Heavy-to-light-quark decays with two-loop accuracy

We present a determination of a new class of three-loop Feynman diagrams describing heavy-to-light transitions. We apply it to find the O(alpha2(s)) corrections to the top quark decay t --> bW and to the distribution of lepton invariant mass in the semileptonic b quark decay b --> ulnu. We also confirm the previously determined total rate of that process as well as the O(alpha2) corrections to the muon lifetime.     

Mass effects in muon and semileptonic b-->c decays

Quantum chromodynamics (QCD) effects in the semileptonic decay b-->clnu are evaluated to the second order in the coupling constant, O(alpha(s){2}), and to several orders in the expansion in quark masses, m{c}/m{b}. Corrections are calculated for the total decay rate as well as for the first two moments of the lepton energy and the hadron system energy distributions. Translated into QED and applied to the muon decay, they decrease its predicted rate by -0.43 ppm.     

Revised alpha4 term of lepton g-2 from the Feynman diagrams containing an internal light-by-light scattering subdiagram

The alpha(4) contribution to the lepton g-2 from a gauge-invariant set of 18 Feynman diagrams containing a light-by-light scattering subdiagram internally has been reevaluated by a method independent of the previous approach. Comparison of two methods revealed a program error in the first version. Correcting this error, the contributions of these 18 diagrams become -0.990 72(10)(alpha/pi)(4) and -4.432 43(58)(alpha/pi)(4) for the electron and muon g-2, respectively. The correction is not large enough to affect the comparison between theory and experiment for the muon g-2, but it does alter the inferred value for the fine structure constant alpha(-1) by 6 ppb.     

Decay of PSI and upsilon into a lepton pair and gluons

We calculate the decay of a heavy vector quarkonium state into a lepton pair and two gluon jets, in lowest order QCD. We present branching ratios, and the lepton pair spectrum as a function of its invariant mass, and of the missing mass recoiling against it.     

Experimental constraints on left-right symmetric models from muon decay

The TWIST Collaboration has completed a new measurement of the energy-angle spectrum of positrons from the decay of highly polarized muons. A simultaneous measurement of the muon decay parameters ρ, δ, and P(μ)(π)ξ tests the standard model in a purely leptonic process and provides improved limits for relevant extensions to the standard model. Specifically, for the generalized left-right symmetric model |(g(R)/g(L))ζ|<0.020 and (g(L)/g(R))m(2)>578 GeV/c(2), both 90% C.L.     

Order alpha(3) ln(1/alpha) corrections to positronium decays

The logarithmically enhanced alpha(3)ln(1/alpha) corrections to the para- and orthopositronium decay widths are calculated in the framework of dimensionally regularized nonrelativistic quantum electrodynamics. In the case of parapositronium, the correction is negative, approximately doubles the effect of the leading logarithmic alpha(3)ln (2)(1/alpha) one, and is comparable to the nonlogarithmic O(alpha(2)) one. As for orthopositronium, the correction is positive and almost cancels the alpha(3)ln (2)(1/alpha) one. The uncertainty in the theoretical prediction for the parapositronium decay width is reduced to 10(-2) &mgr;s(-1).     

Search for the lepton family number violating process nu(mu)e(-) --> mu(-)nu(e)

The NuTeV experiment at Fermilab has used a sign-selected neutrino beam to perform a search for the lepton number violating process nu(mu)e(-)-->mu(-)nu(e), and to measure the cross section of the standard model inverse muon decay process nu(mu)e(-)-->mu(-)nu(e). NuTeV measures the inverse muon decay asymptotic cross-section slope sigma/E to be (13.8 +/- 1.2 +/- 1.4) x 10(-42) cm(2)/GeV. The experiment also observes no evidence for lepton number violation and places one of the most restrictive limits on the cross-section ratio sigma(nu(mu)e(-)-->mu(-)nu(e))/sigma(nu(mu)e(-)-->mu(-)nu(e)) < or = 1.7% at 90% C.L. for V-A couplings and < or = 0.6% for scalar couplings.     

