Parity Violating Deep-Inelastic Scattering
Jian-ping Chen, Jefferson Lab
for the JLab SoLID collaboration
Lanzhou Workshop, July 31 - August 1, 2009
 Introduction
 Physics potential of PVDIS
Test of Standard Model
Precision study of hadronic properties:
•Charge symmetry violation (CSR)
•Higher twist
•Parton distributions d/u at high x
• Experimental Setup and Plan
• Acknowledgements: E. Chudakov, P. Souder, X. Zheng …
Interactions and Structure
• Standard Model:
EM and Weak (Electro-weak) Interactions well understood
Strong Interaction, difficult at low energy (nucleon scale)
• Nucleon and nuclear structure mainly due to strong interaction
• EM or weak interaction clean probe to study nucleon/nuclear structure
• Search for new physics beyond the Standard Model
Look for deviations from Standard Model
Often try to avoid complications from structure
Weak Neutral Current (WNC) Interactions
Low energy Weak NC interactions (Q2<<MZ2)
Z0
Historical Context:
•
1960s: An Electroweak Model of Leptons (and quarks)
• SU(2)L X U(1)Y gauge theory predicted the Z boson
•
1973: antineutrino-electron scattering
• First weak neutral current observation
•
Mid-70s: Does the Weak Neutral Current interfere with the Electromagnetic
Current?
• Central to establishing SU(2)L X U(1)Y
Parity is conserved
Consider fixed target
electron scattering
Parity is violated
First Electron Parity Experiment
APV in Deep Inelastic Scattering off liquid Deuterium: Q2 ~ 1 (GeV)2
APV ~ 104  Q2 (GeV2)
This experiment convinced the world that the Z-boson violated parity

•Cleanly observed weak-electromagnetic interference
•sin2W = 0.224 ± 0.020: same as in neutrino scattering
•Established experimental technique: (APV) < 10 ppm
Electroweak Interaction – The Standard Model
Mixing of the SU(2)L and UEM(1)g is giving by the Weak Mixing angle sin W
A  B cosW  W3 sin W
( m  0)
Z   B sin W  W3 cosW
( m  0)
Electron and quark neutral currents are given by vector and axial couplings
In the Standard Model
NC
J
NC
J
1 e
(e)  ueg  ( gV  g Ae g 5 )ue
2
1 q
(q )  uqg  ( gV  g Aq g 5 )uq
2
Fermions
nA, n
e- , u, c
d, s
gAf
1
2
1

2
1
2
1

2
g Vf
1
2
1
  sin 2 W
2
1 4 2
 sin W
2 3
1 2
  sin 2 W
2 3
PV Electron Scattering on Hadron
(gAegVT + gVegAT)
•The couplings depend on electroweak physics as well as on the weak vector
and axial-vector hadronic current
•Both new physics at high energy scales as well as interesting features of
hadronic structure come into play
•A program with many targets and a broad kinematic range can untangle the
physics
Electron-Quark Phenomenology
A
V
V
A
Moller PV is insensitive to the Cij
C1u and C1d will be determined to high precision by Qweak, APV Cs
C2u and C2d are small and poorly known:
one combination can be accessed in PV DIS
New physics such as compositeness, leptoquarks:
Deviations to C2u and C2d might be fractionally large
Deep Inelastic Scattering
e-
eZ*
g*
X
N
APV
GF Q 2

a(x)  Y (y) b(x)

2
y 1 E / E
 C Q f (x)
a(x) =
 Q f (x)
+
1i
i
i
2 +
i i


fi  fi  f i
i
i
a(x) and b(x) contain
quark distribution
functions fi(x)
 C Q f (x)
b(x) 
 Q f (x)

2i
i
i
i
2 
i i
i
at high x
For an isoscalar target like 2H, structure
functions largely cancel in the ratio at high x

3
0.62s  
a(x) 
(2C1u  C1d )  1  
10
u  d  

At high x, APV becomes independent of x, W,
with well-defined SM prediction for Q2 and y
0
3
 uv  dv 
b(x) 
(2C2u  C2d ) 

 


