arXiv subjects

A. Pop

Publications and source records attributed to A. Pop.

16 recordsLinked to original sources

arXiv2025

Does the suppression shown at LHC in O-O collisions follow the systematics obtained for A-A collisions ?

In this paper we present to what extent recent experimental results obtained for $\pi^{0}$ suppression in O-O collisions at $\sqrt{s_{NN}}$=5.36 TeV fit into the systematics for much heavier systems. The systematics with which the comparison is made was published a few years ago \cite{Pet_1} in terms of charged particles suppression $R_{AA}$ as a function of $\langle N_{part} \rangle$ and $\langle dN_{ch}/d\eta \rangle$. The values of $R_{AA}$ at $\langle dN_{ch}/d\eta\rangle$ and $\langle N_{part} \rangle$ experimentally measured and estimated by Glauber MC, respectively, for O-O collisions are in good agreement with the systematics obtained for A-A collisions.

nucl-ex↗

arXiv2024

Features of strangeness production in pp and heavy ion collisions

Based on the existing experimental data for A-A collisions starting from the AGS energies up to the LHC ones, various systematics related to strange hadrons and anti-hadrons are presented. The ratio between the average transverse momentum and the square root of the total particle multiplicity per unit rapidity and unit transverse overlap area decreases with collision energy for a given centrality or with centrality for a given collision energy, thus supporting the predictions of CGC and percolation based approaches. The dependence on the square root of the total multiplicity per unit rapidity and unit transverse overlap area of the slope and offset extracted from the $\langle p_T\rangle$-particle mass correlation and of the average transverse expansion velocity and kinetic freeze-out temperature parameters obtained from BGBW fits of the pT spectra for strange hadrons is compared to that for pions, kaons and protons. The detailed study of the entropy density dependence of the ratio of strange hadron yields per unit rapidity to the total particle multiplicity per unit rapidity, at different collision energies and centralities, reveals the necessity to study separately strange hadrons and anti-hadrons. The correlation between the ratio of the single- and multi- strange anti-hadron yield per unit rapidity to the total particle multiplicity per unit rapidity and the entropy density is presented as a function of the fireball size. A maximum is evidenced in the similar correlation established for combined and separate species of strange hadrons, at different centralities, in the region where a transition from the baryon-dominated matter to the meson-dominated one takes place. The position of this maximum does not depend on the mass of the corresponding strange hadron. Comparison with pp experimental data reveals another similarity between pp and Pb-Pb collisions at the LHC energies.

hep-ph↗

arXiv2022

Features of hadronic and deconfined matter from AGS to LHC energies

Previous extensive studies on the dependence of the average transverse momentum, its slope as a function of the hadron mass and the average transverse expansion on the particle multiplicity per unit rapidity and unit transverse overlap area of the colliding partners are extended to the ratio of the energy density to the entropy density. The behaviour of the ratio between the average transverse momentum and the square root of the particle multiplicity per unit rapidity and unit transverse overlap area $\langle p_T \rangle/\sqrt{\langle dN/dy\rangle/S_{\perp}}$ as a function of collision energy for a given centrality or as a function of centrality for a given collision energy supports the predictions of CGC and percolation based approaches. The dependence of the ratio of the energy density $\langle dE_{T}/dy\rangle/S_{\perp}$ to the entropy density $\langle dN/dy\rangle/S_{\perp}$ at different collision centralities for A-A collisions from AGS, SPS, RHIC and LHC energies is presented. The trend of this ratio towards a plateau at the highest RHIC energies followed by a steep rise at LHC energies is in agreement with theoretical predictions made 40 years ago that indicate this behaviour as a signature of a phase transition. This pattern strongly depends on the collision geometry, converging towards the dependence that characterizes the pp minimum bias (MB) collisions for the most peripheral A-A collisions. Expected similarities between pp and Pb-Pb collisions at LHC energies are confirmed.

