Search Results (249 total)

The reliability and validity of professionally written multiple-choice exams have been extensively studied for exams such as the SAT, graduate record examination, and the force concept inventory. Much of the success of these multiple-choice exams is attributed to the careful construction of each question, as well as each response. In this study, the reliability and validity of scores from multiple-choice exams written for and administered in the large introductory physics courses at the University of Illinois, Urbana-Champaign were investigated. The reliability of exam scores over the course of a semester results in approximately a 3% uncertainty in students’ total semester exam score. This semester test score uncertainty yields an uncertainty in the students’ assigned letter grade that is less than 1 / 3 of a letter grade. To study the validity of exam scores, a subset of students were ranked independently based on their multiple-choice score, graded explanations, and student interviews. The ranking of these students based on their multiple-choice score was found to be consistent with the ranking assigned by physics instructors based on the students’ written explanations (r>0.94 at the 95% confidence level) and oral interviews (r=0.94_−0.09^+0.06).

We describe several measurements using the decays D⁰→K⁺K^- and π⁺π^-. We find the ratio of partial widths, Γ(D⁰→K⁺K^-)/Γ(D⁰→π⁺π^-), to be 2.96±0.16±0.15, where the first error is statistical and the second is systematic. We observe no evidence for direct CP violation, obtaining A_CP(KK)=(0.0±2.2±0.8)% and A_CP(ππ)=(1.9±3.2±0.8)%. In the limit of no CP violation we measure the mixing parameter y_CP=-0.012±0.025±0.014 by measuring the lifetime difference between D⁰→K⁺K^- or π⁺π^- and the CP neutral state, D⁰→K^-π⁺. We see no evidence for mixing.

We present the first measurement of the D^*+ width using 9/fb of e⁺e^- data collected near the Υ(4S) resonance by the CLEO II.V detector. Our method uses advanced tracking techniques and a reconstruction method that takes advantage of the small vertical size of the CESR beam spot to measure the energy release distribution from the D^*+→D⁰π⁺ decay. We find Γ(D^*+)=96±4 (statistical)±22 (systematic) keV. We also measure the energy release in the decay and compute Δm≡m_D^*+-m_D⁰=145.412±0.002 (statistical)±0.012 (systematic) MeV/c².

We have searched for the charmless hadronic decay of B⁰ mesons into two neutral pions. Using 9.13 fb^-1 taken at the Υ(4S) with the CLEO detector, we obtain an improved upper limit for the branching fraction B(B⁰→π⁰π⁰)<5.7×10^-6 at the 90% confidence level.

We have studied two-body charmless decays of the B meson into the final states ρ⁰ρ⁰, K^*0ρ⁰, K^*0K^*0, K^*0K̅ ^*0, K^*+ρ⁰, K^*+K̅ ^*0, and K^*+K^*- using only decay modes with charged daughter particles. Using 9.7×10⁶ BB̅ pairs collected with the CLEO detector, we place 90% confidence level upper limits on the branching fractions (1.4–14.1)×10^-5, depending on final state and polarization.

We have searched for the two-body decay of the B meson to a light pseudoscalar meson h  =  π^±,K^±,K_S⁰ and a massless neutral feebly interacting particle X⁰ such as the familon, the Nambu-Goldstone boson associated with a spontaneously broken global family symmetry. We find no significant signal by analyzing a data sample containing 9.7×10⁶ BB̅ mesons collected with the CLEO detector at the Cornell Electron Storage Ring, and set 90% C.L. upper limits B(B^±→h^±X⁰)  =  4.9×10^-5 and B(B⁰→K_S⁰X⁰)  =  5.3×10^-5. These limits correspond to a lower bound of approximately 10⁸ GeV on the family symmetry breaking scale with vector coupling involving the third generation of quarks.

We report on the observation of B⁰→D^*0π⁺π⁺π^-π^- decays. The branching ratio is (0.30±0.07±0.06)%. Interest in this particular mode was sparked by Ligeti, Luke and Wise who propose it as a way to check the validity of factorization tests in B⁰→D^*+π⁺π^-π^-π⁰ decays.

