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!"#"$%&!"'()%'&*$&+,-*%./0*1),2$3&4)"#%-1$&5#,6"-*$3&,%&7"8"-'1$&9,:;&
+!4<&,$=&>?++4</@@@
A"$%&+,'#BC"
?+5&5D-*$3&E""2$3?$,B"*FG&H?E,.&IG&JKII
>?++4<&H1)),:1-,21$+!4<&H1)),:1-,21$
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
LB"&M"(%-,)&H(--"$%&,$=&M(#)"1$&0"#%1-&N1-F&N,#%1-'
5%-,$3"&O(,-C'&"P*'%&*$&%B"&$(#)"1$&,%&'B1-%&=*'%,$#"&'#,)"'Q&R1&%B".&D),.&,&-1)"&*$&"),'2#&D-1%1$&'#,6"-*$3S
?
r [fm]0 0.5 1 1.5 2 2.5 3 3.5 4
]-1
[fm
Bre
it
2 r4
0
0.2
0.4
0.6
0.8
1
1.2
r [fm]0 0.5 1 1.5 2 2.5 3 3.5 4
]-1
[fm
Bre
it
2 r4
-0.05
0
0.05
0.1
0.15
0.2
Figure 2.5: On the left is the distribution of the charge within the neutron, the combined result of experiments around the globe that use polarization techniques in electron scattering. On the right is that of the (much larger) proton distribution for reference. The widths of the colored bands represent the uncertainties. A decade ago, as described in the 1999 NRC report (The Core of Matter, the Fuel of Stars, National Academies Press [1999]), our knowledge of neutron structure was quite limited and unable to constrain calculations, but as promised, advances in polarization techniques led to substantial improvement.
But quarks can have a transverse spin preference, denoted as transversity. Because of e!ects of relativity, transversity’s rela-tion to the nucleon’s transverse spin orientation di!ers from the corresponding relationship for spin components along its motion. Quark transversity measures a distinct property of nucleon structure—associated with the breaking of QCD’s fundamental chiral symmetry—from that probed by helicity preferences. "e first measurement of quark transversity has recently been made by the HERMES experiment, exploiting a spin sensitivity in the formation of hadrons from scattered quarks discovered in electron-positron collisions by nuclear scientists in the BELLE Collaboration at KEK in Japan.
Fueled by new experiments and dramatic recent advances in theory, the entire subject of transverse spin sensitivities in QCD interactions has undergone a worldwide renaissance. In contrast to decades-old expectations, sizable sensitiv-ity to the transverse spin orientation of a proton has been observed in both deep-inelastic scattering experiments with hadron coincidences at HERMES and in hadron production in polarized proton-proton collisions at RHIC. "e latter echoed an earlier result from Fermilab at lower energies, where perturbative QCD was not thought to be applicable. At HERMES, but not yet definitively at RHIC, measure-ments have disentangled the contributions due to quark transverse spin preferences and transverse motion preferences within a transversely polarized proton. "e motional prefer-ences are intriguing because they require spin-orbit correla-
tions within the nucleon’s wave function, and may thereby illuminate the original spin puzzle. Attempts are ongoing to achieve a unified understanding of a variety of transverse spin measurements, and further experiments are planned at RHIC and JLAB, with the aim of probing the orbital motion of quarks and gluons separately.
"e GPDs obtained from deep exclusive high-energy reactions provide independent access to the contributions of quark orbital angular momentum to the proton spin. As described further below, these reaction studies are a promi-nent part of the science program of the 12 GeV CEBAF Upgrade, providing the best promise for deducing the orbital contributions of valence quarks.
The Spatial Structure of Protons and NeutronsFollowing the pioneering measurements of the proton
charge distribution by Hofstadter at Stanford in the 1950s, experiments have revealed the proton’s internal makeup with ever-increasing precision, largely through the use of electron scattering. "e spatial structure of the nucleon reflects in QCD the distributions of the elementary quarks and gluons, as well as their motion and spin polarization.
