Ha Lam

Study of the decay B¯(0)→D+l¯ν¯

Using a sample of 484 000 {ital B} mesons collected with the CLEO detector at the Cornell Electron Storage Ring, we have measured {ital B}({ital {bar B}}{sup 0}{r arrow}D{sup *+}l{sup {minus}}{nu}) and found that the polarization of the {ital D}{sup *+} is small. These results are compared with models of semileptonic {ital B} decay.

A search for exclusive penguin decays of B mesons

Abstract We have measured upper limits on branching fractions for rare exclusive decays of B mesons arising from one-loop diagrams in the standard model of electroweak interactions. We also obtain an upper limit for the lepton-number-violating decay B 0 → μ ± e ∓ .

Measurement of the isospin mass splitting Ξ+cΞ0c

Abstract Using the CLEO detector, we present a measurement of the mass of the charged charmed strange baryon Ξ + c and its neutral counterpart the Ξ 0 c . The Ξ + c is observed through its decay to Ξ - π + π + , and its mass is measured to be (2467±3±4) MeV. The isospin mass splitting of the Ξ c system is found to be M ( Ξ + c )- M ( Ξ 0 c )=(−5±4±1)MeV.

Determination of B(Ds+) via observation of Ds+l+1/2

Using the CLEO detector at the Cornell Electron Storage Ring (CESR), we have determined the ratio {Gamma}({ital D}{sub {ital s}}{sup +}{r arrow}{phi}{ital l}{sup +}{nu})/{Gamma}({ital D}{sub {ital s}}{sup +} {r arrow}{phi}{pi}{sup +})=0.49{plus minus}0.10{sub {minus}0.14}{sup +0.10}. We use this measurement to derive {ital B}({ital D}{sub {ital s}}{sup +}{r arrow}{phi}{pi}{sup +}).

Measurement of γγ widths of charmonium states

Abstract Using the CLEO detector at the Cornell Electron Storage Ring, we have searched for two-photon production of charmonium in four-track final states. We have measured Γ γγ ( η c )=5.9 +2.1 −1.8 ±1.9 keV, and we have obtained 95% CL upper limits of Γ γγ ( X c 0 ) Γ γγ ( X c 2 )

Measurement of Ds decay modes

Abstract Using the CLEO detector, we have measured the branching ratios for the exclusive decays of the D s + meson into K ∗0 K + , K 0 K + , and K ∗+ K 0 relative to the decay D s + →φπ + to be close to unity. We have also measured the mass diference between the D s + and D + meson to be 98.5±1.5 MeV/ c 2 .

Two-body D+s decays to ηπ+, η′π+, ηρ+, η′ρ+, and φρ+

We have made measurements of several {ital D}{sub {ital s}} branching ratios, relative to the {phi}{pi}{sup +} mode. We have observed two previously unseen two-body hadronic decays of the {ital D}{sub {ital s}}{sup +}, namely {eta}{rho}{sup +} and {eta}{prime}{rho}{sup +}, and measured relative branching ratios of 2.86{plus minus}0.38{sub {minus}0.38}{sup +0.36} and 3.44{plus minus}0.62{sub {minus}0.46}{sup +0.44}, respectively. We have determined the relative branching ratio for the decay into {phi}{rho}{sup +} to be 1.86{plus minus}0.26{sub {minus}0.40}{sup +0.29}. In addition, we have measured relative branching ratios for the {eta}{pi}{sup +} and {eta}{prime}{pi}{sup +} states, for which there had previously been conflicting measurements; our results are 0.54{plus minus}0.09{plus minus}0.06 and 1.20{plus minus}0.15{plus minus}0.11, respectively. Combining these new measurements with previous results and using (3.7{plus minus}1.2)% for the value of {ital scrB}({ital D}{sub {ital s}}{r arrow}{phi}{pi}{sup +}), we can account for {approx}(79{plus minus}26)% of all {ital D}{sub {ital s}}{sup +} decays. In addition we have also measured relative branching ratios or set upper limits on {ital D}{sup +} decays to all of the above-mentioned final states.