We have measured the first and second moments of the hadronic mass-squared distribution in B→X_cℓν, for P_lepton>1.5 GeV/c. We find 〈M_X²-M̅ _D²〉  =  0.251±0.066 GeV², 〈(M_X²-〈M_X²〉)²〉  =  0.576±0.170 GeV⁴, where M̅ _D is the spin-averaged D meson mass. From that first moment and the first moment of the photon energy spectrum in b→sγ, we find the heavy quark effective theory parameter λ₁ (in the modified minimal subtraction renormalization scheme, to order 1/M_B³ and β₀α_s²) to be -0.24±0.11 GeV². Using these first moments and the B semileptonic width, and assuming parton-hadron duality, we obtain |V_cb|  =  0.0404±0.0013.

We have measured the branching fraction and photon energy spectrum for the radiative penguin process b→sγ. We find B(b→sγ)  =  (3.21±0.43±0.27_-0.10^+0.18)×10^-4, where the errors are statistical, systematic, and from theory corrections. We obtain first and second moments of the photon energy spectrum above 2.0 GeV, 〈E_γ〉  =  2.346±0.032±0.011 GeV, and 〈E_γ²〉-〈E_γ〉²  =  0.0226±0.0066±0.0020 GeV², where the errors are statistical and systematic. From the first moment, we obtain (in the modified minimal subtraction renormalization scheme, to order 1/M_B³ and β₀α_s²) the heavy quark effective theory parameter Λ̅  =  0.35±0.08±0.10 GeV.

We present the first measurement of the D^*+ width using 9/fb of e⁺e^- data collected near the ϒ(4S) resonance by the CLEO II.V detector. Our method uses advanced tracking techniques and a reconstruction method that takes advantage of the small vertical size of the Cornell Electron-positron Storage Ring beam spot to measure the energy release distribution from the D^*+→D⁰π⁺ decay. We find Γ(D^*+)  =  96±4 (stat)±22 (syst) keV. We also measure the energy release in the decay and compute Δm≡m_D^*+-m_D⁰  =  145.412±0.002 (stat)±0.012 (syst) MeV/c².

We present a search for the “wrong-sign” decay D⁰→K⁺π^-π⁺π^- using 9 fb^-1 of e⁺e^- collisions on and just below the Υ(4S) resonance. This decay can occur either through a doubly Cabibbo-suppressed process or through mixing to a D⁰ followed by a Cabibbo-favored process. Our result for the time-integrated wrong-sign rate relative to the decay D⁰→K^-π⁺π^-π⁺ is (0.0041_-0.0011^+0.0012(stat)±0.0004(syst))×(1.07±0.10)(phase space), which has a statistical significance of 3.9 standard deviations.

We have searched a sample of 9.6×10⁶ BB̅ events for the flavor-changing neutral current decays B→Kℓ⁺ℓ^- and B→K^*(892)ℓ⁺ℓ^-. We subject the latter decay to the requirement that the dilepton mass m_ℓℓ exceed 0.5 GeV. There is no indication of a signal. We obtain the 90% confidence level upper limits B(B→Kℓ⁺ℓ^-)<1.7×10^-6 and B(B→K^*(892)ℓ⁺ℓ^-)_{mℓℓ>0.5 GeV}<3.3×10^-6. We also obtain an upper limit on the weighted average 0.65B(B→Kℓ⁺ℓ^-)+0.35B(B→K^*(892)ℓ⁺ℓ^-)_{mℓℓ>0.5 GeV}<1.5×10^-6. The weighted-average limit is only 50% above the standard model prediction.

We search for CP nonconservation in the decays of τ leptons produced via e⁺e^- annihilation at sqrt[s]∼10.6 GeV. The method uses correlated decays of pairs of τ leptons, each decaying to the ππ⁰ν_τ final state. The search is done within the framework of a model with a scalar boson exchange. In an analysis of a data sample corresponding to 12.2×10⁶ produced τ pairs collected with the CLEO detector, we find no evidence of violation of CP symmetry. We obtain a limit on the imaginary part of the coupling constant parametrizing the relative contribution of diagrams that would lead to CP violation to be -0.046<Im(Λ)<0.022 at 90% C.L. This result provides a restriction on CP nonconservation in tau lepton decays. As a cross-check, we study the decay angular distribution and perform a model-independent search for a CP violation effect of a scalar exchange in single τ→ππ⁰ν_τ decays. The limit on the imaginary part of the τ scalar coupling is -0.033<Im(Λ)<0.089 at 90% C.L.