Charge and Magnetization Distributions of Protons and Neutrons. "e fundamental quantities that provide the simplest spatial map of the interior of neutrons and protons are the electromagnetic form factors, which lead to a picture of the average spatial distributions of charge and magnetism.
26 QCD and the Structure of Hadrons
4πr2
ρ Bre
it[fm
−1]
?''(F"&T&O(,-C&U,V1-$%-*:(21$'&%1&V"#%1-&W1-F&W,#%1-';&X(G&X=G&X'
HB,-3"&5.FF"%-.
+T&"O(,21$'&
Y*%BT&($C$1Y$'
GZE,M = (1− 4 sin2 θW)Gp
E,M −GnE,M −Gs
E,M
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
E",'(-*$3&5%-,$3"&0"#%1-&N1-F&N,#%1-'
~ few parts per millionFor a proton:
Forward angle Backward angle
For a spin=0,T=0 4He: GsE only! For deuterium: Enhanced GA
! Z! 2
!
~ 10"4Q2
GeV2
“Anapole” radiative corrections are
problematic
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
4PD"-*F"$%,)&ZV"-V*"Y
5?E+94
>?++4<
>?++4</T;&X4'&[&KQ\J&XE
'&&,%&]J&^&KQ_J&X"0J
+-"#*'*1$&'D"#%-1F"%"-G&*$%"3-,2$3
?`
1D"$&3"1F"%-.G&*$%"3-,2$3G&:,#C/,$3)"&1$).
ZD"$&3"1F"%-.
N,'%($2$3&#,)1-*F"%"-&W1-&:,#C3-1($=&-"a"#21$
N1-Y,-=&,$=&b,#CY,-=&,$3)"'
XK
&&&&&&&&ZD"$&3"1F"%-.
N,'%($2$3&Y*%B&F,3$"2#&'D"#%-1F"%"-&[&LZN&W1-&:,#C3-1($=&-"a"#21$
N1-Y,-=&,$=&b,#CY,-=&,$3)"'&1V"-&,&-,$3"&1W&]J
N1-Y,-=&,$3)"G&,)'1&`>"&,%&)1Y&]J
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
c1-)=&=,%,&1$&X'
• “Form Factor” error: precision of EMFF (including 2!) and Anapole correction
• Significant systematic uncertainty in higher Q2 points
η =τ Gp
M
� GpE
∼ Q2
!!"# !! !$"# $ $"# ! !"#
!$"!#
!$"!
!$"$#
$
$"$#
$"!
$"!#
E
sG
M
sG
%&'()*+,-./
+0120321.-45&
6
&7
6$+89:.;1<421.9=>
?97?&((*@!
?&((*@!?
2 ~ 0.1 GeV
2Q
At Q2=~0.1 GeV2, Gs < few percent of Gp
all forward-angle proton data all low Q2 data
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
X)1:,)&d%&1W&,))&Y1-)=&=,%,
•R,%,&'"%&,DD",-'&%1&'B1Y$'*'%"$%&D-"W"-"$#"&W1-&D1'*2V"&"8"#%•5*3$*d#,$%$%-*:(21$'&,%&B*3B"-&]J&,-"&$1%&-()"=&1(%Q&
!"#$"%&'()*+$,''$-./')$),#,$01$2$3456$7*81$73$7'.9,'$*//./$,''.-*)$#.$:.,#$-"#;$(%"#$&.%+#/,"%#
5*FD)"&d%;
7<+$=$>+?@
7A+$=$B+
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
9",=&/&9(#*%"&H"-"$C1V&5B1Y"-&H,)1-*F"%"-•DB1%1%(:"&#(--"$%&*$%"3-,%"=&1V"-&dP"=&2F"&D"-*1='
3 Data Quality Checks
3.1 Detector Acceptances
Detector acceptances are checked to ensure that the detector is well aligned and not imposing geometric
cut to skew the Q2. The top two plots in Fig. 3.1 are S0 triggered plots, and the bottom two are detector
triggered plots. The S0 paddles are much bigger than the detector and covers the entire detector plane. The
detector x/y distribution plots with detector triggers look identical to the S0 triggered plots, indicating that
the detector does not impose any geometric cuts on the acceptance.
