Concept# T-symmetry

Summary

T-symmetry or time reversal symmetry is the theoretical symmetry of physical laws under the transformation of time reversal,
: T: t \mapsto -t.
Since the second law of thermodynamics states that entropy increases as time flows toward the future, in general, the macroscopic universe does not show symmetry under time reversal. In other words, time is said to be non-symmetric, or asymmetric, except for special equilibrium states when the second law of thermodynamics predicts the time symmetry to hold. However, quantum noninvasive measurements are predicted to violate time symmetry even in equilibrium, contrary to their classical counterparts, although this has not yet been experimentally confirmed.
Time asymmetries (see Arrow of time) generally are caused by one of three categories:
# intrinsic to the dynamic physical law (e.g., for the weak force)

# due to the initial conditions of the universe (e.g., for the second law of thermodynamics)

# due to measurements (e.g., for t

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LHCb is one of the four large experiments hosted at the Large Hadron Collider (LHC) at CERN in Geneva. It will start taking data in September 2008, and will then operate for several years. It consists of a single-arm forward spectrometer dedicated to precise measurements of CP violation and rare decays in the B sector, with the aim of testing the Standard Model and possibly of discovering the first signatures of New Physics. Building such a large experiment as LHCb is a challenge, and many contributions are needed. The Lausanne lab is responsible for the design and the production of the Silicon Inner Tracker (IT) of LHCb. This detector is made of Silicon sensors which need to be cooled to avoid thermal runaway. We present here a contribution to the design of this sub-detector and a description of the production steps. In particular, a study of the cooling of the Inner Tracker is described. It is shown that the cooling abilities of the IT can avoid thermal runaway. CP violation in B meson decays was first observed in the measurement of the so-called "golden channel", in which a Bd0 meson decays into a J/ψ and a Κs0 . The time-dependent CP asymmetry in Bd0 → J/ψΚs0 allows to measure the angle β of the (d, b) unitary triangle. This parameter is now known with 4% accuracy at B factories. However, this determination of sin 2β is made under the assumption that there is only a single amplitude present in this decay : this means that penguin diagrams which might be present have been neglected. In 1999, Robert Fleischer [29] proposed a theoretical method to access those penguin diagrams in the Bd0 → J/ψΚs0 decay, using the Bs0→ J/ψΚs0 channel. This method relies on U-Spin symmetry and also allows to determine the γ angle of the (d, b) unitary triangle. We have developed a selection method for the Bd0 → J/ψΚs0 channel in order to strongly suppress the background and to allow the separation of the Bs0 and Bd0 peaks. We obtained mass resolution of 8 MeV/c2 and a B/S ratio for the channel Bd0 → J/ψΚs0 estimated to belong to [0, 0.039] at 90% confidence level in a ±2σ mass window around the Bd0 mass, after the first level of trigger (L0). For the channel Bs0 → J/ψΚs0 , the B/S ratio is calculated from the result for Bd0 → J/ψΚs0 assuming known branching fractions. It lies in the interval [0, 3.33] at 90% CL. The annual yield is expected to be around 300 events for an integrated luminosity of 2 fb-1. We have simulated with fast Monte Carlo the Bs0 → J/ψΚs0 signal using the parametrization proposed in [29] and taking as input the results of selection obtained for Bd0 → J/ψΚs0 . The simulation has been repeated several times for different integrated luminosities and B/S ratios. We conclude that after 5 years of normal running, LHCb will be able to determine the penguin contribution in the Bd0 → J/ψΚs0 decay with a sensitivity of (0.172 ± 0.004) using this method based on U-spin symmetry.

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Robustness against disorder and defects is a pivotal advantage of topological systems, manifested by the absence of electronic backscattering in the quantum-Hall and spin-Hall effects, and by unidirectional waveguiding in their classical analogues. Two-dimensional (2D) topological insulators, in particular, provide unprecedented opportunities in a variety of fields owing to their compact planar geometries, which are compatible with the fabrication technologies used in modern electronics and photonics. Among all 2D topological phases, Chern insulators are currently the most reliable designs owing to the genuine backscattering immunity of their non-reciprocal edge modes, brought via time-reversal symmetry breaking. Yet such resistance to fabrication tolerances is limited to fluctuations of the same order of magnitude as their bandgap, limiting their resilience to small perturbations only. Here we investigate the robustness problem in a system where edge transmission can survive disorder levels with strengths arbitrarily larger than the bandgap—an anomalous non-reciprocal topological network. We explore the general conditions needed to obtain such an unusual effect in systems made of unitary three-port non-reciprocal scatterers connected by phase links, and establish the superior robustness of anomalous edge transmission modes over Chern ones to phase-link disorder of arbitrarily large values. We confirm experimentally the exceptional resilience of the anomalous phase, and demonstrate its operation in various arbitrarily shaped disordered multi-port prototypes. Our results pave the way to efficient, arbitrary planar energy transport on 2D substrates for wave devices with full protection against large fabrication flaws or imperfections.

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