Aspects of the two-component and four-component neutrino theories in connection with weak lepton and semilepton processes

A comparison is made of the results found in the application of two-component and four-component theories of the two neutrinos to weak lepton processes (muon decay) and semilepton processes. The predictions of the two theories clearly differ in the V-A version of the coupling of electron and muon currents and of muon and baryon currents. In contrast with the theory of two-component neutrinos (the V-A interaction), four-component theory predicts that a V + A interaction of electron and muon currents is responsible for muon decay.     

Neutrinoless double Beta decay and lepton flavor violation

We point out that extensions of the standard model with low scale (approximately TeV) lepton number violation (LNV) generally lead to a pattern of lepton flavor violation (LFV) experimentally distinguishable from the one implied by models with grand unified theory scale LNV. As a consequence, muon LFV processes provide a powerful diagnostic tool to determine whether or not the effective neutrino mass can be deduced from the rate of neutrinoless double beta decay. We discuss the role of mu-->egamma and mu-->e conversion in nuclei, which will be studied with high sensitivity in forthcoming experiments.     

Exclusive Semileptonic Rare Decays B→K(*)ℓ+ℓ- in a Top Quark Two-Higgs-Doublet Model

Employing improved calculations of the decay form factors from light-cone sum rules, we evaluate the invariant mass spectrum, forward-backward asymmetry, and lepton polarizations of the exclusive processes B→K^(*)ℓ⁺ℓ^- in the SM and T2HDM. From the recent measurements of their branching ratios, we find that these processes do provide additional bounds on the new parameters in the model considered here. After the inclusion of the new physics contributions, the large enhancement of FBA, which is unobservably small within the SM and of the lepton polarization at large tanβ, may precisely test the SM or reveal new physics in forthcoming accurate experiments.     

Search for a W' boson via the decay mode W'-->munumu in 1.8 TeV pp collisions

We report the results of a search for a W' boson produced in pp collisions at a center-of-mass energy of 1.8 TeV using a 107 pb-1 data sample recorded by the Collider Detector at Fermilab. We consider the decay channel W'-->&munumu and search for anomalous production of high transverse mass munumu lepton pairs. We observe no excess of events above background and set limits on the rate of W' boson production and decay relative to standard model W boson production and decay using a fit of the transverse mass distribution observed. If we assume standard model strength couplings of the W' boson to quark and lepton pairs, we exclude a W' boson with invariant mass less than 660 GeV/c2 at 95% confidence level.     

The source of trimuon events in neutrino scattering

A comprehensive study indicates that equally likely sources for trimuon events neutrino scattering are (a) charged heavy lepton production (with decay to three muons) and (b) simultaneous production of a neutral lepton (with decay to two muons) and a heavy quark (with decay to one muon). The sequential decay of a heavy quark to two muons is less likely. An intriguing model yielding simultaneous M⁰ and b quark production is proposed.     

Implications of BNL measurement of \delta a_{\mu} on a class of scalar leptoquark interactions

Recently BNL have measured the muon magnetic moment anomaly with increased precision. The world average experimental value at present shows a discrepancy of from the standard model (SM) value. In this paper we investigate the implications of this difference on a class of scalar leptoquark interactions to SM quark–lepton pair. We find that for a leptoquark mass of a few hundred GeV the BNL muon anomaly can arise from couplings much smaller than even the electromagnetic coupling. We also find that the BNL value for the muon anomaly leads to an unambiguous prediction for the electric dipole moment of the muon and a bound on the flavor changing leptoquark coupling relevant for the rare decay . Received: 15 April 2001 / Published online: 6 July 2001     

Study of the charge-exchange reactions\pi ^ - p \to (\pi ^0 ,\eta ,\eta \prime )n at 63 GeV

Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π⁰ production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ _e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10^?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions.     

Dispersion relation formalism for the two-photon exchange correction to elastic muon–proton scattering: elastic intermediate state

We evaluate the two-photon exchange correction to the unpolarized cross section in the elastic muon–proton scattering within dispersion relations. One of the six independent invariant amplitudes requires a subtraction. We fix the subtraction function to the model estimate of the full two-photon exchange at one of three MUSE beam energies and make a prediction for the two other energies. Additionally, we present single and double polarization observables accounting for the lepton mass.     