Detector Plane x (m)-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
Dete
cto
r P
lan
e y
(m
)
-150
-100
-50
50
100
-310!
1
10
210
Detector Plane x (m)
LHRS Detector Plane Dist.
S0 Trigger
Detector Plane x (m)-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
Dete
cto
r P
lan
e y
(m
)
-150
-100
-50
50
100
-310!
1
10
210
Detector Plane x (m)
RHRS Detector Plane Dist.
S0 Trigger
Detector Plane x (m)-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
Dete
cto
r P
lan
e y
(m
)
-150
-100
-50
50
100
-310!
1
10
210
Detector Plane x (m)
LHRS Detector Plane Dist.
det Trigger
Detector Plane x (m)-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
Dete
cto
r P
lan
e y
(m
)
-150
-100
-50
50
100
-310!
1
10
210
Detector Plane x (m)
RHRS Detector Plane Dist.
det Trigger
Figure 3.1: Detector acceptance plots with S0 and detector triggers. The bounding box is the outline of the
detector with the PMT located at about 1.2m in x.
The cuts used to generate these plots are
LHRS::"P.hapadcL>550 && L.tr.n==1 && abs(ExTgtCor_L.th)<0.07
&& abs(ExTgtCor_L.ph)<0.07 && abs(ExTgtCor_L.dp)<0.05"
RHRS::"P.hapadcR>700 && R.tr.n==1 && abs(ExTgtCor_R.th)<0.07
&& abs(ExTgtCor_R.ph)<0.07 && abs(ExTgtCor_R.dp)<0.05"
D.evtype==2/(D.evtypebits&0x4)==0x4 are added to the LHRS/RHRS cuts to plot S0 triggered events.
10
@$%"3-,2$3&*$&%B"&>*3B&!"'1)(21$&5D"#%-1F"%"-'
Entries 2.694749e+07
RMS 3733
-20 -15 -10 -5 0 5 10 15 20310!
1
10
210
310
410
510
610Entries 2.694749e+07
RMS 3733
parts per million
Psuedo-random, rapid helicity flip
0"-.&#)",$&'"D,-,21$&1W"),'2#&"V"$%'&:.&>!5&1D2#'
&$1&+@R&$""="=e&="%"#%1-&'""'&1$).&"),'2#&"V"$%'
Elastic
Inelastic
detector
Q Q
Dipole
Quad
target
HAPPEX-III Beam Polarizations
HAPPEX-III Electron Beam Polarizations
Final HAPPEX-III polarization results:
Compton: 89.41± 0.21 (statistical) ±0.94 (systematic)%
Moller: 89.22± 1.7(systematic)%
� �� �Period 1
� �� �Period 2
� �� �Period 3
� �� �Period 4
M Friend (Carnegie Mellon University) HAPPEX-III Compton Polarimetry APS April Meeting 10 / 12
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
>?++4</@@@&4--1-&b(=3"%f?+0&&gDDFh
f?+0&i&?+0&
+1),-*j,21$ KQJKJ KQk\l]J&E",'(-"F"$% KQI_K KQ_mlb,#C3-1($=' KQIn` KQkJl9*$",-*%. KQIJn KQ\`lN*$*%"&?##"D%,$#" KQK`k KQJKlN,)'"&?'.FF"%-*"' KQK`I KQImlL1%,)&5.'%"F,2#& KQT\T IQ`nl5%,2'2#' KQmm_ TQJmlL1%,)&4PD"-*F"$%,)& KQk\T TQ\nl
Compton + Moller polarimeters