10
u d
C2q inaccessible in elastic scattering
1
PVDIS at High x
2C2u  C2d
~ 0.14
2C1u  C1d
0.5% fractional precision on the
asymmetry is needed!
 APV 
APV
~ 0.5%
 2C2u  C2d 
2C2u  C2d 
~ 5%
Feasible (in narrow kinematics) with existing JLab spectrometers.
JLab 6 GeV experiment: scheduled to run in Hall A Oct.-Dec., 2009
Spokespersons: Michaels, Reimer, Zheng
PhD Students: X. Deng, K. Pan, D. Wang
JLab 11 GeV proposal: Conditional approval
Spokespersons: Paschke, Reimer, Zheng
• Experimental systematic errors challenging
• Averaged over large Q2, W, and x range
Hall C HMS / SHMS
spectrometers
PVDIS with SoLID
• Solenoid (from BaBar, CDF or CLEOII)
contains low energy backgrounds
trajectories measured after baffles
• Fast tracking, particle ID, calorimetry,
and pipeline electronics
• Precision polarimetry (0.4%)
•
•
•
•
•
•
High Luminosity on LH2 & LD2
Better than 1% errors for small bins
x-range 0.25-0.75
W2 > 4 GeV2
Q2 range a factor of 2 for each
Moderate running times
Statistical Errors (%) vs Kinematics
For SOLID Spectrometer
Error bar σA/A (%)
shown at center of bins
in Q2, x
4 months at 11 GeV
2 months at 6.6 GeV
PAC34
Why do we need so many data points?
• Possible new physics
• New interactions
• Charge symmetry violation (CSV)
• Higher twist effects
Like neutron beta decay experiments:
many diverse physics topics
Sensitivity: C1 and C2 Plots : 6 GeV E08-011
PDG best fit
R. Young
SAMPLE
(combined)
SLAC/
Prescott
R. Young
Cs APV
(PVES)
Qweak
(expected)
R. Young
(combined)
MIT/
Bates
SLAC/Prescott
Expected: JLab 6 GeV PV-DIS E08-011
12 GeV PVDIS Sensitivity: C1 and C2 Plots
World’s data
6 GeV
PVDIS
Precision Data
Qweak
Cs
PVDIS
Search for CSV in PV DIS
u (x)  d (x)?
p
n
d (x)  u (x)?
p
n
• u-d mass difference
• electromagnetic effects
u(x)  u p (x)  d n (x)
d(x)  d p (x)  u n (x)
•Direct observation of parton-level CSV would be very exciting!
•Important implications for high energy collider pdfs

•Could explain significant portion of the NuTeV anomaly
For APV in electron-2H DIS:
APV
APV
 0.28
u  d
ud
Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as x  1
CSV Theory and Data
Londergan & Thomas, (also B. Ma)
MRST PDF global with fit of CSV
Martin, Roberts, Stirling, Thorne [Eur Phys J C35, 325 (04)]:
Analytic calculation
similar to global fit
Sensitivity with PVDIS
RCSV 
 APV x 
APV x 
 0.28
 u x   d x 
u x  d x 
Higher Twist
•
Deep-inelastic Scattering (DIS)
structure functions, unpolarized and polarized.
•
Operator-product expansion (OPE) – twist expansion
expansion in terms of power of 1/Q
•
Leading twist (twist-2): parton distributions
another series in terms of s: LO, NLO, NNLO,…
•
Twist-3: quark-gluon correlations
•
Twist-4: quark-quark correlations
Leading twist
Higher twist
Higher Twist in F2
Analysis of
Blumlein and
Botcher
Higher twist is clearly
seen at the PVDIS
kinematics. What
can we add?
MRST Fits
F2
(x,Q2)=F
2
(x)(1+D(x)/Q2)
D/Q2min(%)
D/Q2min(%)
LO
NNNLO
0.5
-14
2
0.003
1.0
-11
0.0
-.06
-0.001
1.7
-3.5
-0.5
0.4-0.5
.22
0.11
2.6
8
4
0.5-0.6
.85
0.39
3.8
22
10
0.6-0.7
2.6
1.4
5.8
45
24
0.7-0.8
7.3
4.4
9.4
78
47
x
MRST,
PLB582,
222 (04)
Q2min=Q2(W=2)
Q2=(W2-M2)/(1/x-1)
D(x)
D(x)
LO
NNNLO
0.1-0.2
-.007
0.001
0.2-0.3
-.11
0.3-0.4
Q2min
APV=APV(1+C(x)/Q2)
MRST fit of F2: order of DGLAP affects HT
F2(x,Q2)=F2(x)(1+D(x)/Q2)
Order of DGLAP
influences size
of HT
Higher twist
falls slowly
compared to PDF’s
at large x.
Why HT in PVDIS is Special
• Twist-2 (mostly) cancel in asymmetry
• Twist-4 is (basically) leading twist
• Clean access twist-4 effect: free from twist-2 order
dependence
• Study quark-quark correlations
Coherent Program of PVDIS Study
Strategy: requires precise kinematics and broad range
Fit data to:

