Krishna Kumar

1
Symmetries in Nuclear Physics

• Krishna Kumar
• University of Massachusetts
• Editorial Board
• Parity Violation K. K, D. Mack, M.
  Ramsey-Musolf, P. Reimer, P. Souder
• Low Energy QCD B. Bernstein, A. Gasparian, J.
  Goity
• Jlab 12 GeV PAC Meeting, January 10, 2005

2
Symmetry Tests at 12 GeV

• Strong Interaction
• Chiral symmetry breaking
• Axial Anomaly
• Charge symmetry violation
• Spin-Flavor symmetry breaking
• Electroweak Interaction
• TeV scale physics

3
Outline

• Primakoff Production of Pseudoscalar Mesons
• 2? decay widths of ? and ?
• Transition Form Factors at low Q2
• Parity-Violating Møller Scattering
• Ultimate Precision at Q2ltltMZ2 25 TeV reach
• Parity-Violating Deep Inelastic Scattering
• New Physics at 10 TeV in Semileptonic Sector
• Charge Symmetry Violation
• d/u at High x
• Higher Twist Effects

4
Lightest Pseudoscalar Mesons

• Spontaneous breaking of Chiral SUL(3)xSUR(3)
  
• Goldstone bosons
• Chiral anomalies
• - Mass of ?0
• - 2? decay widths
• Flavor SU(3) breaking
• p0, ?, ? mixing

Test fundamental QCD symmetries via the
Primakoff Effect
5
Setup with Energy Upgrade

• Larger X-Section
• Lighter Nuclei 1H and 4He
• Better background separation

• New high energy photon tagger
• Improved PbWO4 calorimeter

6
From 2? to 3p to Quark Mass Ratio
Leutwyler
7
Major Physics Impact

• Determination of quark mass ratio
• The nature of the ? Goldstone boson?
• Interaction Radii of p0, ?, ?
• Chiral anomaly predictions
• Number of colors Nc
• Tests of QCD models
• Tests of future lattice calculations
• Input to light-by-light amplitude for (g-2)?

8
PV Asymmetries
to
(gAegVT ? gVegAT)
For electrons scattering off nuclei or nucleons
Z couplings provide access to different linear
combination of underlying quark substructure
9
Parity Violation at Jlab

• Electron Beam Quality
• Simple laser transport system pioneers in PV
  experiments with high polarization cathodes
  (HAPPEX-I)
• CW beam alleviates many higher order effects
  especially in energy fluctuations
• HAPPEX-II preliminary result Araw correction
  60 ppb
• High Luminosity
• High beam current AND high polarization
• Dense cryogenic targets with small density
  fluctuations
• Progression of Precision Experiments
• Facilitates steady improvements in technology
• Strong collaboration between accelerator and
  physics divisions

?(APV)/APV ?1
?(APV) ?1 part per billion
10
The Annoying Standard Model
(it just wont break!)
Nuclear Physics Long Range Plan What is the new
standard model?
Low Q2 offers unique and complementary probes of
new physics

• Rare or Forbidden Processes
• Symmetry Violations
• Electroweak One-Loop Effects

- Double beta decay.. - neutrinos, EDMs.. - Muon
g-2, beta decay..

• Precise predictions at level of 0.1
• Indirect access to TeV scale physics

Low energy experiments are again relevant in the
neutral current sector
11
World Electroweak Data
16 precision electroweak measurements
?2/dof 25.4/15 Probability lt 5
Leptonic and hadronic Z couplings seem
inconsistent
Perhaps the Standard Model is already broken
Perhaps there are bigger effects elsewhere
12
Electroweak Physics at Low Q2
Q2 ltlt scale of EW symmetry breaking
Logical to push to higher energies, away from the
Z resonance
LEPII, Tevatron, LHC access scales greater than L
10 TeV
Q2ltltMZ2
Complementary
Parity Violating vs Parity Conserving
13
Fixed Target Møller Scattering
Purely leptonic reaction QWe 1 - 4sin2?W
Figure of Merit rises linearly with Elab

• Maximal at 90o in COM (EElab/2)
• Highest possible Elab with good P2I
• Moderate Elab with LARGE P2I

SLAC E158
Jlab at 12 GeV
Unprecedented opportunity The best precision at
Q2ltltMZ2 with the least theoretical uncertainty
until the advent of a linear collider or a
neutrino factory
14
Design for 12 GeV
APV 40 ppb
E 3-6 GeV
?lab 0.53o-0.92o
4000 hours
150 cm LH2 target
Ibeam 100 µA
?(APV)0.58 ppb
Toroidal spectrometer ring focus

• Beam systematics steady progress
• (E158 Run III 3 ppb)
• Focus alleviates backgrounds
• ep ? ep(?), ep ? eX(?)
• Radiation-hard integrating detector
• Normalization requirements similar
• to other planned experiments
• Cryogenics, density fluctuations
• and electronics will push the state-
• of-the-art

15
New Physics Reach
Jlab Møller
LHC
?ee 25 TeV
New Contact Interactions
Complementary 1-2 TeV reach
LEP200
?ee 15 TeV

• SUSY provides a dark matter candidate if baryon
  (B) and lepton (L) numbers are conserved

Kurylov, Ramsey-Musolf, Su

• However, B and L need not be conserved in SUSY,
  leading to neutralino decay (RPV)

