Electroweak Hadron Physics

1
Electroweak Hadron Physics
2
Short History

• b decay
• - effective GF
• - V-A current
• E122 Parity Violation in ed DIS, first
  confirmation of Electroweak SM (1978)

sin2qw 0.224 0.020

• High precision Z-pole measurements e- beam
  technology
• ? weak interactions are a new perturbative
  probe of
• hadronic matter

3
Weak Interactions Hadrons

• Semi-Leptonic e- scattering
• Pure hadronic PV meson-hadron couplings

NC

• n beams
• e- beam?

CC
4
e- Neutral Current
Q2ltltMZ2
e-(k)
e-(k)
Mg e2/Q2
qk-k
Z0
MZ g2/MZ2
e g sinqw
? Cant access NC via a cross section measurement
5
Parity Violation
a
e-
a
e-
Z0
ltlt 1
6
Observables from e- NC
Only Vector/Axial interference contributes
V coupling to the lepton
e-
a
a
e-
V

• Suppressed by 1 - 4sin2qW 0
• Axial form factor GA(Q2)
• Anapole moment

q
Z0
A
7
Observables from e- NC
V coupling to the target dominates
a
e-
a

• Weak charge QW f(Z,N, sin2qW)
• ? Low E tests of SM
• QW(Q2)
• ?Weak FF (See K. Paschkes talk)
• Complementary probe (accuracy, kine.)
• ? Rn (elastic e-Pb), u/d (PVDIS),

e-
A
q
Z0
V
8
Running of sin2qW

• sin2qW parametrizes all vector weak couplings
• Loop corrections sin2qW ? sin2qW(Q2)

3 types of measurements at Q2ltltMZ2

• E158 Parity violation
• in e--e- scattering

• Atomic parity violation

3

• NuTeV neutrino
• NC/CC cross sections

9
SLAC Experiment E158
Detector
a
a
e
e-e- scattering
50 GeV
Liquid Hydrogen
s - s
APV
s s
2
m E GF
16 sin q
1
(
)
APV
-

sin2qw
At tree level
2
4
2p ?
(3 cos q)2
In practice
APV

1.5 x 10-7
Small but very sensitive
10
Experimental Challenges

• Statistics

• integrated rate 4 GHz
• 1016 e- detected
• DA 10-8

• Background

• e-p elastic
• p production
• radiative inelastic e-p
• 2 g and AT

11
Experimental Challenges

• Beam monitoring
• resolution

• jitter versus
• statistics

?toroid ? 30 ppm
12
Experimental Challenges

• Beam systematics

Slow reversals
? false asymmetries
13
E158 Results
Phys.Rev.Lett.95081601,2005
APV(Q20.026 GeV2) -131 ? 14stat ? 10syst ppb
sin2?Wexp 0.2397 0.0010 0.0008
sin2?Wtheo 0.2381 0.0006
Limits on physics beyond SM (95 CL)

• LLL 10 TeV
• SO(10) Z 900 GeV
• lepton flavor violating coupling
• 0.01GF

14
Running of sin2qW
15
NuTeV
Iron target
m
n
n
n
Z
W
16
NuTeV
n-hadron neutral current
17
NuTev Results
Phys. Rev. Lett. 88, 091802 (2002)
sin2?Wexp 0.2360 0.0013stat 0.0009syst
sin2?Wtheo 0.2309 0.0004
3s discrepancy ! ? New physics or spurious
nuclear effect?

• NLO Corrections
• QCD symmetry violations (isospin, sea quarks)

Sensitivity to many nuclear effects but no
obvious explanation so far
Need more experimental constraints
18
Atomic PV
Semi-leptonic sector
Radiative transition in the weak field of the
nucleus (q 1 MeV)
APV x . QW
Atomic structure
Weak charge
QW (2ZN)C1u(2NZ)C1d Z(1-4sin2qW)-N
-N
Less sensitive but sub-percent accuracy !
19
Atomic PV

• Z3 law ? Heavy Atoms
• Control of the atomic structure x
• ? Cesium, chain of isotopes
• Highly suppressed QED transition
• ?

ns1/2gt

ltns1/2Dns1/2gt E1 M1
Forbiden
Suppressed
20
Boulder Experiment
133Cs
m4
F4
7s1/2
m-4
m-3
F3
m3
m4
F4
6s1/2
m-4
? QW(exp) -72.71 0.29(exp) 0.39(theo)
e 6p1/2
m-3
QW(theo) -73.19 0.13
1s agreement
F3
m3
21
Boulder Experiment
First measurement of a non-zero nuclear anapole
moment
APV(6s?7s, DF-1)
- 1 (4.8 0.7) 10-2
(7 s !)
rhf
APV(6s?7s, DF1)

