An experimental investigation of the structure of identified quark and gluon jets is presented. Observables related to both the global and internal structure of jets are measured; this allows for test
The measured jet broadening distributions (B) in quark and gluon jets seperately.
Measured distributions of -LN(Y2), where Y2 is the differential one-subjet rate, that is the value of the subjet scale parameter where 2 jets appear from the single jet.
The mean subjet multiplicity (-1) for gluon jets and quark jets for different values of the subject resolution parameter Y0.
A search is performed for the production of the ψ(2S) in e+e− annihilation at a center-of-mass energy of 4.03 GeV using the BES detector operated at the Beijing Electron Positron Collider (BEPC). The kinematic features of the reconstructed ψ(2S) signal are consistent with its being produced only in association with an energetic photon resulting from initial state radiation (ISR). Limits are placed on ψ(2S) production from the decay of unknown charmonia or metastable hybrids that might be produced in e+e− annihilations at 4.03 GeV. Under the assumption that the observed cross section for ψ(2S) production is due entirely to ISR, the partial width Γee of the ψ(2S) is measured to be 2.07±0.32keV.
PSI(UNSPEC) is considered as a new 3D2 charmonium state. CHI/C(UNSPEC) is considered as any unknown charmonium state. EXOTIC is considered as a metastable hybrid.
A systematic study of the spectra and yields of K+ and K− is reported by experiment E866 as a function of centrality in Au+Au collisions at 11.6A GeV/c. The invariant transverse spectra for both kaon species are well described by exponentials in mt, with inverse slope parameters that are largest at midrapidity and which increase with centrality. The inverse slopes of the K+ spectra are slightly larger than the inverse slopes of the K− spectra. The kaon rapidity density peaks at midrapidity with the K+ distribution wider in rapidity than K−. The integrated total yields of K+ and K− increase nonlinearly and steadily with the number of projectile participants. The yield per participant for kaons is two to three times larger than the yield from N−N collisions. This enhancement suggests that the majority of kaons in central Au+Au reactions are produced in secondary hadronic collisions. There is no evidence for an onset of additional kaon production from a possible small volume of baryon-rich quark-gluon plasma. The differences between K+ and K− rapidity distributions and transverse spectra are consistent with a lower phase space for K− production due to a higher energy threshold. These differences also exclude simple thermal models that assume emission from a common equilibrated system.
In this case FRAGB=NUCLEAR FRAG + PROTONS.
In this case FRAGB = NUCLEAR FRAG + PROTONS.
This paper presents a large solid angle measurement of the positive pion absorption cross section on 4He and its decomposition into partial channels. The total absorption cross sections at incident pion kinetic energies of Tπ+=70, 118, 162, and 239 MeV are 35±5, 52±4, 51±5, and 27±2 mb, respectively. These values are lower than those reported in some previous experiments. At all pion energies a large fraction of the absorption cross section is due to multinucleon channels.
Data with (C=PRC) are taken from PR C56, 1872.
The total cross section of the 4He(π+,π−) reaction was measured for π+ kinetic energies ranging from 70 to 130 MeV using the CHAOS spectrometer at TRIUMF and a liquid 4He target. Around Tπ=90MeV, total cross sections exceed conventional model predictions by a factor of 3, whereas at Tπ=70MeV and for Tπ>130MeV the data are consistent with these calculations. An attempt is made to understand this behavior by assuming the production of the hypothetical d′ dibaryon.
Double charge exchange reaction. section.
We have studied the two reactions 12C(π+,pp) and 12C(π+,ppp) in one experiment, using the CHAOS spectrometer at TRIUMF, at incident pion energies of 200, 240, and 280 MeV. In both cases, we are able to distinguish between reaction mechanisms involving only the detected protons, and those in which additional nucleons must have participated, on the basis of missing momentum. In the case of 12C(π+,ppp), we identify events due to the two step process of π+p quasielastic scattering followed by two-nucleon absorption. Estimates are made for the total cross sections for the various absorption mechanisms.
The total observed cross sections are not corrected for limited experimental acceptance. No errors are given. The comments (C=MNKO), (C=2NP), and (C=GT2NP) stand for multy nucleon knockout, 2 nucleons participated, and more than 2 nucleons participated, respectively.
A high resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive ( p , e + e − ) and ( p , γ) reactions on deuterium at 98 and 176 MeV. The ( p , e + e − ) cross sections, obtained at 40° and 80°, are compared with the corresponding data for the ( p , γ) reaction measured with the same apparatus. At small virtual photon masses the ( p , e + e − ) cross sections show significant enhancement over what is expected from model calculations, a behaviour which has earlier been observed also for the 11 B( p , e + e − ) 12 C reaction.
No description provided.
Data in the range of virtual photon masses: (2*mass(electron) - 8 ) Me V.
New experimental results on the π + d → π + π − pp and π + d → π + π + nn reactions at T π 1 = 283 MeV are presented. In-plane coincidence data were taken with the CHAOS spectrometer using pions from the M11 channel at TRIUMF. Because of the quasi-free nature of the pion-production reaction, the present study is equivalent to studying the elementary π + N → π + π ± N reactions on protons and neutrons simultaneously. These exclusive measurements provide a set of many-fold differential cross sections which are an ideal testing ground for microscopic models describing the πN → ππN reaction. The interpretation of the data relies on a model which is based on effective chiral Lagrangians to describe the piece of the reaction that includes only π's and N 's, and on effective Lagrangians to account for intermediate Δ's and N ∗ ' s . The measured many-fold differential cross sections are used to constrain some parameters of the model (ξ, f Δ , C, g N ∗ Δπ and g N ∗ Nπ ). Finally, the π + π ± invariant mass distributions display no evidence of strongly interacting pion pairs in either the I = J = 0 or the I = 2 J = 0 channels.
No description provided.
No description provided.
Enhanced production of strange baryons and anti-baryons at central rapidity in S-W and S-z.sbnd;S with respect to p-A reactions has been reported by the CERN experiments WA85 and WA94. The WA97 experiment is extending such a study to Pb Pb collisions making use of the newly developed silicon pixel detectors. Results on Λ, Ξ − and Ω − production in Pb Pb collisions at 158 A GeV/ c at central rapidity are presented. Transverse mass spectra and particle ratios are presented. Hyperon yields are given as a function of the collision centrality and compared with those obtained from p-Pb collisions using the same experimental setup.
No description provided.
No description provided.
No description provided.
Data on φ -production obtained by the CERN NA49 experiment for central Pb+Pb collisions at 158 GeV/u are presented. Compared with pp interactions the φ -yield shows substantial strangeness enhancement: the φ /π ratio is found to increase by a factor of 2.6 ± 0.6, which is approximately the square of the K/π enhancement.
5% most central collosions, MT - M0 = 0 - 1.4 GeV, preliminary data.
5% most central events.
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