Search Results (147 total)

We report on a study of exclusive radiative decays of the Υ(1S) resonance into the final states γπ⁰π⁰, γηη and γπ⁰η, using 1.13  fb^-1 of e⁺e^- annihilation data collected at sqrt[s]=9.46  GeV with the CLEO III detector operating at the Cornell Electron Storage Ring. In the channel γπ⁰π⁰, we measure the branching ratio for the decay mode Υ(1S)→γf₂(1270) to be (10.5±1.6(stat)_-1.8^+1.9(syst))×10^-5. We place upper limits on the product branching ratios for the isoscalar resonances f₀(1500) and f₀(1710) for the π⁰π⁰ and ηη decay channels. We also set an upper limit on the Υ(1S) radiative decay into π⁰η.

Using data taken with the CLEO III detector at the Cornell Electron Storage Ring, we have investigated the direct photon spectrum in the decays Υ(1S)→γgg, Υ(2S)→γgg, Υ(3S)→γgg. The latter two of these are first measurements. Our analysis procedures differ from previous ones in the following ways: (a) background estimates (primarily from π⁰ decays) are based on isospin symmetry rather than a determination of the π⁰ spectrum, which permits measurement of the Υ(2S) and Υ(3S) direct photon spectra without explicit corrections for π⁰ backgrounds from, e.g., χ_bJ states, (b) we estimate the branching fractions with a parametrized functional form (exponential) used for the background, and c) we use the high-statistics sample of Υ(2S)→ππΥ(1S) to obtain a tagged sample of Υ(1S)→γ+X events, for which there are no QED backgrounds. We determine values for the ratio of the inclusive direct photon decay rate to that of the dominant three-gluon decay Υ→ggg  (R_γ=B(ggγ)/B(ggg)) to be R_γ(1S)=(2.70±0.01±0.13±0.24)%, R_γ(2S)=(3.18±0.04±0.22±0.41)%, and R_γ(3S)=(2.72±0.06±0.32±0.37)%, where the errors shown are statistical, systematic, and theoretical model dependent, respectively. Given a value of Q², one can estimate a value for the strong coupling constant α_s(Q²) from R_γ.

From e⁺e^- collision data acquired with the CLEO detector at the Cornell Electron Storage Ring, we observe the non-DD̅ decay ψ(3770)→γχ_c1 with a statistical significance of 6.6 standard deviations, using the two-photon cascades to J/ψ and J/ψ→ℓ⁺ℓ^-. We determine σ(e⁺e^-→ψ(3770))×B(ψ(3770)→γχ_c1)=(18.0±3.3±2.5)  pb and branching fraction B(ψ(3770)→γχ_c1)=(2.8±0.5±0.4)×10^-3. We set 90% C.L. upper limits for the transition to χ_c2 (χ_c0): σ×B<5.7  pb (<282  pb) and B<0.9×10^-3 (<44×10^-3). We also determine Γ(ψ(3770)→γχ_c1)/Γ(ψ(3770)→π⁺π^-J/ψ)=1.5±0.3±0.3 (>1.0 at 90% C.L.), which bears upon the interpretation of X(3872).

The two-photon width of χ_c2(³P₂) state of charmonium has been measured using 14.4  fb^-1 of e⁺e^- data taken at sqrt[s]=9.46–11.30  GeV with the CLEO III detector. The γγ-fusion reaction studied is e⁺e^-→e⁺e^-γγ, γγ→χ_c2→γJ/ψ→γe⁺e^-(μ⁺μ^-). We measure Γ_γγ(χ_c2)B(χ_c2→γJ/ψ)B(J/ψ→e⁺e^-+μ⁺μ^-)=13.2±1.4(stat)±1.1(syst)  eV, and obtain Γ_γγ(χ_c2)=559±57(stat)±48(syst)±36(br)  eV. This result is in excellent agreement with the result of γγ-fusion measurement by Belle and is consistent with that of the p̅ p→χ_c2→γγ measurement, when they are both reevaluated using the recent CLEO result for the radiative decay χ_c2→γJ/ψ.

We present the first experimental limits on high-q² contributions to charmless semileptonic B decays of the form expected from the weak annihilation (WA) decay mechanism. Such contributions could bias determinations of |V_ub| from inclusive measurements of B→X_ulν. Using a wide range of models based on available theoretical input we set a limit of Γ_WA/Γ_b→u<7.4% (90% confidence level) on the WA fraction, and assess the impact on previous inclusive determinations of |V_ub|.

We measure the cross section for e⁺e^-→ψ(3770)→hadrons at E_c.m.=3773  MeV to be (6.38±0.08_-0.30^+0.41)  nb using the CLEO detector at the CESR e⁺e^- collider. The difference between this and the e⁺e^-→ψ(3770)→DD̅ cross section at the same energy is found to be (-0.01±0.08_-0.30^+0.41)  nb. With the observed total cross section, we extract Γ_ee(ψ(3770))=(0.204±0.003_-0.027^+0.041)  keV. Uncertainties shown are statistical and systematic, respectively.

