Transcript Results from the G0 Measurement Colleen Ellis, University of Maryland  Parity-violating electron scattering from the nucleon  Hydrogen and deuterium targets  Strange quark.

Results from the G0 Measurement
Colleen Ellis, University of Maryland

Parity-violating electron scattering from the nucleon
 Hydrogen and deuterium targets
 Strange quark contributions to electromagnetic form factors
1988 Kaplan and Manohar—sea quark contributions to ground state nucleon properties,
i.e. spin, charge, and magnetic movements from neutral weak probes ( νN scattering)
1989 McKeown then Beck outlined a PVES program that could measure strange quark
contributions to the proton’s charge and magnetism.
D.Kaplan and A.V. Manohar, Nucl. Phys. B310, 527 (1988)
R.D. McKeown, Phys Lett. B219, 140 (1989)
D.H. Beck, Phys. Rev. D39, 3248 (1989)

e

p e

p
2
Parity Violating elastic e-N scattering
Q (EM) QW
u
2/3
d
-1/3
s
-1/3
charge symmetry
Access via form
factors:
contribution to
nucleon charge
and magnetism
Q2 behavior well-understood
Measured in G0
Parity Violating elastic e-N Form Factors
M M Z
   
A

   
M

AE  GE G
2
Z
E
AM  GM GMZ

AA  (1 4sin W ) G GM
2
'
AD  (GE ) 2   (GM ) 2

e
A
AE  AM  AA
{
}
AD
Q2

4M2
1





  1 2(1  )tan2 
2 

'
PV asymmetries
from EM and weak
interference terms

e

p e

p
2
1   1  
 can be varied between zero and unity
for a fixed Q2 by varying 
the beam energy
and electron scattering angle.
Two kinematics, two targets gives
3 linear combinations of EM and
C. Ellis/UMD
weak form factors
2
proton
APV
GEs (Q2 )
(  5,10)
 proton
 s 2
APV (  110)  GM (Q )
 deuteron
 e 2
(  110)
APV
GA (Q )
3
Axial form factor seen by PV electron scattering
GAe (Q2 )  GAZ (Q2 )  (FA (Q2 )  Re )  GAs (Q2 )
e'
Z0
e


+
e
e

++ +
PV PV
e
Z

Z
+ ...+ ...
e
(FA + Re) at Q2=0 computed
by Zhu etal,
PRD 62 (2000) 033008
SAMPLE deuterium asymmetry data
agree well
but Q2 behavior is not well
constrained
slide thanks to E. Beise
4
Asymmetries to Form Factors
Aphys  a0  aEGEs  aM GMs  aAGAe
Electromagnetic form factors: Kelly (PRC 70 (2004))
does not include new low Q2 data from BLAST or JLab
eventually use new fits (Arrington & Melnitchouk for p, Arrington & Sick for n)
differences in fits become 0.5 – 1 % in the asymmetry
also used in Schiavilla calculation for D
(see Diaconescu, Schiavilla & van Kolck, PRC 63 (2001) 044007)
Two-boson exchange corrections to Asymmetry: 0.5 -1.2%
(see Tjon, Blunden & Melnitchouk, arXiv:0903.2759v1)
Ameas  1    ABorn
 1   Z      Z  
 ABorn



1    


5
G0 –Path to extracting vector form factors
A
M M Z
   

   
M
2
{
AE  AM  AA
s
s
e(T 1)
}

a

a
G

a
G

a
G
0
1 E
2 M
3 A
(GE ) 2   (GM ) 2
At Q2 = 0.62 and 0.23 (GeV/c)2, there are three measurements:
AF : forward angle H (recoil protons) (D.S. Armstrong, et al., PRL 95, 092001 (2005))
AB : backward angle H (D. Androic, et al., PRL 104, 012001 (2010))
Ad : backward angle D
s
AF  a1F
  
AB  a1B
  
Ad  a1d
a1 (ppm)
at Q2
= 0.62 GeV2
C. Ellis/UMD
a2F
a2B
a2d
a2 (ppm)
a3F GE  a0F 
 s   
a3B GM  a0B 
 e   
a3d 
GA  a0d 
a3 (ppm)
a0 (ppm)
AF 79.39
42.87
2.46
-23.68
AB
21.57
62.84
12.10
-38.28
Ad
12.12
12.49
9.50
-53.29
G0 Forward Angle Experiment
• Forward angle measurement
completed May 04
• LH2 target, detect recoil protons
• Q2 = 0.12-1.0 (GeV/c)2, E=3.03GeV
• Spectrometer sorts protons by Q2 in
focal plane detectors (16 rings in total)
• Detector 16: “super-elastic”, crucial
for measuring the background
• Beam bunches separated by 32 ns
• Time-of-flight separates protons from
pions
• Results published in :
• D.S. Armstrong, et al.,
PRL 95, 092001 (2005)
77
G0 Forward angle Results
G  G
s
E
s
M
4 2  GEp   GMp

