Conclusions and Perspectives
Krishna Kumar
UMass Amherst
PAVI06
20 May 2006
ΜΗΛΟΣ
20 May 2006
Conclusions & Perspectives
Acknowledgements
Pictures, thoughts and ideas from:
B. Holstein, K. Paschke, M.J. Ramsey-Musolf, P. Souder, M. Vanderhaeghen
and all the speakers
• Many thanks for the invitation:
– K. De Jager, S. Kox, D. Lhuillier, F. Maas,
S. Page, C. Papanicolas, S. Stiliaris
• Ideal workshop setting:
– Great location, organization and staff
• Excellent Scientific Program:
– Many exciting and interconnected subfields
20 May 2006
Conclusions & Perspectives
Come On!
Disclaimer
I am a dumb experimentalist: The following is a personal view
of the status of the field and its immediate future. I apologize in advance for any omissions
• Many thanks for the invitation:
– Thanks for a sleepless week!
• Ideal workshop setting:
– How are you supposed to get anything done?!
– Didn’t you know this island has good ouzo?!
• Excellent Scientific Program:
– Hey, I did’nt know it was going to be this
broad when I accepted! You tricked me!!!
• But I learned a lot….
20 May 2006
Conclusions & Perspectives
Neutral Weak Interactions
• The 50’s
– Yang-Mills Theory
– Zel’dovich and parity violation
• The 60’s
– Weinberg and SU(2)L X U(1)Y Theory: the Z boson
• The 70’s
– Neutrino electron scattering
– Prescott and Weak Electromagnetic Interference
• The 80’s
–
–
–
–
Observation of W and Z bosons
Atomic Parity Violation
High statistics parity violating electron scattering
Beginning of the LEP/SLC era: Z factories
Low Energy WNC Interactions address a whole range of physics topics:
since the 90s, it has become a precision tool
20 May 2006
Conclusions & Perspectives
WNC Interconnections
Electroweak Physics
Valence Quark Physics
Atomic Physics
Nucleon Physics
20 May 2006
Nuclear Physics
Conclusions & Perspectives
The Beginnings
• Gargamelle: neutrino scattering
– First weak neutral current observation
– Became centerpiece of electroweak theory
Gargamelle found one  e- event in 1973!
(two more by 1976)
• SLAC E122: Parity-violating Electron Scattering
– Central to establishing SU(2)LXU(1)Y
– Established the experimental technique
Parity is violated
20 May 2006
Parity is conserved
Conclusions & Perspectives
10 billion events!
Weak Neutral Currents
and the Atom
20 May 2006
Conclusions & Perspectives
Atomic Parity Violation
Boulder Experiment
Power build-up cavity
( F=100 000 )
E
xp
Bp
polarizes
the atoms
|F,m=±F>
dye laser
beam
depletes
one HF
level
B
xex
Reexcitation of the
depleted HF levell
diode laser,
tuned to the
depleted HF
level
I
Ecole Normale Supérieure, Paris
fluo
APV signal: odd in
E, xex, B, Bp, xp
Derevianko, Lintz, Gwinner, Chardonnet,
Budker, Sanguinetti, Tsigutkin
Tremendous interest in weak charge, anapole moment and EDM
measurements in the larger physics community
20 May 2006
Conclusions & Perspectives
Atomic Parity Violation
Electric and magnetic fields define handedness
Photo-multiplier tubes

Rotational Invariant:   B
Oven
Collimator
Ytterbium
atoms
 E    B 
Budker, Tsigutkin
Light
guide
PBC mirror
y
z
E
ε
B
x
Parabolic
reflector
649-nm light
Magnetic field coils
408-nm light
Electric field plates
Berkeley Yb Apparatus
Anapole Moment
We also heard from:
•A. Derevianko with a nice theoretical overview
•C. Chardonnet with an update on the search for parity violation in molecules
•G. Gwinner with an update on Francium APV and anapole moment
measurement preparations
•S. Sanguinetti on the TRAP-RAD experiment to trap Francium
Two comments:
•It would be interesting to see another nonzero anapole moment, though connections to N-N
interaction seem challenging
•Is it worth doing the isotope measurements to access the neutron radius by assuming the
Standard Model? There is tremendous interest in obtaining more information.
20 May 2006
Conclusions & Perspectives
Weak Neutral Currents
and the Nucleus
20 May 2006
Conclusions & Perspectives
Hadronic PV EFT






LANSCE, 
SNS

Done
p)
mN  pp  1.22 AL (p
Short Range






 


