symmetries in nuclear physics

10 January, 2005 Symmetries in Nuclear Physics

Symmetries in Nuclear Physics

Krishna KumarUniversity of Massachusetts

Editorial Board:Parity Violation: K. K, D. Mack, M. Ramsey-Musolf, P. Reimer, P.

SouderLow Energy QCD: B. Bernstein, A. Gasparian, J. Goity

Jlab 12 GeV PAC Meeting, January 10, 2005


Symmetry Tests at 12 GeV

• Strong Interaction– Chiral symmetry breaking– Axial Anomaly– Charge symmetry violation– Spin-Flavor symmetry breaking

• Electroweak Interaction– TeV scale physics


Outline• Primakoff Production of Pseudoscalar Mesons

– 2 decay widths of and ’– Transition Form Factors at low Q2

• Parity-Violating Møller Scattering– Ultimate Precision at Q2<<MZ

2: 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


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 π0, , ’ mixing

Test fundamental QCD symmetries via the

Primakoff Effect


Setup with Energy Upgrade• Larger X-Section• Lighter Nuclei: 1H and 4He• Better background separation

•New high energy photon tagger•Improved PbWO4 calorimeter


From 2 to 3π to Quark Mass Ratio

Q2 ms

2 m 2

md2 mu

2, where ˆ m

1

2(mu md )

Leutwyler


Major Physics Impact

• Determination of quark mass ratio•The nature of the ’: Goldstone boson?•Interaction Radii of π0, , ’•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)


PV Asymmetries

10 4 Q2

10 5 Q2

to

For electrons scattering off nuclei or nucleons:

Z couplings provide access to different linear combination of underlying quark substructure

(gAegV

T + gV

egAT)


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) 1 part per billion (APV)/APV 1%


The Annoying Standard Model

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

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

Nuclear Physics Long Range Plan:What is the new standard model?

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

Low energy experiments are again relevant in the neutral current sector

Low Q2 offers unique and complementary probes of new physics

(it just wont break!)


World Electroweak Data

2/dof ~ 25.4/15Probability < 5%

Leptonic and hadronicZ couplings seem inconsistent

Perhaps the Standard Model is already broken

Perhaps there are bigger effects elsewhere

16 precision electroweak measurements:


Electroweak Physics at Low Q2

LEPII, Tevatron, LHC access scales greater than ~ 10 TeV

Logical to push to higher energies, away from the Z resonance

Parity Violating vs Parity Conserving

Q2 << scale of EW symmetry breaking

Complementary:

Q2<<MZ2


Fixed Target Møller Scattering

Purely leptonic reaction QW

e ~ 1 - 4sin2W

1

E lab

APV me E lab (1 4sin2 W )

- Maximal at 90o in COM (E’=Elab/2)- Highest possible Elab with good P2I- Moderate Elab with LARGE P2I

(sin2 W )

sin2 W

0.05(APV )

APV

Figure of Merit rises linearly with Elab

SLAC E158Jlab at 12 GeV

Unprecedented opportunity: The best precision at Q2<<MZ2 with the least

theoretical uncertainty until the advent of a linear collider or a neutrino factory


Design for 12 GeVE’: 3-6 GeV lab = 0.53o-0.92o APV = 40 ppb

Ibeam = 100 µA 4000 hours

(APV)=0.58 ppb

150 cm LH2 target

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


New Physics Reach

ee ~ 25 TeV

Jlab Møller

ee ~ 15 TeV

LEP200

LHC

Complementary; 1-2 TeV reach

New Contact Interactions

•SUSY provides a dark matter candidate if baryon (B) and lepton (L) numbers are conserved•However, B and L need not be conserved in SUSY, leading to neutralino decay (RPV)

QeW and Qp

W would havenew contributions from RPV

Kurylov, Ramsey-Musolf, Su


Electroweak PhysicsQW

e

modified

sin2W runs with Q2

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

(sin2W) ~ 0.0003

Marciano and Czarnecki


Parity Violating Electron DIS

APV GFQ2

2a(x) f (y)b(x)

a(x)C1iQi f i(x)

Qi2 f i(x)

b(x)C2iQi f i(x)

Qi2 f i(x)

C1i 2gAe gV

i

C2i 2gVe gA

i

fi(x) are quark distribution functions

e-

N X

e-

Z* *

a(x)1.15

TeV scale physics

a(x)3

10(2C1u C1d )

4

15

s(x)

u(x) d(x)

For an isoscalar target like 2H, structure functions largely cancel in the ratio

b(x)3

10(2C2u C2d )

q(x) q (x)

u(x) d(x)

+ small corrections b(x) is a factor of 5 to 10 smaller

Elastic scattering measures C1i, but C2i are less well-known

1% measurements feasible

12 GeV: Moderate x, high Q2, W2


2H PV DIS at 11 GeVE’: 6.8 GeV ± 10% lab = 12.5o APV = 290 ppm

Ibeam = 90 µA 400 hours

(APV)=1.5 ppm

60 cm LD2 target

1 MHz DIS rate, π/e ~ 1 HMS+SHMS or MAD

xBj ~ 0.45Q2 ~ 3.5 GeV2

W2 ~ 5.23 GeV2

• 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


Charge symmetry: assume

u(x)up (x) dn (x)

d(x)d p (x) un (x)are negligible

Small effects are possible from:•u-d mass difference•electromagnetic effects

Search for unambiguous signal of CSV at the partonic level

From pdf fits: 1/3 of NuTeV discrepancy from CSVBut at 90% C.L., effect could be 3 to 4 times bigger….

Charge Symmetry Violation (CSV)

For PV DIS off 2H:

APV

APV

0.28u du d

10% effect possible if u+d falls off more rapidly than u-d at x ~ 0.7

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

Strategy for PV DIS:

No theoretical issues at high Q2, W2

Londergan & Thomas


Higher Twist Effects

• 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.

Brodsky


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 GFQ2

2a(x) f (y)b(x)

a(x)u(x) 0.91d(x)

u(x) 0.25d(x)

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

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

+ small corrections

APV in DIS on 1H


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 x~0.7)

• Moderate running times

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

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


A Concept for PV DIS Studies•CW 100 µA at 11 GeV•20 to 40 cm LH2 and LD2 targets•Luminosity > 1038/cm2/s

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

• 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


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 W<2 (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 A1

p and A1n


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

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