Cornell Electron-positron Storage Ring Research Articles

Novel method of measuring electron positron colliding beam parameters

Through the simultaneous measurement of the transverse size as a function of longitudinal position, and the longitudinal distribution of luminosity, we are able to measure β y * (the vertical envelope function at the collision point), vertical emittance, and bunch length of colliding beams at the Cornell Electron–positron Storage Ring (CESR). This measurement is possible due to the significant “hourglass” effect at CESR and the excellent tracking resolution of the CLEO detector.

First measurement of gamma(D*(+)).

We present the first measurement of the D*(+) width using 9/fb of e(+)e(-) data collected near the Upsilon(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*(+)-->D(0)pi(+) decay. We find gamma(D*(+)) = 96+/-4 (stat)+/-22 (syst) keV. We also measure the energy release in the decay and compute Delta m identical with m(D*(+))-m(D(0)) = 145.412+/-0.002 (stat)+/-0.012 (syst) MeV/c(2).

Multiple bunch longitudinal dynamics measurements at the Cornell Electron-Positron Storage Ring

The Cornell Electron-Positron Storage Ring (CESR) has a longitudinal dipole-coupled-bunch instability that limits the total amount of current that can be stored in the ring without feedback. As a result, it is one of the major limitations for higher stored current and luminosity. This paper reports the measurements of multiple bunch longitudinal dynamics done on CESR with a streak camera. The camera was used to measure the dependence of the bunch distribution on current and accelerating rf voltage, for multiple bunches stored in CESR, as well as the effects of the longitudinal instability on the bunch distribution. Measurements of the beam's longitudinal bunch distribution with multiple bunches present in the ring help give an understanding of the instability, how it affects the bunch distribution, and possibly give insight into a cure of the instability.

CLEO B physics results

I summarize some recent results on B meson physics from the CLEO collaboration obtained with the Cornell electron–positron storage ring operating at the ϒ(4S) resonance: (a) determinations of the elements of the CKM matrix from semileptonic decays and (b) rare nonleptonic decays to charmless final states.

Single bunch longitudinal measurements at the Cornell Electron-Positron Storage Ring

Measurements of the beam's bunch length in the Cornell Electron-Positron Storage Ring (CESR) have been made using a streak camera. The streak camera uses visible synchrotron radiation produced by the beam to measure its longitudinal distribution. A description of CESR, the experimental setup, the streak camera used, and systematic errors and analysis techniques of the streak camera are described in this paper. The dependence of the bunch distribution on the current and accelerating rf voltage for a single bunch CESR was measured and compared with a theoretical model of CESR. The CESR vacuum chamber impedance is determined from the measured bunch distributions and is presented in this paper.

Design, performance and status of the CLEO III silicon detector

Abstract The CLEO III silicon detector is part of a general upgrade of the CLEO detector to allow for operation at a luminosity of 2×10 33 cm −2 s −1 , which will be provided by the Cornell Electron–Positron Storage Ring (CESR) beginning in 1999. The silicon detector is a four-layer barrel design covering radii from 2.5 to 10.2 cm with 93% solid angle coverage. The silicon sensors are DC-coupled and double-sided with double-metal readout on the p-side. The n-type strips measure φ , with 50 μ m pitch while the p-type strips measure z , the coordinate along the beam axis, with 100 μ m pitch. The readout electronics are mounted on BeO hybrids attached to the conical support structure and connected to the silicon sensors via a thin kapton flex cable. The electronics consist of an R / C chip with bias resistors and decoupling capacitors, a low-noise preamp/shaper chip and a digitizer/sparsifier chip. Readout is done using VME-based sequencer boards. Production of all detector components is nearing completion and installation of the detector will take place in early 1999.

The CESR-CLEO program: Present and future

The research program of the Cornell Electron-positron Storage Ring and the CLEO experiment concentrates on heavy quark and lepton physics near the e +e − → b b threshold. Since progress in b weak interaction physics is paced by the size of the data samples, the storage ring is now being upgraded to provide higher luminosity and the detector is being upgraded for improved sensitivity. A possible future upgrade now under consideration would bring CESR to a peak luminosity of 3 × 10 34 /cm 2sec.

Investigation of SemileptonicBMeson Decays top-Wave Charm Mesons

We have studied semileptonic $B$ meson decays with a P-wave charm meson in the final state using 3.29 x 10^6 B\bar{B} events collected by the CLEO~II detector at the Cornell Electron-positron Storage Ring. We find a value for the exclusive semileptonic product branching fraction: Br(B^- -> D_1^0 l^- \bar{\nu}) x Br(D_1^0 -> D^{*+}\pi^-) = (0.373 \pm 0.085 \pm 0.052 \pm 0.024)% and an upper limit for Br(B^- -> D_2^{*0} l^- \bar{\nu}) x Br(D_2^{*0} -> D^{*+}\pi^-) < 0.16%$ (90% C.L.). These results indicate that at least 20% of the total B^- semileptonic rate is unaccounted for by the observed exclusive decays, B^- -> D^0 l^- \bar{\nu}, B^- -> D^{*0} l^- \bar{\nu}, B^- -> D_1^0 l^- \bar{\nu}, and B^- -> D_2^{*0} l^- \bar{\nu}.

Observation of the dynamic beta effect at the Cornell Electron-Positron Storage Ring with the CLEO detector

Using the silicon strip detector of the CLEO experiment operating at the Cornell Electron-positron Storage Ring (CESR), we have observed that the horizontal size of the luminous region decreases in the presence of the beam-beam interaction from what is expected without the beam-beam interaction. The dependence on the bunch current agrees with the prediction of the dynamic beta effect. This is the first direct observation of the effect.