GF Q 2  GEp 1  RV( 0 )
2
2


A
phys
 ANVS 
EM form factors:
J.J.Kelly, PRC 70,
068202 (2004)
G0 Backward
HAPPEX-3
D.S. Armstrong et al.,
PRL 95 (2005) 092001
8
G0 Backward Angle
• Hydrogen and deuterium targets
• Electron beam energy :
• 362 MeV : Q2=0.23 GeV2
• 687 MeV : Q2=0.62 GeV2
• Completed running in March 2007
• Particle detection and identification
:
CED + Cherenkov
FPD
• 16 Focal Plan Detectors
• 9 Cryostat Exit Detectors
elastic and inelastic electron
separation
• Čerenkov detectors electron and
pion separation
e- beam
e- beamline
C. Ellis/UMD
target
9
Polarized Beam Properties


Measurements of Møller asymmetry
at 687 MeV
Mott scattering for 362 MeV
measurements
687 MeV Møller Results
April 2006
Mott asymmetry measured at 5 MeV
in injector
 New work on effect of background
improves agreement with Møller

Beam Parameter
charge asymmetry
Achieved
(OUT-IN)/2
0.09 +/- 0.08
“Specs”
-19 +/- 3
40 nm
y position difference
-17 +/- 2
40 nm
x angle difference
-0.8 +/- 0.2
4 nrad
y angle difference
0.0 +/- 0.1
4 nrad
energy difference
2.5 +/- 0.5
34 eV
< 0.3 x 10
-6
Sep.-Dec. 2006
2 ppm
x position difference
Beam halo (out 6 mm)
March 2007
-6
10
10
Pe(687 MeV) = 85.78 ± 0.07 ± 1.38%
Pe(362 MeV) =
± 2.05%
Hydrogen raw electron data
d
362 MeV
octant # (azimuthal distribution)
687 MeV
11
Hz/uA
Hz/uA
Deuterium raw electron data
d
d
362 MeV
octant # (azimuthal distribution)
687 MeV
12
Hz/uA
Hz/uA
Analysis Strategy
Blinding
Factors
~10-50 ppm
H, D Raw Asymmetries, Ameas
× 0.75-1.25
4% on asymmetry
Electromagnetic
radiative corrections
(from simulation)
Q2 Determination
(from simulation)
± 0.003 GeV2
Corrections
Scaler counting correction
Rate corrections from electronics
Helicity-correlated corrections
Background corrections
Beam polarization
< 1% of Aphys
< 0.1 ppm
P= 0.8578
± 0.0007 (stat)
± .014 (sys)
Unblind
H, D Physics Asymmetries, Aphys
s
E
s
M
e
A
G ,G ,G
13
Rate Corrections
Correct the yields for random
coincidences and electronic dead
time prior to asymmetry calculation
Randoms small except for D-687 (due
to higher pion rate)
Direct (out-of-time) randoms
measured
Validated with simulation of the
complete electronics chain
CED
Correction
to Yield (%)
Asymmetry systematic
Correction error (ppm)
(ppm)
H 362 8
-0.31
0.08
H 687 4
-1.28
0.18
D 362 7
-0.58
0.21
D 687 -10
-7.0
1.8
Cerenkov
Trigger
CFD
MT
CFD
Trigger CEDxFPD
FPD
Data
set
CFD
Coincidence
1 CED
1 FPD
1 Trigger
electro
n
MT
CFD
pion
14
Backgrounds: Magnetic Field
Scans
D-687
CED 7, FPD 13
Use simulation shapes to
help determine dilution
factors
Main contributions are
Aluminum windows
(~10%), pions (for D-687
data only).
Data set
Asymmetry
Correction (ppm)
systematic error
(ppm)
H 362
0.50
0.37
H 687
0.13
0.78
D 362
0.06
0.02
D 687
2.03
0.37
15
Experimental “Physics” Asymmetries
all entries in ppm
Data Set
Asymmetry
Stat
Sys pt
Global
H 362
-11.25
0.86
0.27
0.43
D 362
-16.93
0.81
0.41
0.21
H 687
-45.9
2.4
0.8
1.00
D 687
-55.5
33
2.0
0.7
Largest correction is due to the 85% beam polarization
--dominates H systematic uncertainties
--for D-687, contributes about equally with rate corrections to the
systematic uncertainty
16
Form Factor Results
•
Using interpolation of G0 forward measurements
G0 forward/backward
PVA4: PRL 102 (2009)
Q2 = 0.1 GeV2 combined
(G0,HAPPEX, SAMPLE & PVA4)
Global uncertainties
G0 forward/backward
SAMPLE
Zhu, et al. PRD 62 (2000)
Some calculations:
Leinweber, et al. PRL 97 (2006) 022001
