Search for scalar top quark production in p&pmacr; collisions at sqrt

We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb(-1) of p&pmacr; collisions at sqrt[s] = 1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c(2) and scalar neutrino masses of at least 40 GeV/c(2), we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios.     

Spin correlation in t&tmacr; production from p&pmacr; collisions at radicals = 1.8 TeV

The D0 collaboration has performed a study of spin correlation in t&tmacr; production for the process t&tmacr;-->bW(+)&bmacr;W-, where the W bosons decay to enu or &mgr;nu. A sample of six events was collected during an exposure of the D0 detector to an integrated luminosity of approximately 125 pb(-1) of sqrt[s] = 1.8 TeV p&pmacr; collisions. The standard model (SM) predicts that the short lifetime of the top quark ensures the transmission of any spin information at production to the t&tmacr; decay products. The degree of spin correlation is characterized by a correlation coefficient kappa. We find that kappa>-0.25 at the 68% confidence level, in agreement with the SM prediction of kappa = 0.88.     

Study of B0 --> J/psiK(*)0pi(+)pi(-) decays with the collider detector at Fermilab

We report a study of the decays B0 --> J/psiK(*)0pi(+)pi(-), which involve the creation of a uu or dd quark pair in addition to a b -->c(cs) decay. The data sample consists of 110 pb(-1) of pp collisions at square root[s] = 1.8 TeV collected by the CDF detector at the Fermilab Tevatron collider during 1992-1995. We measure the branching fractions to be B(B0 --> J/psiK(*0)pi(+)pi(-)) = (6.6 +/- 1.9 +/- 1.1)x10(-4) and B(B0 --> J/psiK0pi(+)pi(-)) = (10.3 +/- 3.3 +/- 1.5)x10(-4). Evidence is seen for contributions from psi(2S)K(*)0, J/psiK0rho(0), J/psiK(*+)pi(-), and J/psiK1(1270).     

Measurement of the decay amplitudes of B0 --> J/psiK*0 and B(s)(0) --> J/psistraight phi decays

An angular analysis of B0-->J/psiK(*0) and B(0)(s)-->J/psistraight phi has been used to determine the decay amplitudes with parity-even longitudinal ( A0) and transverse ( A( parallel)) polarization and parity-odd transverse ( A( perpendicular)) polarization. The measurements are based on 190 B0 and 40 B(0)(s) candidates obtained from 89 pb(-1) of &pmacr;p collisions at the Fermilab Tevatron. The longitudinal decay amplitude dominates with |A0|(2) = 0.59+/-0. 06+/-0.01 for B0 and |A0|(2) = 0.61+/-0.14+/-0.02 for B(0)(s) decays. The parity-odd amplitude is found to be small with |A( perpendicular)|(2) = 0.13(+0.12)(-0.09)+/-0.06 for B0 and |A( perpendicular)|(2) = 0.23+/-0.19+/-0.04 for B(0)(s) decays.     

Production of Upsilon(1S) mesons from chi(b) decays in p&pmacr; collisions at sqrt

We have reconstructed the radiative decays chi(b)(1P)-->Upsilon(1S)gamma and chi(b)(2P)-->Upsilon(1S)gamma in p&pmacr; collisions at sqrt[s] = 1.8 TeV, and measured the fraction of Upsilon(1S) mesons that originate from these decays. For Upsilon(1S) mesons with p(Upsilon)(T)>8.0 GeV/c, the fractions that come from chi(b)(1P) and chi(b)(2P) decays are [27.1+/-6.9(stat)+/-4. 4(syst)]% and [10.5+/-4.4(stat)+/-1.4(syst)]%, respectively. We have derived the fraction of directly produced Upsilon(1S) mesons to be [50.9+/-8.2(stat)+/-9.0(syst)]%.     

