Antibaryon Production Research Articles

Evidence for a phase with high specific entropy in nuclear collisions.

We determine the entropy-per-baryon content of the central reaction region in terms of the charged particle multiplicity. We study the consistency of our findings with recent data on strange antibaryon production at 200A GeV in S-A collisons (A\ensuremath{\sim}200) assuming formation of a central fireball. Hadron gas models which do not invoke strong medium modifications of hadron masses do not provide enough entropy and are inconsistent with the combined experimental results. In contrast the quark-gluon plasma hypothesis explains them naturally.

Strange particle production in sulphur-tungsten interactions at 200 GEV/C per nucleon

Multi-strange baryon and anti-baryon production is expected to be a useful probe in the search for Quark-Gluon Plasma formation. We present the transverse mass distributions of negative particles, K os, Λs, Λs, and Ξ − s produced in sulphurtungsten interactions at 200 GeV/c per nucleon and give the corrected ratios ΛΛ, Ξ −Λ and Ξ −/Λ . We note that our ratio Ξ −/ Λ appears large in comparison to that from p p interactions.

Strange and hot matter

I consider the strangeness degree of freedom in hot nuclear matter and its significance for the observation and identification of a quark-gluon plasma. Particular attention is given to the interpretation of new and intriguing results on strange antibaryon production.

Formula omitted] production in sulphur-tungsten interactions at 200 GeV/ c per nucleon

Multi-strange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We present the transverse mass distributions of negative particles, Λ' s, Λ' s and Ξ −' s produced in sulphur-tungsten interactions at 200 GeV/ c per nucleon and give the corrected rations Λ/Λ, Ξ −/Λ and Ξ − / Λ . Our ratio Ξ − / Λ appears to be larger than that from pp interactions.

Strange anti-baryons from quark-gluon plasma

Experimental results on strange anti-baryon production in nuclear S→W collisions at 200 A GeV are described in terms of a simple model of an explosively disintegrating quark-lepton plasma (QGP). The importance of the strange anti-baryon signal for the identification of the QGP state and for the diagnosis of its properties is demonstrated.

Production of multistrange baryons and antibaryons in sulphur-tungsten interactions at 200 GeV/c per nucleon

Production of Ξ − and Ξ − has been observed for the first time in heavy ion interactions by the WA85 Experiment. Multistrange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We describe the procedure used to select these cascade candidates and show that Ξ − and Ξ − decays can be identified. The ratio of Ξ Ξ production, corrected for geometrical acceptances and reconstruction efficiencies, is 0.39 ± 0.07 for sulphur-tungsten interactions in the central rapidity interval 2.3< Y lab<3.0 and p T>1.1 GeV/ c.

Baryons and the QCD phase transition

Lattice simulations in full QCD have shown that the baryon susceptibility rises rapidly near the high temperature phase transition. This rise is a possible consequence of the restoration of chiral symmetry. Supporting evidence from numerical simulations with a Skyrme-like model is given. The results obtained further support the idea that the cooling of the quark plasma results in copious antibaryon production. They also provide a natural bridge between the high temperature and high density phase transitions.

Multi-strange baryon and antibaryon production in sulphur-tungsten and proton-tungsten interactions at 200 GeV/c per nucleon

Production of multi-strange baryons and antibaryons is expected to be a useful indicator in the search for Quark-Gluon Plasma formation. Production of Ξ − and Ξ − has been observed for the first time in ultra-relativistic heavy ion interactions by the WA85 Experiment. We describe the procedure used to select these cascade candidates and show that Ξ − and Ξ − decays can be identified. Preliminary ratios of Ξ/Ξ production in sulphur-tungsten and proton-tungsten interactions are also presented.

Role of baryons in chiral-symmetry restoration at high temperature.

