Hot Hadronic Medium Research Articles

Dilepton production from hot and magnetized hadronic matter

The rate of dilepton emission from a magnetized hot hadronic medium is calculated in the framework of real time formalism of finite temperature field theory. We evaluate the one loop self-energy of neutral rho-meson containing thermo-magnetic propagators for the charged pions in the loop. The in-medium thermo-magnetic spectral function of rho obtained by solving the Dyson-Schwinger equation is shown to be proportional to the dilepton production rate. The study of the analytic structure of the neutral rho-meson spectral function in such a medium shows that in addition to the usual contribution coming from the Unitary cut beyond the two-pion threshold there is a non-trivial yield in the low invariant mass region originating due to the fact that the charged pions occupy different Landau levels before and after scattering with the neutral rho-meson and is purely a finite magnetic field effect.

Signatures of chiral symmetry restoration and its survival throughout the hadronic phase interactions

The effect of the chiral symmetry restoration (CSR) on observables from heavy-ion collisions is studied in the energy range [see formula in PDF]=3–20 GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach. The PHSD includes the deconfinement phase transition as well as essential aspects of CSR in the dense and hot hadronic medium, which are incorporated in the Schwinger mechanism for the hadronic particle production. We adopt different parametrizations of the nuclear equation of state from the non-linear σ - ω model, which enter in the computation of the quark scalar density for the CSR mechanism, in order to estimate the uncertainty in our calculations. For the pion-nucleon ∑-term we adopt ∑π ≈ 45 MeV which corresponds to a ’world average’. Our systematic studies show that chiral symmetry restoration plays a crucial role in the description of heavy-ion collisions at [see formula in PDF]=3–20 GeV, realizing an increase of the hadronic particle production in the strangeness sector with respect to the non-strange one. We identify particle abundances and rapidity spectra to be suitable probes in order to extract information about CSR, while transverse mass spectra are less sensitive ones. Our results provide a microscopic explanation for the "horn" structure in the excitation function of the K+/π+ ratio: the CSR in the hadronic phase produces the steep increase of this particle ratio up to [see formula in PDF] ≈ 7 GeV, while the drop at higher energies is associated to the appearance of a deconfined partonic medium.

Evidence for chiral symmetry restoration in heavy-ion collisions

We study the effect of the chiral symmetry restoration (CSR) on heavy-ion collisions observables in the energy range sNN=3–20GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach. The PHSD includes the deconfinement phase transition as well as essential aspects of CSR in the dense and hot hadronic medium, which are incorporated in the Schwinger mechanism for particle production. Our systematic studies show that chiral symmetry restoration plays a crucial role in the description of heavy-ion collisions at sNN=3–20GeV, realizing an increase of the hadronic particle production in the strangeness sector with respect to the non-strange one. Our results provide a microscopic explanation for the horn structure in the excitation function of the K+/π+ ratio: the CSR in the hadronic phase produces the steep increase of this particle ratio up to sNN≈7GeV, while the drop at higher energies is associated to the appearance of a deconfined partonic medium. Furthermore, the appearance/disappearance of the horn structure is investigated as a function of the system size. We additionally present an analysis of strangeness production in the (T,μB)-plane (as extracted from the PHSD for central Au+Au collisions) and discuss the perspectives to identify a possible critical point in the phase diagram.

Chiral symmetry restoration versus deconfinement in heavy-ion collisions at high baryon density

The effect of the chiral symmetry restoration (CSR) on observables from heavy-ion collisions is studied in the energy range within the Parton-Hadron-String Dynamics (PHSD) transport approach. The PHSD includes the deconfinement phase transition as well as essential aspects of CSR in the dense and hot hadronic medium, which are incorporated in the Schwinger mechanism for the hadronic particle production. We adopt different parametrizations of the nuclear equation of state from the non-linear σ − ω model, which enter in the computation of the quark scalar density for the CSR mechanism, in order to estimate the uncertainty in our calculations. For the pion-nucleon Σ-term we adopt Σπ ≈ 45 MeV which corresponds to some ‘world average’. Our systematic studies show that chiral symmetry restoration plays a crucial role in the description of heavy-ion collisions at , realizing an increase of the hadronic particle production in the strangeness sector with respect to the non-strange one. We identify particle abundances and rapidity spectra to be suitable probes in order to extract information about CSR, while transverse mass spectra are less sensitive. Our results provide a microscopic explanation for the “horn” structure in the excitation function of the K+/π+ ratio: the CSR in the hadronic phase produces the steep increase of this particle ratio up to , while the drop at higher energies is associated to the appearance of a deconfined partonic medium.

Chiral symmetry restoration in heavy-ion collisions at intermediate energies

We study the effect of the chiral symmetry restoration (CSR) on heavy-ion collisions observables in the energy range $\sqrt{s_{NN}}$=3-20 GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach. The PHSD includes the deconfinement phase transition as well as essential aspects of CSR in the dense and hot hadronic medium, which are incorporated in the Schwinger mechanism for the hadronic particle production. We adopt different parametrizations of the nuclear equation of state from the non-linear $\sigma-\omega$ model, which enter in the computation of the quark scalar density for the CSR mechanism, in order to estimate the uncertainty in our calculations.

