Evidence for the decay sigma+ --> pmu+ mu-

We report the first evidence for the decay Sigma(+)-->pmu(+)mu(-) from data taken by the HyperCP (E871) experiment at Fermilab. Based on three observed events, the branching ratio is B(Sigma(+)-->pmu(+)mu(-))=[8.6(+6.6)(-5.4)(stat)+/-5.5(syst)]x10(-8). The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Sigma(+)-->pP(0),P0-->mu(+)mu(-) with a P0 mass of 214.3+/-0.5 MeV/c(2) and branching ratio B(Sigma(+)-->pP(0),P0-->mu(+)mu(-))=[3.1(+2.4)(-1.9)(stat)+/-1.5(syst)]x10(-8).     

Search for very light CP-odd Higgs Boson in radiative decays of Upsilon(1S)

We search for a non-SM-like CP-odd Higgs boson (a(1)(0)) decaying to tau(+)tau(-) or mu(+)mu(-) in radiative decays of the Upsilon(1S). No significant signal is found, and upper limits on the product branching ratios are set. Our tau(+)tau(-) results are almost 2 orders of magnitude more stringent than previous upper limits. Our data provide no evidence for a Higgs state with a mass of 214 MeV decaying to mu(+)mu(-), previously proposed as an explanation for 3 Sigma(+)-->pmu(+)mu(-) events observed by the HyperCP experiment. Our results constrain NMSSM models.     

Search for the lepton-flavor-violating leptonic B(0)-->mu(+/-)tau(-/+) and B(0)-->e(+/-)tau(-/+)

We have searched a sample of 9.6 x 10(6) BB events for the lepton-flavor-violating leptonic B decays, B(0)-->mu(+/-)tau(-/+) and B(0)-->e(+/-)tau(-/+). The tau lepton was detected through the decay modes tau-->lnunu(-) , where l=e, mu. There is no indication of a signal, and we obtain the 90% confidence level upper limits B(B(0)-->mu(+/-)tau(-/+))<3.8 x 10(-5) and B(B(0)-->e(+/-)tau(-/+))<1.3 x 10(-4).     

Branching ratio measurement of the decay K(L) --> e(+)e(-)mu(+)mu(-)

We have collected a 43 event sample of the decay K(L)-->e(+)e(-)mu(+)mu(-) with negligible backgrounds and measured its branching ratio to be (2.62+/-0.40+/-0.17)x10(-9). We see no evidence for CP violation in this decay. In addition, we set the 90% confidence upper limit on the combined branching ratios for the lepton flavor violating decays K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+) at B(K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+))< or =1.23x10(-10), assuming a uniform phase space distribution.     

Observation of the decay K- --> pi(-)mu(+)mu(-) and measurements of the branching ratios for K+/- --> pi(+/-)mu(+)mu(-)

Using data collected with the HyperCP (E871) spectrometer during the 1997 fixed-target run at Fermilab, we report the first observation of the decay K--->pi(-)mu(+)mu(-) and new measurements of the branching ratios for K+/--->pi(+/-)mu(+)mu(-). By combining the branching ratios for the decays K+-->pi(+)mu(+)mu(-) and K--->pi(-)mu(+)mu(-), we measure Gamma(K+/--->pi(+/-)mu(+)mu(-))/Gamma(K+/--->all) = (9.8+/-1.0+/-0.5)x10(-8). The CP asymmetry between the rates of the two decay modes is [Gamma(K+-->pi(+)mu(+)mu(-))-Gamma(K--->pi(-)mu(+)mu(-))]/[Gamma(K+-->pi(+)mu(+)mu(-))+Gamma(K--->pi(-)mu(+)mu(-))] = -0.02+/-0.11+/-0.04.     

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.     

Observation of Upsilon(4S) decays to pi(+)pi(-)Upsilon(1S) and pi(+)pi(-)Upsilon(2S)

Observation of Upsilon(4S) decays to pi(+)pi(-)C and pi(+)pi(-)Upsilon(2S)We present the first measurement of Upsilon(4S) decays to pi(+)pi(-)Upsilon(1S) based on a sample of 230 x 106(4S) mesons collected with the BABAR detector. We measure the product branching fractions Beta(Upsilon(4S) --> pi(+)pi(-)Upsilon(1S)) x BetaUpsilon(1S) --> mu(+)mu(-) = (2.23 +/- 0.25(stat) +/- 0.27(syst))x 10(-6) and Beta(Upsilon(4S) --> pi(+)pi(-)Upsilon(2S) x Beta(Upsilon(2S) --> mu(+)mu(-))=(1.69 +/-0.26(stat) +/- 0.20(syst)) x 10(-)6, from which we derive the partial widths Gamma(Upsilon(4S) --> pi(+)pi(-)Upsilon(1S))=(1.8 +/-0.4) keV and Gamma(Upsilon(4S) --> pi(+)pi(-)Upsilon(2S))=(2.7 +/- 0.8) keV.     

