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J. G. Contreras

Publications and source records attributed to J. G. Contreras.

36 records · Page 2Linked to original sources
arXiv2019

A next-generation LHC heavy-ion experiment

The present document discusses plans for a compact, next-generation multi-purpose detector at the LHC as a follow-up to the present ALICE experiment. The aim is to build a nearly massless barrel detector consisting of truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors with MAPS technology, featuring an unprecedented low material budget of 0.05% X$_0$ per layer, with the innermost layers possibly positioned inside the beam pipe. In addition to superior tracking and vertexing capabilities over a wide momentum range down to a few tens of MeV/$c$, the detector will provide particle identification via time-of-flight determination with about 20~ps resolution. In addition, electron and photon identification will be performed in a separate shower detector. The proposed detector is conceived for studies of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher than possible with the upgraded ALICE detector, enabling a rich physics program ranging from measurements with electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector.

physics.ins-det↗
arXiv2019

Collinearly improved kernel suppresses Coulomb tails in the impact-parameter dependent Balitsky-Kovchegov evolution

We solved the impact-parameter dependent Balitsky-Kovchegov equation with the recently proposed collinearly imporved kernel. We find that the solutions do not present the Coulomb tails that have affected previous studies. We also show that once choosing an adequate initial condition it is possible to obtain a reasonable description of HERA data on the structure function of the proton, as well as on the cross section for the exclusive production of a $\mathrm{J/}ψ$ vector meson off proton targets. As a further application of the solutions, we computed the impact-parameter dependent Weiszäcker-Williams gluon distribution.

hep-ph↗
arXiv2018

Dissociative production of vector mesons at electron-ion colliders

We present predictions for the exclusive and dissociative production of vector mesons off protons in an electron-ion collider. The computation is based on the energy-dependent hot spot model that has successfully described the available photoproduction data. We find that the model also describes correctly all available electroproduction data. In addition, we find that the cross section for dissociative production as a function of the center-of-mass energy of the photon-proton system has a maximum, whose position depends on the virtuality of the photon and the mass of the vector meson. We use these maxima to define a geometrical saturation scale and find that it grows linearly with energy as a function of the scale of the process. This phenomenon can be studied at the proposed electron-ion colliders, JLEIC, eRHIC and LHeC.

hep-ph↗
arXiv2018

Mass dependence of vector meson photoproduction off protons and nuclei within the energy-dependent hot-spot model

We study the photoproduction of vector mesons off proton and off nuclear targets. We work within the colour dipole model in an approach that includes subnucleon degrees of freedom, so-called hot spots, whose positions in the impact-parameter plane change event-by-event. The key feature of our model is that the number of hot spots depends on the energy of the photon--target interaction. Predictions are presented for exclusive and dissociative production of $ρ^{0}$, $\mathrm{J/}ψ$, and $Υ(1S)$ off protons, as well as for coherent and incoherent photoproduction of $ρ^{0}$ off nuclear targets, where Xe, Au, and Pb nuclei are considered. We find that the mass dependence of dissociative production off protons as a function of the energy of the interaction provides a further handle to search for saturation effects at HERA, the LHC and future colliders. We also find that the coherent photonuclear production of $ρ^{0}$ is sensitive to fluctuations in the subnucleon degrees of freedom at RHIC and LHC energies.

hep-ph↗
arXiv2017

LHC Forward Physics

The goal of this report is to give a comprehensive overview of the rich field of forward physics, with a special attention to the topics that can be studied at the LHC. The report starts presenting a selection of the Monte Carlo simulation tools currently available, chapter 2, then enters the rich phenomenology of QCD at low, chapter 3, and high, chapter 4, momentum transfer, while the unique scattering conditions of central exclusive production are analyzed in chapter 5. The last two experimental topics, Cosmic Ray and Heavy Ion physics are presented in the chapter 6 and 7 respectively. Chapter 8 is dedicated to the BFKL dynamics, multiparton interactions, and saturation. The report ends with an overview of the forward detectors at LHC. Each chapter is correlated with a comprehensive bibliography, attempting to provide to the interested reader with a wide opportunity for further studies.

hep-ph↗
arXiv2017

Small $x$ gluon shadowing from LHC data on coherent $\mathrm{J/}ψ$ photoproduction

The cross section for coherent $\mathrm{J/}ψ$ photoproduction in Pb-Pb collisions is the sum of two contributions, one from low-, the other from high-energy photon-nucleus interactions. A novel method to disentangle both contributions allowing one to extract the coherent photo-nuclear cross section for coherent $\mathrm{J/}ψ$ production, $σ_{γ\rm Pb}$, is presented. The utility of the method is demonstrated using measurements from peripheral and ultra-peripheral Pb-Pb collisions at the LHC. Applying the proposed method to the available data it is possible to obtain $σ_{γ\rm Pb}$ up to a photon-lead centre-of-mass energy of 470 GeV, which corresponds to $x$ of 4.4x10$^{-5}$. To illustrate a possible use of the extracted photo-nuclear cross sections, the corresponding nuclear suppression factors are computed and they are compared to predictions of gluon shadowing calculated in the leading-twist approximation approach.