Measurement of the helicity of W bosons in top quark decays

We use the transverse momentum spectrum of leptons in the decay chain t-->bW with W-->lnu to measure the helicity of the W bosons in the top quark rest frame. Our measurement uses a t&tmacr; sample isolated in 106+/-4 pb(-1) of data collected in p&pmacr; collisions at sqrt[s] = 1.8 TeV with the CDF detector at the Fermilab Tevatron. Assuming a standard V-A weak decay, we find that the fraction of W's with zero helicity in the top rest frame is F0 = 0.91+/-0. 37(stat)+/-0.13(syst), consistent with the standard model prediction of F0 = 0.70 for a top mass of 175 GeV/c(2).     

Search for second-generation leptoquark pairs in &pmacr;p collisions at radicals = 1.8 TeV

We have searched for second-generation leptoquark (LQ) pairs in the &mgr;&mgr;+jets channel using 94+/-5 pb(-1) of &pmacr;p collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the &mgr;nu+jets and nunu+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c(2) for beta = 1(1 / 2) are set at the 95% C.L. on the mass of scalar LQ. Mass limits are also set on vector leptoquarks as a function of beta.     

Observation of B(+)-->pppi+, B0-->ppK0, and B(+)-->ppK(*+)

We report the first observation of a b-->u type charmless baryonic B decay, B+-->pppi(+), as well as b-->s type B0-->ppK0 and B+-->ppK(*+) decays. The analysis is based on a 78 fb(-1) data sample recorded on the Upsilon(4S) resonance with the Belle detector at KEKB. We find B(B+-->pppi(+))=(3.06(+0.73)(-0.62)+/-0.37)x10(-6), B(B0-->ppK0)=(1.88(+0.77)(-0.60)+/-0.23)x10(-6), and B(B+-->ppK(*+))=(10.3(+3.6+1.3)(-2.8-1.7))x10(-6). We also update B(B+-->ppK+)=(5.66(+0.67)(-0.57)+/-0.62)x10(-6) and present an upper limit on B(B0-->ppK(*0)) at the 90% confidence level. A common feature of the observed decay modes is threshold peaking in baryon pair invariant mass.     

Observation of time-dependent CP violation in B0 --> eta'K0 decays and improved measurements of CP asymmetries in B0 --> phiK0, KS0KS0KS0 and B0 --> J/psiK0 decays

We present improved measurements of CP-violation parameters in B(0) --> phiK(0), eta(')K(0), KS(0)KS(0)KS(0) decays based on a sample of 535 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. We obtain sin2phi1(eff)=+0.64+/-0.10(stat)+/-0.04(syst) for B(0) --> eta(')K(0), +0.50+/-0.21(stat)+/-0.06(syst) for B(0) --> phiK(0), and +0.30+/-0.32(stat)+/-0.08(syst) for B(0) --> KS(0)KS(0)KS(0) decays. We have observed CP violation in the B(0) --> eta(')K(0) decay with a significance of 5.6 standard deviations. We also perform an improved measurement of CP asymmetries in B(0) --> J/psiK(0) decays and obtain sin2phi1=+0.642+/-0.031(stat)+/-0.017(syst).     

Measurement of the Lambda0b lifetime in the decay lambda0b--> J/psiLambda0 with the D0 detector

We present measurements of the Lambda(0)(b) lifetime in the exclusive decay channel Lambda(0)(b)--> J/psiLambda(0), with J/psi--> mu(+)mu(-) and Lambda(0)--> ppi(-), the B0 lifetime in the decay B0-->J/psiK(0)(S) with J/psi--> mu(+)mu(-) and K(0)(S)-->pi(+)pi(-), and the ratio of these lifetimes. The analysis is based on approximately 250 pb(-1) of data recorded with the D0 detector in pp collisions at sqrt[s] = 1.96 TeV. The Lambda(0)(b) lifetime is determined to be tau(Lambda(0)(b)) = 1.22(+0.22)(-0.18)(stat) +/- 0.04(syst) ps, the B0 lifetime tau(B0) = 1.40(+0.11)(-0.10)(stat) +/- 0.03(syst) ps, and the ratio tau(Lambda(0)(b))/tau(B0) = 0.87(+0.17)(-0.14)(stat) +/- 0.03(syst). In contrast with previous measurements using semileptonic decays, this is the first determination of the Lambda(0)(b) lifetime based on a fully reconstructed decay channel.     