more later from Megan Friend, CMU
Spectrometer Calibration
more later from Kiadtisak Saenboonruang, UVa
Fle
xio
Boar
d
AD
C B
oar
d
System
PMT
LEDs
Data Acquisition
DIFF ENABLE
BASELINE ENABLE
Pulser Electronics
Linearity StudiesHRS Backgrounds
more later from Rupesh Silwal, UVa
Systematic uncertainties are well controlled -
experiment is statistics
dominated
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
>?++4</@@@&E",'(-"F"$%&1W&?+0
ARAW = -21.591 ± 0.688 (stat) ppm
Additional corrections are then applied:•backgrounds (1.1%)•acceptance averaging (0.5%)•beam polarization (11%)
This includes•beam asymmetry correction (-0.01 ppm)•charge normalization (0.20 ppm)
TQJ_l&g'%,%ho&IQ`nl&g'.'%h%1%,)--"#21$&pJQ\l&[&D1),-*j,21$
?$,).'*'&b)*$="=&o&JQ\&DDF
0 5 10 15 20 25-40-30-20-10
0102030
= 1.00, P=0.512!OUT A=21.086 +/- 0.975 ppm, N=381, = 1.09, P=0.092!IN A=22.170 +/- 0.989 ppm, N=409,
= 1.05, P=0.182!AVG A=21.620 +/- 0.694 ppm, N=791, part
s pe
r mill
ion
data “slug”
combined 2-arm data
L-,a"#%1-.&,%&%,-3"%&,V"-,3"=&%1&qT$FGqKQ\$-,=&
OUT / IN from “slow” spin reversals to cancel systematics0 5 10 15 20 25 30
-4-3-2-1012
OUT A=-0.368 +/- 0.224 ppmIN A=-0.032 +/- 0.221 ppm
AVG A=-0.202 +/- 0.157 ppmasym_bcm1
0 5 10 15 20 25 30-0.08-0.06-0.04-0.02
00.020.040.060.08
0.1OUT A=-5.990 +/- 3.246 nm
IN A=0.261 +/- 3.465 nmAVG A=-2.916 +/- 2.372 nm
diff_bpm4ax
0 5 10 15 20 25 30-0.06-0.04-0.02
00.020.040.06
OUT A=-12.992 +/- 4.184 nmIN A=9.842 +/- 4.178 nm
AVG A=-1.763 +/- 2.957 nm
diff_bpm4ay
0 5 10 15 20 25 30-0.08-0.06-0.04-0.02
00.020.040.060.08
0.1OUT A=-2.220 +/- 3.258 nm
IN A=0.872 +/- 3.579 nmAVG A=-0.700 +/- 2.416 nm
diff_bpm4bx
0 5 10 15 20 25 30-0.06-0.04-0.02
00.020.040.06
OUT A=-13.068 +/- 3.957 nmIN A=8.999 +/- 3.901 nm
AVG A=-2.217 +/- 2.779 nm
diff_bpm4by
0 5 10 15 20 25 30-0.1
-0.050
0.050.1
0.15OUT A=-35.402 +/- 5.332 nm
IN A=61.049 +/- 5.186 nmAVG A=12.025 +/- 3.721 nm
diff_bpm12x
slug
mic
ron
Position Differences
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
>?++4</@@@&!"'()%'APV = -23.742 ± 0.776 (stat) ± 0.353 (syst) ppm
Q2 = 0.6241 ± 0.0028 (GeV/c)2
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
>?++4</@@@&!"'()%'APV = -23.742 ± 0.776 (stat) ± 0.353 (syst) ppm
Q2 = 0.6241 ± 0.0028 (GeV/c)2
?gX'^Kh&^&/J`QI\k&DDF&C&KQ__T&DDF
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
