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.     

Higgs production at next-to-next-to-leading order

We describe the calculation of inclusive Higgs boson production at hadronic colliders at next-to-next-to-leading order (NNLO) in perturbative quantum chromodynamics. We have used the technique developed in ref. [4]. Our results agree with those published earlier in the literature.     

Rare decay K+ --> pi+ nunu at the next-to-next-to-leading order in QCD

We calculate the charm quark contribution to the rare decay Kappa(+)--> pi(+) nunu in the next-to-next-to-leading order of QCD. This new contribution reduces the theoretical uncertainty in the relevant parameter Pc from +/-10.1% down to +/-2.4%, corresponding to scale uncertainties of +/-1.3%, +/-1.0%, +/-0.006, and +/-1.2 degrees in Beta(Kappa(+) --> pi(+) nunu) and in |V(td)|, sin2(Beta), and gamma extracted from the Kappa --> pinunu system. The error in Rho(c) = 0.37 +/- 0.04 is now fully dominated by the current uncertainty of +/-3.8% in the charm quark mass m(c). We find Beta(Kappa(+) --> pi(+)nunu) = (8.0 +/- 1.1) x 10(-11), where the quoted error stems almost entirely from the present uncertainties in m(c) and the Cabibbo-Kobayashi-Maskawa elements.     

On top-pair hadro-production at next-to-next-to-leading order

We study the QCD corrections at next-to-next-to-leading order (NNLO) to the cross section for the hadronic pair-production of top quarks. We present new results in the high-energy limit using the well-known framework of _kt$k_t$-factorization. We combine these findings with the known threshold corrections and present improved approximate NNLO results over the full kinematic range. This approach is employed to quantify the residual theoretical uncertainty of the approximate NNLO results which amounts to about 4% for the Tevatron and 5% for the LHC cross section predictions. Our analytic results in the high-energy limit will provide an important check on future computations of the complete NNLO cross sections.     

Search for pair production of doubly charged Higgs bosons in the H++H- - -->mu+ mu+ mu- mu- final state

We report the results of a search for pair production of doubly charged Higgs bosons via pp over-->H++H - - X-->mu+ mu+ mu- mu- X at sqrt s=1.96 TeV. We use a data set corresponding to an integrated luminosity of 1.1 fb(-1) collected from 2002 to 2006 by the D0 detector at the Fermilab Tevatron Collider. In the absence of an excess above the standard model background, lower mass limits of M(H L +/- +/-) >150 GeV/c2 and M(H R+/- +/-) >127 GeV/c2 at 95% C.L. are set, respectively, for left-handed and right-handed doubly charged Higgs bosons assuming a 100% branching ratio into muons.     

Threshold corrections in bottom and charm quark hadroproduction at next-to-next-to-leading order

We calculate threshold soft-gluon corrections to total cross sections and transverse momentum distributions for bottom and charm quark production in fixed target experiments, considering both pp and interactions. We investigate the quality of the near-threshold soft-gluon approximation at next-to-leading order (NLO) and calculate next-to-next-to-leading order (NNLO) corrections through next-to-next-to-next-to-leading-logarithmic (NNNLL) accuracy, including some virtual terms. We find that the NNLO threshold corrections reduce the factorization and renormalization scale dependence of the cross sections.Received: 26 April 2004, Published online: 2 July 2004     

Observation of the decay xi0 --> sigma+ mu- nu(mu)

The xi0 muon semileptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the xi0 beta decay mode and yields a value for the ratio of decay rates gamma(xi0 --> sigma+ mu- nu(mu))/gamma(xi0 --> sigma+ e- nu(e)) of [1.8(-0.5)(+0.7)(stat) +/- 0.2(syst)] x 10(-2). This is in agreement with the SU(3) flavor symmetric quark model.     

Low- and high-energy expansion of heavy-quark correlators at next-to-next-to-leading order

We calculate three-loop corrections to correlation functions of heavy-quark currents in the low- and high-energy regions. We present 30 coefficients both in the low-energy and the high-energy expansion of the scalar and the vector correlator with non-diagonal flavour structure. In addition we compute 30 coefficients in the high-energy expansion of the diagonal vector, axial-vector, scalar and pseudo-scalar correlators. Possible applications of our new results are improvements of lattice-based quark-mass determinations and the approximate reconstruction of the full momentum dependence of the correlators.     

Search for decays of B0-->e+ e-, B0-->mu+ mu-, B0-->e +/- mu-/+

We present a search for the decays B0-->e+ e-, B0-->mu+ mu-, and B0-->e (+/-) mu (-/+) in data collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC B Factory. Using a data set of 111 fb(-1), we find no evidence for a signal in any of the three channels investigated and set the following branching fraction upper limits at the 90% confidence level: B(B0-->e+ e-) < 6.1 x 10(-8), B(B0-->mu+ mu-) < 8.3 x 10(-8), and B(B0-->e (+/-) mu (-/+) )<18 x 10(-8).     

Search for [corrected] B0(s) --> mu+ mu- and B0(d) [corrected] --> mu + mu- decays in pp collisions with CDF II

We report on a search for B0(s) --> mu+ mu- and B0(d) --> mu + mu- decays in pp collisions at square root(s) = 1.96 TeV using 364 pb(-1) of data collected by the CDF II detector at the Fermilab Tevatron Collider. After applying all selection requirements, we observe no candidates inside the B0(s) or B0(d) mass windows. The resulting upper limits on the branching fractions are B(B0(s) --> mu+ mu-) < 1.5 x 10(-7) and B(B0(d) --> mu+ mu-) < 3.9 x 10(-8) at 90% confidence level.     

Lattice chiral effective field theory with three-body interactions at next-to-next-to-leading order

We consider low-energy nucleons at next-to-next-to-leading order in lattice chiral effective field theory. Three-body interactions first appear at this order, and we discuss several methods for determining three-body interaction coefficients on the lattice. We compute the energy of the triton and low-energy neutron-deuteron scattering phase shifts in the spin-doublet and spin-quartet channels using Lüscher’s finite-volume method. In the four-nucleon system we calculate the energy of the -particle using auxiliary fields and projection Monte Carlo.     

Implications on supersymmetry-breaking mediation mechanisms from observing Bs-->mu+mu- and the muon g-2

We consider B(s)-->mu(+)mu(-) and the muon (g-2)(mu) in various supersymmetry-breaking mediation mechanisms. If the decay B(s)-->mu(+)mu(-) is observed at Tevatron Run II with a branching ratio larger than approximately 2 x 10(-8), the noscale supergravity (including the gaugino mediation), the gauge mediation scenario with a small number of messenger fields and low messenger scale, and a class of anomaly mediation scenarios will be excluded, even if they can accommodate a large muon (g-2)(mu). On the other hand, the minimal supergravity scenario and similar mechanisms derived from string models can accommodate this observation.