hep-ph↗

arXiv2021

Geometrical scaling for light flavor hadrons

As it is well known by now, the pre-partonic phase in hadron collisions is successfully described by the Color Glass Condensate (CGC) approach. Previous studies, based on experimental data obtained on a wide range of energies at the Relativistic Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC) for $\pi^+$, $K^+$ and $p$, evidenced that observables related to the dynamics of the collision, i.e. the mean transverse momentum ($\langle p_T \rangle$), the slope of the $\langle p_T \rangle$ dependence on the mass of the hadrons and the average transverse flow velocity obtained from the simultaneous fits of the $p_T$ spectra of the particles with the Boltzmann-Gibbs Blast Wave (BGBW) expression, scale rather well as a function of the square root of the ratio of the particle density over unit of rapidity to the overlapping area of the colliding nuclei ($\sqrt{(dN/dy)/S_\perp}$), the relevant scale in the gluon saturation picture. Results of a similar study extended to strange and multi-strange hadrons, for both proton-proton (\textit{pp}) and heavy-ion (\textit{A-A}) collision systems are presented in the present paper. The similarities and differences in the behaviour of strange hadrons relative to non-strange hadrons are discussed.

hep-ph↗

arXiv2020

Considerations on the suppression of charged particles and $\pi^0$ in high energy heavy ion collisions

Experimental results related to charged particle and $\pi^{0}$ suppression obtained at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven for Au-Au (Cu-Cu) collisions and at the Large Hadron Collider (LHC) at CERN for Pb-Pb (Xe-Xe) collisions are compiled in terms of the usual nuclear modification factors, $R_{AA} $ and $R_{CP}$, and of the newly introduced $R^{N}_{AA}$ and $R^{N}_{CP}$ as a function of $\langle N_{part} \rangle$ and $\langle dN_{ch}/d\eta\rangle$. The studies are focused on a $p_T$ range in the region of maximum suppression evidenced in the experiments. The core contribution to $R_{AA}$ is presented. Considerations on the missing suppression in high charged particle multiplicity events for pp collisions at 7 TeV are presented. The trends of $R_{CP}$ and $R^N_{CP}$ for charged particles and $R_{AA}^{\pi^0}$ and $(R_{AA}^N)^{\pi^0}$ as a function of $\sqrt{s_{NN}}$, measured at RHIC in Au-Au collisions and at LHC in Pb-Pb collisions, show a suppression that becomes larger from $\sqrt{s_{NN}}$ = 39 GeV up to $\sqrt{s_{NN}}$=200 GeV, followed by a saturation up to the highest energy of $\sqrt{s_{NN}}$ =5.02 TeV in Pb-Pb collisions. A clear change in the dependence of $(1-R_{AA}^{\pi^0})/\langle dN/dy \rangle$ for the most central collisions as a function of collision energy is evidenced in the region of $\sqrt{s_{NN}}$ =62.4 - 130 GeV.

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arXiv2018

Geometrical scaling for energies available at the BNL Relativistic Heavy Ion Collider to those at the CERN Large Hadron Collider

Based on the recent RHIC and LHC experimental results, the $\langle p_T\rangle$ dependence of identified light flavour charged hadrons on $\sqrt{(\frac{dN}{dy})/S_{\perp}}$, relevant scale in gluon saturation picture, is studied from $\sqrt{s_{NN}}$=7.7 GeV up to 5.02 TeV. This study is extended to the slopes of the $\langle p_T\rangle$ dependence on the particle mass and the $\langle\beta_T\rangle$ parameter from Boltzmann-Gibbs Blast Wave (BGBW) fits of the $p_T$ spectra. A systematic decrease of the slope of the $\langle p_T\rangle$ dependence on $\sqrt{(\frac{dN}{dy})/S_{\perp}}$ from BES to the LHC energies is evidenced. While for the RHIC energies, within the experimental errors, the $\langle p_T\rangle$/$\sqrt{(\frac{dN}{dy})/S_{\perp}}$ does not depend on centrality, at the LHC energies a deviation from a linear behaviour is observed towards the most central collisions. The influence of the corona contribution to the observed trends is discussed. The slopes of the $\langle p_T\rangle$ particle mass dependence and the $\langle\beta_T\rangle$ parameter from BGBW fits scale well with $\sqrt{(\frac{dN}{dy})/S_{\perp}}$. Similar systematic trends for pp at $\sqrt{s}$=7 TeV are in a good agreement with the ones corresponding to Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV and 5.02 TeV pointing to a system size independent behaviour.

