Observation of B_s Production at the Y(5S) Resonance

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 ^*)=[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_(B_s^*=[5.414±0.001(stat)±0.003(syst)]  GeV/c^2

Test beam studies of silicon timing for use in calorimetry

The high luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN is expected to provide instantaneous luminosities of 5×10^(34) cm^(−2) s^(−1). The high luminosities expected at the HL-LHC will be accompanied by a factor of 5–10 more pileup compared with LHC conditions in 2015, further increasing the challenge for particle identification and event reconstruction. Precision timing allows us to extend calorimetric measurements into such a high density environment by subtracting the energy deposits from pileup interactions. Calorimeters employing silicon as the active component have recently become a viable choice for the HL-LHC and future collider experiments which face very high radiation environments. In this paper, we present studies of basic calorimetric and precision timing measurements using a prototype composed of tungsten absorber and silicon sensor as the active medium. We show that for the bulk of electromagnetic showers induced by electrons in the range of 20–30 GeV, we can achieve time resolutions better than 25 ps per single pad sensor

Precision Timing with Silicon Sensors for Use in Calorimetry

The high luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN is expected to provide instantaneous luminosities of 5 × 10^(34) cm^(−2) s^(−1). The high luminosities expected at the HL-LHC will be accompanied by a factor of 5 to 10 more pileup compared with LHC conditions in 2015, causing general confusion for particle identification and event reconstruction. Precision timing allows to extend calorimetric measurements into such a high density environment by subtracting the energy deposits from pileup interactions. Calorimeters employing silicon as the active component have recently become a popular choice for the HL- LHC and future collider experiments which face very high radiation environments. We present studies of basic calorimetric and precision timing measurements using a prototype composed of tungsten absorber and silicon sensor as the active medium. We show that for the bulk of electromagnetic showers induced by electrons in the range of 20 GeV to 30 GeV, we can achieve time resolutions better than 25 ps per single pad sensor

The factorizable amplitude in B0→π+π−B^0 \to \pi^+ \pi^-

Using the measured spectrum shape for $B \to \pi \ell \nu$, the rate for $B^+ \to \pi^+ \pi^0$, information on the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $|V_{ub}|$, and theoretical inputs from factorization and lattice gauge theory, we obtain an improved estimate of the ``tree'' contribution to $B^0 \to \pi^+ \pi^-$. We find the branching ratio \b(B^0 \to \pi^+ \pi^-)|_{\rm tree} = (5.25^{+1.67}_{-0.50}) \times 10^{-6}, to be compared with the experimental value \b(B^0 \to \pi^+ \pi^-) = (4.55 \pm 0.44) \times 10^{-6}. The fit implies $|V_{ub}| = (3.62 \pm 0.34) \times 10^{-3}$. Implications for tree-penguin interference in $B^0 \to \pi^+ \pi^-$ and for other charmless $B$ decays are discussed.Comment: 11 pages, LaTeX, 3 figures, to be submitted to Phys. Rev.

Inclusive Measure of |V_ub| with the Analytic Coupling Model

By analyzing B -> X_u l nu_l spectra with a model based on soft-gluon resummation and an analytic time-like QCD coupling, we obtain |V_ub| = (3.76 +-0.13 +- 0.22)*10^(-3), where the first and the second error refers to experimental and theoretical errors, respectively. The V_ub value is obtained from the available measured semileptonic branching fractions in limited regions of the phase-space. The distributions in the lepton energy E_l, the hadron invariant mass m_X, the light-cone momentum P_+ = E_X - p_X, together with the double distributions in (m_X,q^2) and (E_l,s_h^max), are used to select the phase-space regions. The q^2 is the dilepton squared momentum and s_h^max is the maximal m_X^2 at fixed q^2 and E_l. The V_ub value obtained is in complete agreement with the value coming from exclusive B decays and from an over-all fit to the Standard Model parameters. We show that the slight disagreement (up to +2 sigma) with respect to previous inclusive measurements is not related to different choices for the b (and c) masses but to a different modelling of the threshold (Sudakov) region.Comment: 19 pages, 2 figures, revised version accepted in Eur.Phys.J.