We report on the observation of B̅ →D^*π⁺π^-π^-π⁰ decays. The branching ratios for D^*+ and D^*0 are (1.72±0.14±0.24)% and (1.80±0.24±0.27)%, respectively. Each final state has a D^*ωπ^- component, with branching ratios (0.29±0.03±0.04)% and (0.45±0.10±0.07)% for the D^*+ and D^*0 modes, respectively. We also observe B̅ →Dωπ^- decays. The branching ratios for D⁺ and D⁰ are (0.28±0.05±0.04)% and (0.41±0.07±0.06)%, respectively. A spin parity analysis of the ωπ^- system in the Dωπ^- final state shows a preference for a wide 1^- resonance. A fit to the ωπ^- mass spectrum finds a central mass of (1349±25_-5⁺¹⁰) MeV and width of (547±86_-45⁺⁴⁶) MeV. We identify this object as the ρ(1450) or the ρ^′.

We report on a search for the radiative decay ϒ(1S)→γη^′ in 61.3 pb^-1 of data taken with the CLEO II detector at the Cornell Electron Storage Ring. Three decay chains were investigated, all involving η^′→π⁺π^-η, followed by η→γγ, η→π⁰π⁰π⁰, or η→π⁺π^-π⁰. We find no candidate events in any of the three cases and set a combined upper limit of 1.6×10^-5 at 90% C.L., significantly smaller than the previous limit. We compare our result to other radiative ϒ decays, to radiative J/ψ decays, and to theoretical predictions.

We report on a search for the decay B⁺→D^*+K_S⁰ and its charge conjugate with the CLEO detector at the Cornell Electron Storage Ring (CESR). No candidates are found in 9.10 fb^-1 of data. The background is estimated to be 0.29±0.05 leading to an upper limit B(B⁺→D^*+K⁰)=9.5×10^-5 (90% confidence level).

We present an observation and time-integrated rate measurement of the decay D⁰→K⁺π^-π⁰ produced in 9 fb^-1 of e⁺e^- collisions near the ϒ(4S) resonance. The signal is inconsistent with an upward fluctuation of the background by 4.9 standard deviations. We measured the time-integrated rate of D⁰→K⁺π^-π⁰ normalized to the rate of D⁰̅ →K⁺π^-π⁰ to be 0.0043_-0.0010^+0.0011 (stat)±0.0007 (syst). This decay can be produced by doubly Cabibbo-suppressed decays or by the D⁰ evolving into a D⁰̅ through mixing, followed by a Cabibbo-favored decay to K⁺π^-π⁰. We also found the CP asymmetry A  =  (9_-22⁺²⁵)% be consistent with zero.

Using 12.7 fb^-1 of data collected with the CLEO detector at CESR, we observed two-photon production of the cc̅ states χ_c0 and χ_c2 in their decay to π⁺π^-π⁺π^-. We measured Γ_γγ(χ_c)×B(χ_c→π⁺π^-π⁺π^-) to be 75±13(stat)±8(syst) eV for the χ_c0 and 6.4±1.8(stat)±0.8(syst) eV for the χ_c2, implying Γ_γγ(χ_c0)  =  3.76±0.65(stat)±0.41(syst)±1.69(br) keV and Γ_γγ(χ_c2)  =  0.53±0.15(stat)±0.06(syst)±0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of Γ_γγ(χ_c0)/Γ_γγ(χ_c2), evaluated to be 7.4±2.4(stat)±0.5(syst)±0.9(br), with QCD-based predictions.

We have measured the CP asymmetry A_CP≡[Γ(b→sγ)-Γ(b̅ →s̅ γ)]/[Γ(b→sγ)+Γ(b̅ →s̅ γ)] to be A_CP  =  (-0.079±0.108±0.022) (1.0±0.030), implying that, at 90% confidence level, A_CP lies between -0.27 and +0.10. These limits rule out some extreme non-standard-model predictions, but are consistent with most, as well as with the standard model.

