Recent highlights from BRAHMS

Bearden, I. G.

doi:10.1088/0954-3899/34/8/s05

Cited by 328 publications

(752 citation statements)

References 16 publications

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“…6). For central Pb-Pb collisions at SPS energies, the typical results for transverse surface velocity and thermal freezeout temperature are (β s ⊥ /c, T fo [MeV]) = (0.65 ± 0.1, 120 ± 10) [79,80,81,82], which is quite comparable to the values used here for InIn. We emphasize that all contributions to the dilepton spectrum (QGP, ρ, ω, φ, and four-pion) are tied to the same evolution, thus fixing their relative weights.…”

Section: Thermal Fireball Evolutionsupporting

confidence: 76%

Dilepton radiation at the CERN super-proton synchrotron

2008

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A quantitative evaluation of dilepton sources in heavy-ion reactions is performed taking into account both thermal and non-thermal production mechanisms. The hadronic thermal emission rate is based on an electromagnetic current-correlation function with a low-mass region (LMR, M 1 GeV) dominated by vector mesons (ρ, ω, φ) and an intermediate-mass region (IMR, 1 GeV ≤ M ≤ 3 GeV) characterized by (the onset of) a multi-meson continuum. A convolution of the emission rates over a thermal fireball expansion results in good agreement with experiment in the low-mass spectra, confirming the predicted broadening of the ρ meson in hadronic matter in connection with the prevalence of baryon-induced medium effects. The absolute magnitude of the LMR excess is mostly controlled by the fireball lifetime, which in turn leads to a consistent explanation of the dilepton excess in the IMR in terms of thermal radiation. The analysis of experimental transversemomentum (qT ) spectra reveals discrepancies with thermal emission for qT 1 GeV in noncentral In-In collisions, which we address by extending our calculations by: (i) a refined treatment of ρ decays at thermal freezeout, (ii) primordially produced ρ's subject to energy-loss, (iii) Drell-Yan annihilation, and (iv) thermal radiation from t-channel meson exchange processes. We investigate the sensitivity of dilepton spectra to the critical temperature and hadro-chemical freezeout of the fireball. The ρ broadening in the LMR turns out to be robust, while in the IMR Quark-Gluon Plasma radiation is moderate unless the critical temperature is rather low.

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Section: Thermal Fireball Evolutionsupporting

confidence: 76%

Dilepton radiation at the CERN super-proton synchrotron

2008

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“…For central heavy-ion (Au+Au or Pb+Pb) collisions at the AGS, SPS and RHIC accelerators, the approximate p T value at which the invariant cross sections of protons and positive pions at mid-rapidity approach each other is plotted. Data (with the percentile of most central events) are taken from the E802 [10] (4%), NA44 [11] (3.7%), NA49 [12] (5%), PHENIX [4,6] (5%) and PHOBOS (15%) experiments. A remarkably smooth collision energy dependence of the 'crossing' p T value is observed.…”

Section: Resultsmentioning

confidence: 99%

“…They are more precisely measurable than invariant cross sections, and provide quantitative input to models concentrating on the hadro-chemistry of the collisions, such as statistical thermal models. Antiproton to proton ratios and net proton yields provide information on baryon transport and baryon production in these ultrarelativistic collisions, and are relevant quantities to estimate the fraction of the total collision energy that is available for particle production [3].…”

Section: Introductionmentioning

confidence: 99%

Antiparticle to particle ratios and identified hadron spectra in Cu+Cu and Au+Au collisions

Veres¹,

Collaboration²

2007

J. Phys. G: Nucl. Part. Phys.

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Abstract. New results on antiparticle to particle ratios in Cu+Cu and Au+Au collisions at √ s N N = 62.4 and 200 GeV from the PHOBOS experiment at RHIC are presented. Transverse momentum spectra of pions, kaons, protons and antiprotons from Au+Au collisions at √ s N N = 62.4 GeV close to mid-rapidity are also discussed. Antiparticle to particle ratios are found to be remarkably independent of the collision centrality in both colliding systems. The collision energy dependence of the p/p ratios is very significant in Cu+Cu collisions. Baryons are found to have substantially harder transverse momentum spectra than mesons. The p T region in which the proton to pion ratio reaches unity in central Au+Au collisions at √ s N N = 62.4 GeV fits into a smooth trend as a function of collision energy. The observed particle yields at very low p T are comparable to extrapolations from higher p T for kaons, protons and antiprotons. The net proton yield at mid-rapidity is found to be proportional to the number of participant nucleons in Au+Au collisions at 62.4 and 200 GeV energies.

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“…These new solutions are simple, although their finding was a complicated process that lasted for decades. BRAHMS pointed out before [12], that the rapidity distribution of negative pions in Au+Au collisions at √ s N N = 200 GeV is flatter than a Gaussian, but not completely flat, hence neither the Landau-Khalatnikov, nor the Hwa-Bjorken solution describes it. Our new exact solutions describe well these BRAHMS observations.…”

Section: Relation To Earlier Solutionsmentioning

confidence: 99%

New family of simple solutions of relativistic perfect fluid hydrodynamics

2008

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A new class of accelerating, exact and explicit solutions of relativistic hydrodynamics is foundmore than 50 years after the previous similar result, the Landau-Khalatnikov solution. Surprisingly, the new solutions have a simple form, that generalizes the renowned, but accelerationless, HwaBjorken solution. These new solutions take into account the work done by the fluid elements on each other, and work not only in one temporal and one spatial dimensions, but also in arbitrary number of spatial dimensions. They are applied here for an advanced estimation of initial energy density and life-time of the reaction in ultra-relativistic heavy ion collisions.

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Recent highlights from BRAHMS

Abstract: We present an overview of highlights from the BRAHMS Collaboration.

Cited by 328 publications

References 16 publications

Dilepton radiation at the CERN super-proton synchrotron

Dilepton radiation at the CERN super-proton synchrotron

Antiparticle to particle ratios and identified hadron spectra in Cu+Cu and Au+Au collisions

New family of simple solutions of relativistic perfect fluid hydrodynamics

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