Leinweber, et al. PRL 94 (2005) 152001
Wang, et al arXiv:0807.0944 (Q2 = 0.23 GeV2)
Doi, et al, arXiv:0903.3232
17
Summary
• Q2 behavior of strangeness contribution to proton’s charge and magnetism:
continue to be small
• first results for the Q2 behavior of the anapole contributions to the axial form
factor
• other results to come soon from G0:
 transverse beam spin asymmetries (2- exchange) in H and D
 PV in the N-D transition: axial transition f.f.
 PV asymmetry in inclusive  production
(0)
E,M
G
1 u
d
s
 (GE,M  GE,M
 GE,M
)
3
18
The G0 Collaboration (backward angle run)
Caltech, Carnegie Mellon, William and Mary, Hendricks College, Orsay, Grenoble, LA Tech, NMSU,
Ohio, JLab, TRIUMF, Illinois, Kentucky, Manitoba, Maryland, Winnipeg, Zagreb, Virginia Tech,
Yerevan Physics Institute
PhD students: C. Capuano, A. Coppens, C. Ellis, J. Mammei, M. Muether, J. Schaub, M. Veerstegen, S. Bailey
Analysis Coordinator: F. Benmokhtar
19
• Backups
G0: N → D
Measurement: Parity-violating asymmetry of
electrons scattered inelastically
ANΔ gives direct access to GANΔ
Directly measure the axial (intrinsic spin) response
during N →Δ+ transition
Will find GANΔ over a range of Q2
0.05 GeV/c2 < Q2 < 0.5 GeV/c2.
First measurement in neutral current process
Data: Inelastic electrons measured by G0
Scattered from both LH2 and LD2, each at two
energies (362MeV & 687MeV)
IN
Asymmetry (ppm)
Asymmetry (ppm) vs Octant (LH2 @ 687MeV)
OUT
BLINDED
Octant
Raw Asymmetry (averaged over inelastic region)
Transverse Asymmetry 2 photon exchange
An 
M  Im M 
M
2
Inclusion of the real part of the
2γ exchange in the cross section
may account for the difference
between measurements of GE/GM
from unpolarized cross section and
polarization transfer measurements
It also tests the theoretical framework that calculates the
contribution of γZ and W+W- box diagrams that are important
corrections to precision electroweak measurements
Asymmetry Uncertainties--Hydrogen, 687 MeV
Value
(ppm)
Measured Asymmetry
Background Asymmetry
-38.14
Stat Sys Pt Sys Gl
(ppm) (ppm) (ppm)
Total
(ppm)
2.43
0.40
-38.27
Dilution Correction
0.47
Transverse Correction
0.52
0.008
Rate Correction
-38.39
0.17
Beam Polarization
-44.76
0.52
EM Radiative Correction
-46.14
0.16
Physics Asymmetry
-46.14
2.43
0.84
0.53
0.75
2.68
Asymmetry Uncertainties--Deuterium, 687 MeV
Value
(ppm)
Measured Asymmetry
Background Asymmetry
-44.02
Stat Sys Pt Sys Gl
(ppm) (ppm) (ppm)
Total
(ppm)
3.34
0.050
-46.05
Dilution Correction
0.38
Transverse Correction
0.009
Rate Correction
-46.35
1.82
Beam Polarization
-54.03
0.62
EM Radiative Correction
-55.87
0.19
Physics Asymmetry
-55.87
3.34
1.98
0.008
0.64
0.64
3.92
Correction due to misidentified pions
3 Ways to calculate
• runs with special beam structure providing timing reference allowing particle TOF
• PMT Multiplicity (two versus three of the cerenkov PMT’s firing)
• Pulse heights (waveform digitized)
cerenkov detector
4 pmts
counts
687 MeV
red: pions
blue: electrons
aerogel
 contamination to
threshold
# single photo electrons
electron yield (A ~ 0)
D 362: 0.5%
D 687: 4%
25
D asymmetries: Calculation provided by Rocco Schiavilla
(see Diaconescu, Schiavilla & van Kolck, PRC 63 (2001) 044007)
GF Q 2 vL RLV (q,  )  vT RTV (q,  )  (1  4 sin 2 W )v'T RTA (q,  )
A(q, ,e )  
vL RL  vT RT
2 2
A(q,,e )  a0  a1GEs  a2GMs  a3GAe(T 1)  a4GAs
vL RLV  vT RTV
RA0
a0  Aelem
 a4 0
D
RA  GAs

