This letter reports the full reconstruction of B mesons through the decay chain B±→J/ψ K±, J/ψ→μ+μ−, using data obtained at the Collider Detector at Fermilab in p¯p collisions at √s =1.8 TeV. This exclusive sample, the first observed at a hadron collider, is then used to measure the B-meson cross section, from which we extract the b-quark cross section. We obtain σ=2.8±0.9 (stat) ±1.1(syst) μb for B− mesons with PT>9.0 GeV/c and rapidity ‖y‖<1.0. We obtain σ=6.1±1.9(stat) ±2.4(syst) μb, for b quarks with transverse momentum PT>11.5 GeV/c and rapidity ‖y‖<1.0.
B-meson cross section.
B-quark cross section.
We present the first polarization measurements for pion absorption on a nucleus heavier than the deuteron. The polarization of protons resulting from π+ absorption in the He3 was measured at bombarding energies of 120 and 250 MeV. Protons from absorption in a quasideuteron were selected by applying kinematical constraints. A significant discrepancy was observed between the experimental results and theoretical predictions. At 120 MeV the measured polarizations for He3 are consistent with those of the deuteron. At 250 MeV the angular distribution of the polarization is significantly different than for the deuteron, showing sensitivity to the nuclear density, and thus may be sensitive to short range correlations between nucleons.
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We report measurements of d¯, p¯, K−, and π− produced at 0° in collisions of 14.6A GeV/c Si28 on Al, Cu, and Au targets. A beam-line focusing spectrometer was used to identify particles at rigidities from -2 to -8 GV. The ratio of d¯/p¯ invariant cross sections at midrapidity (y=1.7) is (1±0.7)×10−5, larger than expected from a calculation of dd¯ direct production but smaller than predicted by a simple coalescence model. We also report limits on the production of exotic particles.
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The B0 B¯ 0 average mixing parameter χ has been extracted from eμ and ee events produced in pp¯ collisions at √s =1.8 TeV. In a sample of 900 eμ events, the like-sign to opposite-sign charge ratio R is measured to be 0.556±0.048(stat)−0.042+0.035(syst). In the absence of mixing, the expected value of R would be 0.23±0.06. The corresponding number for 212 ee events is 0.573±0.116(stat)±0.047(syst) with an expected nonmixing value of 0.24±0.07. The observed excess in R leads to a combined determination of χ=0.176±0.031(stat+syst) ±0.032 (model), where the last uncertainty is due to Monte Carlo modeling.
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The value of the strong coupling constant,$$\alpha _s (M_{Z^0 } )$$, is determined from a study of 15 d
Differential jet mass distribution for the heavier jet using method T. The data are corrected for the finite acceptance and resolution of the detector and for initial state photon radiation.
Differential jet mass distribution for the jet mass difference using methodT. The data are corrected for the finite acceptance and resolution of the detec tor and for initial state photon radiation.
Differential jet mass distribution for the heavier jet using method M. The data are corrected for the finite acceptance and resolution of the detector and for initial state photon radiation.
A systematic set of measurements of the global transverse energy distributions, dσ/dET and dET/dη, from beams of protons, O16 and Si28 at 14.6A GeV/c, incident on targets ranging from Be to Au is presented. The detector was a semicircular array of lead-glass blocks, covering polar angles 9°<θ<32°, whose total response provides a good measure of the produced particle yield in the central rapidity region of these reactions. Proton-nucleus spectra exhibit a similar shape on the high-energy tail, independent of target, suggesting that produced particles in such events arise mostly from the first collision of the projectile proton. For targets heavier than Cu, the high-energy edges of the oxygen-nucleus spectra, and of the silicon-nucleus spectra, reach ratios consistent with the geometry of central collisions. Angular distributions, dET/dη, are characterized by Gaussian fits, and an acceptance-independent form of the differential cross section is found, based on the maximum value of dET/dη. The projectile dependence of nucleus-nucleus spectra is studied in terms of two very different models: simple energy scaling and the wounded projectile nucleon model of p+A convolutions.
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The process e + e − →e + e − μ + μ − has been studied in single-tag and double-tag configurations using the TOPAZ detector at TRISTAN. The data correspond to the integrated luminosity of 45.3pb − at center-of-mass energies ranging from 52 to 61.4 GeV. The observed events in both configurations have shown a good agreement with QED predictions in order α 4 . Although the AMY group reported an excess of e + e − →e + e − μ + μ − events in double-tag mode at low muon invariant mass region less than 1.0 GeV/c 2 , we did not observed such excess in our data.
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An experimental study of b-quark jets using high- p T electrons was carried out at √ s =58 GeV with the TOPAZ detector at the e + e − collider TRISTAN at KEK. The forward-backward charge asymmetry of the b-quark was obtained to be A b b ̄ =−0.55±0.27( stat. )±0.07( syst. ) , consistent with the standard model prediction. Also, such jet properties of the b-quark as the average charged multiplicity and the rapidity of charged particles were analyzed. In order to purify the b-quark event samples in this analysis, only events with backward-going electrons or forward-going positrons were used. The energy dependence of these jet properties was studied by making comparisons with the results of the DELCO experiment at the PEP collider (√ s =29 GeV) at SLAC.
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Mean values of jet properties for b-jet sample.
The proton elastic electric and magnetic form factors, GEp(Q2) and GMp(Q2), have been separately measured in the range Q2=1.75 to 8.83 (GeV/c)2, more than doubling the Q2 range of previous data. Scaled by the dipole fit, GD(Q2), the results for GMp(Q2)/μpGD(Q2) decrease smoothly from 1.05 to 0.91, while GEp(Q2)/GD(Q2) is consistent with unity. Comparisons are made to QCD sum rule, diquark, constitutent quark, and vector meson dominance models, none of which agree with all of the new data. The ratio Q2F2/F1 approaches a constant value for Q2>3 (GeV/c)2.
Magnetic form factors.
Electric form factors.
We present a measurement of the cross section for production of isolated prompt photons in p¯p collisions at √s =1.8 TeV. The cross section, measured as a function of transverse momentum (PT), agrees qualitatively with QCD calculations but has a steeper slope at low PT.
Additional normalization systematic uncertainty of 27 pct for first eleven entries, and +32 pct(-46 pct) for last four entries.
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