Observation Of Time Reversal Violation Research Articles

Novel T-Violation observable open to any pair of decay channels at meson factories

Quantum entanglement between the two neutral mesons produced in meson factories has allowed the first indisputable direct observation of Time Reversal Violation in the time evolution of the neutral meson between the two decays. The exceptional meson transitions are directly connected to semileptonic and CP eigenstate decay channels. The possibility of extending the observable asymmetries to more decay channels confronts the problem of the “orthogonality condition”, which can be stated with this tongue-twister: Given a decay channel f, which is the decay channel f′ such that the meson state not decaying to f′ is orthogonal to the meson state not decaying to f? In this Letter we propose an alternative T-Violation asymmetry at meson factories which allows its opening to any pair of decay channels. Instead of searching which is the pair of decay channels associated to the T-reverse meson transition, we build an asymmetry which tags the initial states of both the Reference and the T-reverse meson transitions. This observable filters the appropriate final states by means of two measurable survival probabilities. We discuss the methodology to be followed in the analysis of the new observable and the results expected in specific examples.

Observation of Time-Reversal Violation in theB0Meson System

Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time reversal violation. The decays of entangled neutral B mesons into definite flavor states ($B^0$ or $\bar{B}^0$), and $J/\psi K_S^0$ or $c\bar{c} K_S^0$ final states (referred to as $B_+$ or $B_-$), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, $\bar{B}^0 \rightarrow B_-$ and $B_- \rightarrow \bar{B}^0$, as a function of the time difference between the two B decays. Using 468 million $B\bar{B}$ pairs produced in $\Upsilon(4S)$ decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding $\Delta S_T^+ = -1.37 \pm 0.14 (stat.) \pm 0.06 (syst.)$ and $\Delta S_T^- = 1.17 \pm 0.18 (stat.) \pm 0.11 (syst.)$. These nonzero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.

Direct observation of time reversal violation

In this presentation a model independent and genuine test of T violation, disentangled from CP and CPT, is built. In the second section, a Monte Carlo simulation is done to show the possibility to perform this analysis at B factories.

Measurement of the transverse e+ polarization from the decay of polarized [formula omitted] and its implications on GF and time reversal invariance

The transverse polarization of the e+ from the decay of polarized μ+ has been measured at the Paul Scherrer Institute. From the energy dependence of the transverse polarization component PT1 which lies in the plane spanned by muon spin and positron momentum, the decay parameters η and η″ are derived, the first of which yields an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component PT2, which is perpendicular to the plane mentioned above, would be the first observation of time reversal violation in a purely leptonic decay. From the energy dependence of PT2 the two decay parameters α′/A and β′/A are deduced. Part of the data (40×108 annihilation events) have been evaluated. Both PT1 and PT2, averaged over the positrons' energy, are consistent with zero in full agreement with the standard model. The precision obtained is Δ〈PT1〉=Δ〈PT2〉=8×10−3. which is an improvement by a factor of three as compared to the results of the previous experiment [H. Burkard et al., Phys. Lett. 160 B (1985) 343].

Measurement of the polarization vector of the e+ from the decay of polarized μ+ as a test of time reversal invariance

The complete polarization vector of the positrons from the decay of polarized muons has been measured for the first time with one experimental setup. The μPT experiment at the Paul Scherrer Institute determines the three polarization components simultaneously with the same apparatus by making use of three different effects (spatial and temporal dependence of annihilation-in-flight with polarized electrons as well as muon decay asymmetry). The use of a stroboscopic method greatly reduces systematic errors. The energy dependence of the transverse polarization component PT1, which lies in the plane spanned by muon spin and positron momentum, yields the low energy parameter η and thus an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component PT2, which is perpendicular to the above-mentioned plane, would be the first observation of time reversal violation in a purely leptonic decay. The preliminary results are PT1 = (5 +/- 16) × 10−3, PT2 = (1 +/- 16) × 10−3 and PL = (1.09 +/- 0.15).

Polarized muon decay: Measurement of the polarization vector of the decay positrons as a test of time reversal invariance

The μ PT experiment at the Paul Scherrer Institut has determined the three polarization components of positrons from polarized muon decay simultaneously with the same apparatus by making use of three different effects (spatial and temporal dependence of annihilation-in-flight with polarized electrons and muon decay asymmetry). The use of a stroboscopic method greatly reduces systematic errors. The energy dependence of the transverse polarization component P T 1 , which lies in the plane spanned by muon-spin and positron momentum, yields the low energy parameter η and thus an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component P T 2 , which is perpendicular to the above mentioned plane, would be the first observation of time reversal violation in a purely leptonic decay. The preliminary results are P T 1 = (5 ± 16) × 10 −3, P T 2 = (1 ± 16) × 10 −3and P L = 1.09 ± 0.15.