Medium Range
Long Range
Ramsey-Musolf, Holstein,
Schiavella, Desplanques,
Hyun
mN t   9.35 AL (np  d )
HARD*
mN  pn  1.6 AL (pp)  3.7 AL (p )  37 A (np  d )  2 P (np  d )
mN t  0.4 AL (pp)  0.7 AL (p )  7 A (np  d )  P (np  d )
d n
mN nn  1.6 AL (pp)  0.7 AL (p )  33.3 A (np  d ) 1.08 P (np  d ) 0.83
dz
Pionless th’y: 5 exp’ts
Dynamical pions: 7 exp’ts
20 May 2006
NIST,SNS
Ab initio few-body calculation
required
Conclusions & Perspectives
Hadronic PV Experiments
Transverse Polarization
N-4He Spin Rotation Experiment
y
Bowman, Snow
Medium with
Parity Violation
z
φ
Helicity
Components
Optical
Rotation
We also heard about the npd at
LANSCE
New versions of these
experiments will be launched at
the Spallation Neutrion Source
Theoretical developments and the SNS have allowed these
experiments to gather new momentum
20 May 2006
Conclusions & Perspectives
Probing Neutron-Rich Matter
Piekerewicz, Michaels
Constrain neutron halo for APV
Constrain neutron star crust thickness
QpEM ~ 1
QnW ~ 1
QnEM ~ 0
QpW ~ 1 - 4sin2W

20 May 2006
Conclusions & Perspectives
PREx at Jefferson Lab
(APV) ~ 3%
(Rp-Rn) ~ 1%
Piekerewicz, Michaels
Q2 ~ 0.01 GeV2
APV ~ 0.5 ppm
A technically demanding measurement:
•Rate ~ 2 GHz
•Separate excited state at 2.6 MeV
•Stat. Error ~ 15 ppb
•Syst. Error ~ 1 to 2 %
208
Data collection at JLab
Hall A likely in 2008
Pb
12
beam
C
•Tight control of beam properties
•New “warm” septum
•New 18-bit ADC
•New radiation-hard detector
•Polarimetry upgrade
Diamond Backing:
• High Thermal Conductivity
• Negligible Systematics
20 May 2006
Conclusions & Perspectives
Weak Neutral Currents
and the Nucleon
20 May 2006
Conclusions & Perspectives
Nucleon Structure & Strangeness
Schaefer, Leader, Procureur
QCD is intractable at low Q2; what is its relationship to hadron structure?
Why don’t sea quarks destroy Quark Model predictions?
Strange quarks are relatively light
What can we say about its role?
Neutrino deep inelastic scattering
s ~ N s   5s N

Breaking of SU(3) flavor symmetry
introduces uncertainties
Semi-inclusive: s = 0.03 ± 0.03
fragmentation function
20 May 2006
Conclusions & Perspectives
N scattering:
Strange mass: 0-20%
Elastic Electroweak Scattering
Armstrong, Real, Baunack, Kox, Glaeser, Moffit
Kaplan & Manohar (1988)
McKeown (1990)
GEs(Q2), GMs(Q2)
Helium: Unique GE sensitivity
Deuterium: Enhanced GA sensitivity
  GF Q 2  AE  AM  AA ~ few parts per million
A

