Constraints on Parity-Even Time Reversal Violation in the Nucleon-Nucleon System and Its Connection to Charge Symmetry Breaking

Abstract

Parity-even time reversal violation (TRV) in the nucleon-nucleon interaction is reconsidered. The TRV r-exchange interaction on which recent analyses of measurements are based is necessarily also charge symmetry breaking (CSB). Limits on its strength g r relative to regular r exchange are extracted from recent CSB experiments in neutron-proton scattering. The result g r # 6.7 3 10 23 (95% C.L.) is considerably lower than limits inferred from direct TRV tests in nuclear processes. Properties of a 1 exchange and limit imposed by the neutron electric dipole moment are briefly discussed. [S0031-9007(97) Investigations of time-reversal violation (TRV) orders of magnitude above the weak interaction scale and thus necessarily of nonweak origin continue to enjoy popularity in nuclear and nucleon-nucleon physics [1][2][3][4][5][6][7][8].Since otherwise its presence would long have been detected in experimental investigations of parity violation, TRV above the weak interaction level must be parity even. This imposes severe restrictions on the possible ways a TRV interaction can be constructed. Indeed, contrary to the case of a parity-odd TRV interaction which naturally arises in the u term of QCD, no "natural" implementation of P-even TRV is possible [2,[9][10][11].Also in an effective theory at the hadronic level, parity conservation imposes restrictions which render most of the experimental searches for P-even TRV rather elusive. For boson exchange interactions in the nucleon-nucleon system these constraints were analyzed in Ref. [12]. The main features, deduced for on-shell amplitudes, are the following:(i) P-even TRV is restricted to partial waves with total angular momentum J $ 1.(ii) Total angular momentum zero exchange (one p or s, etc.) cannot contribute.(iii) Natural parity exchange (r) must be charged and necessarily contains the nucleon-nucleon isovector charge exchange operator 2i͑t 1 1 t 2 2 2 t 2 1 t 1 2 ͒ ͑ t 1 3 t 2 ͒ z and thus cannot contribute in the nn or pp system [13].Restrictions due to parity conservation are found also directly in elastic scattering of nucleons on a spin zero nucleus: After decomposition into angular momentum and parity eigenstates the scattering matrix is diagonal and thus symmetric and automatically time-reversal invariant. This shows also that a T -odd interaction introduced at the nucleon-nucleon level is suppressed in nuclei since it is ineffective in the interaction of single nucleons with the spin zero core [14]. This ineffectiveness, emphasized already in Ref.[15] has recently been verified also for processes in heavy nuclei governed by the statistical model [3,4], for which high sensitivity has long been claimed, as well as in other calculations [5,7,8].Since charged r is the lightest meson meeting the constraints (ii) and (iii) above, it provides the longest range possible P-even TRV one boson exchange interaction between nucleons. Following [3] most recent analyses of P-even TRV in nuclear systems are therefore based on the r-exchange interaction proposed in Refs. [12,1...

Proton-Deuteron Scattering and Test of Time-Reversal Invariance

“…We discuss some symmetry arguments to clarify a cause for the vanishing contribution of the g -term. The g -optical potential [11] and the corresponding coupling constant of the ρ−meson to the nucleonḡ ρ is widely used as a measure of intensity of the TVPC effects [12,13]. Since the g -term gives zero contribution to σ within the Glauber theory, this parameter cannot be applied straightforwardly for the nucleondeuteron scattering as a scale of the TVPC interactions at large enough energies.…”

“…However, the g -term can give contribution to the null-test signal σ if this interaction is included into the deuteron bound state [6]. One-pion exchange is excluded from the TVPC NN-interaction [12], however, two-pion exchange probably contributes similarly to the P-violating pp-interaction [14]. Finally, TVPC NN forces can contribute to the electromagnetic p-d interaction due to the toroidal quadrupole form factor of the deuteron [15].…”

Constraints of a Parity-Conserving/Time-Reversal-Non-Conserving Interaction

“…As shown above a T-odd / P-even interaction corresponds to a term in the scattering amplitude which is simultaneously charge symmetry breaking. Thus, Simonius [15] deduced an upper limit on a T-odd / P-even CSB interaction from a comparison of the experimental results with the theoretical predictions for the above mentioned three CSB experiments. The upper limit so derived is |g ρ | < 6.…”

Constraints on a Parity-Conserving/Time-Reversal-Non-Conserving Interaction

“…As shown above a T-odd / P-even interaction corresponds to a term in the scattering amplitude which is simultaneously charge symmetry breaking. Thus, Simonius [15] deduced an upper limit on a T-odd / P-even CSB interaction from a comparison of the experimental results with the theoretical predictions for the above mentioned three CSB experiments. The upper limit so derived is |g ρ | < 6.7 × 10 −3 [95% C.L.].…”