First observation of the decay XI(+)(C)-]XI(0)E+NU(E) and an estimate of the XI(+)(C)/XI(0)(C) lifetime ratio

Using the CLEO II detector at the Cornell Electron Storage Ring we have observed the decay modes {Xi}{sup +}{sub {ital c}}{r_arrow}{Xi}{sup 0}{ital e}{sup +}{nu}{sub {ital e}} and {Xi}{sup 0}{sub {ital c}}{r_arrow}{Xi}{sup {minus}}{ital e}{sup +}{nu}{sub {ital e}} by the detection of a {Xi}-positron pair of appropriate invariant mass. We find {ital B} ({Xi}{sup +}{sub {ital c}}{r_arrow}{Xi}{sup 0}{ital e}{sup +}{nu}{sub {ital e}}){sigma}({ital e}{sup +}{ital e}{sup {minus}}{r_arrow} {Xi}{sup +}{sub {ital cX}})=1.55{plus_minus}0.33{plus_minus}0.25 pb, {ital B} ({Xi}{sup 0}{sub {ital c}}{r_arrow}{Xi}{sup {minus}}{ital e}{sup +}{nu}{sub {ital e}}){sigma}({ital e}{sup +}{ital e}{sup {minus}}{r_arrow} {Xi}{sup 0}{sub {ital cX}})=0.63{plus_minus}0.12{plus_minus}0.10 pb, {ital B} ({Xi}{sup +}{sub {ital c}}{r_arrow}{Xi}{sup {minus}}{pi}{sup +}{pi}{sup +})/ {ital B} ({Xi}{sup +}{sub {ital c}}{r_arrow}{Xi}{sup 0}{ital e}{sup +}{nu}{sub {ital e}})= 0.44{plus_minus}0.11{sub {minus}0.06}{sup +0.11}, and {ital B} ({Xi}{sup 0}{sub {ital c}}{r_arrow}{Xi}{sup {minus}}{pi}{sup +})/{ital B} ({Xi}{sup 0}{sub {ital c}}{r_arrow}{Xi}{sup {minus}}{ital e}{sup +}{nu}{sub {ital e}})= 0.32{plus_minus}0.10{sub {minus}0.03}{sup +0.05}. Assuming the {Xi}{sup +}{sub {ital c}} and {Xi}{sup 0}{sub {ital c}} are equally produced in {ital e}{sup +}{ital e}{sup {minus}} annihilation events at 10 GeV, the lifetime ratio of {Xi}{sup +}{sub {ital c}}/{Xi}{sup 0}{sub {ital c}} is measured to be 2.46{plus_minus}0.70{sub {minus}0.23}{sup +0.33}.

2 Measurements of B-0(B)over-bar(0) mixing

We have measured the [ital B][sup 0][ital [bar B]0] mixing probability, [chi][sub [ital d]], using a sample of 965 000 [ital B[bar B]] pairs from [Upsilon](4[ital S]) decays. Counting dilepton events, we find [chi][sub [ital d]]=0.157[plus minus]0.016[plus minus]0.018[sub [minus]0.021][sup +0.028]. Using tagged [ital B][sup 0] events, we find [chi][sub [ital d]]=0.149[plus minus]0.023[plus minus]0.019[plus minus]0.010. The first (second) error is statistical (systematic). The third error reflects a [plus minus]15% uncertainty in the assumption, made in both cases, that charged and neutral [ital B] pairs contribute equally to dilepton events. We also obtain a limit on the [ital CP] impurity in the [ital B][sub [ital d]][sup 0] system, [vert bar]Re([epsilon][sub [ital B]][sup 0])[vert bar][lt]0.045 at 90% C.L.

Measurement of the D -> pipi branching fractions

Using data from CLEO II at the Cornell Electron Storage Ring we provide a new measurement of the branching fraction for [ital D][sup 0][r arrow][pi][sup +][pi][sup [minus]], and we present the first measurements of [ital D][sup 0][r arrow][pi][sup 0][pi][sup 0] and of [ital D][sup +][r arrow][pi][sup +][pi][sup 0], which is due to an isospin changing [Delta][ital I]=3/2 transition. From these data we extract the ratio of isospin amplitudes [vert bar][ital A][sub 2]/[ital A][sub 0][vert bar], and the cosine of the relative phase [delta]=[delta][sub 2][minus][delta][sub 0] between these amplitudes, for [ital D][r arrow][pi][pi] decays. Unlike the situation in kaon decay where [ital A][sub 2] is strongly suppressed, we find [vert bar][ital A][sub 2]/[ital A][sub 0][vert bar]=0.72[plus minus]0.13[plus minus]0.11 and cos[delta]=0.14[plus minus]0.13[plus minus]0.09.