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Ivan Melo

Publications and source records attributed to Ivan Melo.

18 recordsLinked to original sources
arXiv2024

Bridging the gap between cutting-edge science and school: non-formal education in high-energy physics

We report mainly on the global flagship outreach activity in particle physics: the International Particle Physics Masterclasses. It is illustrated on the example of Slovakia and the Czech Republic. The Masterclasses are described and their long-term impact is studied with the help of a survey among former participants. The positive effect of Masterclasses in shifting the attitude towards science is shown. We also discuss the modification of Masterclasses for a pandemic situation. Finally, we present CASCADE projects as a way to foster the interest in a field which has been strongly enhanced by previous experience, e.g., at Masterclasses.

physics.ed-ph↗
arXiv2019

Higgs potential and fundamental physics

Physics associated with the Higgs field potential is rich and interesting and deserves a concise summary for a broader audience to appreciate the beauty and the challenges of this subject. We discuss the role of the Higgs potential in particle physics, in particular in the spontaneous symmetry breaking and in the mass generation using an example of a simple reflection symmetry, then continue with the temperature and quantum corrections to the potential which lead us to the naturalness problem and the vacuum stability.

physics.gen-ph↗
arXiv2019

Kinetic freeze-out in central heavy-ion collisions between 7.7 and 2760 GeV per nucleon pair

We fit the single-particle $p_t$ spectra of identified pions, kaons, and (anti)protons from central collisions of gold or lead nuclei at energies between 7.7 and 2760~GeV per nucleon pair. Blast wave model with included resonance production and with an assumption of partial chemical equilibrium is used and the fits are performed with the help of a Gaussian emulator process. A kinetic freeze-out temperature is found about 100~MeV for the lowest collision energies and 80~MeV at the LHC. The average transverse expansion velocity grows with increasing $\sqrt{s_{NN}}$ from 0.45 to 0.65. Due to partial chemical equilibrium, the influence of resonance decays on the shape of the $p_t$ spectra for $\sqrt{s_{NN}}$ above 27~GeV is small.

nucl-th↗
arXiv2019

Benchmark values for the net proton number fluctuations

We formulate a baseline model for the net-proton number fluctuations in ultrarelativistic heavy-ion collisions. Our model includes total baryon number conservation, fluctuations of the participating nucleon number, limited acceptance, and a possibility that isospin is remembered by the participating wounded nucleons. Most importantly, we formulated the model as consisting of two components: wounded nucleons and the produced nucleon-antinucleon pairs. Those two components have different rapidity distributions. Owing to this feature we obtain also predictions for the rapidity dependence of the cumulants of the net-proton number distribution and their ratios.

nucl-th↗
arXiv2018

Bringing particle physics into classrooms

Exciting scientific results such as the discovery of the Higgs boson offer a great opportunity to engage young people in particle physics. International Particle Physics Masterclasses highlight how high school students across the world can be exposed to real data from CERN's LHC accelerator in a stimulating and productive atmosphere in just a single day.

physics.ed-ph↗
arXiv2016

Generation of random deviates for relativistic quantum-statistical distributions

We provide an algorithm for generation of momenta (or energies) of relativistic particles according to the relativistic Bose-Einstein or Fermi-Dirac distributions. The algorithm uses rejection method with effectively selected comparison function so that the acceptance rate of the generated values is always better than 0.9. It might find its use in Monte-Carlo generators of particles from reactions in high-energy physics.

physics.comp-ph↗
arXiv2015

Reconstructing the final state of Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV

We fit the single-hadron transverse-momentum spectra measured in Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV with the blast-wave model that includes production via resonance decays. Common fit to pions, kaons, (anti)protons, and lambdas yields centrality dependence of the freeze-out temperature and transverse expansion velocity. In the most central collisions we see $T=98$ MeV and $\langle v_t \rangle = 0.654$. The $K^*$ resonance fits into this picture but the $ϕ$ meson might freeze-out a little earlier. Multistrange baryons seem to decouple at higher temperature and weaker transverse flow. Within our model we observe hints of chemical potential for the charged pions.

nucl-th↗
arXiv2015

Observables of non-equilibrium phase transition

A rapidly expanding fireball which undergoes first-order phase transition will supercool and proceed via spinodal decomposition. Hadrons are produced from the individual fragments as well as the left-over matter filling the space between them. Emission from fragments should be visible in rapidity correlations, particularly of protons. In addition to that, even within narrow centrality classes, rapidity distributions will be fluctuating from one event to another in case of fragmentation. This can be identified with the help of Kolmogorov-Smirnov test. Finally, we present a method which allows to sort events with varying rapidity distributions in such a way, that events with similar rapidity histograms are grouped together.

nucl-th↗
arXiv2011

A brief outline of the top-BESS model

This is a brief outline of the top-BESS model and its properties. The top-BESS model is the higgsless effective description of the strong electroweak symmetry breaking with a single new SU(2)_L+R triplet vector resonance. In contrast with the universality of the fermion interactions of the BESS model, the top-BESS vector resonance couples directly to the third quark generation only. The complete formulation of the model along with its phenomenology can be found in arXiv:1107.0570.