1
2
A  A1   HT
  CSV x 
3
2
(1  x) Q


C(x)=βHT/(1-x)3
• Measure AD in NARROW bins of x, Q2 with 0.5% precision
• Cover broad Q2 range for x in [0.3,0.6] to constrain HT
• Search for CSV with x dependence of AD at high x
• Use x>0.4, high Q2, and to measure a combination of the Ciq’s
x
y
Q2
New Physics
no
yes
no
CSV
yes
no
no
Higher Twist
yes
no
yes
Other Targets
• Hydrogen: d/u
• EMC effect
PVDIS on the Proton: d/u at High x
u ( x)  0.91d ( x)
a ( x) 
u ( x)  0.25d ( x)
P
Deuteron analysis has large
nuclear corrections (Yellow)
APV for the proton has no such
corrections
(complementary to BONUS)
3-month run
The challenge is to get statistical and systematic errors ~ 2%
CSV in Heavy Nuclei: EMC Effect
Additional
possible
application of
SoLID
5% Isovector-vector
mean
field. (Cloet,
Bentz,
and Thomas)
SoLID Spectrometer
Gas Cerenkov
Shashlyk
Baffles
GEM’s
Baffles
Rates in detectors reduced
by more than 10
Kinematics at large x
Physics Resolution (%) vs Detector Resolution
and Angle
p
2
Q

x
SoLID Collaboration
P. Bosted, J. P. Chen,
E. Chudakov, A. Deur,
O. Hansen, C. W. de Jager,
D. Gaskell, J. Gomez,
D. Higinbotham, J. LeRose,
R. Michaels, S. Nanda,
A. Saha, V. Sulkosky,
B. Wojtsekhowski
Jefferson Lab
P. A. Souder, R. Holmes
Syracuse University
K. Kumar, D. McNulty,
L. Mercado, R. Miskimen
U. Massachusetts
H. Baghdasaryan, G. D. Cates,
D. Crabb, M. Dalton, D. Day,
N. Kalantarians, N. Liyanage,
V. V. Nelyubin, B. Norum,
K. Paschke, S. Riordan,
O. A. Rondon, M. Shabestari,
J. Singh, A. Tobias, K. Wang,
X. Zheng
University of Virginia
J. Arrington, K. Hafidi,
P. E. Reimer, P. Solvignon
Argonne
L. El Fassi, R. Gilman,
R. Ransome, E. Schulte
P. Markowitz
Rutgers
Florida International
W. Chen, H. Gao, X. Qian,
Y. Qiang, Q. Ye
X. Jiang
O. Glamazdin, R. Pomatsalyuk
Los Alamos
Duke University
W. Korsch
K. A. Aniol
University of Kentucky
NSC Kharkov Institute for
Physics and Technology
California State
J. Erler
G. M. Urciuoli
Universidad Autonoma de
Mexico
INFN, Sezione di Roma
A. Lukhanin, Z. E. Meziani,
B. Sawatzky
Temple University
P. M. King, J. Roche
Carnegie Mellon
G. Ron
D. Armstrong, T. Averett,
J. M. Finn
Tel Aviv University
William and Mary
T. Holmstrom
P. Decowski
Smith College
Longwood University
B.-Q. Ma, Y. J. Mao
Beijing University
China Institute of Atomic
Energy
C. Keppel
Hampton University
University of Science and
Technology of China
Benmokhtar, G. Franklin,
B. Quinn
Tsinghua University
University of Wisconsin
E. Beise
MIT
Z. G. Xiao
X. M. Li, J. Luan, S. Zhou
H. Lu, X. Yan, Y. Ye, P. Zhu
W. Bertozzi, S. Gilad,
W. Deconinck, S. Kowalski,
B. Moffit
Louisiana Tech
M. J. Ramsey-Musolf
Ohio University
University of Maryland
K. Grimm, K. Johnston,
N. Simicevic, S. Wells
N. Morgan, M. Pitt
B. T. Hu, Y. W. Zhang,
Y. Zhang
Lanzhou University
C. M. Camacho, E. Fuchey,
C. Hyde, F. Itard
J.-C. Peng
LPC Clermont, Université
Blaise Pascal
University of Illinois
A. Deshpande
Virginia Tech
H. P. Cheng, R. C. Liu,
H. J. Lu, Y. Shi
Huangshan University
SUNY Stony Brook
A. T. Katramatou,
G. G. Petratos
S. Choi, Ho. Kang, Hy. Kang B. Lee, Y. Oh
Kent State University
Seoul National University
J. W. Martin
J. Dunne, D. Dutta
Mississippi State
University of Winnipeg
STATUS and PLANS
•
•
•
•
Jan. 2009: Conditional approval
Jan. 2010: Seek full approval
Fall 2010: Director’s review
Spring 2011: Seek CD0
Conclusions
• PVDIS addresses many physics topics
•
•
•
•
•
Electroweak couplings
CSV at the quark level
Higher Twist
d/u for the proton
Nuclear-induced CSV
• SOLID spectrometer can deliver the physics