Time Reversal Invariance in electromagnetic interactions

Alessandra FantoniINFN - Laboratori Nazionali di Frascati

• Introduction• Processes• Experimental Situation • Perspectives

International Workshop on Nucleon Form Factors, LNF 12-14 Ottobre 2005

Introduction –1-

Not all processes are invariant under every simmetry operation:

• weak interaction violates invariance under space reflection (parity P)

• decay of neutral K meson violates invariance under combined charge conjugation (C) and parity operations (CP)

Invariance of the laws of physics under discrete symmetry operations reflect fundamental properties of matter

For certain whether C, P and CP conserving interactions are also invariant under time reversal (T): NOT known !!!

T invariance is reflected in the law of conservation of energy for systems with conservative forces

Introduction -2-

CP invariance T invarianceCP violation T

violation

Fundamental theorem of relativistic field theory All interactions must be invariant under CPT operation

No direct tests of T invariance in CP conserving interactionsStrong interaction Hh: invariant under Ph, Th and Ch

E.m. interaction H: invariant under P, T and C

Introduction -3-

Hh and Hinvariant under Ph = P and CPT= ChPhTh

Difficulty of detection Ch or Th violations:

• electromagnetic effects well described by lowest order (Born approximation)•Gauge invariance

Test for Th are challenging in electromagnetic interactions of leptons with nucleons

For strong interacting particles no complete theory of electromagnetic interaction exists:

No evidence H invariant under Ch or Th

Processes

A ≠ 0:

• violation of Th invariance

• higher order effects (3) : interference between 1and 2 amplitudes without requiring T invariance violation:

– A(3) small– A(3) charge dependent

Inelastic lepton scattering on polarised target:

l± + N l± + d ≈ aW1 + bW2 + ST (k × k‘) cW3

W3 ≠ 0 H violates Th invariance (and also Ch)

A

Literature: Bernstein et al. PR139 (1965) 1650; Christ & Lee PR143 (1966) 1310

Karpman et al PRL16 (1966) 633; Karpman et al. PR174 (1968) 1957

Experimental Situation -1-

Inelastic scattering on h.e. e- from polarized pTarget: 92% C2H5OH, 8% H20 PT=22%

E(e-) = 4, 6 GeV I = 3 nA

Assumption: one-single-photon-exchangeResults:

No asymmetry at Q2 = 0.2 ÷ 0.7Accuracy = 4 ÷ 12%

a) Cambridge: J.R.Chen et al. PRL 21 (1968) 1279

J.A.Appel et al. PRD 1 (1970) 1285

Experimental Situation -1-

a) Cambridge: J.R.Chen et al. PRL 21 (1968) 1279

J.A.Appel et al. PRD 1 (1970) 1285

Experimental Situation -2-

b) SLAC: S.Rock et al. PRL 24 (1970) 748

Target: 95% butanol, 5% H20 PT=35%

E(e-) = 15, 18 GeV Q2 = 0.4, 0.6, 1.0E(e+) = 12 GeV Q2 = 0.4e- , e+ but not covering same kinematic range

Experimental Situation -2-

b) SLAC: S.Rock et al. PRL 24 (1970) 748

Data everywhere consistent with A = 0

Experimental Situation -2-

b) SLAC: S.Rock et al. PRL 24 (1970) 748

Data everywhere consistent with A = 0

difficult explanation

3 bins at 1200 MeV: A =

(4.5±1.4)%

Experimental Situation -3-

• Old data NOT very accurate• Conclusions hard to extract• Points still open for discussion• Jlab LoI 01-002

• How to better investigate the problem ?

• What is needed?

Perspectives -1-

same sign for e+ and e-

≈ 2)()(

)()(A

eeee

eeeeTviol

• no FSI interaction (no hadron detected)

• e- and e+ A free of 3 effects

e+ and e- in the same kinematic rangeEmin (e+/e-) = 1.2 GeV (first resonance)

Edes (e+/e-) = 3 GeV

a) Inelastic lepton scattering on polarised target:

l± + N l± +

Perspectives -2-

• no FSI interaction (no hadron detected)

• detection of polarization vector of outgoing nucleon• same case as before

b) Unpolarised target, polarised outgoing particle:

l± + N l± + N*

Perspectives -3-

same sign for e+ and e-

≈ 2)()(

)()(A

eeee

eeeeTviol

c) Exclusive process: hadron detected in final state

l± + N l± + N +

free of FSIdifferent sign for e+ and e-

Model dependent)()(

)()(A 3

eeee

eeee

• FSI interaction (hadron detected)

• need to evaluate A(3) effects(2 exchange)

access to T-odd GPDs

Perspectives inside LNF

• LNF is studying perspectives for the future• Increase of energy of DANE• Possibility to use upgraded DANE Linac

Courtesy of SPARC/X

Collaboration

Courtesy of SPARC/X

Collaboration

Courtesy of SPARC/X Collaboration

Courtesy of SPARC/X Collaboration

Courtesy of SPARC/X Collaboration

Courtesy of SPARC/X

Collaboration

Perspectives• LNF is studying scenarios for near-mid-long range• MIUR funds for SPARXino R&D• Proposal within beginning 2006 from SPARC/X

Collaboration for Dane Linac upgrade from 800 MeV to 1.2-1.5 GeV

• Possibility to E=1.8 GeV under study(new cavities 11 GHz instead of 3 GHz ; new technology for LNF)

• e+ beam available (PC)• Possibility to use these beams for dedicated

proposalssuch as Time invariance in em interaction

• Further developments depend on approval/decisions