Analysis of the 33-133-133-1final state in photon-photon collisions

The reactione ⁺ e ^- e ⁺ e ^{- 00}e ⁺ e ^- 6 has been analysed using the full data sample taken with the Crystal Ball detector at the DORIS II storage ring at DESY. The ⁰⁰ invariant mass spectrum is dominated by the ', for which we determine the radiative width (') to be (4.5±0.3±0.5)keV. Near 1.9 GeV/c² we observe a second enhancement in the ⁰⁰ mass distribution. Assuming that these events are created by the production and subsequent decay of a wide resonanceX(1900), we have investigated the decay modes, the invariant mass distributions of the ⁰ and ⁰⁰ subsystems and the angular distributions of the final state mesons. We find that the data is best described byJ ^PC=2. For thisJ ^P assignment the resonance parameters are (X) BR(X)=(0.95±0.27±0.20) keV _tot (X)=(221±92±44)MeV, andM(X)=(1881±32±40) MeV/c².Deceased     

Hadron production by ep collisions at HERA

TheP distribution of hadrons from deep-inelastic ep collisions of the H1 experiment determines for the hadrons in the final state, a temperature 277±14 MeV220 MeV of the critical temperature predicted by QCD, suggesting the formation of quark-gluon plasma (QGP). From their forward to backward ratio, it is found an excess of hadrons arising from the deconfinement of quarks inside the proton.     

Experimental evidence for the box anomaly inη/η′ decays and the electric charge of quarks

Motivated by nearly unanimous claim that the observed mass spectrum ^+- is not that expected from pure ⁰ dominance, we reanalyze all the published data on / ^+- decays. We find non-resonant contributions. In order to evaluate precisely the magnitude of these terms, we also refit the e⁺e^{- +-} data to get reliably the ⁰ parameters and decay amplitude. We show that identifying the non-resonant contribution with the box anomaly predicted by QCD and chiral theories, one achieves a consistent picture. Several checks are performed which show the consistency of our fitted parameters. From four measurements, we determinef ₁,f ₈ and _PS on purely experimental grounds, and we find them in the expected range. Presently available data allow for two solutions, one is consistent with QCD, the other favours integral charge quark models. We show that presently available data do not allow to choose among these two solutions. We discuss the interrelation of uncertainties in e⁺e^{- +-} physics with our two solutions.     

LargeP T P−P collisions to probe the gluonic and sea spin distribution in the proton

We parametrise the polarised gluon and sea distribution functions incorporating the interpretation of the EMC experiment that, due to the axial anomaly the observed quark contribution to proton spin at Q ²>=10.7 GeV². Typical processes to isolate the gluonic and sea content of the proton studied here are the largeP _T direct photon production processes (a) using single polarized protonPPX and (b) polarized beam and target protonPPX. In both the above process the dominant contribution comes from the Compton subprocess and so can be used as a clean probe of the gluonic content of the proton. LargeP _T muon pair production PP(^+–)X are also studied and we find that the annihilation subprocess dominates, but not much larger than the Compton subprocess and so may not be a clean probe of the sea content of the proton. The effect of two loop corrections to the parametrisation and asymmetries are also considered, and are found to be negligible.     

LargeN expansion of QED: asymptotic photon propagator and contributions to the muon anomaly,for any number of loops

We calculate analytical contributions to then-loop asymptotic photon propagator from diagrams withn–1 electron loops, i.e. theO(1/N) terms in the largeN limit. The corresponding contributions to the on-shell -function, ()=6 log / logm reduced to rational combinations of _s = _p p ^–s . For the -function of the MOM scheme (i.e. the Gell-Man-Low function) we obtain theO(1/N) terms of

A measurement of the π0, η and η′ electromagnetic form factors

We present measurement of the ^0*, ^* and ^* form factors. The ⁰-form factor is for the first time observed in the space-like region. The transition form factor of the -meson is determined from its decay modes ^+–0, ^+– and the neutral decay mode . The decay of the is observed in the decay channels , ^+– with and in the four charged prong final state stemming from ^+– with the decaying into ^+–(⁰/). All form factors agree well with a simple -pole predicted by the vector meson dominance model and also with the QCD inspired Brodsky-Lepage model.     

A study of Bose-Einstein correlations ine+e? annihilation at 91 GeV

This paper describes a study of Bose-Einstein correlations made using the ALEPH detector at LEP. The correlations are found to enhance the two particle differential cross section for pairs of identical pions by a factor which can be roughly parametrized byR(Q)=1+ exp(-Q²²), whereQ is the difference in the 3-momenta of the two pions in their centre of mass frame, =0.51±0.04±0.11 and =3.3±0.2±0.8 GeV^–1, which corresponds to a source size of 0.65±0.04±0.16 fm. The large systematic errors on these results reflect their strong dependence on the choice of the reference sample used in the analysis. This problem is believed to occur primarily because of uncertainties in the rates of resonance production and a lack of knowledge about the pion-pion strong interaction. No significant correlations are seen amongst like-charged pion-kaon pairs.Supported by CAICYT, Spain     

The special status ofη 1 in QCD

On the basis of the approximate vanishing of the singlet axial charge of the nucleon, it is argued that ₁ should decouple from all hadrons constructed out of the constituentu, d ors quarks in theU(3) _L ×U(3) _R chiral limit for largeN _c . Furthermore ₁ should dominate the processesJ/, . A phenomenological analysis of the and couplings to many hadronic states is consistent with these results.     