Limit on the Two-Photon Production of the Glueball CandidatefJ(2220)at the Cornell Electron Storage Ring

We use the CLEO detector at the Cornell electron-positron storage ring, CESR, to search for the two-photon production of the glueball candidate f_J(2220) in its decay to K_s K_s. We present a restrictive upper limit on the product of the two-photon partial width and the K_s K_s branching fraction. We use this limit to calculate a lower limit on the stickiness, which is a measure of the two-gluon coupling relative to the two-photon coupling. This limit on stickiness indicates that the f_J(2220) has substantial glueball content.

Operational experience of novel vacuum chambers incorporating massive titanium-sublimation pumping in the Cornell electron–positron storage ring interaction region

New vacuum chambers have recently been installed in the interaction region of the Cornell electron-positron storage ring (CESR) in order to improve the pumping and reduce the operating pressure of the collider in the vicinity of the (CLEO) detector as the beam currents are increased by a large factor. Lost-particles generated by the beams interacting with the residual gas are a major source of background in CLEO and could lead to radiation damage of sensitive components such as the new silicon vertex detector electronics installed around a two-centimeter radius beryllium beampipe. This article shows how titanium-sublimation pumps are used as an inexpensive and efficient way to attain pressures in the low nanotorr range in the face of large outgassing induced by intense synchrotron radiation. Laboratory measurements of pumping speed in these chambers using calibrated leaks are compared against performance in the ring. A history of the dynamic pressure rise in the ring (Torr/mA) since the most recent start-up of CESR will also be shown.

Measurement of the Tau Lepton lifetime at CLEO II

The τ lepton lifetime has been measured using τ + τ − pairs in which one or both of the τ 's decays into three charged particles. The method employed measures the displacement of the reconstructed tau decay vertices using 2 fb −1 of data, corresponding to approximately 2 million produced tau pairs, at energies near the(4 S ). This data was collected with the CLEO-II detector at the Cornell Electron-Positron Storage Ring (CESR). For events where both τs decayed to 3 charged tracks, the measured lifetime was τ τ =(2.85 ± 0.13 ± 0.10) × 10 −13 s. The measure lifetime for events where one τ decayed into three charged track, and the other decayed into a single charged track was τ τ =(2.91 ± 0.04 ± 0.07) × 10 −13 s.

Observations of the coherent beam-ion interaction in the CESR storage ring

The coherent interaction between the electron beam and trapped ions in the Cornell Electron/positron Storage Ring (CESR) has been seen by shaking the beam and observing the resulting beam oscillation amplitude. A linear theory is developed which enables the calculation of ion densities from the experimental measurements. Nonlinearities in the beam-ion force are shown to be important in understanding the ion trapping effects including frequency shifts of the betatron sideband resonances.

A muon identification detector for B-physics near [formula omitted] threshold

We describe the construction and performance of the muon identification system for the CLEO II detector at the Cornell Electron-positron Storage Ring (CESR). The system, based on plastic proportional tubes interleaved with an iron absorber, covers 0.85 of the total solid angle, has an identification efficiency between 0.89 and 0.99, depending on track penetration requirement, and a probability of misidentification about 0.007 for pions of 2.5 GeV and 0.030 for kaons of the same momentum.

Quantitive analysis of Laue diffraction patterns recorded with a 120 ps exposure from an X-ray undulator

X-ray Laue diffraction patterns with an exposure time of 120 ps have been obtained from single crystals of an indole alkaloid and of the enzyme lysozyme using the X-rays emitted as a single bunch of electrons traverses a hard X-ray undulator inserted in CESR, the Cornell Electron–Positron Storage Ring. The patterns were recorded on a sensitive storage-phosphor detector. Despite complexities posed by the sharp variation of the incident X-ray spectrum with wavelength and the weakness of the diffraction patterns, accurate crystallographic structure amplitudes were extracted from the Laue intensities by the generalized scale-factor approach to the determination of the wavelength- and position-dependent correction factors. The results show that crystallography is feasible on the 100 ps time scale and open up the prospect of time-resolved measurements of ultra-rapid changes in molecular structure.

MacCHESS--a macromolecular diffraction resource at the Cornell High Energy Synchrotron Source.

The Cornell High Energy Synchrotron Source (CHESS) operates within the Wilson Synchrotron Laboratory of the Laboratory of Nuclear Studies at Cornell University. CHESS runs three beamlines at the Cornell Electron-Positron Storage Ring (CESR), which are generally operated in a parasitic mode. CHESS is a national facility funded by the National Science Foundation. MacCHESS is a biomedical technology resource to promote macromolecular diffraction at CHESS, funded by the National Institutes of Health.

Particle identification by ionization measurements: Description of the CLEO [formula omitted] system

We describe the design, construction and performance of a pressurized proportional chamber system intended to identify particles by means of their energy loss in thin gas samples. The system is part of the CLEO detector at the Cornell Electron-Positron Storage Ring (CESR).

CESR shows bare-bottomed mesons

In its first year of operation, the Cornell electron–positron storage ring, CESR, has provided strong evidence for the existence of a fifth quark flavor. The three narrow upsilon mesonic states near 10 GeV, first seen at Fermilab in 1977 and 1978, had offered the initial experimental evidence for a hadronic building block heavier than the charmed quark (see PHYSICS TODAY, October 1977, page 17 and January 1979, page 17). The Γ, Γ′ and Γ″ were generally believed to be bound states of a massive new “bottom” quark, b, and its antiparticle.