To help provide insight into the apparent remarkable rise in baryon susceptibility at the high-temperature phase transition in QCD, we study the three-dimensional lattice SU(2) chiral model at finite temperature. The purpose of this study is to determine the extent to which a rising susceptibility is a natural consequence of chiral-symmetry restoration in a nonlinear {sigma} model. Indeed the susceptibility, defined in terms of a discrete (nonconserved) version of the winding number, is found to rise rapidly in the vicinity of the phase transition, suggesting that a proliferation of baryons and antibaryons (i.e., Skyrmions) plays a significant role in the restoration of the chiral symmetry. These results support the idea that the cooling of the quark plasma could result in copious antibaryon production.

Anti-baryon production in heavy-ion collisions

We consider baryon and antibaryon production in heavy-ion collisions in the context of the Skyrme model of nucleons as topological solitons. In this model the abundances of baryons and antibaryons are not controlled by thermodynamic Boltzmann factors, but by the sizes of coherence domains for the low-temperature quark condensate. Strong violations of naive chemical equilibrium by the formation process are thus possible. The B B production rate is bounded from above by energy and entropy conservation, but may be much larger than the naive Boltzmann expectation. The maximal production rate corresponds to a physically plausible domain size for the chiral domains. We stress the importance of measuring B production in heavy-ion collisions as a probe of nonperturbative QCD.

Baryon antibaryon production in the central region at 85 GeV/c

In a search for glueballs and exotic states decaying into baryons and antibaryons we have investigated the production of baryon antibaryon pairs produced centrally in the reactions π+/pp → π+/p(X 0)p at 85 GeV/c. In particular, channels whereX 0 goes to\(p\bar p,p\bar p\pi ^ + \pi ^ - ,p\bar p2\pi ^ + 2\pi ^ - \) and\(\Lambda \bar \Lambda \) have been observed. No significant new structure is observed in the mass spectra.

SO(10) vortices and the electroweak phase transition

We examine the effects of electroweak symmetry breaking (ESB) on vortex excitations appearing in an SO(10) grand unified model. The vortices are topologically stable before and after the inclusion of ESB, but the corresponding minimal energy configurations differ for the two cases. Consequently, the vortex mass per unit length and dynamics differ for the two cases. Also, after ESB, certain directions in the internal symmetry space cannot be globally defined in the nontrivial topological sector, contrary to the case before ESB. Higher vortex excitations exist in the model and are known to have zero-energy bound states with fermions. It is also known that such states induce fractional fermion numbers to the soliton. We find that the existence and number of zero-mode states depends, in general, upon whether ESB is present or not. As a result, certain vortex excitations can have half-integer-valued baryon number before ESB and integer-valued baryon number after. Consequently, if such vortices were present during the electroweak phase transition in the early universe, they may have induced baryon or antibaryon production.

Time evolution of strange-particle densities in hot hadronic matter

The kinetic equations for production in hot nuclear matter of rare, strange antibaryons are studied numerically. Strange antibaryons are confirmed as viable characteristic signatures of the quark-gluon plasma. We find four orders of magnitude enhancement in the abundance of Ω multiply-strange antibaryons. Strange antibaryon production in the hadronic gas phase is shown to have a relatively slow characteristic time constant of ∼ 10 −21 sec to be compared with the 100 times faster equilibration in quark-gluon plasma.

Antibaryon production in the central region at the ISR

Using annihilation in a calorimeter as a trigger on antiprotons, we have measured the relative production cross sections of p, Λ and Ξ at y∼0 in the transverse momentum range 1 to 2 GeV/c in pp collisions at √s=63 GeV. We investigate correlations between the antibaryons and associated produced particles, and find evidence for local baryon number conservation.

Are antibaryons a signal for a phase transition in ultrarelativistic nucleus-nucleus collisions?

In this paper, it is speculated that antibaryon production in relativistic nucleus-nucleus collisions is a signal for a phase transition from a high-temperature Debye-screened and chirally symmetric phase to a low-temperature confined and chirally broken phase. In a chiral model for the transition where baryons are topological excitations the production of baryons and antibaryons takes place by the Kibble mechanism. A qualitative discussion of possible experimental signatures is given.