Observation and mass measurement of the baryon Xib-

We report the observation and measurement of the mass of the bottom, strange baryon Xi(b)- through the decay chain Xi(b)- -->J/psiXi-, where J/psi-->mu+mu-, Xi- -->Lambdapi-, and Lambda-->ppi-. A signal is observed whose probability of arising from a background fluctuation is 6.6 x 10(-15), or 7.7 Gaussian standard deviations. The Xi(b)- mass is measured to be 5792.9+/-2.5(stat) +/- 1.7(syst) MeV/c2.     

Search for the rare decays B-->Kl(+)l(-) and B-->K(*)l(+)l(-)

We present results from a search for the flavor-changing neutral current decays B-->Kl(+)l(-) and B-->K(*)l(+)l(-), where l(+)l(-) is either an e(+)e(-) or mu(+)mu(-) pair. The data sample comprises 22.7 x 10(6) Upsilon(4S)-->B(-)B decays collected with the BABAR detector at the PEP-II B Factory. We obtain the 90% C.L. upper limits B(B-->Kl(+)l(-))<0.51 x 10(-6) and B(B-->K(*)l(+)l(-))<3.1 x 10(-6), close to standard model predictions for these branching fractions. We have also obtained limits on the lepton-family-violating decays B-->Ke+/-mu(-/+) and B-->K(*)e(+/-)mu(-/+).     

Search for pi(0)-->nu(mu)nu(mu) decays in the LSND detector

We observe a net beam excess of 8.7+/-6.3(stat)+/-2.4(syst) events, above 160 MeV, resulting from the charged-current reaction of nu(micro) and/or nu;(mu) on C and H in the LSND detector. No beam-related muon background is expected in this energy regime. Within an analysis framework of pi(0)-->nu(mu)nu;(mu), we set a direct upper limit for this branching ratio of Gamma(pi(0)-->nu(mu)nu;(mu))/Gamma(pi(0)-->all)<1.6 x 10(-6) at 90% confidence level.     

Measurement of the spin of the omega(-) hyperon

A measurement of the spin of the Omega(-) hyperon produced through the exclusive process Xi(c)(0)-->Omega(-)K(+) is presented using a total integrated luminosity of 116 fb(-1) recorded with the BABAR detector at the e(+)e(-) asymmetric-energy B factory at SLAC. Under the assumption that the Xi(c)(0) has spin 1/2, the angular distribution of the Lambda from Omega(-)-->LambdaK(-) decay is inconsistent with all half-integer Omega(-) spin values other than 3/2. Lower statistics data for the process Omega(c)(0)-->Omega(-)pi(+) from a 230 fb(-1) sample are also found to be consistent with Omega(-) spin 3/2. If the Xi(c)(0) spin were 3/2, an Omega(-) spin of 5/2 could not be excluded.     

Direct observation of the strange b baryon Xib-

We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psiLambda) = 0.28+/-0.09(stat)(-0.08)(+0.09)(syst).     

Measurement of the branching ratio and form factor of K(L)-->mu(+)mu(-)gamma

We report on the analysis of the rare decay K(L)-->mu(+)mu(-)gamma the 1997 data from the KTeV experiment at Fermilab. A total of 9327 candidate events are observed with 2.4% background, representing a factor of 40 increase in statistics over the current world sample. We find that B(K(L)-->mu(+)mu(-)gamma) = (3.62 +/- 0.04(stat) +/- 0.08(syst)) x 10(-7). The form factor parameter alpha(K*) is measured to be alpha(K*) = -0.160(+0.026)(-0.028). In addition, we make the first measurement of the parameter alpha from the D'Ambrosio-Isidori-Portolés form factor, finding alpha = -1.54 +/- 0.10. In that model, this alpha measurement limits the Cabibbo-Kobayashi-Maskawa parameter rho>-0.2.     