p
4

2


proton:
AE   GEp GEZ ,
AM   GMp GMZ ,
Forward angle
20 May 2006


AA   1  4 sin 2 W  'GMp G Ae
Backward angle
Conclusions & Perspectives
Overview of Experiments
Armstrong, Real, Baunack, Kox, Glaeser, Moffit
A4
SAMPLE
Open geometry
open geometry,
integrating
GM
HAPPEX
s,
(GA) at
Q2
= 0.1
GeV2
Fast counting calorimeter
for background rejection
GEs + 0.23 GMs at Q2 = 0.23 GeV2
GEs + 0.10 GMs at Q2 = 0.1 GeV2
GMs, GAe at Q2 = 0.1, 0.23, 0.5 GeV2
GEs + 0.39 GMs at Q2 = 0.48 GeV2
Superconducting
Coils
GEs + 0.08 GMs at Q2 = 0.1 GeV2
GE
s
at
Q2
= 0.1
GeV2
G0
(4He)
Particle
Detectors
Electron Beam
Open geometry
LH2 Target
Fast counting with magnetic spectrometer
+ TOF for background rejection
GEs + h GMs over Q2 = [0.12,1.0] GeV2
GMs, GAe at Q2 = 0.23, 0.62 GeV2
20 May 2006
Conclusions & Perspectives
Current Status
Over the past two years:
New data from A4, G0 and
HAPPEX
Q2 ~ 0.1 GeV2
•Forward angle data nearly finished
•One high precision point at Q2~0.6
•Await backward angle measurements
from A4, G0
•Deuterium running will provide
constraints on GA
20 May 2006
Conclusions & Perspectives
Strangeness Theory
Strangeness in the nucleon has challenged model builders for two decades
• Quark Model (Riska)
– While the ss-bar component is very compact, specific 5 quark
states (with s-bar in the ground state) leads to positive GMs
• Chiral Quark Soliton Model (Goeke)
– Interesting Q2 dependence will be tested soon!
• Heavy Quark Contribution (Toublan)
– Raises the issue of the sign of the disconnected light and heavy
quark loops
• VMD Approach (Bijker, Dubnicka)
– Some sensitivity to the assumed asymptotic behaviour of the
strange form factors
• Lattice Gauge Theoretic Approach (Zanotti, Young)
– Nice way to access sea quark dynamics, but a critical
component involves a hadronic model without consensus on the
assigned error
20 May 2006
Conclusions & Perspectives
Axial Form Factor
Bodek, Schindler
•Neutrino oscillations experiments need accurate cross-sections
•Discrepancy between neutrino and electroproduction data understood
•PV experiments need Q2 dependence for backward angle measurements
Minerva will make accurate measurements
20 May 2006
Conclusions & Perspectives
Charge Symmetry Breaking
Lewis
Chiral perturbation theory with resonance saturation
20 May 2006
Conclusions & Perspectives
Nucleon EM Form Factors
Alarcon, Pacetti, Dubnicka
BLAST at MIT-Bates
Low Q2 data critical to reduce systematic error in extraction of Gs
20 May 2006
Conclusions & Perspectives
Personal Outlook
•
•
•
•
Forward Angle
– Fast variation in the range 0<Q2<0.3 GeV2 ruled out by latest HAPPEX
data
– Still a window to see non-zero strangeness at Q2~0.6 GeV2
– Charge symmetry, radiative corrections and EM form factor
uncertainties preclude any further precision at any Q2
Backward Angle
– New G0 and A4 data sensitive to cancellations at intermediate Q2
– Knowledge of GA and background asymmetries will limit further precision
than already proposed
Theory
– Models are challenged in dealing with properties purely of the sea
– Ultimate insight must come from unquenched lattice calculations with
light chiral quarks
Where are we?
– We have answered a 20 year-old question about nucleon structure: do
strange quark contribute to the charge and magnetization distributions
of nucleons? The answer seems to be: smaller than expected but we
have to complete the approved program. Beyond that, it is in the realm
of lattice QCD.
20 May 2006
Conclusions & Perspectives
Beam-Normal Asymmetries
beam :
Vanderhaeghen, Pasquini, Kaufman, Capozza
'
'
•Imaginary part of two-photon exchange amplitude
•“background” for parity-violation experiments
A4 Preliminary at 300 MeV
20 May 2006
Conclusions & Perspectives
Beam-Normal Asymmetries at JLab
Kaufman, Vanderhaeghen
First measurement on a nucleus
HAPPEX
Hydrogen target
HAPPEX
11 GeV beam at different Q2 values
20 May 2006
Conclusions & Perspectives
Gluon Polarization
Leader, Proceureur
lepton beam
proton beam
 or 
 or 
0, (PHENIX),
jets (STAR)
 or 
heavy flavor,
high pT
 or 
nucleon target
proton beam
STAR
•Strangeness and gluon polarization are
the only two “purely sea”
experimentally accessible observables
•RHIC and lepton DIS experiments
both agree G is small
•They will make inroads, but the
ultimate measurements will require a
lepton-ion collider: obtain G directly
and by DGLAP evolution of g1
20 May 2006
Conclusions & Perspectives
Weak Neutral Currents
and the Valence Quark
20 May 2006
Conclusions & Perspectives
NuTeV Anomaly
Londergan
3σ below SM
agree with SM
After ~ three years, no consensus yet
No “good” new physics scenario
Assumptions:
• Isoscalar target (N=Z)
• include only light (u, d) quarks
• neglect heavy quark masses
• assume isospin symmetry for PDFs
• no nuclear effects (parton shadowing, EMC, ….)
• no contributions outside Standard Model
Community Prejudice: some combination of isospin violation,
nuclear effects, strangeness asymmetry and systematics on
radiative corrections
20 May 2006
Conclusions & Perspectives
PV DIS
Reimer, Souder, Zheng
Address outstanding issues in high x physics
APV
GF Q2

a(x)  f (y)b(x)
2
 C Q f (x)
a(x) 
 Q f (x)
1i
C1i  2g g
e i
A V
C2i  2g g
e
V
i
A
i i
i

