The calorimetric spectrum of the electron-capture decay of 163^{163}Ho. The spectral endpoint region

The electron-neutrino mass (or masses and mixing angles) may be directly measurable in weak electron-capture decays. The favoured experimental technique is "calorimetric". The optimal nuclide is $^{163}$Ho, and several experiments (ECHo, HOLMES and NuMECS) are currently studying its decay. The most relevant range of the calorimetric-energy spectrum extends for the last few hundred eV below its endpoint. It has not yet been well measured. We explore the theory, mainly in the cited range, of electron capture in $^{163}$Ho decay. A so far neglected process turns out to be most relevant: electron-capture accompanied by the shake-off of a second electron. Our two main conclusions are very encouraging: the counting rate close to the endpoint may be more than an order of magnitude larger than previously expected; the "pile-up" problem may be significantly reduced.Comment: Clarifying changes suggested by a referee. Results unchanged. 14 pages, 15 figure

The calorimetric spectrum of the electron-capture decay of 163^{163}Ho. A preliminary analysis of the preliminary data

It is in principle possible to measure directly the electron neutrino mass (or masses and mixing angles) in weak electron-capture decays. The optimal nuclide in this respect is $^{163}$Ho. The favoured experimental technique, currently pursued in various experiments (ECHo, HOLMES and NuMECS) is "calorimetric". The calorimetric energy spectrum is a sum over the unstable vacant orbitals, or "holes", left by the electrons weakly captured by the nucleus. We discuss the current progress in this field and analize the preliminary data. Our conclusion is that, as pointed out by Robertson, the contribution of two-hole states is not negligible. But --in strong contradistinction with the tacit conclusion of previous comparisons of theory and observations-- we find a quite satisfactory agreement. A crucial point is that, in the creation of secondary holes, electron shakeoff and not only electron shakeup must be taken into account.Comment: 6 pages, 5 figures. Section IV and Fig.3 added. Minor text modification

Charm nonleptonic decays and final state interactions

A global previous analysis of two-body nonleptonic decays of $D$ mesons has been extended to the decays involving light scalar mesons. The allowance for final state interaction also in nonresonant channels provides a fit of much improved quality and with less symmetry breaking in the axial charges. We give predictions for about 50 decay branching ratios yet to be measured. We also discuss long distance contributions to the difference $\Delta \Gamma$ between the $D_S$ and $D_L$ widths.Comment: 14 pages, no figures, plain TeX, uses harvmac.tex and tables.te

BcB_c Physics at Hadron Colliders

In this paper we summarize the results of the theory working group dedicated to the analysis of $B_c$ production at hadron colliders.Comment: 7 pages, LaTe

Neutrino Decay and Atmospheric Neutrinos

We reconsider neutrino decay as an explanation for atmospheric neutrino observations. We show that if the mass-difference relevant to the two mixed states \nu_\mu and \nu_\tau is very small (< 10^{-4} eV^2), then a very good fit to the observations can be obtained with decay of a component of \nu_\mu to a sterile neutrino and a Majoron. We discuss how the K2K and MINOS long-baseline experiments can distinguish the decay and oscillation scenarios.Comment: 9 pages, Revtex, uses epsf.sty, 3 postscript figures. Additions and corrections to references, minor changes in the text and to some number

Lifetimes of b-flavoured hadrons

I discuss the heavy quark expansion for the inclusive widths of heavy-light hadrons, which predicts quite well the experimental ratios of B_q meson lifetimes. As for $\Lambda_b$, current determinations of ${\cal O}(m_b^{-3})$ contribution to $\tau(\Lambda_b)$ do not allow to explain the small measured value of $\tau(\Lambda_b)/\tau(B_d)$. As a final topic, I discuss the implications of the measurement of the B_c lifetime.Comment: LaTex, 4 pages, 1 figure. Talk given at the "U.K. Phenomenology Workshop on Heavy Flavours and CP violation" Durham, 17-22 Sep. 2000 (Mixing and Lifetimes Working Group

Radiative Leptonic BcB_c Decays

We analyze the radiative leptonic $B_c$ decay mode: $B_c \to \ell \nu \gamma$ ($\ell=e, \mu$) using a QCD-inspired constituent quark model. The prediction: ${\cal B}(B_c \to \ell \nu \gamma)\simeq 3 \times 10^{-5}$ makes this channel experimentally promising in view of the large number of $B_c$ mesons which are expected to be produced at the future hadron facilities.Comment: LaTex, 12 pages, 2 figures. A discussion on gauge invariance added. Numerical results update

CP violating asymmetries in charged D meson decays

The CP violating asymmetries for Cabibbo suppressed charged D meson decays in the standard model are estimated in the factorized approximation, using the two-loop effective hamiltonian and a model for final state interactions previously tested for Cabibbo allowed D decays. No new parameters are added. The predictions are larger than expected and not too far from the experimental possibilities.Comment: 13 pages, Roma n. 91

A New Estimate of ε′/ε\varepsilon '/\varepsilon

We discuss direct $CP$ violation in the standard model by giving a new estimate of $\varepsilon'/\varepsilon$ in kaon decays. Our analysis is based on the evaluation of the hadronic matrix elements of the \mbox{$\Delta S =1$} effective quark lagrangian by means of the chiral quark model, with the inclusion of meson one-loop renormalization and NLO Wilson coefficients. Our estimate is fully consistent with the $\Delta I =1/2$ selection rule in $K\to \pi\pi$ decays which is well reproduced within the same framework. By varying all parameters in the allowed ranges and, in particular, taking the quark condensate---which is the major source of uncertainty---between $(-200\ {\rm MeV})^3$ and $(-280\ {\rm MeV})^3$ we find $$-5.0 \times 10^{-3}\ <\varepsilon'/\varepsilon <\ 1.4 \times 10^{-3}\ .$$ Assuming for the quark condensate the improved PCAC result \mbox{\vev{\bar qq} = -(221\: \pm 17\ {\rm MeV})^3} and fixing $\Lambda_{\rm QCD}^{(4)}$ to its central value, we find the more restrictive prediction $$\varepsilon '/\varepsilon = ( 4 \pm 5 ) \,\times \,10^{-4}\ ,$$ where the central value is defined as the average over the allowed values of Im $\lambda_t$ in the first and second quadrants. In these estimates the relevant mixing parameter Im $\lambda_t$ is self-consistently obtained from $\varepsilon$ and we take $m_t^{\rm pole} = 180 \pm 12$ GeV. Our result is, to a very good approximation, renormalization-scale and $\gamma_5$-scheme independent.Comment: 40 pages, uuencoded LATEX2e file including 13 eps figures, revised version to appear in Nucl. Phys.