hep-ph↗
arXiv2011

Top-BESS model and its phenomenology

We introduce the top-BESS model which is the effective description of the strong electroweak symmetry breaking with a single new SU(2)_L+R triplet vector resonance. The model is a modification of the BESS model in the fermion sector. The triplet couples to the third generation of quarks only. This approach reflects a possible extraordinary role of the top quark in the mechanism of electroweak symmetry breaking. The low-energy limits on the model parameters found provide hope for finding sizable signals in the LHC Drell-Yan processes as well as in the s-channel production processes at the ILC. However, there are regions of the model parameter space where the interplay of the direct and indirect fermion couplings can hide the resonance peak in a scattering process even though the resonance exists and couples directly to top and bottom quarks.

hep-ph↗
arXiv2011

Generating heavy particles with energy and momentum conservation

We propose a novel algorithm, called REGGAE, for the generation of momenta of a given sample of particle masses, evenly distributed in Lorentz invariant phase space and obeying energy and momentum conservation. In comparison to other existing algorithms, REGGAE is designed for the use in multiparticle production in hadronic and nuclear collisions where many hadrons are produced and a large part of the available energy is stored in the form of their masses. The algorithm uses a loop simulating multiple collisions which lead to production of configurations with reasonably large weights.

nucl-th↗
arXiv2009

The use of Kolmogorov-Smirnov test in event-by-event analysis

We propose to use the Kolmogorov-Smirnov test to uncover non-statistical differences between events created in heavy ion collisions within the same centrality class. The advantage of the method over other approaches which are currently in use, is that it is sensitive to any difference between the events and is not restricted to simple moments of the distribution of hadrons. The particular application examined here is the identification of the fireball decay due to spinodal fragmentation and/or sudden rise of the bulk viscosity.

nucl-th↗
arXiv2009

The Kolmogorov-Smirnov test and its use for the identification of fireball fragmentation

We propose an application of the Kolmogorov-Smirnov test for rapidity distributions of individual events in ultrarelativistic heavy ion collisions. The test is particularly suitable to recognise non-statistical differences between the events. Thus when applied to a narrow centrality class it could indicate differences between events which would not be expected if all events evolve according to the same scenario. In particular, as an example we assume here a possible fragmentation of the fireball into smaller pieces at the quark/hadron phase transition. Quantitative studies are performed with a Monte Carlo model capable of simulating such a distribution of hadrons. We conclude that the Kolmogorov-Smirnov test is a very powerful tool for the identification of the fragmentation process.

nucl-th↗
arXiv2007

Fragmentation of the fireball and how to observe it

We argue that fragmentation at hadronisation is likely scenario in ultrarelativistic nuclear collisions. In case of crossover phase transition it is driven by a singularity of the bulk viscosity. We claim that such a scenario can explain the ``HBT puzzle'' and can be identified by non-statistical differences between event-wise rapidity distributions and by proton-proton rapidity correlations.

nucl-th↗
arXiv1996

The phenomenology of neutral heavy leptons

Naturally small neutrino masses can arise in some grand unified models. The mechanism of neutrino mass generation in these models typically requires the existence of neutral heavy leptons. We study the low-energy phenomenology of these new fermions. Concentrating on loop corrections due to neutral heavy leptons, we examine how the flavour-conserving leptonic decays of the Z boson, universality breaking in these decays, and the W boson mass depend on the mass and mixings of the neutral heavy leptons. Working within the framework of a superstring-inspired SU(2)_L x U(1)_Y model, we show that these flavour-conserving processes have some virtues over the traditionally considered flavour-violating decays.

hep-ph↗
arXiv1996

Phenomenology of neutral heavy leptons

We continue our previous work on the flavour-conserving leptonic decays of the Z boson with neutral heavy leptons (NHL's) in the loops by considering box, vertex, and self-energy diagrams for the muon decay. By inclusion of these loops (they contribute to the input parameter M_W) we can probe the full parameter space spanned by the so-called flavour-conserving mixing parameters ee_(mix), μμ_(mix), ττ_(mix) in a superstring-inspired model of neutrino mass. We compare the results of our analysis with the existing work in this field and conclude that flavour-conserving decays have certain advantages over traditionally considered flavour-violating ones.

hep-ph↗
arXiv1996

Single Neutral Heavy Lepton Production at e^+e^- and μ^+ μ^- Colliders

Many extensions of the Standard Model include extra fermions. We here consider a model containing Dirac neutral heavy leptons in addition to massless neutrinos. These neutral heavy leptons can be produced singly along with a massless neutrino in $e^+ e^-$ and $μ^+ μ^-$ collisions. The production rates depend on the neutral heavy lepton masses and mixing parameters. We here consider the rates for this process and potential signatures for the machine energies and luminosities suggested for the Snowmass study.

hep-ph↗