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20 May 2006 Conclusions & Perspectives
Conclusions and PerspectivesKrishna KumarUMass Amherst
PAVI0620 May 2006
ΜΗΛΟΣΜΗΛΟΣ
20 May 2006 Conclusions & Perspectives
Acknowledgements
• 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
Pictures, thoughts and ideas from:B. Holstein, K. Paschke, M.J. Ramsey-Musolf, P. Souder, M.
Vanderhaeghenand all the speakers
20 May 2006 Conclusions & Perspectives
Come On!
• 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….
DisclaimerI 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
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
Atomic Physics
Nuclear PhysicsNucleon Physics
Valence Quark Physics
Electroweak Physics
20 May 2006 Conclusions & Perspectives
The Beginnings
• Gargamelle: neutrino scattering– First weak neutral current observation– Became centerpiece of electroweak theory
• SLAC E122: Parity-violating Electron Scattering– Central to establishing SU(2)LXU(1)Y
– Established the experimental technique
Gargamelle found one e- event in 1973! (two more by 1976)
Parity is violated Parity is conserved 10 billion events!
20 May 2006 Conclusions & Perspectives
Weak Neutral Currents
and the Atom
20 May 2006 Conclusions & Perspectives
Atomic Parity Violation
Power build-up cavity ( F=100 000 )
dye laser
beam
ex
E
B
Reexcitation of the depleted HF levell
depletes one HF
level
Bp
p
polarizes the atoms
|F,m=±F>
diode laser, tuned to the depleted HF
level APV signal: odd in E, ex, B, Bp, p
I fluo
Boulder Experiment
Derevianko, Lintz, Gwinner, Chardonnet, Budker, Sanguinetti, Tsigutkin
Tremendous interest in weak charge, anapole moment and EDM measurements in the larger physics community
Ecole Normale Supérieure, Paris
20 May 2006 Conclusions & Perspectives
Atomic Parity ViolationElectric and magnetic fields define handedness
CollimatorYtterbium atoms
Oven
PBC mirror
Parabolic reflector
Lightguide
BE
zx
y
Photo-multiplier tubes
Electric field plates
Magnetic field coils
408-nm light
649-nm lightε
( )( )Rotational Invariant: B E Bε ε⋅ × ⋅r r rr r
Berkeley Yb Apparatus Anapole MomentWe 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
Budker, Tsigutkin
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 EFTLong Range Medium Range
€
π
€
π
€
+L
€
π
€
+L
€
+L
Short Range
€
π
€
π
€
π
€
π
€
+
€
mN λ pp = −1.22 AL (r p p)
mN ρ t = − 9.35 AL (r n p → dγ)
mN λ pn = 1.6 AL (r p p) − 3.7 AL (
r p α ) + 37 Aγ (
r n p → dγ ) − 2 Pγ (
r n p → dγ)
mN λ t = 0.4 AL (r p p) − 0.7 AL (
r p α ) + 7 Aγ (
r n p → dγ ) + Pγ (
r n p → dγ)
mN λ nn = 1.6 AL (r p p) − 0.7 AL (
r p α ) + 33.3 Aγ (
r n p → dγ ) −1.08 Pγ (
r n p → dγ)+ 0.83
dφnα
dz
Pionless th’y: 5 exp’ts Dynamical pions: 7 exp’ts
Done
NIST,SNS
LANSCE, SNS
HARD*
Ab initio few-body calculation required
Ramsey-Musolf, Holstein, Schiavella, Desplanques, Hyun
20 May 2006 Conclusions & Perspectives
Hadronic PV ExperimentsBowman, Snow
y
z
HelicityComponents
Transverse Polarization
OpticalRotation
φ
Medium withParity Violation
N-4He Spin Rotation Experiment
We also heard about the npd at LANSCENew 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
QpEM ~ 1 Qn
EM ~ 0
QpW ~ 1 - 4sin2WQn
W ~ 1
Constrain neutron halo for APV
Constrain neutron star crust thickness
Piekerewicz, Michaels
20 May 2006 Conclusions & Perspectives
PREx at Jefferson Lab
A technically demanding measurement:
•Rate ~ 2 GHz•Separate excited state at 2.6 MeV•Stat. Error ~ 15 ppb•Syst. Error ~ 1 to 2 %
Data collection at JLab Hall A likely in 2008
(APV) ~ 3% (Rp-Rn) ~ 1% Q2 ~ 0.01 GeV2 APV ~ 0.5 ppm
Pb
C
208
12
Diamond Backing:
• High Thermal Conductivity• Negligible Systematics
beam
•Tight control of beam properties•New “warm” septum•New 18-bit ADC•New radiation-hard detector•Polarimetry upgrade
Piekerewicz, Michaels
20 May 2006 Conclusions & Perspectives
Weak Neutral Currents
