A. Buzzo

New measurements of the resonance parameters of the χc0(13P0) state of charmonium

Abstract The resonance parameters of the χ c 0 , the 1 3 P 0 state of charmonium, have been measured at the Fermilab Antiproton Accumulator in the reaction p p→χ c0 →γJ/ψ→γ(e + e − ) . A large data sample collected during the year 2000 run yields the results: M ( χ c 0 )=3415.4±0.4±0.2xa0MeV/ c 2 , Γ ( χ c 0 )=9.8±1.0±0.1xa0MeV, B (χ c0 → p p)× B (χ c0 →γJ/ψ)× B (J/ψ→(e + e − ))=(1.61±0.11±0.08)×10 −7 . Taking B (χ c0 →γJ/ψ) and B (J/ψ→e + e − ) from the literature, we obtain B (χ c0 → p p)=(4.1±0.3 +1.6 −0.9 )×10 −4 and Γ(χ c0 → p p)=(4.0±0.4 +1.6 −0.9 ) xa0keV.

Precision measurements of the total and partial widths of the ψ (2 S) charmonium meson with a new complementary-scan technique in over(p, ̄) p annihilations

We present new precision measurements of the {Psi}(2S) total and partial widths from excitation curves obtained in antiproton-proton annihilations by Fermilab experiment E835 at the Antiproton Accumulator in the year 2000. A new technique of complementary scans was developed to study narrow resonances with stochastically cooled antiproton beams. It relies on precise revolution-frequency and orbit-length measurements, while making the analysis of the excitation curve almost independent of machine lattice parameters. For the {Psi}(2S) meson, by studying the processes {bar p}p {yields} e{sup +}e{sup -} and {bar p}p {yields} J/{Psi} + X {yields} e{sup +}e{sup -} + X, we measure the width {Gamma} = 290 {+-} 25(sta) {+-} 4(sys) keV and the combination of partial widths {Gamma}{sub e{sup +}e{sup -}}{Gamma}{sub {bar p}p}/{Gamma} = 579 {+-} 38(sta) {+-} 36(sys) meV, which represent the most precise measurements to date.

Measurement of the resonance parameters of the χ1(13P1) and χ2(13P2) states of charmonium formed in antiproton–proton annihilations

The authors have studied the {sup 3}P{sub J} ({chi}{sub e}) states of charmonium in formation by antiproton-proton annihilations in experiment E835 at the Fermilab Antiproton Source. The authors report new measurements of the mass, width, and B({chi}{sub cJ} {yields} {bar p}p) x {Lambda}({chi}{sub eJ} {yields} J/{psi} + anything) for the {chi}{sub c1} and {chi}{sub c2} by means of the inclusive reaction {bar p}p {yields} {chi}{sub cJ} {yields} J/{psi} + anything {yields} (e{sup +}e{sup -}) + anything. Using the subsample of events where {chi}{sub cJ} {yields} {gamma} + J/{psi} {yields} {gamma} + (e{sup +}e{sup -}) is fully reconstructed, we derive B({chi}{sub cJ} {yields} {bar p}p) x {Lambda}({chi}{sub cJ} {yields} J/{psi} + {gamma}). They summarize the results of the E760 (updated) and E835 measurements of mass, width and B({chi}{sub cJ} {yields} {bar p}p){Lambda}({chi}{sub cJ} {yields} J/{psi} + {gamma}) (J = 0,1,2) and discuss the significance of these measurements.

Measurement of the resonance parameters of the charmonium ground state, ηc(11S0)

Abstract The resonance parameters of the charmonium ground state, η c (1 1 S 0 ) , have been measured by means of the reaction p p→η c →γγ . The mass and total width are determined to be 2984.1±2.1±1.0xa0MeV/ c 2 and 20.4 +7.7 −6.7 ±2.0xa0MeV, respectively. The product of branching ratios B( p p→η c )B(η c →γγ) is determined to be 22.4 +3.8 −3.7 ±2.0 ×10 −8 , from which B(η c →γγ)= 1.87 +0.32+0.95 −0.31−0.50 ×10 −4 , and Γ ( η c → γγ )=3.8 +1.1+1.9 −1.0−1.0 xa0keV are derived using B(η c → p p)=(12±4)×10 −4 from the literature.

Proton - antiproton annihilations to φφ mesons: results from JETSET at LEAR

The πp → φφ reaction has been studied in an internal target experiment at LEAR using antiprotons at various laboratory momenta spanning the region between 1 and 2 GeV/c (cms energies between 2.08 and 2.43 GeV). Cross sections have been measured at a total of 16 different energy settings over the above range. Preliminary cross sections are reported.

CHI formation by antiproton annihilations on hydrogen: Results from experiment R704 at the CERN ISR

Recent measurements of masses, total widths and branching ratios to pp of χ1 and χ2 charmonium states are reported: a novel experimental technique (circulating p beams+gas jet target) has provided excellent energy resolution, together with small background and reduced systematics.

Measurement of the angular distribution in p¯p→ψ(2S)→e+e−

We present the first measurement of the angular distribution for the exclusive process

Charmonium spectroscopy at the ISR using an antiproton beam and a hydrogen gas "jet target"

bar p p to psi(2S)to e^+e^-

Measurement of the two photon decay of the χc0(13P0) state of charmonium

based on a sample of 6844 events collected by the Fermilab E835 experiment. We find that the angular distribution is well described by the expected functional form

Measurement of the two photon decay of the ? c 0 (1 3 P 0) state ofcharmonium

frac{dN}{dcostheta^{*}}