2,554 research outputs found
Flow of entropy in the evolution of the B^0 anti B^0 system: Upper bound on CP violation from unidirectionality
We have previously studied the time-dependence of a B anti B meson mixture in
terms of its density matrix. The requirement that the absolute value of the
Stokes vector zeta(t) should evolve monotonically from its initial value
zeta(0)=0 to its final value zeta(infinity)=1 was shown to lead to an upper
bound on the CP violating overlap . In the present note we consider an
entropy variable S as an alternative measure of mixing. We show that exactly
the same upper bound emerges from the requirement that the flow of entropy is
unidirectional (dS/dt<0). We compare the entropic current dS/dt with and
without CP violation and identify certain physical features that appear when
the bound on is violated.Comment: 8 pages, 4 figures. Typos corrected, comment on entropy added. To be
published in Physical Review
Interference and Partial Width Asymmetry in Top and Antitop Decays
We re-examine the question of a possible difference in the partial decay
widths of and , induced by an intermediate scalar boson
with -violating couplings. The interference of and exchanges is
analysed by constructing the propagator matrix of the
system, and determining its absorptive part in terms of fermion loops. Results
are obtained for the partial rate difference in the channels
and , which fulfil explicitly the constraints of
invariance. These results are contrasted with those in previous work.Comment: 14 pages, report PITHA 94/1
An upper limit on CP violation in the system
In a previous publication we noted that the time dependence of an incoherent
mixture undergoes a qualitative change when the magnitude of CP
violation exceeds a critical value. Requiring, on physical grounds,
that the system evolve from an initial incoherent state to a final pure state
in a monotonic way, yields a new upper limit for . The recent
measurement of the wrong charge semileptonic asymmetry of mesons
presented by the D0 collaboration is outside this bound by one standard
deviation. If this result is confirmed it implies the existence of a new
quantum mechanical oscillation phenomenon.Comment: 7 pages, 2 figures, version submitted for publication (Physical
Review
Angular Distribution and CP Asymmetries in the Decays B->K^-pi^+e^-e^+ and B->pi^-pi^+e^-e^+
The short-distance Hamiltonian describing b->s(d)e^-e^+ in the standard model
is used to obtain the decay spectrum of \bar{B}->K^-pi^+e^-e^+ and
\bar{B}->pi^-pi^+e^-e^+, assuming the Kpi and pipi systems to be the decay
products of K^* and rho respectively. Specific features calculated are (i)
angular distribution of K^- (or pi^-) in the K^-pi^+ (or pi^-pi^+)
centre-of-mass (c.m.) frame; (ii) angular distribution of e^- in the e^-e^+
c.m. frame; and (iii) the correlation between the meson and lepton planes. We
also derive CP-violating observables obtained by combining the above decays
with the conjugate processes B->K^+pi^-e^-e^+ and B->pi^-pi^+e^-e^+.Comment: 19 pages, REVTeX, no figures. Equations (2.19a), (2.19b), (5.5)-(5.7)
have been corrected; all results remain unchanged. These changes will appear
in an Erratum submitted to Phys. Rev.
Lepton Mass Effects in Single Pion Production by Neutrinos
We reconsider the Feynman-Kislinger-Ravndal model applied to
neutrino-excitation of baryon resonances. The effects of lepton mass are
included, using the formalism of Kuzmin, Lyubushkin and Naumov. In addition we
take account of the pion-pole contribution to the hadronic axial vector
current. Application of this new formalism to the reaction nu(mu) + p --> mu +
Delta at E(nu) approx 1 GeV gives a suppressed cross section at small angles,
in agreement with the screening correction in Adler's forward scattering
theorem. Application to the process nu(tau) + p --> tau + Delta at E(nu) approx
7 GeV leads to the prediction of right-handed tau polarization for
forward-going leptons, in line with a calculation based on an isobar model. Our
formalism represents an improved version of the Rein-Sehgal model,
incorporating lepton mass effects in a manner consistent with PCAC.Comment: 14 pages, 5 figures. Typos in eq. 9 and 27 corrected. Numbers in
table I for coherent cross sections (RSA and RSC) corrected (normalization
error). Figs 3 and 4 changed accordingly. These corrections also apply to the
published version PRD 76, 113004 (2007
CP Violation and Arrows of Time Evolution of a Neutral or Meson from an Incoherent to a Coherent State
We study the evolution of a neutral meson prepared as an incoherent equal
mixture of and . Denoting the density matrix by \rho(t) =
{1/2} N(t) [\1 + \vec{\zeta}(t) \cdot \vec{\sigma} ] , the norm of the state
is found to decrease monotonically from one to zero, while the magnitude
of the Stokes vector increases monotonically from zero to
one. This property qualifies these observables as arrows of time. Requiring
monotonic behaviour of for arbitrary values of and
yields a bound on the CP-violating overlap , which is similar to, but weaker than, the known unitarity
bound. A similar requirement on yields a new bound,
which is particularly effective in limiting
the CP-violating overlap in the - system. We obtain the Stokes
parameter which shows how the average strangeness of the beam
evolves from zero to . The evolution of the Stokes vector from
to 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
Magnetic and axial vector form factors as probes of orbital angular momentum in the proton
We have recently examined the static properties of the baryon octet (magnetic
moments and axial vector coupling constants) in a generalized quark model in
which the angular momentum of a polarized nucleon is partly spin and partly orbital . The orbital momentum was
represented by the rotation of a flux-tube connecting the three constituent
quarks. The best fit is obtained with ,
. We now consider the consequences of this
idea for the -dependence of the magnetic and axial vector form factors. It
is found that the isovector magnetic form factor
differs in shape from the axial form factor by an amount that
depends on the spatial distribution of orbital angular momentum. The model of a
rigidly rotating flux-tube leads to a relation between the magnetic, axial
vector and matter radii, , where , . The shape of is found to be close to a dipole
with GeV.Comment: 18 pages, 5 ps-figures, uses RevTe
Pair production and correlated decay of heavy Majorana neutrinos in e+e- collisions
We consider the process e^+e^-\to N_1N_2, where N_1 and N_2 are heavy Majorana particles, with relative CP given by \eta_{CP}=+1 or -1 decaying subsequently via N_1,N_2\to W^{\pm}e^{\mp}. We derive the energy and angle correlation of the dilepton final state, both for like-sign (e^{\mp}e^{\mp}) and unlike-sign (e^-e^+) configurations. Interesting differences are found between the cases \eta_{CP}=+1 and -1. The characteristics of unlike-sign e^+e^- dileptons originating from a Majorana pair N_1N_2 are contrasted with those arising from the reaction e^+e^-\to N\bar{N}\to W^+e^-W^-e^+, where N\bar{N} is a Dirac particle-antiparticle pair
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