We observe signals for the decays ψ(3770)→XJ/ψ from data acquired with the CLEO detector operating at the CESR e⁺e^- collider with sqrt[s]=3773  MeV. We measure the following branching fractions B(ψ(3770)→XJ/ψ) and significances: (189±20±20)×10^-5 (11.6σ) for X=π⁺π^-, (80±25±16)×10^-5 (3.4σ) for X=π⁰π⁰, and (87±33±22)×10^-5 (3.5σ) for X=η, where the errors are statistical and systematic, respectively. The radiative return process e⁺e^-→γψ(2S) populates the same event sample and is used to measure Γ_ee[ψ(2S)]=(2.54±0.03±0.11)  keV.

Using data obtained with the CLEO III detector, running at the Cornell Electron Storage Ring (CESR), we report on a new study of exclusive radiative Υ(1S) decays into the final states γπ⁺π^-, γK⁺K^-, and γpp̅ . We present branching ratio measurements for the decay modes Υ(1S)→γf₂(1270), Υ(1S)→γf₂^′(1525), and Υ(1S)→γK⁺K^-; helicity production ratios for f₂(1270) and f₂^′(1525); upper limits for the decay Υ(1S)→γf_J(2200), with f_J(2220)→π⁺π^-, K⁺K^-, pp̅ ; and an upper limit for the decay Υ(1S)→γX(1860), with X(1860)→γpp̅ .

Using data collected at the ψ(3770) resonance with the CLEO-c detector at the Cornell e⁺e^- storage ring, we present searches for 25 charmless decay modes of the ψ(3770), mostly multibody final states. No evidence for charmless decays is found.

We have searched for the di-pion transition χ_b(2P)→ππχ_b(1P) in the CLEO III sample of Υ(3S) decays in the exclusive decay chain: Υ(3S)→γχ_b(2P), χ_b(2P)→ππχ_b(1P), χ_b(1P)→γΥ(1S), Υ(1S)→ℓ⁺ℓ^-. Our studies include both π⁺π^- and π⁰π⁰, each analyzed both in fully-reconstructed events and in events with one pion undetected. We show that the null hypothesis is not substantiated. Under reasonable assumptions, we find the partial decay width to be Γ(χ_b(2P)→ππχ_b(1P))=(0.83±0.22±0.08±0.19)  keV, with the uncertainties being statistical, internal CLEO systematics, and common systematics from outside sources.

Using the CLEO detector at the Cornell Electron Storage Ring, we have observed the B_s meson in e⁺e^- annihilation at the Υ(5S) resonance. We find 14 candidates consistent with B_s decays into final states with a J/ψ or a D_s^(*)-. The probability that we have observed a background fluctuation is less than 8×10^-10. We have established that at the energy of the Υ(5S) resonance B_s production proceeds predominantly through the creation of B_s^*B̅ _s^* pairs. We find σ(e⁺e^-→B_s^*B̅ _s^*)=[0.11_-0.03^+0.04(stat)±0.02(syst)]  nb, and set the following limits: σ(e⁺e^-→B_sB̅ _s)/σ(e⁺e^-→B_s^*B̅ _s^*)<0.16 and [σ(e⁺e^-→B_sB̅ _s^*)+σ(e⁺e^-→B_s^*B̅ _s)]/σ(e⁺e^-→B_s^*B̅ _s^*)<0.16 (90% C.L.). The mass of the B_s^* meson is measured to be M_Bs^*=[5.414±0.001(stat)±0.003(syst)]  GeV/c².

We describe a search for ψ(3770) decay to two-body non-DD̅ final states in e⁺e^- data produced by the CESR collider and analyzed with the CLEO-c detector. Vector-pseudoscalar production ρ⁰π⁰, ρ⁺π^-, ωπ⁰, ϕπ⁰, ρη, ωη, ϕη, ρη^′, ωη^′, ϕη^′, K^*0K⁰̅ , and K^*+K^- is studied along with that of b₁π (b₁⁰π⁰ and b₁⁺π^-) and π⁺π^-π⁰. The largest amount of disagreement between the expected rate for e⁺e^-→γ^*→X and that for e⁺e^-→X at sqrt[s]=3.773   GeV is found for X=ϕη, at an excess cross section of (2.4±0.6)   pb [Γ_ϕη^ψ(3770)=(7.4±1.6)   keV], and a suggestive suppression is seen for π⁺π^-π⁰ and ρπ. We conclude with form factor determinations for ωπ⁰, ρη, and ρη^′.