QeW and QpW would have new contributions from RPV
16
Electroweak Physics
QWe modified
Marciano and Czarnecki
sin2?W runs with Q2

• Semileptonic processes have
• significant uncertainties
• E158 established running,
• probing vector boson loops
• Jlab measurement would
• probe scalar loops

?(sin2?W) 0.0003
17
Parity Violating Electron DIS
e-
e-
?
Z
X
N
fi(x) are quark distribution functions
For an isoscalar target like 2H, structure
functions largely cancel in the ratio
b(x) is a factor of 5 to 10 smaller
small corrections
Elastic scattering measures C1i, but C2i are less
well-known
Moderate x, high Q2, W2
12 GeV
TeV scale physics
1 measurements feasible
18
2H PV DIS at 11 GeV
APV 290 ppm
E 6.8 GeV 10
?lab 12.5o
400 hours
60 cm LD2 target
Ibeam 90 µA
xBj 0.45 Q2 3.5 GeV2 W2 5.23 GeV2
1 MHz DIS rate, p/e 1 HMSSHMS or MAD
?(APV)1.5 ppm

• Systematic limit Beam polarization
• Beam systematics easily controlled
• moderate running time
• Best constraint on 2C2u-C2d
• Similar sensitivity to NuTeV
• Theoretical interpretability issues
• Important in themselves!

PV DIS can address these issues
19
Charge Symmetry Violation (CSV)
Charge symmetry assume
are negligible

• u-d mass difference
• electromagnetic effects

Small effects are possible from
Search for unambiguous signal of CSV at the
partonic level
No theoretical issues at high Q2, W2
For PV DIS off 2H
10 effect possible if ud falls off more rapidly
than ?u-?d at x 0.7
From pdf fits 1/3 of NuTeV discrepancy from
CSV But at 90 C.L., effect could be 3 to 4 times
bigger.
Londergan Thomas
Strategy for PV DIS

• measure or constrain higher twist effects at x
  0.5-0.6
• precision measurement of APV at x 0.7 to search
  for CSV

20
Higher Twist Effects
Brodsky
?

• APV sensitive to diquarks ratio of weak to
  electromagnetic charge depends on amount of
  coherence
• If Spin 0 diquarks dominate, likely only 1/Q4
  effects.
• Novel interference terms might contribute
• Other higher twist effects may cancel, so APV may
  have little dependence on Q2.

21
d/u at High x

• SU(6) breaking (scalar diquark dominance), expect
  d/u 0
• Perturbative QCD prediction for x 1 d/u 0.2
• No consensus on existing deuteron structure
  function data
• Proposed methods have nuclear corrections

APV in DIS on 1H
small corrections

• d/u measurement on a single proton!
• No nuclear corrections!

• Must control higher twist effects
• Verify Standard Model at low x
• Must obtain 1 stat. errors at x 0.7

22
PV DIS Program

• Hydrogen and Deuterium targets
• 1 to 2 errors
• It is unlikely that any effects are larger than
  10
• x-range 0.3-0.7
• W2 well over 4 GeV2
• Q2 range a factor of 2 for each x point
• (Except x0.7)
• Moderate running times

TeV physics, higher twist probe, CSV probe,
precision d/u

• The Standard Model test can be done with
  proposed Hall upgrade equipment
• A dedicated spectrometer/detector package is
  needed for rest of program

23
A Concept for PV DIS Studies

• Magnetic spectrometer
• would be too expensive
• Calorimeter to identify
• electron clusters and reject
• hadrons a la A4 at Mainz
• Toroidal sweeping field to
• reduce neutrals, low energy
• Mollers and pions
• Cherenkov detectors for pion
• rejection might be needed

• CW 100 µA at 11 GeV
• 20 to 40 cm LH2 and LD2 targets
• Luminosity gt 1038/cm2/s

• solid angle gt 200 msr
• Count at 100 kHz
• pion rejection of 102 to 103

24
High x Physics Outlook

• Parity-Violating DIS can probe exciting new
  physics at high x
• One can start now (at 6 GeV)
• Do 2 low Q2 points (P-05-007, X. Zheng contact)
• Q2 1.1 and 1.9 GeV2
• Either bound or set the scale of higher twist
  effects
• Take data for Wlt2 (P-05-005, P. Bosted contact)
• Duality
• Could help extend range at 11 GeV to higher x
• A short run to probe TeV physics in PV DIS off
  2H Hall A or C
• The bulk of the program requires a dedicated
  spectrometer/detector
• CSV can also be probed via electroproduction of
  pions
• 6 GeV beam can probe x 0.45 (P-05-006, K.
  Hafidi contact)
• Should be able to go to higher x with 12 GeV beam
• Other physics topics could be addressed
• Transverse (beam-normal) asymmetries in DIS
• Polarized targets g2 and g3 structure functions
• Higher twist studies of A1p and A1n

25
Summary

• New window to symmetry tests opened by 12 GeV
  upgrade
• Precision measurements of pseudoscalar meson
  properties tests of low energy QCD and
  extraction of fundamental parameters
• APV in Møller scattering has unique sensitivity
  to leptonic contact interactions to 25 TeV
• APV in DIS off 2H at x 0.45 would probe for TeV
  physics in axial-vector quark couplings
• An exciting array of important topics in high x
  physics can be addressed by a new, dedicated
  spectrometer/detector concept