Diffusion of hidden charm mesons in hadronic medium

The drag and diffusion coefficients of a hot hadronic medium have been evaluated by using hidden charm mesons as probes. The scattering amplitudes required for the evaluation of these coefficients are calculated using an effective theory and scattering lengths obtained from lattice QCD calculations. It is found that although the magnitude of the transport coefficients are small their temperature variation is strong. The insignificant momentum diffusion of J/ψ in the hadronic medium keeps their momentum distribution largely unaltered. Therefore, the task of characterization of quark gluon plasma by using the observed suppression of J/ψ at high momentum will be comparatively easier.

Diffusion ofΛcin hot hadronic medium and its impact onΛc/Dratio

The drag and diffusion coefficients of the $\Lambda_c(2286$ MeV) have been evaluated in the hadronic medium which is expected to be formed in the later stages of the evolving fire ball produced in heavy ion collisions at RHIC and LHC energies. The interactions between the $\Lambda_c$ and the hadrons in the medium have been derived from an effective hadronic Lagrangian as well as from the scattering lengths, obtained in the framework of heavy baryon chiral perturbation theory (HB$\chi$PT). In both the approaches, the magnitude of the transport coefficients are turn out to be significant. A larger value is obtained in the former approach with respect to the latter. Significant values of the coefficients indicate substantial amount of interaction of the $\Lambda_c$ with the hadronic thermal bath. Furthermore, the transport coefficients of the $\Lambda_c$ is found to be different from the transport coefficients of $D$ meson. Present study indicates that the hadronic medium has a significant impact on the $\Lambda_c/D$ ratio in heavy ion collisions.

Effect of in-medium spectral density of D and mesons on the dissociation in hadronic matter

The one-loop self-energy of the D and D ⁎ mesons in a hot hadronic medium is evaluated using the real time formalism of thermal field theory. The interaction of the heavy open-charm mesons with the thermalized constituents ( π , K , η ) of the hadronic matter is treated in the covariant formalism of heavy meson chiral perturbation theory. The imaginary parts are extracted from the discontinuities of the self-energy function across the unitary and the Landau cuts. The non-zero contribution from the latter to the spectral density of D and D ⁎ mesons opens a number of subthreshold decay channels of the J / ψ leading to a significant increase in the dissociation width in hadronic matter.

Light-flavour hadron production in pp and Pb–Pb collisions in the ALICE experiment at the LHC

Nuclear matter under extreme conditions of temperature and density can be investigated in ultrarelativistic heavy-ion collisions. The measurement of transverse momentum (p T ) distributions and yields of identified particles is a fundamental step in understanding collective and thermal properties of the matter produced in such collisions. At intermediate transverse momentum, it allows for testing the “recombination models” where hadrons could be formed by the coalescence of quarks from a deconfined quark-gluon plasma (QGP). At higher transverse momenta, particle spectra allow one to investigate the mechanism of parton energy loss in the hot and dense hadronic medium. The measurement of spectra in pp collisions not only provides the baseline for the heavy-ion data but also allows for the tuning and optimization of QCD-inspired models. The latest ALICE results on identified and inclusive light-flavour charged particles in pp collisions at √s = 0.9, 2.76 and 7 TeV and Pb-Pb collisions at √s NN = 2.76 TeV is reviewed. p T spectra, yields and ratios in pp as a function of the collision energy is shown and compared to previous experiments and Monte Carlo predictions. Recent Pb–Pb results in different centrality intervals is presented and compared to √s NN = 200 GeV Au–Au collisions at RHIC. Comparison with predictions from thermal and hydrodynamic models is also discussed.

Drag and diffusion coefficients ofBmesons in hot hadronic matter

The drag and diffusion coefficients of a hot hadronic medium consisting of pions, kaons and eta using open beauty mesons as a probe have been evaluated. The interaction of the probe with the hadronic matter has been treated in the framework of chiral perturbation theory. It is observed that the magnitude of both the transport coefficients is significant, indicating a substantial amount of interaction of the heavy mesons with the thermal bath. The results may have significant impact on the experimental observables like the suppression of single-electron spectra originating from the decays of heavy mesons produced in nuclear collisions at Relativistic Heavy Ion Collider and LHC energies.

