesman
Target service module
G0 in Hall C : The key elements
Detectors (Mini-Ferris wheel)CED+Cherenkov
Forward Angle Data
Successful run in spring 2004• Different components
separated by t.o.f.• Beam systematics
understood:- 73.7 % polarization- small helicity-
correlation- effect of leakage beam
understood• Background under elastic
peak is main analysis issue
Corresponds to:
701 h at 40 A (100 C)
19 x 106 quartets
76 x 106 MPS
Spin2006 Kyoto 10/6/06
Strange Quark Contribution to Proton
)0(
22
2 1
24
VpE
pM
pE
F RG
GG
QG
NVSphys AA s
EG sMG
G
GpE
pM
, Data @ Q2 = 0.1 GeV2
http://www.npl.uiuc.edu/exp/G0/Forward
= -0.013 0.028 GEs
GMs= +0.62 0.31
Contours
1, 2 68.3, 95.5% CL
Theories1. Leinweber, et al.
PRL 94 (05) 2120012. Lyubovitskij, et al.
PRC 66 (02) 0552043. Lewis, et al.
PRD 67 (03) 0130034. Silva, et al.
PRD 65 (01) 014016
GEs GM
s
. , Data @ Q2 = 0.1 GeV2GEs GM
s
HAPPEx He
• HAPPEx calculation: Q2 = 0.1 GeV2
GM = 0.28 ± 0.20s
GE = -0.006 ± 0.016 s
G0 Backward Angle StatusQ2 = 0.23 and 0.62 GeV2/c2
• March 15 – May 1: 0.62 GeV2/c2
- 200 hours LH2, 50 hours LD2 (at 10 A) - 80 hours “parity quality” data w/ LH2 at 60 A• May15-18: 0.23 GeV2/c2
- first look at LD2 at low beam current - outstanding beam delivery• July 19- Sept 1 (0.23) / Sept 22- Dec 22 (0.62) production
First hand look at data so far:
- Elastic asymmetry near expected
- good elastic/inelastic electron separation
- pion asymmetry smaller than elastic
- Deuterium data shows high background rates in Cerenkov (probably neutrons)
Summary• Forward angle production run successfully completed
• Results published
Phys. Rev. Lett. 95, 092001 (2005)
i. Interesting Q2-dependence for the strange quark contribution to the nucleon form factors
ii. Agreement at low Q2 with previous experiments
• Backward angle measurement has begun!
Spin2006 Kyoto 10/6/06
Backup
Summary of Systematic Effects
Source Uncertainty
Electronics deadtime 0.05 ppm
Helicity-correlated differences in beam properties
0.01 ppm
499 MHz (2 ns) leakage beam 0.14 ppm
Beam polarization (Hall C Møller) 1 %
Transverse beam polarization 0.01 ppm
Inelastic background subtraction 0.2-9 ppm
Radiative corrections 0.3 %
Detector Q2 1 %
G0 in Hall C
beammonitoring girder
superconducting magnet (SMS)
scintillation detectors
cryogenic supply
cryogenic target ‘service module’
electron beamline
Strange Quark Contribution to Proton
http://www.npl.uiuc.edu/exp/G0/Forward D. Armstrong, et al. PRL 95 (2005) 092001
)0(
22
2 1
24
VpE
pM
pE
F RG
GG
QG
NVSphys AA s
EG sMG
Analysis Overview
Aphys
+ GEs GM
s
Blinding Factor
Raw Asymmetries, Ameas
“Beam” corrections:Leakage beam asymmetry
Helicity-correlated beam propertiesDeadtime
Beam polarization
Background correction
Q2
Elastic form factors
Unblinding
Helicity-Correlated Beam Parameters1. How much does the yield change when
the beam “moves”? understood (simulation & data agree)
2. ‘Instrumental’ (false) asymmetries
– e.g. if beam current changes in helicity-correlated manner
– e.g. if beam position on target changes in helicity-correlated manner
Helicity-correlated
change
Correction
X position 3 4 nm ~ 1 ppb
X angle 1 1 nr ~ few ppb
Y position 4 4 nm ~ 1 ppb
Y angle 1.5 1 nr ~ 10 ppb
Beam energy 29 4 eV ~ 1 ppb
Beam current -0.14 0.32 ppm ~ 10 ppb
False asymmetries from helicity-correlated parameters small (~10-8) compared to physics asymmetry (~10-5 – 10-6)
• Strange quark contribution to asymmetry depends on:
- ANVS = No vector strange asymmetry- EM form factors (Kelly parametrization)
Strange Quark Contribution
pE
pM
i G
GEQ
,2
http://www.npl.uiuc.edu/exp/G0/Forward
)0(
22
2 1
24
VpE
pM
pE
F RG
GG
QG
NVSphys AA s
EG sMG
Strange Quark Contribution to Proton
Where Were We?• From HAPPEX H preprint nucl-ex/0506011
Similar angular kinematics to G0
Polarized source and beam High polarization has been reached routinely using superlattice GaAs cathodes New Fiber laser for Hall C (adjustable pulse repetition rate) Allows flexible time structure (1-2h for setting) : 32 ns used for Cherenkov study 780 nm is at polarization peak (P ~ 85%) for superlattice GaAs
60 A of low energy beam New optics, beam dump and halo issue handled
Moeller polarimeter in Hall C Energy smaller than 800 MeV (design) Need to move quadrupoles closer to target Difficult tune (beam position, magnet settings)
Finally successful at 686 MeV 1 um foil = -86.36 +/- 0.36% (stat) 4 um foil = -85.94 +/- 0.33% (stat) Systematic error 2 %, expected to be reduced
New features and specificities
Commissioning (I)
Beam properties Hall C instrumentation OK Beam properties 35 h IN and 42 h OUT at 60 A (LH2) Adiabatic damping, PITA, RWHP, IA Room for improvement (position feedback) Halo within a 6 mm diameter was determined to be < 0.3 x 10-6 (spec : 10-6 )
Target and Lumi detectors LH2 and LD2 target
(“Flyswatter” and gas target for cell contribution) Target boiling from Lumi detectors Intensity up to 60 A (limitation by window on beam dump) Very flat behavior (rates/beam current) Ratio LD2:LH2:C12 are the ones expected
Beam Param. Achieved in G0
(IN-OUT)Spec
s
Charge asym. -0.4 ± 0.24 ppm 2 ppm
X-Y position diff.
