Thermal rates for baryon and antibaryon production

Kapusta, Joseph I.; Shovkovy, Igor

doi:10.1103/physrevc.68.014901

Cited by 24 publications

(32 citation statements)

References 40 publications

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“…Moreover, τ ≈ 10 fm c was also obtained in Ref. [5] using a fluctuation-dissipation theorem and a significant deviation was found in the population number of various (anti-)baryons from experimental data in the 5% most central Au-Au collisions [6]. These discrepancies suggest that hadrons are "born" into equilibrium, i.e., the system is already in a chemically frozen out state at the end of the phase transition [7,8].…”

Section: Pacs Numbersmentioning

confidence: 60%

Fast Equilibration of Hadrons in an Expanding Fireball

2008

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Due to long chemical equilibration times within standard hadronic reactions during the hadron gas phase in relativistic heavy ion collisions it has been suggested that the hadrons are "born" into equilibrium after the quark gluon plasma phase. Here we develop a dynamical scheme in which possible Hagedorn states contribute to fast chemical equilibration times of baryon anti-baryon pairs (as well as kaon anti-kaon pairs) inside a hadron gas and just below the critical temperature. Within this scheme, we use master equations and derive various analytical estimates for the chemical equilibration times. Applying a Bjorken picture to the expanding fireball, the kaons and baryons as well as the bath of pions and Hagedorn resonances can indeed quickly chemically equilibrate for both an initial overpopulation or underpopulation of Hagedorn resonances. Moreover, a comparison of our results to (B +B)/π + and K/π + ratios at RHIC, indeed, shows a close match. PACS numbers:(Anti-)strangeness enhancement was first observed at CERN-SPS energies by comparing anti-hyperons, multistrange baryons, and kaons to pp-data. It was considered a signature for quark gluon plasma (QGP) because, using binary strangeness production and exchange reactions, chemical equilibrium could not be reached within the hadron gas phase [1]. It was then proposed that there exists a strong hint for QGP at SPS because strange quarks can be produced more abundantly by gluon fusion, which would account for strangeness enhancement following hadronization and rescattering of strange quarks. Later, multi-mesonic reactions were used to explain secondary production of anti-protons and antihyperons [2,3]. At SPS they give a typical chemical equilibration time τȲ ≈ 1 − 3 fm c using an annihilation cross section of σ ρȲ ≈ σ ρp ≈ 50mb and a baryon density of ρ B ≈ ρ 0 to 2ρ 0 , which is typical for SPS. Therefore, the time scale is short enough to account for chemical equilibration within a cooling hadronic fireball at SPS.A problem arises when the same multi-mesonic reactions were employed in the hadron gas phase at RHIC temperatures where experiments show that the particle abundances reach chemical equilibration close to the phase transition [4]. At RHIC at T = 170 MeV, where σ ≈ 30mb and ρ eq B ≈ ρ eq B ≈ 0.04fm −3 , the equilibrium rate for (anti-)baryon production is τ ≈ 10 fm c , which is considerably longer than the fireball's lifetime in the hadronic stage of τ < 5 fm c . Moreover, τ ≈ 10 fm c was also obtained in Ref.[5] using a fluctuation-dissipation theorem and a significant deviation was found in the population number of various (anti-)baryons from experimental data in the 5% most central Au-Au collisions [6]. These discrepancies suggest that hadrons are "born" into equilibrium, i.e., the system is already in a chemically frozen out state at the end of the phase transition [7,8].In order to circumvent such long time scales it was suggested that near T c there exists an extra large particle density overpopulated with pions and kaons, which drive the baryo...

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Section: Pacs Numbersmentioning

confidence: 60%

Fast Equilibration of Hadrons in an Expanding Fireball

2008

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“…That set of studies included all baryons in the octet [13] n; p; ; ; 0 ; ÿ ; 0 ; ÿ and in the decuplet [14] ; ; 0 ; ÿ ; ; 0 ; ÿ ; 0 ; ÿ ; . We have used those formulas to compute the chemical relaxation time p for antiprotons in the temperature range of 100 to 200 MeV.…”