hep-ph↗

arXiv2017

Core-corona interplay in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV

A simple approach based on the separation of wounded nucleons in an A-A collision in two categories, those suffering single collisions - corona and the rest - core, estimated within a Glauber Monte-Carlo approach, explains the centrality dependence of the light flavor hadrons production in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV. The core contribution does not include any dependence of any process on the fireball shape as a function of the impact parameter. Therefore, the ratios of the $p_T$ distributions to the one corresponding to the minimum bias pp collisions at the same energy, each of them normalised to the corresponding charged particle density, the $\langle p_T\rangle$ and transverse energy per unit of rapidity are reproduced less accurate by such an approach. The results show that the corona contribution plays an important role also at LHC energies and it has to be considered in order to evidence the centrality dependence of different observables related to the core properties and dynamics.

nucl-th↗

arXiv2014

Recent results and open questions on collective type phenomena from A-A to pp collisions

A review of the main results on the collective type expansion of the compressed and hot fireball formed in heavy ion collisions and some remarks to be considered when comparing multiplicity wise phenomena taking place in A-A, p-A and pp collisions, are followed by a discussion of the experimental results which seem to evidence collective type phenomena in pp collisions at $\sqrt{s}$ = 7 TeV at high charged particle multiplicity. Correlations among the kinetic freeze-out temperature, the average transverse expansion velocity and its profile, as a function of centrality and multiplicity, extracted from the fits of experimental transverse momentum spectra with an expression inspired by hydrodynamical models, estimates on Bjorken energy densities and perspectives in selecting soft and close to azimuthal isotropic events in pp collisions are presented.

nucl-ex↗

arXiv2012

Kinematical coincidence method in transfer reactions

A new method to extract high resolution angular distributions from kinematical coincidence measurements in binary reactions is presented. Kinematic is used to extract the center of mass angular distribution from the measured energy spectrum of light particles. Results obtained in the case of 10Be+p-->9Be+d reaction measured with the CHIMERA detector are shown. An angular resolution of few degrees in the center of mass is obtained.

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arXiv2012

Correlations between isospin dynamics and Intermediate Mass Fragments emission time scales: a probe for the symmetry energy in asymmetric nuclear matter

We show new data from the $^{64}$Ni+$^{124}$Sn and $^{58}$Ni+$^{112}$Sn reactions studied in direct kinematics with the CHIMERA detector at INFN-LNS and compared with the reverse kinematics reactions at the same incident beam energy (35 A MeV). Analyzing the data with the method of relative velocity correlations, fragments coming from statistical decay of an excited projectile-like (PLF) or target-like (TLF) fragments are discriminated from the ones coming from dynamical emission in the early stages of the reaction. By comparing data of the reverse kinematics experiment with a stochastic mean field (SMF) + GEMINI calculations our results show that observables from neck fragmentation mechanism add valuable constraints on the density dependence of symmetry energy. An indication is found for a moderately stiff symmetry energy potential term of EOS.

