We present a measurement of the photon structure functionF2γ in the reactionee→eeX forQ2 in the range 0.2<Q2<7 GeV2, using 9,200 multihadron events obtained with the TPC/Two-Gamma detector at PEP. The data have been corrected for detector effects using a regularized unfolding procedure and are presented as a function ofx andQ2. The structure function shows scaling in the region 0.3<Q2<1.6 GeV2,x<0.3 and rises for higherQ2. AtQ2=5.1 GeV2 the results are compared with QCD and, within the scheme of Antoniadis and Grunberg, rather conservative bounds for the QCD scale parameter of 133±50<\(\Lambda _{\overline {{\rm M}S} } \)<268±98 MeV are obtained. A study of the final state structure shows that the rise ofF2γ is consistent with being entirely due to the pointlike component of the photon.
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A search for stableH-dibaryon ofI=0,Y=0,JP=0+ was undertaken in negative pion-, neutron-,12C-nucleus- and proton-propane interactions at 4.0, 7.0, 50.4 and 10 GeV/c, respectively, using 55 cm and 2 m propane bubble chambers. This technique permite one to examine the whole range of possibleH-mass value. In the range ofMH>2MΛ=2231.2 MeV/c2 an enhancement ofMΛΛ=(2365.3±9.6) MeV/c2, ΓΛΛ=(47.2±15.1) MeV/c2 with production cross section σ=(24.2±7.0) μb per carbon nucleus was found. The mass rangeMΣ−p<MH<2MΛ was explored via the search for a weak decay modeH→Σ−+p. AV0-particle was found pointing to a two-prong interaction and satisfying the kinematics of the above two-body decay mode with a high confidence level. The possibility of imitation of the observed event by background processes was investigated for a series of two-step strong reactions and weak decays. We succeeded to show the significance of theH-production hypothesis on a deuteron-mass nuclear fluctuon via thepd→HpK+K0 reaction. The mass of the event treated as aH→Σ−+p weak decay appeared to be (2173.94±1.32) MeV/c2, its life-time being 0.668·10−10 s. Both are in agreement with predictions of the MIT Bag Model for the so-calledH-dihyperon. The formally determined production cross section of theH in proton-propane interactions at 10 GeV/c is estimated to be 40 nb. Perhaps, this event can be considered as a first evidence for a six-quark bound state-H-dihyperon. An independent way for the search for theH-particle, based on a specific conversion processHN→YYN, peculiar to its intranuclear strong interactions was proposed and tried. For this purpose all events with two Λ-hyperons and identified protons were tested for the hypothesesHp→ΛΛp at three fixed masses:MH=1880.00, 2173.94 MeV/c2 and the ΛΛ invariant mass for the event in question. The kinematics of this reaction fits successfully only one event and only atMH=2173.94 MeV/c2. It seems worthy of note that the final state ΛΛ invariant massMΛΛ=2344 MeV/c2 is rather close to the observed peak at 2365 MeV/c2. It is shown that the intranuclear conversion processes Ξ−p→ΛΛ and Ξ0n→ΛΛ fail to imitate the observed event. The ΛΛp invariant mass of this event equal to 3363 MeV/c2 is out of a 3568 MeV/c2 peak region of the ΛΛp invariant mass spectrum observed earlier. TheH conversion cross section exceeds the production one. Thus, we consider this event as providing a new evidence for the stableH-dibaryon ofMH=(2173.94±1.32) MeV/c2.
Claime of DIBARYON(S=-2) with mass M=(2365.3+-9.6) MeV and width G=(47.2+-15.1) MeV.
We compare the particle flow in the event plane of three-jet qq¯g (quark-antiquark-gluon) events with the particle flow in radiative annihilation events qq¯γ (quark-antiquark-photon) for similar kinematic configurations. In the angular region between quark and antiquark jet, we find a significant decrease in particle density for qq¯g as compared to qq¯γ. This effect is predicted in QCD as a result of destructive interference between soft-gluon radiation from quark, antiquark, and hard gluon.
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We measure an inclusive branching fraction of (13.9 ± 2.0−2.2+1.9)% for the decay τ−→ντπ−π0+nh0(n>~1), where h0 is a π0 or an η. The data sample, obtained with the time-projection-chamber detector facility at the SLAC e+e− storage ring PEP, corresponds to an integrated luminosity of 72 pb−1 at 29 GeV center-of-mass energy. The measured branching fraction is somewhat greater than the theoretical prediction and, with errors taken into account, could resolve the present difference between the inclusive and the sum of the exclusive τ± branching fractions into one charged prong.
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FOR PARTICLES WITH ABSORPTION CROSS SECTION OF 1.E-23 CM**2 NAME EXOTIC IS USED.
We report measurements of the two-photon processes e+e−→e+e−π+π− and e+e−→e+e−K+K−, at an e+e− center-of-mass energy of 29 GeV. In the π+π− data a high-statistics analysis of the f(1270) results in a γγ width Γ(γγ→f)=3.2±0.4 keV. The π+π− continuum below the f mass is well described by a QED Born approximation, whereas above the f mass it is consistent with a QCD-model calculation if a large contribution from the f is assumed. For the K+K− data we find agreement of the high-mass continuum with the QCD prediction; limits on f′(1520) and θ(1720) formation are presented.
Data read from graph. Additional overall systematic error 20% not included.
Data read from graph.. Additional overall systematic error 20% not included.
Data read from graph.. Additional overall systematic error 20% not included.. The Q**2 dependence is normalized to unity for the bin centred on Q**2 = 0.
The multiplicities per event of π ± and K ± are measured separately for e + e - annihilation into c c , b b , and light quark pairs at E cm=29 GeV. The K ± multiplicity is higher for heavy quark events than for light quark events. The π ± multiplicity and the π ± scaled differential cross section at low x = E beam/ E beam are found to be higher for b b events than for other events.
Numerical values requested from authors. Data given separately for (b bbar), (c cbar) and light quark jets.
Measured multiplicities for (b bbar) jets.
Measured multiplicities for (c cbar) jets.
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