Lepton mixing under the lepton charge nonconservation, neutrino masses and oscillations and the “forbidden” decay µ− → e − + γ

The lepton-charge (L _e , L _μ , L _τ ) nonconserving interaction leads to the mixing of the electron, muon, and tau neutrinos, which manifests itself in spatial oscillations of a neutrino beam, and also to the mixing of the electron, negative muon, and tau lepton, which, in particular, may be the cause of the “forbidden” radiative decay of the negative muon into the electron and γ quantum. Under the assumption that the nondiagonal elements of the mass matrices for neutrinos and ordinary leptons, connected with the lepton charge nonconservation, are the same, and by performing the joint analysis of the experimental data on neutrino oscillations and experimental restriction for the probability of the decay µ^? → e ^? + γ per unit time, the following estimate for the lower bound of neutrino mass has been obtained: m ^(ν) > 1.5 eV/c ².     

Harmonic measure and winding of conformally invariant curves

The exact joint multifractal distribution for the scaling and winding of the electrostatic potential lines near any conformally invariant scaling curve is derived in two dimensions. Its spectrum f(alpha,lambda) gives the Hausdorff dimension of the points where the potential scales with distance r as H approximately r(alpha) while the curve logarithmically spirals with a rotation angle phi=lambdalnr. It obeys the scaling law f(alpha,lambda)=(1+lambda(2))f(alpha)-blambda(2) with alpha=alpha/(1+lambda(2)) and b=(25-c)/12, and where f(alpha) identical with f(alpha,0) is the pure harmonic measure spectrum, and c the conformal central charge. The results apply to O(N) and Potts models, as well as to stochastic L?wner evolution.     

Measurements of the Decay KL-->e+ e- mu+ mu-

The KTeV experiment at Fermilab has isolated a total of 132 events from the rare decay K(L)-->e+ e- mu+ mu-, with an estimated background of 0.8 events. The branching ratio of this mode is determined to be [2.69+/-0.24(stat)+/-0.12(syst)]x10(-9), with a radiative cutoff of M(2)(ee mu mu)/M(2)(K)>0.95. The first measurement using this mode of the parameter alpha from the D'Ambrosio-Isidori-Portolès (DIP) model of the K(L)gamma*gamma* vertex yields a result of -1.59+/-0.37, consistent with values obtained from other decay modes. Because of the limited statistics, no sensitivity is found to the DIP parameter beta. We use this decay mode to set limits on CP and lepton violation.     

Observation of new states decaying into Lambda+(c)pi(-)pi(+)

Using 13.7 fb(-1) of data recorded by the CLEO detector at the Cornell Electron Storage Ring, we investigate the spectrum of charmed baryons which decay into Lambda+(c)pi(-)pi(+) and are more massive than the Lambda+(c)(2625) baryon. We find evidence for two new states: one is broad and has an invariant mass roughly 480 MeV above that of the Lambda+(c) baryon; the other is narrow with an invariant mass of 596+/-1+/-2 MeV above the Lambda+(c) mass.     

Low mass lepton pair production and pion dynamics in ultrarelativistic heavy ion collisions

The production of lepton pairs with low invariant mass as probes for the pion dynamics in relativistic nuclear collisions is discussed in some detail. We emphasize the implications of a possible large positive pion chemical potential for the production rate of lepton pairs. We find a strong enhancement in the low invariant mass region, \(2m_\pi \leqslant M_{\mu ^ + \mu ^ - } \leqslant 600\,MeV\) , for lepton pairs which are produced via the annihilation of pions in the hot and dense collision zone. Various sources of background which could mask this enhancement are discussed in some detail. We present and compare calculations for dilepton mass spectra based on different nuclear collision scenarios. It is found that the di-muon mass spectrum can serve as a useful probe to distinguish between these different scenarios.