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arXiv2012

The DWARF project: Eclipsing binaries - precise clocks to discover exoplanets

We present a new observational campaign, DWARF, aimed at detection of circumbinary extrasolar planets using the timing of the minima of low-mass eclipsing binaries. The observations will be performed within an extensive network of relatively small to medium-size telescopes with apertures of ~20-200 cm. The starting sample of the objects to be monitored contains (i) low-mass eclipsing binaries with M and K components, (ii) short-period binaries with sdB or sdO component, and (iii) post-common-envelope systems containing a WD, which enable to determine minima with high precision. Since the amplitude of the timing signal increases with the orbital period of an invisible third component, the timescale of project is long, at least 5-10 years. The paper gives simple formulas to estimate suitability of individual eclipsing binaries for the circumbinary planet detection. Intrinsic variability of the binaries (photospheric spots, flares, pulsation etc.) limiting the accuracy of the minima timing is also discussed. The manuscript also describes the best observing strategy and methods to detect cyclic timing variability in the minima times indicating presence of circumbinary planets. First test observation of the selected targets are presented.

astro-ph.SR↗

arXiv2012

Correlations between emission timescale of fragments and isospin dynamics in $^{124}$Sn+$^{64}$Ni and $^{112}$Sn+$^{58}$Ni reactions at 35 AMeV

We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of $<$N/Z$>$ isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio $<$N/Z$>$ distributions than those produced in sequential statistical emission. All these effects support the concept of isospin "migration", that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy.

nucl-ex↗

arXiv2012

Persistence of odd-even staggering in charged fragment yields from the 112Sn+58Ni collision at 35 MeV/nucleon

Odd-even staggering effects on charge distributions are investigated for fragments produced in semiperipheral and central collisions of 112Sn+58Ni at 35 MeV/nucleon. For fragments with Z<16 one observes a clear overproduction of even charges, which decreases for heavier fragments. In peripheral collisions staggering effects persist up to Z about 40. For light fragments, staggering appears to be substantially independent of the centrality of the collisions, suggesting that it is mainly related to the last few steps in the decay of hot nuclei.

nucl-ex↗

arXiv2009

Collective Phenomena in Heavy Ion Collisions

A review of the main results of detailed flow analysis in highly central and semi-central heavy ion collisions at SIS energies is presented in the first part of this paper. The influence of the mass of the colliding nuclei and centrality on the collective expansion and the information on the equation of state of compressed and hot baryonic matter is discussed. The second part is dedicated to a similar type of analysis, based on the behaviour of the average transverse momentum as a function of mass of different hadrons, at the other extreme of energy range, where free baryonic fireballs are produced. Information on the partonic and hadronic expansion, temperature and degree of thermal equilibrium in p+p and Au+Au central collisions at 200 A.GeV is presented.

nucl-ex↗

arXiv2008

Isospin Dependence of Incomplete Fusion Reactions at 25 Mev/a

40Ca+40,48Ca,46Ti reactions at 25 MeV/A have been studied using the 4p CHIMERA detector. An isospin effect on the competition between incomplete fusion and dissipative binary reaction mechanisms has been observed. The probability of producing a compound system is observed to be lower in the case of N=Z colliding systems as compared to the case of reactions induced on the more neutron rich 48Ca target. Predictions based on CoMD-II calculations show that the competition between fusion-like and dissipative reactions, for the selected centrality, can strongly constraint the parameterization of symmetry energy and its density dependence in the nuclear equation of state.

nucl-ex↗

arXiv2005

Non-statistical fluctuations for deep inelastic processes in 27Al + 27Al

The excitation functions for different fragments produced in the 27Al + 27Al dissipative collisions have been measured in steps of 250 keV in the energy range 122 - 132 MeV. Deep inelastic processes have been selected by integrating events over a total kinetic energy loss window of 12 MeV between 20 and 32 MeV. Large fluctuations have been observed in all the studied excitation functions. Non-satistical origin of these fluctuations is confirmed by large channel cross correlations coefficients. Energy autocorrelation function of cross section excitation function presents damped oscillation structure as predicted for the case when a di-nuclear system with a lifetime similar with its revolution period is formed. The periodicity of the energy autocorrelation function is used to obtain information on the deformation of the 27Al + 27 Al di-nucleus.

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