Search for nu(mu)-->nu(e) and nu(mu)-->nu(e) oscillations at NuTeV

Limits on nu(mu)-->nu(e) and nu(mu)-->nu(e) oscillations are extracted using the NuTeV detector with sign-selected nu(mu) and nu(mu) beams. In nu(mu) mode, for the case of sin(2)2alpha = 1, Delta(m)(2)>2.6 eV(2) is excluded, and for Delta(m)(2)>1000 eV(2), sin(2)2alpha>1.1 x 10(-3). The NuTeV data exclude the high Delta(m)(2) end of nu(mu)-->nu(e) oscillation parameters favored by the LSND experiment without the need to assume that the oscillation parameters for nu and nu are the same. We present the most stringent experimental limits for nu(mu)(nu(mu))-->nu(e)(nu(e)) oscillations in the large Delta(m)(2) region.     

Search for the flavor-changing neutral current decay B0s--> mu(+) mu(-) in pp Collisions at sqrt[s] = 1.96 TeV with the D0 detector

We present the results of a search for the flavor-changing neutral current decay B(0)(s)--> mu(+) mu(-) using a data set with integrated luminosity of 240 pb(-1) of pp collisions at sqrt[s] = 1.96 TeV collected with the D0 detector in run II of the Fermilab Tevatron collider. We find the upper limit on the branching fraction to be B(B(0)(s)--> mu(+) mu(-)) < or= 5.0 x 10(-7) at the 95% C.L. assuming no contributions from the decay B(0)(d)--> mu(+) mu(-) in the signal region. This limit is the most stringent upper bound on the branching fraction B(0)(s)--> mu(+) mu(-) to date.     

Search for the invisible decay of J/psi in psi(2S) --> pi(+)pi(-) J/psi

Using psi(2S) --> pi(+)pi(-) J/psi events in a sample of 14.0 x 10(6) psi(2S) decays collected with the BES-II detector, a search for the decay of the J/psi to invisible final states is performed. No signal is found, and an upper limit at the 90% confidence level is determined to be 1.2 x 10(-2) for the ratio B(J/psi --> invisible)/B(J/psi-->mu(+)mu(-)). This is the first search for J/psi decays to invisible final states.     

Experimental study of the radiative decays K+-->mu(+)nue(+)e(-) and K+-->e(+)nue(+)e(-)

Experiment 865 at the Brookhaven Alternating Gradient Synchrotron obtained 410 K+-->e(+)nue(+)e(-) and 2679 K+-->mu(+)nue(+)e(-) events including 10% and 19% background. The branching ratios were measured to be [2.48+/-0.14(stat)+/-0.14(syst)]x10(-8) (m(ee)>150 MeV) and (7.06+/-0.16+/-0.26)x10(-8) (m(ee)>145 MeV), respectively. Results for the decay form factors are presented.     

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.     

Observation of B(0)(s)-->Psi(2S)Phi and measurement of the ratio of branching fractions Beta(B(0)(s)-->Psi(2S)Phi)/Beta(B(0)(s)-->J/PsiPhi)

We report the first observation of B(0)(s)-->Psi(2S)Phi decay in p(p_) collisions at square root of 8=1.96 TeV using 360 pb(-1) of data collected by the CDF II detector at the Fermilab Tevatron. We observe 20.2 +/- 5.0 and 12.3 +/- 4.1 B(0)(s)-->Psi(2S)Phi candidates, in Psi(2S)-->mu(+)mu(-) and Phi(2S)-->J/Phipi(+)pi(-) decay modes, respectively. We present a measurement of the relative branching fraction Beta(B(0)(s)-->Psi(2S)Phi)/Beta(B(0)(s)-->J/PsiPhi)=0.52 +/- 0.13(stat) +/- 0.04(syst) +/- 0.06(BR) using the Psi(2S)-->mu(+)mu(-) decay mode.     

Search for doubly charged higgs boson pair production in the decay to mu(+)mu(+)mu(-)mu(-) in pp collisions at sqrt[s]=1.96 TeV

A search for pair production of doubly charged Higgs bosons in the process pp -->H(++)H(--) -->mu(+)mu(+)mu(-)mu(-) is performed with the D0 run II detector at the Fermilab Tevatron. The analysis is based on a sample of inclusive dimuon data collected at an energy of sqrt[s]=1.96 TeV, corresponding to an integrated luminosity of 113 pb(-1). In the absence of a signal, 95% confidence level mass limits of M(H(+/-+/-)(L))>118.4 GeV/c(2) and M(H(+/-+/-)(R))>98.2 GeV/c(2) are set for left-handed and right-handed doubly charged Higgs bosons, respectively, assuming 100% branching into muon pairs.