The role of valence quarks in proton fragmentation

Following earlier theoretical and experimental work (Kalinowski et al. [6], Bourquin et al. [7]), baryon production by fragmentation of incident protons in high energy hadron collisions is re-investigated in terms of a fragmentation-recombination mechanism similar to a model proposed by Fukuda and Iso [4]. The multiplicitiesnf(B) for the various types of baryonsB produced in proton fragmentation are expressed in terms of the probabilitiesai fori=0, ..., 3 valence quarks of the incident proton to emerge in the baryonB and 3−i to emerge in mesons (following [7] we suppose that antibaryon production is mostly due to baryon-antibaryon pair production by a mechanism of non-fragmentation type, and this is taken into account in deducingnf(B) from baryon and antibaryon multiplicity data). The positivity of theai is found to impose remarkably narrow constraints on thenf(B) for (meta)stableB, and we find the data to satisfy these constraints. We show furthermore that the data are compatible with uncorrelated behaviour of the valence quarks of the incident proton, each of them having a probability ≃ 0.6 to emerge in the fragmentation baryonB, and a probability ≃ 0.4 to emerge in a meson. We also briefly discuss the relation of our analysis to previous work on the recombination model of proton fragmentation and its possible extension to meson fragmentation.

Charged baryon and antibaryon production in the fragmentation region by 240 GeV protons

Measurements of the production inp-BeO collisions of charged baryons and antibaryons with strangeness between −3 and +3 at $$\sqrt s = 21.2GeV$$ x=0.48, andp T =600MeV/c are reported. The experimental results can be interpreted within the framework of a simple proton fragmentation-recombination model.

Lepton-hadron relation, average multiplicities of various charged secondary particles in pp scattering and some comments on the rising pp total cross-section at ISR energies

By applying a lepton-hadron relation, average multiplicities of charged (π, K) mesons and baryons-antibaryons in pp scattering have been found out which are in excellent agreement with experimental results. The proposed linkage between the rising total pp cross-section phenomenon and the antibaryon production has also been investigated and the result is found to be negative. The explanation of this rising pp cross-section phenomenon, in this model, is however attributed to the diffraction effects in which the black-core radius expands logarithmically with energy (R∼R0 lns) as suggested by Cheng, Walker and Wu.

Inclusive Strange-Particle Production byνpInteractions in the 10—200-GeV Region

Data are presented on charged-current inclusive strange-particle production in 10-200-GeV/c $\ensuremath{\nu}p$ interactions. Final states with ${V}^{0}$ decay topologies are reported: ${{K}_{s}}^{0}$, ${\ensuremath{\Lambda}}^{0}({\ensuremath{\Sigma}}^{0})$, ${\overline{\ensuremath{\Lambda}}}^{0}({\overline{\ensuremath{\Sigma}}}^{0})$. Neutrino energy, charged multiplicity, ${Q}^{2}$, $W$, $x$, and $y$ distributions are shown. The corrected relative ${V}^{0}$ production rate is 0.16\ifmmode\pm\else\textpm\fi{}0.03 per event. The first example of neutrino-induced antibaryon ($\overline{\ensuremath{\Lambda}}$) production is observed. The 90%-confidence upper limit on $\ensuremath{\Delta}S=\ensuremath{-}\ensuremath{\Delta}Q$ inclusive $\ensuremath{\Lambda}$ production is 0.036 of all charged-current $\ensuremath{\nu}p$ interactions above 10 GeV/c.

Antibaryon production and high-energy oscillations

We employ multiperipheral models to investigate the proposal that the experimentally observed production of antibaryons can account for most or all of the rise in the pp total cross section at ISR energies. Our models support the proposal, and furthermore predict that this rise is the first part of a long-wavelength damped oscillation as a function of energy. We find that a variety of models accommodate the antibaryon effect, and show that these all lead to total cross sections consistent with present data and displaying an oscillation at higher energies. We attempt to understant the antibaryon cross section itself within the special case of the ABFST model, and find that the observed energy threshold emerges naturally, but that the predicted magnitude is somewhat small. The oscillations are simply parametrized in terms of complex Regge poles, and one of the models studied suggests that the leading complex pole be identified with the P′.