>?++4</@@@&!"'()%'APV = -23.742 ± 0.776 (stat) ± 0.353 (syst) ppm
Q2 = 0.6241 ± 0.0028 (GeV/c)2
?gX'^Kh&^&/J`QI\k&DDF&C&KQ__T&DDF
X'4&[&KQ\J&X'
E&^&&&&&&&&&&&&&&&KQKK\&C&KQKIKg'%,%h&C&KQKK`g'.'%h&C&KQKKkgNNh
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
N*%G&c1-)=&R,%,
X'4&[&KQ\J&X'
E&^&&&&&KQKK\&C&KQKIKg'%,%h&C&KQKK`g'.'%h&C&KQKKkgNNh
Wtih HAPPEX-3 result at Q2 = 0.624 GeV2:
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
H1$'*="-*$3&1$).&%B"&`&>?++4<&F",'(-"F"$%'
NS / A NS - APV A -0.3 -0.2 -0.1 0 0.1 0.2 0.3
HAPPEX-I (1999) 2 = 0.479 GeV2QMs+0.39GE
sG
HAPPEX-II (2006) Ms+0.09GE
sG 2 = 0.107 GeV2Q
HAPPEX-II He (2006) EsG 2 = 0.078 GeV2Q
HAPPEX-III (2011) Ms+0.52GE
sG 2 = 0.624 GeV2Q
•High precision•Small systematic error•Clean theoretical interpretation
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
c1-)=&R,%,&1$&5%-,$3"&NN
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4-0.15
-0.1
-0.05
0
0.05
0.1
0.15
EsG
MsG
H)1
G0-backw
ard (
G0-forward
HAPPEX-3
68.3%95%
•&>?++4</@@@&D-1V*="'&,&#)",$G&D-"#*'"&F",'(-"&1W&?+0&,%&]J^KQ_J&X"0JG&,$=&d$='&%B,%&*%&*'$'*'%"$%&Y*%B&$1&'%-,$3"$"''$%-*:(21$Q&&
•&Recent lattice results indicate values smaller than these FF uncertainties
•&N(-%B"-&*FD-1V"F"$%'&*$&D-"#*'*1$&Y1()=&-"O(*-"&,==*21$,)&%B"1-"2#,)&,$=&"FD*-*#,)&*$D(%&W1-&*$%"-D-"%,21$
Q2 = 0.62 GeV2
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
&c",C&HB,-3"&R*'%-*:(21$&1W&>",V.&M(#)"*M(#)",-&%B"1-.&D-"=*#%'&,&$"(%-1$&
r'C*$s&1$&B",V.&$(#)"*
208Pb
M"(%-1$&=*'%-*:(21$&*'&$1%&,##"''*:)"&%1&%B"&#B,-3"/'"$'*2V"&DB1%1$Q
D-1%1$ $"(%-1$
4)"#%-*#&#B,-3" I K
c",C&#B,-3" pKQKk I
!
!
MEM =4"#
Q2Fp Q
2( )
!
MPVNC =
GF21" 4sin2#W( )Fp Q2( ) " Fn Q2( )[ ]
!
APV "GFQ
2
4#$ 2Fn Q
2( )Fp Q
2( )
Q2 ~ 0.01 GeV2 APV ~ 0.6 ppmRate ~1.5 GHz5o scattering angle
PREX (Pb-Radius EXperiment)
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
MFT fit mostly by data other than neutron densities
Involve strong probes
Most spins couple to zero.
• !Proton-Nucleus Elastic
• Pion, alpha, d Scattering
• Pion Photoproduction
• Heavy ion collisions
• Rare Isotopes (dripline)
• Magnetic scattering
• PREX
• Theory
E",'(-"F"$%'&1W&$"(%-1$&'C*$
Electroweak probe
5.6 5.65 5.7 5.75 5.8
rn in
208Pb (fm)
0.25
0.26
0.27
0.28
0.29
0.3
Fn(Q
2)/
N
Skyrme
covariant mesoncovariant point coupling
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
?&#-(#*,)&#,)*:-,21$&D1*$%&W1-&$(#)",-&%B"1-.