s
cs
v
R

v
R
 L L T T  1
a1  Aelem
D
GEs (Q2 )
vT RTs
1
a2  Aelem
 s 2
D
GM (Q )
a3  Aelem

D
a4 C. A
elem
Ellis/UMD
D  vL RL (q, )  vT RT (q, )
  R  

A 10
LT
(1 4 sin W )vT ' R
2
GF Q 2
Aelem  
2 2
broken down by isospin
(1 4 sin W )vT ' R
2
absorbs isoscalar axial term
D
A 11
LT

  R  
A 00
LT
A 01
LT
1
GAe(T 1) (Q2 )


1
  0
s
2 
R

G
(Q
)
 A
A
26
Quasielastic PV (ee’) in Deuterium
Use Quasielastic scattering from deuterium as lever arm for GAe(Q2)
Ad 
 p Ap  n An
d
Parity conserving nuclear corrections to the asymmetry are generally small, 1-3% at
backward angles. Calculation provided to us by R. Schiavilla includes final state
interactions and 2-body effects.
Diaconescu, Schiavilla + van Kolck,
PRC 63 (2001) 044007
Schiavilla, Carlson + Paris,
PRC 67 (2003) 032501
See also
Hadjimichael, Poulis + Donnelly, PRC45 (1992) 2666
Schramm + Horowitz, PRC 49 (1994) 2777
Kuster + Arenhovel, NPA 626 (1997) 911
Liu, Prezeau, + Ramsey-Musolf,
PRC 67 (2003) 035501
E. Beise, U Maryland
27
Deuterium model comparison to cross section data
calculation from R. Schiavilla
see also
R.S., J. Carlson, and M. Paris,
PRC70, 044007 (2004).
• AV18 NN potential
• relativistic kinematics
• J.J. Kelly fit to nucleon
form factors
data from:
S. Dytman, et al., Phys. Rev. C 38, 800 (1988)
B. Quinn, et al., Phys. Rev. C 37, 1609 (1988)
E. Beise, U Maryland
28
2-body effects in the D asymmetry
calculations from R. Schiavilla, see also R.S., J. Carlson, and M. Paris, PRC70, 044007 (2004).
leading term
of the
asymmetry
axial form
factor coefficient
has ~15%
correction from
2-body effects
E. Beise, U Maryland
29
Scaler Counting Issue with Electronics

Electronics sorts detector coincidences (CEDi and
FPDj) into separate scaler channels


~ 1% of events have such miscounts
Such pulse pairs can cause scaler to drop or add
bits


FPGA-based system in North American electronics (4
octants)
Because of error in FPGA programming, two short
(~3 ns) pulses could be sent to scaler in < 7 ns


Data
Detailed simulation of ASIC with propagation delays
between (flip flop) elements
Simulation
Effect on asymmetry is <0.01 Aphys

Test by cutting data; compare with French octants
30
The Gzero Collaboration
College of William and Mary, Institut de Physique Nucléaire d'Orsay, Yerevan Physics
Institute, Laboratoire de Physique Subatomique et de Cosmologie Grenoble,
University of Illinois, University of Maryland, Thomas Jefferson National Accelerator
Facility, University of Manitoba, Carnegie Mellon University, California Institute of
Technology, University of Kentucky, TRIUMF, Louisiana Tech University, Virginia
Tech, University of Northern British Columbia, New Mexico State University
,University of Winnipeg, Ohio University, Hampton University, Hendricks College,
University of Zagreb
U.S. G0 participation jointly supported by DOE and NSF. Significant additional
contributions to G0 from NSERC (Canada) and CNRS (FR)
C. Ellis/UMD
31
Summary of the G0 Backangle Run
Run
Coulombs
Hours
Gbytes data
H 687
86
400
600
H 362
119
550
825
D 362
66
520
800
D 687 I
40
520
780
D 687 II
15
240
340
total
330
2300
3450
Run start to run end ~ 8940 hours
Beise Run Coordinator report March 2007