20-24 ± 5 nm 40 nm
X-Y angle diff. -2 to -4 ± 2 nrad
4 nrad
Energy diff. 2 ± 4 eV 30 eV
Pions
60 A, LH2 10 A, LD2
Particle ID : CED-FPD + Cherenkov(rates in Hz/A per octant)
Electrons
Loss/random issue
Fraction (%) of loss I
LH2
60 A
LD2
10 A
Fraction (%) of random I2
Asymmetries : Electron plane and LH2
IN OUT
Asymmetries : Electron plane and LH2
IN OUT
Data taking in 2006 (I)
First period of running at 682 MeV Commissioning and data taking … in a row !!As usual a risky business and a scary/tough period !!
Many new features handled successfully Beam : low energy … but no compromise on intensity and Parity Quality New settings (polarimeter, target, …) New set-up (CED, Cherenkov, electronics …)
Analysis underway (remember this ended … 15 days ago !!)
Remained to be fixed for running in the Fall
Work/tests underway to reach 60 A with LD2
Cherenkov (anode current and random coincidences) Gas flow in diffusion box (Ar (not working), CO2), gain/HV reduction, M > 2
CED-FPD (random/loss) Use backplane scintillators of FPD counters (factor 10 reduction)
G0 Backward angle … What’s next in 2006
Still a long way to go … and maybe some new challenges at 362 MeV Adiabatic damping Halo issue (if due to processes in residual gas) Test run underway this week at JLab
More work on Moeller polarimeter
Hopefully by the end of 2006 …
+
Lab Update Slides – Sept. 15
G0 362 MeV UpdateD. Beck UIUC
Sept. 06• Hydrogen data taking at 362 MeV completed– 86 C out of ~ 120 C possible as scheduled– 170 C proposed: 80 A for 30 d
• 75% polarization proposed, 84% delivered
• Very clean hydrogen elastic signal– all backgrounds total ~ 5-10%
Deuterium test run (May)
CE
D
Rat
e (k
Hz/A
)
Hydrogen data (Aug.)
FPD
(quasi) elastic electrons
G0 362 MeV: Deuterium Tests• High singles rates in Cherenkov detectors with deuterium target– traced to low energy neutrons capturing in boroscilicate glass PMT
windows: B(n,)Li– measurements at NIST, Grenoble confirm effect
• each produces 6 p.e.– recalibration of NIST neutron beam flux (10 p.e. → 6 p.e.)
– PMTs with quartz windows• reduce counting rates for ~thermal neutrons by x100 (NIST, Grenoble)
• Based on July/August testing– various combinations of 5 in. boroscilicate and 2 in. boroscilicate and
quartz tubes
– extrapolate from comparison of LH2 and C targets
– with new 5 in. quartz tubes for Cherenkov detectors: bottom lineExpect 0.5 – 1.5 x LH2 rate (→ successful run)
• Successful reduction of FPD accidentals (x4)– alternate front and back tubes
362 MeV Beam
• Helicity-correlated beam properties well within spec
Measured SpecCharge symmetry
0.03±0.12 ppm
2 ppm
X position difference
-12±4 nm 40 nm
Y position difference
1±4 nm 40 nm
• Beam polarization– measurement with Moller not feasible
• std. solenoid field not compatible with beam transport• chkd longitudinal polarization
– concurrent Hall A, Mott measurements at beginning of run
– periodic Mott measurements throughout run• individual measurements average ~84±1.5%
G0 362 MeV Online LH2 Asymmetries
• Low backgrounds (5-10%), small deadtimes (4-8%)• BLINDED online results
– fraction of data set– no corrections for h.c. beam parameters, deadtime, …
G0 362 MeV Online LH2 AsymmetriesElastic
Background
P R E
L I
M I
N A R
Y
Octant
Octant
• Low backgrounds (5-10%), small deadtimes (4-8%)
• BLINDED online results – fraction of data set
– no corrections for h.c. beam parameters, deadtime, …
G0 362 MeV Online LH2 Asymmetries
• Also measured asymmetry with transverse polarization to correct longitudinal asymmetry– beam angle limited to ~ 50 mr from longitudinal– asymmetry in octant azimuthal scattering angles limited to ~ 20 mr– correction < 0.1 ppm
G0 362 MeV LH2 Transverse Asymmetry
• BLINDED online results – no corrections for h.c. beam parameters, deadtime, …
Transverse: Elastic
P R E L I M I N A R Y
Octant
Outlook for 687 MeV
• Direct resumption of production data-taking as soon as halo/background from April restored
• Lower accidental rates in FPDs (as in summer run)
• Expect switch to LD2 near end of October (as soon as tubes arrive
– possible LD2 test (~ 2 days) in early October to finalize plans for trigger with new Cherenkov tubes
• Expect near 100 C of data for both LH2 and LD2 at 687 MeV assuming– Cherenkov tubes arrive before end of October
– rate projections for LD2 correct