Transcript
Page 1: The G 0  Experiment Strange quark contribution to proton structure

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

Page 2: The G 0  Experiment Strange quark contribution to proton structure

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

Page 3: The G 0  Experiment Strange quark contribution to proton structure

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

Page 4: The G 0  Experiment Strange quark contribution to proton structure

Jefferson Laboratory

A B CInjector/Source

linacs

Page 5: The G 0  Experiment Strange quark contribution to proton structure

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

Page 6: The G 0  Experiment Strange quark contribution to proton structure

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

Page 7: The G 0  Experiment Strange quark contribution to proton structure

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

Page 8: The G 0  Experiment Strange quark contribution to proton structure

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

Page 9: The G 0  Experiment Strange quark contribution to proton structure

, 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

Page 10: The G 0  Experiment Strange quark contribution to proton structure

. , 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

Page 11: The G 0  Experiment Strange quark contribution to proton structure

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)

Page 12: The G 0  Experiment Strange quark contribution to proton structure

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

Page 13: The G 0  Experiment Strange quark contribution to proton structure

Backup

Page 14: The G 0  Experiment Strange quark contribution to proton structure

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 %

Page 15: The G 0  Experiment Strange quark contribution to proton structure

G0 in Hall C

beammonitoring girder

superconducting magnet (SMS)

scintillation detectors

cryogenic supply

cryogenic target ‘service module’

electron beamline

Page 16: The G 0  Experiment Strange quark contribution to proton structure

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

Page 17: The G 0  Experiment Strange quark contribution to proton structure

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

Page 18: The G 0  Experiment Strange quark contribution to proton structure

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)

Page 19: The G 0  Experiment Strange quark contribution to proton structure

• 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

Page 20: The G 0  Experiment Strange quark contribution to proton structure

Strange Quark Contribution to Proton

Page 21: The G 0  Experiment Strange quark contribution to proton structure

Where Were We?• From HAPPEX H preprint nucl-ex/0506011

Similar angular kinematics to G0

Page 22: The G 0  Experiment Strange quark contribution to proton structure

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

Page 23: The G 0  Experiment Strange quark contribution to proton structure

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

Page 24: The G 0  Experiment Strange quark contribution to proton structure

Pions

60 A, LH2 10 A, LD2

Particle ID : CED-FPD + Cherenkov(rates in Hz/A per octant)

Electrons

Page 25: The G 0  Experiment Strange quark contribution to proton structure

Loss/random issue

Fraction (%) of loss I

LH2

60 A

LD2

10 A

Fraction (%) of random I2

Page 26: The G 0  Experiment Strange quark contribution to proton structure

Asymmetries : Electron plane and LH2

IN OUT

Page 27: The G 0  Experiment Strange quark contribution to proton structure

Asymmetries : Electron plane and LH2

IN OUT

Page 28: The G 0  Experiment Strange quark contribution to proton structure

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)

Page 29: The G 0  Experiment Strange quark contribution to proton structure

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 …

+

Page 30: The G 0  Experiment Strange quark contribution to proton structure

Lab Update Slides – Sept. 15

Page 31: The G 0  Experiment Strange quark contribution to proton structure

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

Page 32: The G 0  Experiment Strange quark contribution to proton structure

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

Page 33: The G 0  Experiment Strange quark contribution to proton structure

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%

Page 34: The G 0  Experiment Strange quark contribution to proton structure

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, …

Page 35: The G 0  Experiment Strange quark contribution to proton structure

G0 362 MeV Online LH2 AsymmetriesElastic

Background

P R E

L I

M I

N A R

Y

Octant

Octant

Page 36: The G 0  Experiment Strange quark contribution to proton structure

• 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

Page 37: The G 0  Experiment Strange quark contribution to proton structure

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

Page 38: The G 0  Experiment Strange quark contribution to proton structure

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


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