( R.J. Furnstahl )
D,%)$E*,+(/"%F$/G$H"%+$).-%$#;*$+IEE*#/I$*%*/FI
24 26 28 30 32 34 36 38 40 42 44
symmetry energy a4 (MeV)
0.05
0.1
0.15
0.2
0.25
0.3
0.35
r n!
rp (
fm)
24 26 28 30 32 34 36 38 40 42 44
symmetry energy a4 (MeV)
0.05
0.1
0.15
0.2
0.25
0.3
0.35
r n!
rp (
fm)
Skyrme
relativistic mesonrelativistic point coupling
24 26 28 30 32 34 36 38 40 42 44
symmetry energy a4 (MeV)
0.05
0.1
0.15
0.2
0.25
0.3
0.35
r n!
rp (
fm)
The single measurement of Fn translates to a measurement of Rn via mean-field nuclear models
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
Nuclear Structure: Symmetry energy variation with neutron density is a fundamental observable that remains elusive.
Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of
n.m. densityratio proton/neutrons
•Slope unconstrained by data
•Adding Rn from 208Pb will eliminate the dispersion in the plot.
Slide adapted from J. Piekarewicz
N-1F&JKk+:&%1&,&M"(%-1$&5%,-Rn calibrates the equation of state of
neutron rich matter
Crust ThicknessExplain Glitches in Pulsar Frequency ?
Combine PREX Rn with observed neutron star radii
Some neutron stars seem too cold
Strange star ? Quark Star ?
Cooling by neutrino emission (URCA)0.2 fm URCA probable, else not
Phase Transition to “Exotic” Core ?
Crab Nebula
pres
sure
dens
ity
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
Measured Asymmetry
Weak Density at one Q2
Neutron Density at one Q2
Correct for CoulombDistortions
Small Corrections forG n
E GsE MEC
Assume Surface Thickness Good to 25% (MFT)
Atomic Parity Violation
Mean Field & Other Models
Neutron Stars
R n
PREX Physics Output
Slide adapted from C. Horowitz
20% corrections, calculated to precision by multiple groups
see later talk in last session
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
HB,))"$3*$3&4PD"-*F"$%
Compton Polarimeter
10X more precise than any previous e--nucleus scattering!
Similar to the HAPPEX measurements• Use Hall A spectrometers• integrating technique
Injector magnetic spin manipulation
Source optimization - reduce position difference and spot-size asymmetry
Precise kinematics calibration
Low energy electron beam polarimetry
Target survivability
Electronics noisenew low-noise ADCs
Integrating photon detection
Beam False Asymmetries
New modulation system for calibrating corrections
Water cell calibrationHigh rate tracking with GEMSLow current beam position monitors
20 ppb absolute measurement3% relative error
Ultimate goal:
upgrade to SC magnetFADC DAQ upgrade
upgrade IR to Green light
Moller Polarimeter
"(APV)/APV ~ 3%"(Rn)/Rn ~ 1%
see later talk by Zafar Ahmed
see later talk by Luis Mercado
Transverse Asymmetry see later talk by Bob Michaels
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
target
HRS-L
HRS-RcollimatorSeptum Magnet collimator
calibration collimators
\1&5"D%(F&%1&,(3F"$%&%B"&>!5
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
Detector integrates the elastic peak.Backgrounds from inelastics are suppressed.
4- Momentum (GeV/c)C 1st excited state
Pb excited states3-5- PbC
Ground States
Carbon Ground State
>*3B&!"'1)(21$&5D"#%-1F"%"-
2.6 MeV
Negligible contributions from inelastic events rescattering in spectrometer
p (GeV/c)p (GeV/c)
LeadCarbon
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Slug # ( ~ 1 day)
mic
rons
Average with signs = what exp’t feels
Points: Not sign corrected
mic
rons
+,-*%.&](,)*%.&b",FHelicity – Correlated Position Differences < ~ 4 nm
Injector spin manipulation proved important for cancellation
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
&&4--1-&&&51(-#" ?:'1)(%"&&&gDDFh !"),2V"&&g&&l&h
J.',/"K,L.%$gIh 3433MN N4N
"#$%!!&'(%%#)*+#'&(2) 3433M1 N4N
O*#*&#./$$P"%*,/"#I 3433MN N4N
QRA$$P"%*,/"#I 3433N3 341
S*+&,T*/"%F 34333N 3
U/,%+V*/+*$$J.',/"K,L.%$ 3433N1 341$
01$$$$gIh 34331W 34X$
U,/F*#$$U;"&Y%*++ 343336 34NN1R$$Z+IEE*#/I$$$gJh 343316 34X
[%*',+L&$$\#,#*+ 3 3
LZL?9 KQKITK JQK
Systematic Errors
(1) Normalization Correction applied(2) Nonzero correction (the rest assumed zero)
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+!4<&?'.FF"%-.