2
i i
 C Q f (x)
b(x) 
 Q f (x)
i
• Charge Symmetry Violation

– Partonic level CSV has never
been observed

 high precision with inclusive scattering
– Needs
• d(x)/u(x) at as x  1
– Longstanding QCD prediction
– Needs high precision without nuclear effects
• Higher Twist
– Absence of significant higher twist a surprise
– Needs high precision on “predictable” reaction
20 May 2006
Conclusions & Perspectives
2i
i i
i
2
i i
i
PV DIS with JLab Upgrade
Souder, Londergan
Charge Symmetry Violation at High x: clean observation possible
For an isoscalar target like 2H
a(x) 
3
(2C1u  C1d ) 
10
APV (x)

APV (x)
APV
For hydrogen
a(x) 

u(x)  d(x)
 u(x)  d(x)
u(x)  u p (x)  d n (x)
d(x)  d p (x)  u n (x)
GF Q2

a(x)  f (y)b(x)
2
u(x)  0.91d(x)
u(x)  0.25d(x)
Longstanding issue: d/u as x1
•Allows d/u measurement
on a single proton!

•Vector quark current! (electron is axial-vector)
20 May 2006
3 
uv (x)  dv (x) 
(2C

C
)
 2u

2d
10 
u(x)  d(x) 

Global fits allow

x3 larger effects
1H:
 0.3
b(x) 
Conclusions & Perspectives
1% APV
measurements
A Vision for PV DIS Physics
Souder
•
•
•
•
•
•
Hydrogen and Deuterium targets
Better than 2% errors
– It is unlikely that any effects are larger
than 10%
x-range 0.25-0.75
W2 well over 4 GeV2
Q2 range a factor of 2 for each x point
– (Except x~0.75)
Moderate running times
•CW 90 µA at 11 GeV
•40 cm liquid H2 and D2 targets
•Luminosity > 1038/cm2/s
•solid angle > 200 msr
•Count at 100 kHz
• online pion rejection of 102 to 103
Goal: Form a collaboration, start real design and simulations, and make
pitch to US community at the next nuclear physics long range plan (2007)
20 May 2006
Conclusions & Perspectives
Weak Neutral Currents
and TeV Physics Beyond the
Standard Model
20 May 2006
Conclusions & Perspectives
Beyond Standard Model @ Low Q2
KK
•Precise predictions @ 0.1%
•Indirect access to TeV scale
•World electroweak data has marginal 2, but no discernable pattern
•Data used to put limits on energy scale of new physics effects
•Parity-conserving contact interactions probed at 20-30 TeV level
•Parity-violating contact interactions probed at 5-10 TeV level
20 May 2006
Conclusions & Perspectives
SLAC E158
KK
sin2eff = 0.2397 ± 0.0010 ± 0.0008
APV = (-131 ± 14 ± 10) x 10-9
* Limit on LLL ~ 7 or 16 TeV
* Limit on SO(10) Z’ ~ 1.0 TeV
* Limit on lepton flavor violating coupling ~ 0.01GF
20 May 2006
End of the SLAC
Fixed Target Program
Conclusions & Perspectives
The LHC
Erler
• LHC to begin data collection in 2008
• Focus is on EW symmetry breaking
– Standard Model Higgs hard below 150 GeV and above
500 GeV
• Energy frontier: look for the unexpected
– The unexpected at LHC likely to remain ill-defined!
– The more obscure the signal, the more important are
low energy constraints!
• Electroweak Physics at the LHC
– Factor of 3 improvement in W Mass
– Factor of 5 improvement in Top Mass
– Weak Mixing Angle: Improve constraints on new
parity-conserving contact interactions
20 May 2006
Conclusions & Perspectives
Qweak at JLab
Region 1: GEM
Gas Electron Multiplier
Region 2: Horizontal
drift chamber
location
Mini-torus
Page
Quartz Cerenkov Bars
(insensitive to
non-relativistic particles)
e- beam
MNC
Lumi Monitors
QTOR Magnet
Collimator System
Trigger Scintillator
Region 3: Vertical
Drift chambers
•Design, simulation, prototyping, construction
•Installation in 2009
•Complementary to LHC
•Important constraint should LHC see anomaly
20 May 2006
Conclusions & Perspectives
C1i’s measured to
unprecedented precision
Beyond SM with PV DIS
Zheng, Reimer
For an isoscalar target like 2H,
structure functions largely cancel in the ratio:
a(x) 
3
(2C1u  C1d ) 
10
3 
uv (x)  dv (x) 
b(x)  (2C2u  C2d )

