Phi meson production is studied by the NA49 collaboration in central Pb+Pb collisions at 20A, 30A, 40A, 80A and 158A GeV beam energy. The data are compared to measurements at lower and higher energies and to microscopic and thermal models. The energy dependence of yields and spectral distributions is compatible with the assumption that partonic degrees of freedom set in at low SPS energies.
PHI transverse momentum spectra at incident energy 20 GeV/nucleon integrated over the rapidity range 0 to 1.8.
PHI transverse momentum spectra at incident energy 30 GeV/nucleon integrated over the rapidity range 0 to 1.8.
PHI transverse momentum spectra at incident energy 40 GeV/nucleon integrated over the rapidity range 0 to 1.5.
Results on charged pion and kaon production in central Pb+Pb collisions at 20A and 30A GeV are presented and compared to data at lower and higher energies. A rapid change of the energy dependence is observed around 30A GeV for the yields of pions and kaons as well as for the shape of the transverse mass spectra. The change is compatible with the prediction that the threshold for production of a state of deconfined matter at the early stage of the collisions is located at low SPS energies.
Transverse mass spectra for pion production in the central rapidity region for collisions at 20 GeV per nucleon.
Transverse mass spectra for pion production in the central rapidity region for collisions at 30 GeV per nucleon.
Transverse mass spectra for kaon production in the central rapidity region for collisions at 20 GeV per nucleon.
The electroproduction of J/psi and psi(2S) mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers 2 < Q^2 < 80 GeV^2 and photon-proton centre of mass energies 25 < W < 180 GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic J/psi production is measured as a function of Q^2 and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic psi(2S) and J/psi meson production is measured as a function of Q^2. The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of J/psi mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
The elastic electroproduction of rho mesons is studied at HERA with the H1 detector for a photon virtuality in the range 1 < Q^2 < 60 GeV^2 and for a hadronic centre of mass energy in the range 30 < W < 140 GeV. The shape of the pipi mass distribution in the rho resonance region is measured as a function of Q^2. The full set of rho spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of 8 +- 3 % of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on Q^2, W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large Q^2, the gamma^*p cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron-hadron cross sections.
Average values of the spin density matrix elements measured for the 1996 data sample.
Spin density matrix elements measured for 3 Q**2 values for the 1996 data sample.
Spin density matrix elements measured for 3 W values for the 1996 data sample.
The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton-nucleus and deuteron-gold interactions, as well as central oxygen-gold and sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus-nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with `temperatures' between 145 +- 11 MeV (p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.
No description provided.
No description provided.
The value YRAP = 4PI is the extrapolation for 4PI acceptance.
The production ofK0, Λ and\(\bar \Lambda \) particles is studied in the E665 muon-nucleon experiment at Fermilab. The average multiplicities and squared transverse momenta are measured as a function ofxF andW2. Most features of the data can be well described by the Lund model. Within this model, the data on the K0/π± ratios and on the averageK0 multiplicity in the forward region favor a strangeness suppression factors/u in the fragmentation process near 0.20. Clear evidence for QCD effects is seen in the average squared transverse momentum ofK0 and Λ particles.
No description provided.
No description provided.
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AUTHORS FIT D2(SIG)/D(XL)/D(PT**2) BY (1-XL)**POWER*EXP(-SLOPE*PT**2).
AUTHORS FIT D2(SIG)/D(XL)/D(PT**2) BY (1-XL)**POWER*EXP(-SLOPE*PT**2).
AUTHORS FIT D2(SIG)/D(XL)/D(PT**2) BY (1-XL)**POWER*EXP(-SLOPE*PT**2).
Data are presented on exclusive ρ0 and ϕ production in deep inelastic muon scattering from a target consisting mainly of nitrogen. The ratio of the total cross sections for ρ0 and ϕ production is found to be 9∶(1.6±0.4) at 〈Q2〉=7.5 GeV2, consistent with theSU(3) prediction of 9∶2. Thet dependence for exclusive ρ0 production is found to become shallover asQ2 increases and, for largeQ2, thet dependence is typical of that for a hard scattering process. Furthermore, the ratio of the cross sections for coherent: incoherent production from nitrogen is found to decrease rapidly withQ2. Such behaviour indicates that even for exclusive vector meson production the virtual photon behaves predominantly as an electromagnetic probe.
No description provided.
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We study the internal structure of a forward-going pπ + π − π + π − system, with invariant mass in the range 2.5-4 GeV, produced through diffractive dissociation of a beam proton at the ISR. The shape of the system, as seen in its center-of-mass, deviates strongly from isotropic phase space and possesses, rather, a longitudinal structure with a major axis along the incoming proton direction. The final state proton momentum is aligned in the direction of the incoming proton, an effect which becomes more pronounced with increasing diffractive mass.
Acceptance corrected distribution of momentum transfer to the diffractive (p-4pi) system. Data requested from authors.
No description provided.
Diffractive production of the 3 π system has been studied at 63 and 94 GeV using a two magnet spectrometer with high, uniform acceptance. The total number of events used in the analysis is ∼600 000. The A 2 meson is shown to be diffractively produced. The existence of a resonant component in both the 1 + and 2 − enhancements is established and resonance parameters for the corresponding A 1 and A 3 mesons are given. There are several indications in the data of states which would correspond to radial excitations in the quark model.
SEE C. DAUM ET AL., PL 89B, 276 (1980) (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+486> RED = 486 </a>), AND THE RECORD (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+420> RED = 420 </a>) OF THE GENEVA CONFERENCE PREPRINT, B. ALPER ET AL. (1979).
SEE C. DAUM ET AL., PL 89B, 281 (1980) (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+487> RED = 487 </a>), AND THE RECORD (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+419> RED = 419 </a>) OF THE GENEVA CONFERENCE PREPRINT, G. THOMPSON ET AL. (1979).
SEE C. DAUM ET AL., PL 89B, 285 (1980) (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+488> RED = 488 </a>), AND THE RECORD (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+421> RED = 421 </a>) OF THE GENEVA CONFERENCE PREPRINT, B. ALPER ET AL. (1979).
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