Small-angle muon and bottom-quark production in p&pmacr; collisions at radicals = 1.8 TeV

This Letter describes a measurement of the muon cross section originating from b-quark decay in the forward rapidity range 2.4<| y(&mgr;)|<3.2 in p&pmacr; collisions at sqrt[s] = 1.8 TeV. The data used in this analysis were collected by the D0 experiment at the Fermilab Tevatron. We find that next-to-leading-order QCD calculations underestimate b-quark production by a factor of 4 in the forward rapidity region.     

Evidence for B+ --> K0K+ and B0 --> K0K0, and measurement of the branching fraction and search for direct CP violation in B+ --> K0pi+

We present evidence for the b --> d penguin-dominated decays B+ --> K0K+ and B0 --> K0K0 in 227 x 10(6) Y(4S) --> BB decays collected with the BABAR detector. We measure the branching fractions B(B+ --> K0K+) = (1.5 +/- 0.5 +/- 0.1) x 10(-6)(< 2.4 x 10(-6)) and B(B0 --> K0K0) = [formula: see text], where the uncertainties are statistical and systematic, respectively. We also present improved measurements of the charge-averaged branching fraction B(B+ --> K0pi+) = (26.0 +/- 1.3 +/- 1.0) x 10(-6) and CP-violating charge asymmetry A(CP) (K0pi+) = -0.09 +/- 0.05 +/- 0.01), where the uncertainties are statistical and systematic, respectively.     

Measurement of the Lambda b lifetime in the exclusive decay Lambda b --> J/psi Lambda

We have measured the Lambda b lifetime using the exclusive decay Lambda b --> J/psi Lambda, based on 1.2 fb(-1) of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda b decays, where the J/psi and Lambda are identified via the decays J/psi --> mu+ mu- and Lambda --> ppi, we measured the Lambda b lifetime to be tau(Lambda b)=1.218 (+0.130)/(-0.115) (stat) +/- 0.042(syst) ps. We also measured the B0 lifetime in the decay B0 --> J/psi(mu+ mu-)K(0)/(S)(pi+ pi-) to be tau(B0)=1.501 (+0.078)/(-0.074) (stat) +/- 0.050(syst) ps, yielding a lifetime ratio of tau(Lambda b)/tau(B0)=0.811 (+0.096)/(-0.087) (stat) +/- 0.034(syst).     

Measurements of branching fraction, polarization, and charge asymmetry of B(+/-)-->rho(+/-)rho(0) and a search for B(+/-)-->rho(+/-)f(0)(980)

We measure the branching fraction (B), polarization (f(L)), and CP asymmetry (A(CP)) of B(+/-)-->rho(+/-)rho(0) decays and search for the decay B(+/-)-->rho(+/-)f(0)(980) based on a data sample of 231.8 x 10(6) Upsilon(4S)-->BB decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy B factory. In B(+/-)-->rho(+/-)rho(0) decays we measure B=(16.8+/-2.2+/-2.3) x 10(-), f(L)=0.905+/-0.042(-0.027)(+0.023), and A(CP)=-0.12+/-0.13+/-0.10, and find an upper limit on the branching fraction of B(+/-)-->rho(+/-)f(0)(980)(-->pi(+)pi(-)) decays of 1.9 x 10(-6) at 90% confidence level.     

Observation of tree-level B decays with ss production from gluon radiation

We report on our search for decays proceeding via a tree-level b-->c quark transition in which a gluon radiates into an ss[over ] pair. We present observations of the decays B;{-}-->D_{s};{+}K;{-}pi;{-} and B[over ];{0}-->D_{s};{+}K_{S};{0}pi;{-} and evidence for B;{-}-->D_{s};{+}K;{-}K;{-} and set upper limits on the branching fractions for B[over ];{0}-->D_{s};{+}K_{S};{0}pi;{-} and B;{-}-->D_{s};{+}K;{-}K;{-} using 383x10;{6} Upsilon(4S)-->BB[over ] events collected by the BABAR detector at SLAC. We present evidence that the invariant mass distributions of D_{s};{+}K;{-} pairs from B;{-}-->D_{s};{+}K;{-}pi;{-} decays are inconsistent with the phase-space model, suggesting the presence of charm resonances lying below the D_{s};{+}K;{-} threshold.     

