Neutron-antineutron Oscillations in the Trapping Box

We have reexamined the problem of $n-\bar n$ oscillations for ultra-cold neutrons (UCN) confined within a trap. We have shown that the growth of the $\bar n$ component with time is to a decent accuracy given by $P(\bar n)= \epsilon^2_{n\bar n} t_Lt,$ where $\epsilon_{n\bar n}$ is the mixing parameter, $t_L\sim 1$ sec in the neutron propagation time between subsequent collisions with the trap walls. Possible corrections to this law and open questions are discussed.Comment: 11 pages, LaTeX2

The Rise Times of High and Low Redshift Type Ia Supernovae are Consistent

We present a self-consistent comparison of the rise times for low- and high-redshift Type Ia supernovae. Following previous studies, the early light curve is modeled using a t-squared law, which is then mated with a modified Leibundgut template light curve. The best-fit t-squared law is determined for ensemble samples of low- and high-redshift supernovae by fitting simultaneously for all light curve parameters for all supernovae in each sample. Our method fully accounts for the non-negligible covariance amongst the light curve fitting parameters, which previous analyses have neglected. Contrary to Riess et al. (1999), we find fair to good agreement between the rise times of the low- and high-redshift Type Ia supernovae. The uncertainty in the rise time of the high-redshift Type Ia supernovae is presently quite large (roughly +/- 1.2 days statistical), making any search for evidence of evolution based on a comparison of rise times premature. Furthermore, systematic effects on rise time determinations from the high-redshift observations, due to the form of the late-time light curve and the manner in which the light curves of these supernovae were sampled, can bias the high-redshift rise time determinations by up to +3.6/-1.9 days under extreme situations. The peak brightnesses - used for cosmology - do not suffer any significant bias, nor any significant increase in uncertainty.Comment: 18 pages, 4 figures, Accepted for publication in the Astronomical Journal. Also available at http://www.lbl.gov/~nugent/papers.html Typos were corrected and a few sentences were added for improved clarit

Free electron lifetime achievements in Liquid Argon Imaging TPC

A key feature for the success of the liquid Argon imaging TPC (LAr-TPC) technology is the industrial purification against electro-negative impurities, especially Oxygen and Nitrogen remnants, which have to be continuously kept at an exceptionally low level by filtering and recirculating liquid Argon. Improved purification techniques have been applied to a 120 liters LAr-TPC test facility in the INFN-LNL laboratory. Through-going muon tracks have been used to determine the free electron lifetime in liquid Argon against electro-negative impurities. The short path length here observed (30 cm) is compensated by the high accuracy in the observation of the specific ionization of cosmic ray muons at sea level as a function of the drift distance. A free electron lifetime of (21.4+7.3-4.3) ms, namely > 15.8 ms at 90 % C.L. has been observed over several weeks under stable conditions, corresponding to a residual Oxygen equivalent of about 15 ppt (part per trillion). At 500 V/cm, the free electron speed is 1.5 m/ms. In a LAr-TPC a free electron lifetime in excess of 15 ms corresponds for instance to an attenuation of less than 15 % after a drift path of 5 m, opening the way to the operation of the LAr-TPC with exceptionally long drift distances.Comment: 15 pages, 10 figures; Accepted for publication in JINS

CPT violation and particle-antiparticle asymmetry in cosmology

General features of generation of the cosmological charge asymmetry in CPT non-invariant world are discussed. If the effects of CPT violation manifest themselves only in mass differences of particles and antiparticles, the baryon asymmetry of the universe hardly can be explained solely by breaking of CPT invariance. However, CPT non-invariant theories may lead to a new effect of distorting the usual equilibrium distributions. If this takes place, CPT violation may explain the baryon asymmetry of the universe.Comment: 7 pages, no figures. Submitted to a special issue of Yadernaya Fizika (Physics of Atomic Nuclei) dedicated to 80th birthday of L.B. Okun. Three references are adde

Neutron-Mirror-Neutron Oscillations in a Trap

We calculate the rate of neutron-mirror-neutron oscillations for ultracold neutrons trapped in a storage vessel. Recent experimental bounds on the oscillation time are discussed.Comment: v4: typos correcte

Neutron-Antineutron Oscillations in Nuclei Revisited

An upper limit on $n-\bar n$ oscillations can be obtained from the stability of matter. This relation has been worked out theoretically and together with data yields $\tau_{n\bar n} > (1 - 2)\times 10^8 sec$. A recent publication claims a different relation and finds a nuclear suppression of the $n\to\bar n$ oscillations which is two orders of magnitude weaker than the previous evaluations. Using the same approach we find, nevertheless, that the earlier estimates are correct and conclude that future experiments with free neutrons from reactors are capable to put a stronger limit on the $n - \bar n$ oscillation time than experiments with large amount of neutrons bound in nuclei.Comment: To be published in proc. of the Workshop on Future Directions in Quark Nuclear Physics, Adelaide, March 9 - 20, 199

Limits on \boldmath n {\bar n} oscillations from nuclear stability

The relationship between the lower limit on the nuclear stability lifetime as derived from the non disappearance of `stable` nuclei ($T_{d}~\gtrsim~5.4~\times~10^{31}$ yr), and the lower limit thus implied on the oscillation time $(\tau_{n \bar n})$ of a possibly underlying neutron-antineutron oscillation process, is clarified by studying the time evolution of the nuclear decay within a simple model which respects unitarity. The order-of-magnitude result $\tau_{n \bar n} \approx 2 (T_{d}/\Gamma_{\bar n})^{1/2} > 2 \times 10^{8}$ sec, where $\Gamma_{\bar n}$ is a typical $\bar n$ nuclear annihilation width, agrees as expected with the limit on $\tau_{n \bar n}$ established by several detailed nuclear physics calculations, but sharply disagreeing by 15 orders of magnitude with a claim published recently in Phys. Rev. CRAP.Comment: 8 pages; this PRC version (accepted for publication, November 4 1999) differs from the original version only by a few minor editorial change

A local trigger system for the large LAr-TPC detector

A special dedicated double-rebinning algorithm has been successfully developed in order to extract the physical hit signal from the TPC wires. This solution has been implemented on digital boards, allowing to realize a local trigger able to identify even localized low-energy small events