D-mesons and charmonium states in hot isospin asymmetric strange hadronic matter

We study the properties of $D$ and $\bar{D}$ mesons in hot isospin asymmetric strange hadronic matter, arising due to their interactions with the hadrons in the hyperonic medium. The interactions of $D$ and $\bar{D}$ mesons with these light hadrons are derived by generalizing the chiral SU(3) model used for the study of hyperonic matter to SU(4). We also study the mass modifications of the charmonium states $J/\psi$, $\psi(3686)$ and $\psi(3770)$ in the isospin asymmetric strange hadronic matter at finite temperatures and investigate the possibility of the decay of the charmonium states into $D\bar D$ pairs in the hot hadronic medium. The mass modifications of these charmonium states arise due to their interaction with the gluon condensates of QCD, simulated by a scalar dilaton field introduced to incorporate the broken scale invariance of QCD within the effective chiral model. We also compute the partial decay widths of the charmonium states to the $D\bar {D}$ pairs in the hadronic medium. The strong dependence on density of the in-medium properties of the $D$, $\bar{D}$ and the charmonium states, as well as the partial decay widths of charmonium states to $D\bar {D}$ pairs, found in the present investigation, will be of direct relevance in observables like open charm enhancement as well as $J/\psi$ suppression in the compressed baryonic matter (CBM) experiments at the future Facility for Antiproton and Ion Research, GSI, where the baryonic matter at high densities is planned to be produced.

Drag coefficient ofDmesons in hot hadronic matter

We evaluate the drag and diffusion coefficients of a hot hadronic medium consisting of pions, nucleons, kaons and eta using open charm mesons as a probe. The interaction of the probe with the hadronic matter has been treated in the framework of effective field theory. It is observed that the magnitude of both the transport coefficients are significant, indicating substantial amount of interaction of the heavy mesons with the thermal hadronic system. The results may have noticeable impact on the experimental observable like the suppression of single electron spectra originating form the decays of heavy mesons in nuclear collisions at relativistic energies.

Charmonium and open charm production in nuclear collisions at SPS/FAIR energies and the possible influence of a hot hadronic medium

We provide predictions for charmonium and open charm production in nuclear collisions at SPS/FAIR energies within the framework of the statistical hadronization model. The increasing importance at lower energies of Λc production is demonstrated and provides a challenge for future experiments. We also demonstrate that, because of the large charm quark mass and the different timescales for charm quark and charmed hadron production, possible modifications of charmed hadrons in the hot hadronic medium do not lead to measurable changes in cross sections for D-meson production. A possible influence of medium effects can be seen, however, in yields of charmonium. These effects are visible at all energies and results are presented for the energy range between charm threshold and RHIC energy.

Heavy ion physics with the CMS experiment at the LHC

The LHC will collide protons at √ s = 14.0 TeV and lead beams at √ SNN = 5.5 TeV as well as other AA and pA combinations. The physics program of the Compact Muon Solenoid (CMS) includes the study of heavy ion collisions. The collision energy, much higher than is available at RHIC, will allow the study the dense partonic system with very hard probes: heavy quarks and quarkonia with emphasis on the b and γ, W ± and Z 0 bosons, high p T jets, photons. The production of these particles is likely to be modified, relative to pp collisions, by the presence of the hot hadronic medium. The CMS detector consists of a 13 m long, 6 m diameter superconducting solenoid which provides a uniform 4T magnetic field. The silicon tracker and electromagnetic and hadronic calorimeters are located inside the magnet while the muon detector is outside. The high granularity, high resolution calorimeters will provide hermetic coverage for | η| ≤ 5.5, making CMS an ideal detector to study high p T nuclear phenomena.

Vacuum fluctuation effects in a thermal hadronic medium

The vacuum fluctuation effects in a dense and hot hadronic medium on the -, - and -meson masses are studied in a one-loop approximation. The change of the nucleon-nucleon interaction potential due to the modification of the meson masses is also calculated.

Soft photon production in a hot hadronic medium

We discuss the emissivity of a thermalized hadronic medium in the soft real-photon region. The contribution due to the bremsstrahlung is calculated and compared with hadron-hadron scattering and hadronic decays. The Landau-Pomeranchuk suppression of photon production is included in our analyses. It is argued that the bremsstrahlung is a dominant source of soft photons with energy ω≲0.8 GeV. The main contribution of more energetic photons in a hot hadronic medium is the reaction πϱ→ A 1→ πγ. The photon production rate due to bremsstrahlung in the quark-gluon plasma is also calculated and compared with the hadronic gas contribution.

Finite-temperature QCD sum rules reexamined: ϱ, ω and A 1 mesons

A new formulation of QCD sum rules at finite temperature ( T) is developed. Because of the factorization in the operator product expansion, all the soft dynamics including the effect of finite T in the hadronic phase is taken into account in the thermal average of local operators 〈¢O〉 T . Unlike for the T = 0 case, 〈¢O〉 T has non-vanishing values for the Lorentz non-scalar operators such as vγ μD v q . On the basis of the observation that the finite-temperature medium can be well approximated by a dilute (non-interacting) pion gas at low T, one can make a sensible estimate of the T-dependence of various condensates, where the current algebra and the experimental information of the pion structure functions turn out to be a useful guide. We applied this method to the light vector mesons ( ϱ, ω and A 1) and found that the change of the four-quark condensate at T ≠ 0 is crucial to the change of meson properties. The lepton pair production rate from the hot hadronic medium near the ϱ-resonance is calculated using the result of the sum rules. This has direct relevance to the detection of the lepton pairs in future projects of the ultra-relativistic heavy-ion collisions such as RHIC and LHC.