Using 20.7  pb^-1 of e⁺e^- annihilation data taken at sqrt[s]=3.671  GeV with the CLEO-c detector, precision measurements of the electromagnetic form factors of the charged pion, charged kaon, and proton have been made for timelike momentum transfer of |Q²|=13.48  GeV² by the reaction e⁺e^-→h⁺h^-. The measurements are the first ever with identified pions and kaons of |Q²|>4  GeV², with the results F_π(13.48  GeV²)=0.075±0.008(stat)±0.005(syst) and F_K(13.48  GeV²)=0.063±0.004(stat)±0.001(syst). The result for the proton, assuming G_E^p=G_M^p, is G_M^p(13.48  GeV²)=0.014±0.002(stat)±0.001(syst), which is in agreement with earlier results.

We use data collected by the CLEO III detector at the Cornell Electron Storage Ring to measure the inclusive yields of D_s mesons as B(Υ(5S)→D_sX)=(44.7±4.2±9.9)% and B(Υ(4S)→D_sX)=(18.1±0.5±2.8)%. From these measurements, we make a model dependent estimate of the ratio of B_s^(*)B̅ _s^(*) to the total bb̅ quark pair production of (16.0±2.6±5.8)% at the Υ(5S) energy.

We extract a relatively precise value for the decay constant of the D⁺ meson by measuring B(D⁺→μ⁺ν)=(4.40±0.66_-0.12^+0.09)×10^-4 using 281  pb^-1 of data taken on the ψ(3770) resonance with the CLEO-c detector. We find f_D⁺=(222.6±16.7_-3.4^+2.8)  MeV, and compare with current theoretical calculations. We also set a 90% confidence upper limit on B(D⁺→e⁺ν)<2.4×10^-5 which constrains new physics models.

The spin-singlet P-wave state of charmonium, h_c(¹P₁), has been observed in the decay ψ(2S)→π⁰h_c followed by h_c→γη_c. Inclusive and exclusive analyses of the M(h_c) spectrum have been performed. Two complementary inclusive analyses select either a range of energies for the photon emitted in h_c→γη_c or a range of values of M(η_c). These analyses, consistent with one another within statistics, yield M(h_c)=[3524.9±0.7  (stat)±0.4  (sys)]  MeV/c² and a product of the branching ratios B_ψ(ψ(2S)→π⁰h_c)×B_h(h_c→γη_c)=[3.5±1.0  (stat)±0.7  (sys)]×10^-4. When the η_c is reconstructed in seven exclusive decay modes, 17.5±4.5 h_c events are seen with an average mass M(h_c)=[3523.6±0.9  (stat)±0.5  (sys)]  MeV/c², and B_ψB_h=[5.3±1.5  (stat)±1.0  (sys)]×10^-4. If combined, the inclusive and exclusive data samples yield an overall mass M(h_c)=[3524.4±0.6  (stat)±0.4  (sys)]  MeV/c² and product of branching ratios B_ψB_h=[4.0±0.8  (stat)±0.7  (sys)]×10^-4. The h_c mass implies a P-wave hyperfine splitting ΔM_HF(1P)≡⟨M(1³P)⟩-M(1¹P₁)=[1.0±0.6  (stat)±0.4  (sys)]  MeV/c².

Using 0.8×10⁶ D⁺D^- pairs collected with the CLEO-c detector at the ψ(3770) resonance, we have searched for flavor-changing neutral current and lepton-number-violating decays of D⁺ mesons to final states with dielectrons. We find no indication of either, obtaining 90% confidence level upper limits of B(D⁺→π⁺e⁺e^-)<7.4×10^-6, B(D⁺→π^-e⁺e⁺)<3.6×10^-6, B(D⁺→K⁺e⁺e^-)<6.2×10^-6, and B(D⁺→K^-e⁺e⁺)<4.5×10^-6.

With the first data sample collected by the CLEO-c detector at the ψ(3770) resonance we have studied four exclusive semileptonic decays of the D⁰ meson. Our results include the first observation and absolute branching fraction measurement for D⁰→ρ^-e⁺ν_e and improved measurements of the absolute branching fractions for D⁰ decays to K^-e⁺ν_e, π^-e⁺ν_e, and K^*-e⁺ν_e.

Using data collected at the ψ(3770) resonance with the CLEO-c detector at the Cornell e⁺e^- storage ring, we present improved measurements of the absolute branching fractions of D⁺ decays to K̅ ⁰e⁺ν_e, π⁰e⁺ν_e, K̅ ^*0e⁺ν_e, and ρ⁰e⁺ν_e, and the first observation and absolute branching fraction measurement of D⁺→ωe⁺ν_e. We also report the most precise tests to date of isospin invariance in semileptonic D⁰ and D⁺ decays.

Using 3.08×10⁶ ψ(2S) decays observed in e⁺e^- collisions by the CLEO detector, we present the results of a study of the ψ(2S) decaying into baryon-antibaryon final states. We report the most precise measurements of the following eight modes: pp̅ , ΛΛ̅ , Σ⁺Σ⁺̅ (first observation), Σ⁰Σ⁰̅ , Ξ^-Ξ^-̅ , and Ξ⁰Ξ⁰̅ (first observation), and place upper limits for the modes Ξ(1530)⁰Ξ(1530)⁰̅ and Ω^-Ω^-̅ .