10 
u(x)  d(x) 
(Q2 >> 1 GeV2 , W2 >> 4 GeV2, x ~ 0.3-0.5)
Complementary to LHC
•Need to characterize nucleon structure at high-x to high precision
•6 GeV experiment launches PV DIS measurements at JLab
•12 GeV experiment requires tight control of normalization errors
•Important constraint should LHC see anomaly
20 May 2006
Conclusions & Perspectives
Møller Scattering @ 12 GeV
Mack
•Comparable to single Z pole measurement: shed light on disagreement
•Best low energy measurement until ILC or -Factory
•Could be done ~ 2012-13
Z pole asymmetries
Address longstanding discrepancy between
hadronic and leptonic Z asymmetries
20 May 2006
Conclusions & Perspectives
Ultrahigh Precision at ILC
KK
Measure contribution from scalars to oblique corrections
t
new
H
physics
b
Z
 mH
mH
10% for  sin 2 W  0.00004
Critical crosscheck
ALR and MW at future colliders:
Systematics extremely challenging!
Energy scale to 10-4, polarimetry to 0.15%
Møller scattering at the ILC
• Fixed target has advantages for systematics
• Could work with ILC “exhaust”beam
20 May 2006
(world average ~0.00016)
E158
LC
Energy (GeV)
48
250-500
Intensity/pulse
4.5  1011
14  1011
Pulse Rate (Hz)
120
120
Pe
85%
90%
Time (s)
4  106
2  107
ALR (ppm)
0.15
1-2
ALR (ppm)
0.015
0.008
sin2(W)
0.001
0.00008
K.K, Snowmass 96
Conclusions & Perspectives
Theoretical Challenges
• Hadron Structure Theory (A. Schäfer)
–
–
–
–
Era of precision QCD requires major effort
Examples of NNLO convergence (e.g. DVCS)
Lattice QCD should enter the realm of dynamical chiral quarks
Balanced effort in perturbative QCD, chiral perturbation theory
and Lattice QCD
• Low Energy EW Measurements & Loops (W. Marciano)
– Gamma-Z and Gamma-W boxes for semi-leptonic processes
– Improved calculation of super-allowed beta decays
– Future applications: APV, neutrino scattering…
• Future Directions (M. Ramsey-Musolf)
– Probing higher-twist effects in PVDIS: precision measurements
with improved leading-twist predictions
– EFT approach to few-body hadronic parity violation
– SUSY implications of precision low energy EW measurements
– CP and T violation probes via EDM with implications for dark
matter and the primordial baryon asymmetry
20 May 2006
Conclusions & Perspectives
Parity Violating Electron
Scattering
Experimental Challenges
20 May 2006
Conclusions & Perspectives
Polarized Source Controls
Aulenbacher, Pashke
Lockin
Sw.
diode-laser
PC
micron
Pulser
5*x’
Grand average: ~ 1 nm
Movable Detektor
with pinhole
4*ppm
4*E/E
Grand average: ~ 0.25 ppb
HAPPEX Position Differences
during run with hydrogen target
More and more demanding and ambitious with every run!
20 May 2006
Conclusions & Perspectives
Cryogenic Targets
E158 at SLAC
G0 target
at Jlab
20 May 2006
Requirements
are becoming ever-demanding!
Conclusions & Perspectives
Hydrogen: 86.7% ± 2%
Polarimetry
Diefenbach, Mack
Signal from A4 Compton Polarimeter
HAPPEX Hydrogen Run
•High future demands for sub-1% polarimetry: Critical to have redundancy
•Promising techniques: “high-field” Moller and Atomic Hydrogen polarimetry
20 May 2006
Conclusions & Perspectives
Where are we going?
Electroweak Physics
Valence Quark Physics
Atomic Physics
Nucleon Physics
Nuclear Physics
We will continue to learn a whole lot along the way
20 May 2006
Conclusions & Perspectives
Personal Thoughts
Studies of Weak Neutral Current Interactions touches on
extraordinarily rich and diverse topics
We learn to appreciate physics over all length scales and there is
much left to learn over the full range
What strikes me in these PAVI meetings is that the participants are not
particle or nuclear or atomic physicists
We are physicists
I look forward to many more rewarding
interactions with you at the next PAVI!!!
20 May 2006
Conclusions & Perspectives
Not into the sunset!
20 May 2006
Conclusions & Perspectives