We have measured the charge asymmetry in like-sign dilepton yields from B⁰B̅ ⁰ meson decays using the CLEO detector at the Cornell Electron Storage Ring. We find a_ℓℓ⁰≡[N(ℓ⁺ℓ⁺)-N(ℓ^-ℓ^-)]/[N(ℓ⁺ℓ⁺)+N(ℓ^-ℓ^-)]  =  +0.013±0.050±0.005. We combine this result with a previous, independent measurement and obtain Re(ε_B)/(1+|ε_B|²)  =  +0.0035±0.0103±0.0015 (uncertainties are statistical and systematic, respectively) for the CP impurity parameter, ε_B.

Using 13.7 fb^-1 of data recorded by the CLEO detector at the Cornell Electron Storage Ring, we investigate the spectrum of charmed baryons which decay into Λ_c⁺π^-π⁺ and are more massive than the Λ_c⁺(2625) baryon. We find evidence for two new states: one is broad and has an invariant mass roughly 480 MeV above that of the Λ_c⁺ baryon; the other is narrow with an invariant mass of 596±1±2 MeV above the Λ_c⁺ mass.

The τ decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(τ^-→2π^-π⁺3π⁰ν_τ)  =  (2.2±0.3±0.4)×10^-4 and B(τ^-→3π^-2π⁺π⁰ν_τ)  =  (1.7±0.2±0.2)×10^-4. A search for substructure in these decays shows that they are saturated by intermediate states with η or ω mesons. We present the first observation of the decay τ^-→2π^-π⁺ων_τ and the branching fraction is measured to be (1.2±0.2±0.1)×10^-4. The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.

Using 13.7 fb^-1 of data recorded by the CLEO detector at Cornell Electron Storage Ring, we report evidence of two new charmed baryons: one decaying into Ξ_c^0′π⁺ with the subsequent decay Ξ_c^0′→Ξ_c⁰γ, and its isospin partner decaying into Ξ_c^+′π^- followed by Ξ_c^+′→Ξ_c⁺γ. We measure the following mass differences for the two states: M(Ξ_c⁰γπ⁺)-M(Ξ_c⁰)  =  318.2±1.3±2.9 MeV and M(Ξ_c⁺γπ^-)-M(Ξ_c⁺)  =  324.0±1.3±3.0 MeV. We interpret these new states as the J^P  =  1 / 2^- Ξ_c1 particles, the charmed-strange analogs of the Λ_c1⁺(2593).

Using 13.6 fb^-1 of continuum two-jet e⁺e^-→cc̅ events collected with the CLEO detector, we have searched for baryon number correlations at the primary quark level. We have measured the likelihood for a Λ_c⁺ charmed baryon to be produced in the hemisphere opposite a Λ̅ _c^- relative to the likelihood for a Λ_c⁺ charmed baryon to be produced opposite an anticharmed meson D̅ ; in all cases, the reconstructed hadrons must have momentum greater than 2.3 GeV/c. We find that, given a Λ̅ _c^- (reconstructed in five different decay modes), a Λ_c⁺ is observed in the opposite hemisphere (0.72±0.11)% of the time (not corrected for efficiency). By contrast, given a D̅ in one hemisphere, a Λ_c⁺ is observed in the opposite hemisphere only (0.21±0.02)% of the time. Normalized to the total number of either Λ̅ _c^- or D̅ “tags,” it is therefore 3.52±0.45±0.42 times more likely to find a Λ_c⁺ opposite a Λ̅ _c^- than a D̅ meson. This enhancement is not observed in the JETSET 7.3 e⁺e^-→cc̅ Monte Carlo simulation.

The CLEO experiment at the CESR collider has used 13.7 fb^-1 of data to search for the production of the Ω_c⁰ (css ground state) in e⁺e^- collisions at sqrt[s]≃10.6 GeV. The modes used to study the Ω_c⁰ are Ω^-π⁺, Ω^-π⁺π⁰, Ξ^-K^-π⁺π⁺, Ξ⁰K^-π⁺, and Ω^-π⁺π⁺π^-. We observe a signal of 40.4±9.0(stat) events at a mass of 2694.6±2.6(stat)±1.9(syst) MeV/c², for all modes combined.