and the Nucleon
20 May 2006 Conclusions & Perspectives
Nucleon Structure & StrangenessQCD 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
€
Δs ~ N s γ μγ 5s N
Breaking of SU(3) flavor symmetry introduces uncertainties
Semi-inclusive: Δs = 0.03 ± 0.03 fragmentation function
Strange mass: 0-20% πN scattering:
Schaefer, Leader, Procureur
20 May 2006 Conclusions & Perspectives
Elastic Electroweak Scattering
Kaplan & Manohar (1988)McKeown (1990)
GEs(Q2), GM
s(Q2)
p
AMEF AAAQGA
σπα++
⎥⎦
⎤⎢⎣
⎡−=
24
2~ few parts per millionproton:
Forward angle Backward angle
( ) eA
pMWA
ZM
pMM
ZE
pEE GGAGGAGGA '2sin41 , , εθτε −−===
Helium: Unique GE sensitivityDeuterium: Enhanced GA sensitivity
Armstrong, Real, Baunack, Kox, Glaeser, Moffit
20 May 2006 Conclusions & Perspectives
Overview of Experiments
Electron Beam
LH2 Target
SuperconductingCoils
Particle Detectors
GMs, (GA) at Q2 = 0.1 GeV2
SAMPLE
HAPPEX GEs + 0.39 GM
s at Q2 = 0.48 GeV2
GEs + 0.08 GM
s at Q2 = 0.1 GeV2
GEs at Q2 = 0.1 GeV2 (4He)
A4
open geometry, integrating
GEs + 0.23 GM
s at Q2 = 0.23 GeV2
GEs + 0.10 GM
s at Q2 = 0.1 GeV2
GMs, GA
e at Q2 = 0.1, 0.23, 0.5 GeV2
Open geometry
Fast counting calorimeter for background rejection
G0
GEs + GM
s over Q2 = [0.12,1.0] GeV2
GMs, GA
e at Q2 = 0.23, 0.62 GeV2
Open geometry
Fast counting with magnetic spectrometer + TOF for background rejection
Armstrong, Real, Baunack, Kox, Glaeser, Moffit
20 May 2006 Conclusions & Perspectives
Current StatusOver 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
• 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 GM
s
• 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
Strangeness in the nucleon has challenged model builders for two decades
20 May 2006 Conclusions & Perspectives
Axial Form Factor•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
Bodek, Schindler
20 May 2006 Conclusions & Perspectives
Charge Symmetry BreakingChiral perturbation theory with resonance saturation
Lewis
20 May 2006 Conclusions & Perspectives
Nucleon EM Form Factors
BLAST at MIT-Bates
Low Q2 data critical to reduce systematic error in extraction of Gs
Alarcon, Pacetti, Dubnicka
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 Asymmetriesbeam :'
'
•Imaginary part of two-photon exchange amplitude•“background” for parity-violation experiments
Vanderhaeghen, Pasquini, Kaufman, Capozza
A4 Preliminary at 300 MeV
20 May 2006 Conclusions & Perspectives
Beam-Normal Asymmetries at JLabKaufman, Vanderhaeghen
First measurement on a nucleus
Hydrogen target
11 GeV beam at different Q2 values
HAPPEX
HAPPEX
20 May 2006 Conclusions & Perspectives
Gluon Polarization
or
lepton beam
or
nucleon target
heavy flavor, high pT
or
or
proton beam
proton beam
π0, (PHENIX),jets (STAR)
STARSTAR
•Strangeness and gluon polarization are the only two “purely sea” experimentally accessible observables•RHIC and lepton DIS experiments both agree ΔG is small•They will make inroads, but the ultimate measurements will require a lepton-ion collider: obtain ΔG directly and by DGLAP evolution of g1
Leader, Proceureur
20 May 2006 Conclusions & Perspectives
Weak Neutral Currents
and the Valence Quark
20 May 2006 Conclusions & Perspectives
NuTeV Anomaly
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
3σ below SM
agree with SM
After ~ three years, no consensus yet
No “good” new physics scenario
Community Prejudice: some combination of isospin violation, nuclear effects, strangeness asymmetry and systematics on radiative corrections
Londergan
20 May 2006 Conclusions & Perspectives
PV DIS
€
C1i ≡ 2gAe gV
i
€
C2i ≡ 2gVe gA
i€
APV =GFQ2
2παa(x) + f (y)b(x)[ ]
€
a(x) =
C1iQi f i(x)i
∑
Qi2 f i(x)
i
∑
€
b(x) =
C2iQi f i(x)i
∑
Qi2 f i(x)
i
∑
• Charge Symmetry Violation– Partonic level CSV has never been observed– Needs high precision with inclusive scattering
• 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