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confidence: 99%

“…The relevant processes are (i) a thermal decays into a and , followed by the muon decay ! e e , and (ii) a thermal muon decays in the same way.An extensive study of the production and annihilation rates of spin-1=2 baryons and antibaryons was performed in [13,14] based on a form of the fluctuation-dissipation theorem. That set of studies included all baryons in the octet [13] n; p; ; ; 0 ; ÿ ; 0 ; ÿ and in the decuplet [14] ; ; 0 ; ÿ ; ; 0 ; ÿ ; 0 ; ÿ ; .…”

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confidence: 99%

Antimatter from microscopic black holes

Daghigh

Kapusta²

2006

Phys. Rev. D

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The spectrum of positrons and antiprotons produced by the outflow of high temperature matter surrounding microscopic black holes is calculated for energies between 5 GeV and the Planck energy. The results may be applicable for the last few hours and minutes of a microscopic black hole's lifetime.Hawking radiation from black holes [1] is of fundamental interest because it involves the interplay between quantum field theory and the strong field limit of general relativity. It is of astrophysical interest if black holes exist with sufficiently small mass that they explode rather than accrete matter and radiation. Since the Hawking temperature and black hole mass are related by T H m 2 P =8M, where m P G ÿ1=2 1:22 10 19 GeV is the Planck mass with natural units @ c k B 1, a presentday black hole will evaporate and eventually explode only if T H > 2:7 K (microwave background temperature). This requires M < 4:6 10 22 kg which is approximately 1% of the mass of the Earth. More massive black holes are cooler and therefore will absorb more matter and radiation than they emit, hence grow with time. Taking into account emission of gravitons, photons, and neutrinos a critical mass black hole today has a Schwarszchild radius of 68 microns and a lifetime of 2 10 43 years.Following earlier work by Heckler [2] and by Cline, Mostoslavsky and Servant [3], one of us showed that a selfconsistent description of the emitted quanta was that of an outgoing fluid just marginally kept in local equilibrium. It required the assumption of sufficient initial particle interaction, and viscosity played a crucial role [4]. That paper was followed by an extensive numerical analysis of the relativistic viscous fluid equations by us [5]. We also calculated the spectrum of high energy gamma rays expected during the last days, hours, and minutes of the black hole's lifetime in that same paper, and later calculated the spectrum of high energy neutrinos as well [6]. We suggested that the most promising route for discovery of such microscopic black holes is to search for point sources emitting gamma rays of ever-increasing energy until suddenly the source shuts off.In this brief report we use our previous results to calculate the emission of high energy antimatter, specifically positrons and antiprotons, from black holes with Hawking temperatures greater than 100 GeV and corresponding masses less than 10 8 kg. It is at these and higher temperatures that new physics will arise. Such a study is especially important in the context of searches for anomalous cosmic sources of high energy antimatter by current and future detectors [7-10]. Previous notable theoretical studies in this area have been carried out by MacGibbon and Webber [11] and by Halzen, Zas, MacGibbon and Weeks [12], who calculated the instantaneous and time-integrated spectra of positrons and antiprotons arising from the decay of quark and gluon jets.We show that antiprotons remain in chemical equilibrium down to the decoupling or freeze-out temperature, T f , which is on the order of 140 MeV...

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“…These same reactions, however, do not produce anti-hyperons quickly enough at RHIC where their chemical equilibration times are W | 10 fm/c, which exceeds the average lifetime of the fireball [4,5].…”

Section: Introductionmentioning

confidence: 91%

Fast chemical equilibration of hadrons in an expanding fireball

2011

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The suggestion of hadrons being "born" into equilibrium arose from long chemical equilibration times of hadrons in the hadron gas phase in relativistic heavy ion collisions. Here we consider possible Hagedorn states, which contribute to fast chemical equilibration times of baryon anti-baryon pairs (as well as kaon anti-kaon pairs) inside a hadron gas and just below the critical temperature. Master equations are used to describe the reactions. Within a Bjorken expansion scenario, the kaons and baryons as well as the bath of pions and Hagedorn resonances can indeed quickly chemically equilibrate.

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Thermal rates for baryon and antibaryon production

Cited by 24 publications

References 40 publications

Fast Equilibration of Hadrons in an Expanding Fireball

Fast Equilibration of Hadrons in an Expanding Fireball

Antimatter from microscopic black holes

Fast chemical equilibration of hadrons in an expanding fireball

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