Ara
w (p
pm)
Slug ~ 1 day
ARAW = 0.593 ± 0.051 (stat) ppmThis includes•beam asymmetry correction (-40 ppb)•charge normalization (96 ppb)
OUT / IN, L/R from “slow” spin reversals to cancel systematics
Additional corrections are then applied:•backgrounds (1.1%)•acceptance averaging (0.3%)•beam polarization (11%)
?$,).'*'&b)*$="=&o&JKK&DD:
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
+!4<&?'.FF"%-.
Ara
w (p
pm)
Slug ~ 1 day
ARAW = 0.593 ± 0.051 (stat) ppmThis includes•beam asymmetry correction (-40 ppb)•charge normalization (96 ppb)
OUT / IN, L/R from “slow” spin reversals to cancel systematics
Additional corrections are then applied:•backgrounds (1.5%)•acceptance averaging (0.3%)•beam polarization (11%)
?$,).'*'&b)*$="=&o&JKK&DD:
at Q2 = 0.00906 GeV2 ! Statistics limited ( 9% )! Systematic error goal achieved ! (2%)
ppm 9.2 % 2.0 %
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
( theory curve, not integrated over acceptance )
arXiv:1010.3246 [nucl-th] Shufang Ban, C.J. Horowitz, R. Michaels
Neutron Skin = RN - RP = 0.34 + 0.15 - 0.17 fm Preliminary estimate from C.J. Horowitz
?'.FF"%-.&)",='&%1&!$
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+!4<&@$%"-D"%,21$
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
+!4<&@$%"-D"%,21$
First electroweak observation of the neutron skin of a heavy nucleus (CL =95%)
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
N(%(-"&!($&#,$&-",#B&DB.'*#'&31,)
Pb
Major experimental questions have been answered!• Lead sandwich target• Precision polarimetry at 1 GeV• HRS optics optimization• Source performance• Transverse Asymmetry
Must address:• Beam vacuum issues• Neutron radiation in the Hall (shielding, reduced beam collimation)
Proposal for a 2nd run is under development
A"$%&+,'#BC" ?+5&?D-*)&E""2$3G&?$,B"*FG&H?&/&E,.&IG&JKII
RN
Surface thickness
RN Surface thickness
ZD21$'&W1-&1%B"-&$(#)"*
E (GeV)Rate
(MHz @ 50 µA)
APV (ppm)
days to 1% on
Rn
208Pb 1.05 1700 0.6 30
120Sn 1.25 810 1.1 20
48Ca 1.7 270 2.5 12
2.2 15 2.8 18
arXiv:1010.3246 [nucl-th]
Parity Violating Electron Scattering Measurements of Neutron Densities Shufang Ban, C.J. Horowitz, R. Michaels
Additional measurements could address • Rn in other nuclei• shape dependence?• isotope dependence?
Plans to pursue 48Ca•far from 208Pb•closer comparison to microscopic calculation•compatible with 12 GeV!
5o scattering at 2 GeV : new septum required
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• LB"&F1'%&D-"#*'"&F",'(-"F"$%&1W&")"#%-1$/$(#)",-&'#,6"-*$3&,'.FF"%-.&."%;&_J&DD:t&
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• +-1D1',)&W1-&,&'"#1$=&-($&*'&*$&D-"D,-,21$
+!4<&&;&&5(FF,-.&&