3,625 research outputs found

### CP Violation and Arrows of Time Evolution of a Neutral $K$ or $B$ Meson from an Incoherent to a Coherent State

We study the evolution of a neutral $K$ meson prepared as an incoherent equal
mixture of $K^0$ and $\bar{K^0}$. Denoting the density matrix by \rho(t) =
{1/2} N(t) [\1 + \vec{\zeta}(t) \cdot \vec{\sigma} ] , the norm of the state
$N(t)$ is found to decrease monotonically from one to zero, while the magnitude
of the Stokes vector $|\vec{\zeta}(t)|$ increases monotonically from zero to
one. This property qualifies these observables as arrows of time. Requiring
monotonic behaviour of $N(t)$ for arbitrary values of $\gamma_L, \gamma_S$ and
$\Delta m$ yields a bound on the CP-violating overlap $\delta =
\braket{K_L}{K_S}$, which is similar to, but weaker than, the known unitarity
bound. A similar requirement on $|\vec{\zeta}(t)|$ yields a new bound,
$\delta^2 < {1/2} (\frac{\Delta \gamma}{\Delta m}) \sinh (\frac{3\pi}{4}
\frac{\Delta \gamma}{\Delta m})$ which is particularly effective in limiting
the CP-violating overlap in the $B^0$-$\bar{B^0}$ system. We obtain the Stokes
parameter $\zeta_3(t)$ which shows how the average strangeness of the beam
evolves from zero to $\delta$. The evolution of the Stokes vector from
$|\vec{\zeta}| = 0$ to $|\vec{\zeta}| = 1$ has a resemblance to an order
parameter of a system undergoing spontaneous symmetry breaking.Comment: 13 pages, 6 figures. Inserted conon "." in title; minor change in
text. To appear in Physical review

### Resolution studies of cosmic-ray tracks in a TPC with GEM readout

A large volume TPC is a leading candidate for the central tracking detector
at a future high energy linear collider. To improve the resolution a new
readout based on micro-pattern gas detectors is being developed. Measurements
of the spatial resolution of cosmic-ray tracks in a GEM TPC are presented. We
find that the resolution suffers if the readout pads are too wide with respect
to the charge distribution at the readout plane due to insufficient charge
sharing. For narrow pads of 2 x 6 mm**2 we measure a resolution of 100
micometer at short drift distances in the absence of an axial magnetic field.
The dependence of the spatial resolution as a function of drift distance allows
the determination of the underlying electron statistics. Our results show that
the present technique uses about half the statistical power available from the
number of primary electrons. The track angle effect is observed as expected.Comment: 18 pages, 8 figures, version as published in Nucl. Inst. Met

### Unstable particles as open quantum systems

We present the probability preserving description of the decaying particle
within the framework of quantum mechanics of open systems taking into account
the superselection rule prohibiting the superposition of the particle and
vacuum. In our approach the evolution of the system is given by a family of
completely positive trace preserving maps forming one-parameter dynamical
semigroup. We give the Kraus representation for the general evolution of such
systems which allows one to write the evolution for systems with two or more
particles. Moreover, we show that the decay of the particle can be regarded as
a Markov process by finding explicitly the master equation in the Lindblad
form. We also show that there are remarkable restrictions on the possible
strength of decoherence.Comment: 11 pp, 2 figs (published version

### Paramaterizations of inclusive cross sections for pion production in proton-proton collisions. II. Comparison to new data

A set of new, precise data have recently been made available by the NA49
collaboration for charged pion production in proton-proton and proton-Carbon
reactions at 158 GeV. The current paper compares this new data to five
currently available arithmetic parameterizations. Although a precise fit is not
expected, two of the parameterizations do not work very well but the other
three are able to provide a moderately good, but not precise fit to the
proton-proton data. The best two of these three parameterizations are scaled to
the proton-Carbon data and again provide a moderately good, but not precise
fit.Comment: 11 pages, 13 figures, Accepted for publication in Physical Review

### Quantum Interference: From Kaons to Neutrinos (with Quantum Beats in between)

Using the vehicle of resolving an apparent paradox, a discussion of quantum
interference is presented. The understanding of a number of different physical
phenomena can be unified, in this context. These range from the neutral kaon
system to massive neutrinos, not to mention quantum beats, Rydberg wave
packets, and neutron gravity.Comment: 12 pages, LaTeX, 3 figure

### Parametrizations of Inclusive Cross Sections for Pion Production in Proton-Proton Collisions

Accurate knowledge of cross sections for pion production in proton-proton
collisions finds wide application in particle physics, astrophysics, cosmic ray
physics and space radiation problems, especially in situations where an
incident proton is transported through some medium, and one requires knowledge
of the output particle spectrum given the input spectrum. In such cases
accurate parametrizations of the cross sections are desired. In this paper we
review much of the experimental data and compare to a wide variety of different
cross section parametrizations. In so doing, we provide parametrizations of
neutral and charged pion cross sections which provide a very accurate
description of the experimental data. Lorentz invariant differential cross
sections, spectral distributions and total cross section parametrizations are
presented.Comment: 32 pages with 15 figures. Published in Physical Review D62, 094030.
File includes 6 tex files. The main file is paper.tex which has include
statements refering to the rest. figures are in graphs.di

### Irreversible Quantum Mechanics in the Neutral K-System

The neutral Kaon system is used to test the quantum theory of resonance
scattering and decay phenomena. The two dimensional Lee-Oehme-Yang theory with
complex Hamiltonian is obtained by truncating the complex basis vector
expansion of the exact theory in Rigged Hilbert space. This can be done for K_1
and K_2 as well as for K_S and K_L, depending upon whether one chooses the
(self-adjoint, semi-bounded) Hamiltonian as commuting or non-commuting with CP.
As an unexpected curiosity one can show that the exact theory (without
truncation) predicts long-time 2 pion decays of the neutral Kaon system even if
the Hamiltonian conserves CP.Comment: 36 pages, 1 PostScript figure include

### Determination of the branching ratios $\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi^+ \pi^- \pi^0)$ and $\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi e \nu )$

Improved branching ratios were measured for the $K_L \to 3 \pi^0$ decay in a
neutral beam at the CERN SPS with the NA31 detector: $\Gamma (K_L \to 3 \pi^0)
/ \Gamma (K_L \to \pi^+ \pi^- \pi^0) = 1.611 \pm 0.037$ and $\Gamma (K_L \to 3
\pi^0) / \Gamma (K_L \to \pi e \nu ) = 0.545 \pm 0.010$.
From the first number an upper limit for $\Delta I =5/2$ and $\Delta I = 7/2$ transitions in neutral kaon decay is derived. Using older results for the
Ke3/K$\mu$3 fraction, the 3$\pi^0$ branching ratio is found to be $\Gamma (K_L
\to 3 \pi^0 )/ \Gamma_{tot} = (0.211 \pm 0.003)$, about a factor three more
precise than from previous experiments

### Time Asymmetric Quantum Physics

Mathematical and phenomenological arguments in favor of asymmetric time
evolution of micro-physical states are presented.Comment: Tex file with 2 figure

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