Address outstanding issues in high x physics
Reimer, Souder, Zheng
20 May 2006 Conclusions & Perspectives
1% APV
measurements
PV DIS with JLab UpgradeCharge Symmetry Violation at High x: clean observation possible
€
u(x) = up (x) − dn (x)
δd(x) = d p (x) − un (x)
For an isoscalar target like 2H
€
a(x) =3
10(2C1u − C1d )[ ] +L
€
b(x) =3
10(2C2u − C2d )
uv (x) + dv (x)
u(x) + d(x)
⎡
⎣ ⎢ ⎤
⎦ ⎥+L
€
APV (x)
APV (x)= 0.3
δu(x) −δd(x)
u(x) + d(x)
Global fits allow x3 larger effects
€
APV =GFQ2
2παa(x) + f (y)b(x)[ ]
€
a(x) =u(x) + 0.91d(x)
u(x) + 0.25d(x)
•Allows d/u measurement on a single proton!•Vector quark current! (electron is axial-vector)
Longstanding issue: d/u as x1
For hydrogen 1H:
Souder, Londergan
20 May 2006 Conclusions & Perspectives
A Vision for PV DIS Physics• 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)
Souder
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
•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
KK
20 May 2006 Conclusions & Perspectives
SLAC E158sin2eff = 0.2397 ± 0.0010 ± 0.0008
APV = (-131 ± 14 ± 10) x 10-9
* Limit on LL ~ 7 or 16 TeV
* Limit on SO(10) Z’ ~ 1.0 TeV* Limit on lepton flavor violating coupling ~ 0.01GFEnd of the SLAC Fixed Target Program
KK
20 May 2006 Conclusions & Perspectives
The LHC
• 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
Erler
20 May 2006 Conclusions & Perspectives
Qweak at JLab
Region 3: Vertical Drift chambers
Region 2: Horizontal
drift chamber location
Region 1: GEMGas Electron Multiplier Quartz Cerenkov Bars
(insensitive to non-relativistic particles)
Collimator System
Mini-torus
QTOR Magnet
Trigger Scintillator
Lumi Monitors
e- beam
C1i’s measured to unprecedented precision
•Design, simulation, prototyping, construction•Installation in 2009•Complementary to LHC•Important constraint should LHC see anomaly
MNC
Page
20 May 2006 Conclusions & Perspectives
Beyond SM with PV DISFor an isoscalar target like 2H,
structure functions largely cancel in the ratio:
€
a(x) =3
10(2C1u − C1d )[ ] +L
€
b(x) =3
10(2C2u − C2d )
uv (x) + dv (x)
u(x) + d(x)
⎡
⎣ ⎢ ⎤
⎦ ⎥+L
(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
Zheng, Reimer
20 May 2006 Conclusions & Perspectives
Møller Scattering @ 12 GeV
Address longstanding discrepancy between hadronic and leptonic Z asymmetries
Z pole asymmetries
•Comparable to single Z pole measurement: shed light on disagreement•Best low energy measurement until ILC or -Factory •Could be done ~ 2012-13
Mack
20 May 2006 Conclusions & Perspectives
Ultrahigh Precision at ILC
(world average ~0.00016)
Measure contribution from scalars to oblique corrections
ALR and MW at future colliders:
Systematics extremely challenging!
t
Z
H
b
new
physics
Critical crosscheck
Energy scale to 10-4, polarimetry to 0.15%
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
• Fixed target has advantages for systematics• Could work with ILC “exhaust”beam
Møller scattering at the ILC
€
mH
mH
≈10% for δ sin2 θW ≈ 0.00004
KK
20 May 2006 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 ControlsΔΔx’x’
micron
4Δ4Δ
4*ppm
Grand average: ~ 1 nm
Grand average: ~ 0.25 ppb
HAPPEX Position Differences during run with hydrogen target
Pulser
diode-laser
Lock-in
Sw.
PC Movable Detektor with pinhole
Aulenbacher, Pashke
More and more demanding and ambitious with every run!
20 May 2006 Conclusions & Perspectives
Cryogenic Targets
G0 targetat Jlab
E158 at SLAC
Requirements are becoming ever-demanding!
20 May 2006 Conclusions & Perspectives
Polarimetry Diefenbach, Mack
Hydrogen: 86.7% ± 2%
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?
Atomic Physics
Nuclear PhysicsNucleon Physics
Valence Quark Physics
Electroweak Physics
We will continue to learn a whole lot along the way
20 May 2006 Conclusions & Perspectives
Personal ThoughtsStudies 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!