B→η(η′)K(π)B \to \eta(\eta') K(\pi) in the Standard Model with Flavor Symmetry

The observed branching ratios for $B\to K \eta'$ decays are much larger than factorization predictions in the Standard Model (SM). Many proposals have been made to reconcile the data and theoretical predictions. In this paper we study these decays within the SM using flavor U(3) symmetry. If small annihilation amplitudes are neglected, one needs 11 hadronic parameters to describe $B\to PP$ decays where $P$ can be one of the $\pi$, $K$, $\eta$ and $\eta'$ nonet mesons. We find that existing data are consistent with SM with flavor U(3) symmetry. We also predict several measurable branching ratios and CP asymmetries for $B \to K (\pi) \eta(\eta')$, $\eta(\eta')\eta(\eta')$ decays. Near future experiments can provide important tests for the Standard Model with flavor U(3) symmetry.Comment: 13 pages, 4 table

First beam tests of prototype silicon modules for the CMS High Granularity Endcap Calorimeter

The High Luminosity phase of the Large Hadron Collider will deliver 10 times more integrated luminosity than the existing collider, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry. As part of its upgrade program, the Compact Muon Solenoid collaboration is designing a high-granularity calorimeter (HGCAL) to replace the existing endcap calorimeters. It will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The electromagnetic section and a large fraction of the hadronic section will be based on hexagonal silicon sensors of 0.5–1 cm^2 cell size, with the remainder of the hadronic section being based on highly-segmented scintillators with silicon photomultiplier readout. The intrinsic high-precision timing capabilities of the silicon sensors will add an extra dimension to event reconstruction, especially in terms of pileup rejection. First hexagonal silicon modules, using the existing Skiroc2 front-end ASIC developed for CALICE, have been tested in beams at Fermilab and CERN in 2016. We present results from these tests, in terms of system stability, calibration with minimum-ionizing particles and resolution (energy, position and timing) for electrons, and the comparisons of these quantities with GEANT4-based simulation

Measurement of the B-Meson Inclusive Semileptonic Branching Fraction and Electron-Energy Moments

We report a new measurement of the B-meson semileptonic decay momentum spectrum that has been made with a sample of 9.4/fb of electron-positron annihilation data collected with the CLEO II detector at the Y(4S) resonance. Electrons from primary semileptonic decays and secondary charm decays were separated by using charge and angular correlations in Y(4S) events with a high-momentum lepton and an additional electron. We determined the semileptonic branching fraction to be (10.91 +- 0.09 +- 0.24)% from the normalization of the electron-energy spectrum. We also measured the moments of the electron energy spectrum with minimum energies from 0.6 GeV to 1.5 GeV.Comment: 36 pages postscript, als available through http://w4.lns.cornell.edu/public/CLNS/, Submitted to PRD (back-to-back with preceding preprint hep-ex/0403052

A Search for Charmless B→VVB\to VV Decays

We have studied two-body charmless decays of the $B$ meson into the final states $\rho^0 \rho^0$, $K^{*0} \rho^0$, $K^{*0} K^{*0}$, $K^{*0} \bar{K^{*0}}$, $K^{*+} \rho^0$, $K^{*+} \bar{K^{*0}}$, and $K^{*+} K^{*-}$ using only decay modes with charged daughter particles. Using 9.7 million $B \bar{B}$ pairs collected with the CLEO detector, we place 90% confidence level upper limits on the branching fractions, $(0.46-7.0)\times 10^{-5}$, depending on final state and polarization.Comment: 8 pages postscript, also available through http://w4.lns.cornell.edu/public/CLN

Correlated /\c-/\cbar production in e+e- annihilations at sqrt{s}~10.5 GeV

Using 13.6/fb of continuum two-jet e+e- -> ccbar 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 /\c+ charmed baryon to be produced in the hemisphere opposite a /\c- relative to the likelihood for a /\c+ charmed baryon to be produced opposite an anticharmed meson Dbar; in all cases, the reconstructed hadrons must have momentum greater than 2.3 GeV/c. We find that, given a /\c- (reconstructed in five different decay modes), a /\c+ is observed in the opposite hemisphere (0.72+/-0.11)% of the time (not corrected for efficiency). By contrast, given a Dbar in one hemisphere, a /\c+ is observed in the opposite hemisphere only (0.21+/-0.02)% of the time. Normalized to the total number of either /\c- or Dbar ``tags'', it is therefore 3.52+/-0.45+/-0.42 times more likely to find a /\c+ opposite a /\c- than a Dbar meson. This enhancement is not observed in the JETSET 7.3 e+e- -> ccbar Monte Carlo simulation.Comment: 19 pages, Latex, one figure separat