• Similar e-/vector-nucleon/axial coupling but 5
  times bigger
• Parity violation through internal meson
  exchange,
• also measured in PV hadron scattering

22
Running of sin2qW
23
Future

• Complementary targets

• Ultra high precision

24
Qweak
Elastic ep
Constrained by other PV measurements at higher Q2
25
Qweak
Kinematics Int. Rate 6.4 GHz ltQ²gt 0.030
GeV2 ltAPVgt 0.29 ppm
Scattered e-
PV in elastic e p
Luminosity Monitors
Region III Drift Chambers
Toroidal Magnet
Region II Drift Chambers
Eight Fused Silica (quartz) Cerenkov Detectors
Region I GEM Detectors
Beam E 1.165 GeV I 180 µA Pe 85
Collimator with 8 openings ? 8 2
DAPV/APV2.2 DQpW/QpW4 Dsin2?W0.0007
35cm Liquid Hydrogen Target
26
Running of sin2qW
27
Future

• Complementary targets

• Ultra high precision

• New hadron probe

• Strange FF, Neutron skin
• PVDIS

28
Neutron Skin
Born Approximation
(DR2R2n-R2p)
dRn/Rn1
See R. Michaels poster
29
Parity Violating DIS
fq(x) quark distribution functions
Judicious choices of kinematics and targets allow
to test

• Valence Quark distributions at high x
• C2qs factors
• Higher twist physics Charge symmetry breaking

30
PVDIS on 2H
Isoscalar target, most of quark distribution
effects cancel out

• TeV scale physics
• Sensitivity to C2q
• Higher twist
• Isospin violation

Jlab 6GeV 12GeV upgrade
31
Running of sin2qW
DIS 12 GeV
32
PVDIS on 1H

• d/u _at_ x?1
• SU(6) 1/2
• pQCD 1/5
• SU(6) breaking 0

Allows d/u measurement on a single nucleon!

• Complementary to other approaches planned for the
  12 GeV upgrade of Jlab
• 3H and 3He structure function ratio
• Deuteron structure functions with tagged slow
  recoiling neutrons

33
High x Measurement

• Multiple APV measurements (Q2, x) with multiple
  targets
• Scattered electrons from 3 to 8 GeV
• Huge asymmetries
• Need large solid angle calorimeter
• A4-like , rates up to a few MHz
• Toroidal sweeping magnet to reject Low E pions

34
Hadrons Weak Interactions
proton, neutron
hw 10-7
gs 1
Z scale 0.001 fm
Repulsive hard core of strong NN interaction
? Meson exchange framework
35
Weak Coupling Constants
fp , h?0, h?1 , h?2 , h?0 , h?1 , h?1

• Longitudunal Asym in Elastic p p ( 15, 45,
  221, MeV )
• AL 14 x 10-7 , Phys. Rev. Lett. 33, 1307,
  (1974) !!
• First non-zero PV in NN-system AL2.30.9 x
  10-7
• Multiple energies separation h?, hw

• Parity Mixed Doublets of Light Nuclei (18F, 19F,
  21Ne )
• Determination fp

• PNC at Atomic Level Anapole Moments (133Cs)
• Determination fp , h?0

36
(No Transcript)
37
LANSCE _at_ LANL
Goal
Aexp - 50.5 x 10-8
n p d g
Accurate measurement of h1p
Taking Data !
38
? d ? p n E(?) 3 8 MeV
The 10 MeV CW-Linac at IASA, Athens
39
Summary
Experimental Advances

• Polarized sources and beam optics
• High rate integrating (few GHz) and counting (few
  MHz)detectors
• Cryogenic Targets
• Polarimetry

Strong Physics cases

• TeV scale physics complementary to colliders
• Nucleon Structure at high Q2 high x
• Strange Form Factors

40
(No Transcript)
41
(No Transcript)
42
Cesium PV Versus Time
Modifications in the theoretical corrections to
the atomic structure
43
Weak meson-N Coupling Constants
D Desplanques KM Kaiser Meissner
DDH Desplanques, Donoghue, Holstein
DZ Dubovic Zenkin FCDH Feldman, Crawford,
Dubach, Holstein