The structure of28Si above 10 MeV excitation energy I: gamma-decay modes and radiative widths of levels

The systematics of-decay modes and radiative widths of highly excited states in²⁸Si has been extended by taking-ray spectra on 60 resonances of the²⁷Al(p,) reaction in the range 1097 keVE _p 4492 keV (12643 keVE _x 15915 keV) and on the²⁴Mg(,) resonances atE =3355, 3431, 4003 keV (E _x =12860, 12925, 13 415 keV). The-decay modes of levels in the sub-resonance region (E _x =10–12.5 MeV) were studied with both the²⁷ A1(p, ) reaction and the²⁷ A1(d, n) reaction at E_d=4,5,6 MeV. Information on radiative widths of levels was obtained by measuring the resonance strengthsS =(2I+1) _p / for 52 resonances of the²⁷Al(p, ) reaction with an emphasis on prospective T=1 states.     

Evidence for higher twist mechanisms in highp ⊥π− p events with prompt ρ0 production at 38 GeV/c

The ^– p interactions with at least one charged secondary produced at polar angle 90° in c.m.s. and having the transverse momentum above 1 GeV/c were investigated. The data were obtained using streamer chamber magnetic spectrometer RISK at 38 GeV/c beam from Serpukhov accelerator. The analyzis of associated production in reconstructed events suggests, that if the transverse momentum of a pair of oppositely charged secondaries compensates the trigger particlep practically completely, this pair is the product of the ⁰ decay in marked fraction of such events. We observed a large spin-alignment for the ⁰-mesons selected as described above: the probability of zero spin projection onto the normal to the ⁰ production plane is equal to ₀₀ ^T =0.86±0.23. The enhancement of the number of events, in which the ⁰ picks up practically full momentum transfer carrying by the exchange, and also the enlarged tensor polarization for the ⁰-mesons in these events could be qualitatively explained as manifestation of direct ⁰-production via the QCD higher twist processes in the highp ^– p collisions. At the same time, the observed effects are markedly larger than the values predicted with QCD model in which the higher twist corrections were included.     

Quantum correlations of bosons and fermions produced in heavy ion collisions

A quantum statistical approach to simulate Bose-Einstein correlations of many boson systems is presented. The extension to fermions and Coulomb-interacting bosons is discussed. This approach appears to be very efficient and is applicable also to cases with very high multiplicities. A technique to analyze pion correlations via their counting distributions is developed. The exact counting distributions for bosons as well as for fermions are derived. The problem of incomplete data occuring in detectors with an acceptance angle <> is studied. The application to Monte Carlo generated pion distributions show that this technique offers a valuable supplement to the usual Hanbury-Brown, Twiss method.     

Search for contact interactions in the reactionse+e?→l+l? ande+e?→γγ

Contact interactions are searched for using the differential cross sections for the reactionse ⁺ e ^–e ⁺ e ^–,e ⁺ e ^–µ ⁺ µ ^–,e ⁺ e ^{– + –} ande ⁺ e ^– measured at 12 energies around theZ peak and corresponding to about 20 pb^–1 of cumulated luminosity. Four-fermion contact term models assuming various chiralities of lepton currents are fitted to the lepton data and lower limits on the energy scale of such terms are set at 95% c.l. The limits vary in the range 0.9–4.7 TeV, depending on the model and on the lepton flavour. Theee contact terms are searched for assuming various chiralities. Limits on the energy scale between 79 and 130 GeV are extracted from the data. The results are compared and combined with those reported at lower energies.Deceased     

Strict inequalities for some critical exponents in two-dimensional percolation

For 2D percolation we slightly improve a result of Chayes and Chayes to the effect that the critical exponent for the percolation probability isstrictly less than 1. The same argument is applied to prove that ifL():={(x, y):x=r cos, y=r sin for some r0, or} and():=limpp _c [log(p–p _c )]^–1 log P_cr {itO is connected to by an occupied path inL()}, then() is strictly decreasing in on [0, 2]. Similarly, lim_n [–logn]^–1 logP _cr {itO is connected by an occupied path inL()() to the exterior of [–n, n]×[–n, n] is strictly decreasing in on [0, 2].     

Total cross section of two-photon production of hadrons

The total cross section for hadrons was measured as a function of the invariant massW of the system (1.25 to 4.25 GeV) at thee ⁺ e ^–-collider VEPP-4 with the detector MD-1. For the first time the data were obtained by detecting both scattered leptons with almost zero emission angles. The mean squared four momentum transfer q ² is –0.005 GeV², the rmsW resolution is 100–250 MeV. The data on the mean charged multiplicity n _C are well described by the function n _C =(1.62 ±0.37)+(1.83±0.45)·ln(W(GeV)). TheW dependence of the total cross section is consistent with the theoretical prediction (nb)=240+270/W(GeV).     

Intramolecular Hydrogen Bond in Steroid 5‐Hydroxy‐6‐Ketones and 5‐Hydroxy‐6‐Ketoximes of the Stigmastane Series

The intramolecular hydrogen bond in steroid 5hydroxy6ketones and 5hydroxy6ketoximes of the stigmastane series has been investigated by the method of IR spectroscopy. It is shown that 5hydroxy groups in cisA/Bsteroids are linked by the intramolecular hydrogen bond with polar substituents at C₃ and C₆. These hydrogen bonds are lacking in corresponding transA/Bsteroids. According to the IR spectra, intramolecular associates of polymer type are formed in 5hydroxy6hydroxyminosteroids.