Search for radiative penguin decays B(+)-->rho(+)gamma, B(0)-->rho(0)gamma, and B(0)-->omegagamma

A search for the decays B-->rho(770)gamma and B0-->omega(782)gamma is performed on a sample of 211 x 10(6) Upsilon(4S)-->BB events collected by the BABAR detector at the SLAC PEP-II asymmetric-energy e(+)e(-) storage ring. No evidence for the decays is seen. We set the following limits on the individual branching fractions: B(B+-->rho(+)gamma)<1.8 x 10(-6), B(B0-->rho(0)gamma)<0.4 x 10(-6), and B(B0-->omegagamma)<1.0 x 10(-6) at the 90% confidence level. We use the quark model to limit the combined branching fraction B [B-->(rho/omega)gamma]<1.2 x 10(-6), from which we determine a constraint on the ratio of Cabibbo-Kobayashi-Maskawa matrix elements |V(td)|/|V(ts)|.     

Improved branching ratio measurement for the decay K(0)(L) --> &mgr;(+)&mgr;(-)

We report results from Experiment 871, performed at the BNL AGS, of a measurement of the branching ratio K(0)(L)-->&mgr;(+)&mgr;(-) with respect to the CP-violating mode K(0)(L)-->pi(+)pi(-). This experiment detected over 6200 candidate &mgr;(+)&mgr;(-) events, a factor of 6 more than that seen in all previous measurements combined. The resulting branching ratio gamma(K(0)(L)-->&mgr;(+)&mgr;(-))/gamma(K(0)(L)-->pi(+)pi(-)) = (3. 474+/-0.057)x10(-6) leads to a branching fraction B(K(0)(L)-->&mgr;(+)&mgr;(-)) = (7.18+/-0.17)x10(-9), which is consistent with the current world average, and reduces the uncertainty in this decay mode by a factor of 3.     

Search for the decay K(L) --> pi(0)&mgr;(+)&mgr;(-)

We report on a search for the decay K(L)-->pi(0)&mgr;(+)&mgr;(-) carried out as a part of the KTeV experiment at Fermilab. This decay is expected to have a significant CP violating contribution and a direct measurement will either support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or point to new physics. Two events were observed in the 1997 data with an expected background of 0.87+/-0.15 events, and we set an upper limit B(K(L)-->pi(0)&mgr;(+)&mgr;(-))<3. 8x10(-10) at the 90% confidence level.     

Observation of B(+/-) --> p(-)pK(+/-)

We report the observation of the decay mode B(+/-) --> p(-)pK(+/-)based on an analysis of 29.4 fb(-1) of data collected by the Belle detector at KEKB. This is the first example of a b-->s transition with baryons in the final state. The p(-)p mass spectrum in this decay is inconsistent with phase space and is peaked at low mass. The branching fraction for this decay is measured to be B(B+/--->p(-)pK+/-) = [4.3(+1.1)(-0.9)(stat)+/-0.5(syst)]x 10(-6). We also report upper limits for the decays B(0)-->p(-)pK(S) and B(+/-)-->p(-)p pi(+/-).     

Observation of the decay B(0)-->D(+/-)D(*-/+)

We report the first observation of the decay B(0)-->D(+/-)D(*-/+) with the Belle detector at the KEKB e(+)e(-) Collider operated at the Upsilon(4S) resonance. The sum of branching fractions B(B(0)-->D(+)D(*-))+B(B(0)-->D(-)D(*+)) is measured to be (1.17+/-0.26(+0.22)(-0.25))x10(-3) using the full reconstruction method where both charmed mesons from B0 decays are reconstructed. A consistent value [(1.48+/-0.38(+0.28)(-0.31))x10(-3)] is obtained using a partial reconstruction technique that uses only the slow pion from the D(*-)-->D(-0)pi(-) decay and a fully reconstructed D(+) to reconstruct the B(0).