nucl-ex↗
arXiv2017

Energy dependence of dissociative $\mathrm{J/}ψ$ photoproduction as a signature of gluon saturation at the LHC

We have developed a model in which the quantum fluctuations of the proton structure are characterised by hot spots, whose number grows with decreasing Bjorken-$x$. Our model reproduces the $F_2(x,Q^2)$ data from HERA at the relevant scale, as well as the exclusive and dissociative $\mathrm{J/}ψ$ photoproduction data from H1 and ALICE. Our model predicts that for $W_{γ\mathrm{p}} \approx 500$ GeV, the dissociative $\mathrm{J/}ψ$ cross section reaches a maximum and then decreases steeply with energy, which is in qualitatively good agreement to a recent observation that the dissociative $\mathrm{J/}ψ$ background in the exclusive $\mathrm{J/}ψ$ sample measured in photoproduction by ALICE decreases as energy increases. Our prediction provides a clear signature for gluon saturation at LHC energies.

hep-ph↗
arXiv2015

Heavy-flavour and quarkonium production in the LHC era: from proton-proton to heavy-ion collisions

This report reviews the study of open heavy-flavour and quarkonium production in high-energy hadronic collisions, as tools to investigate fundamental aspects of Quantum Chromodynamics, from the proton and nucleus structure at high energy to deconfinement and the properties of the Quark-Gluon Plasma. Emphasis is given to the lessons learnt from LHC Run 1 results, which are reviewed in a global picture with the results from SPS and RHIC at lower energies, as well as to the questions to be addressed in the future. The report covers heavy flavour and quarkonium production in proton-proton, proton-nucleus and nucleus-nucleus collisions. This includes discussion of the effects of hot and cold strongly interacting matter, quarkonium photo-production in nucleus-nucleus collisions and perspectives on the study of heavy flavour and quarkonium with upgrades of existing experiments and new experiments. The report results from the activity of the SaporeGravis network of the I3 Hadron Physics programme of the European Union 7th Framework Programme.

nucl-ex↗
arXiv2011

Scaling and wavelet-based analyses of the long-term heart rate variability of the Eastern Oyster

Characterisations of the long-term behaviour of heart rate variability in humans have emerged in the last few years as promising candidates to became clinically significant tools. We present two different statistical analyses of long time recordings of the heart rate variation in the Eastern Oyster. The circulatory system of this marine mollusk has important anatomical and physiological dissimilitudes in comparison to that of humans and it is exposed to dramatically different environmental influences. Our results resemble those previously obtained in humans. This suggests that in spite of the discrepancies, the mechanisms of long--term cardiac control on both systems share a common underlying dynamic.

physics.data-an↗
arXiv2009

Higgs FCNC h -> t* c decay at the muon collider

We study the discovery potential of the flavor-changing neutral coupling (FCNC) htc of the Higgs boson and the top quark through the rare tree-body decay h -> Wbc at Muon colliders for a light Higgs boson with mass 114 < m_h < 145 GeV. This decay mode may compete with the SM background induced by the hWW coupling in some models with a tree-level htc coupling and with models that predict this coupling at the one-loop level in the range 10^{-2} - 10^{-1}. A future muon collider could test the scalar FCNC decay t -> hc via Higgs decay h -> t* c -> b W+ c down to values of the coupling g_{tc}=0.5 (that are equivalent to BR(t -> hc) = 5 x 10^{-3}). The LHC could probe values of g_{tc} one order of magnitude smaller, unless other processes beyond the SM appear that through intense multi jet activity may clutter the t -> hc signal.

hep-ph↗
arXiv2006

Working Group Report: Heavy-Ion Physics and Quark-Gluon Plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of Quark-Gluon Plasma believed to have created in heavy-ion collisions and in early universe are reported.

hep-ph↗
arXiv2006

On the scaling properties of the total $γ^*\mathrm{p}$ cross section

We perform a detailed analysis on the scaling properties of the total $γ^*\mathrm{p}$ cross section, $σ_{γ^*\mathrm{p}}$. We write the cross section as a product of two functions $W$ and $V$ representing, respectively, the dynamical degrees of freedom and the contribution from the valence partons. Analyzing data from HERA and fixed target experiments we find that $V$ is nearly independent of $Q^2$ and concentrated at large $x$, while $W$ carries all the information on the $Q^2$ evolution of $γ^*\mathrm{p}$. We define the reduced cross section $\tildeσ_{γ^*\mathrm{p}} \equiv W=σ_{γ^*\mathrm{p}}/V$, and show that it is very close to a generalized homogeneous function. This property gives rise to geometric scaling not only for small $x$, but for all the current measured kinematic plane. As a consequence of our {\em Ansatz} we also obtain a compact parameterization of $σ_{γ^*\mathrm{p}}$ describing all data above $Q^2=1$ GeV$^2$.

hep-ph↗
arXiv2004

The baryon magnetic moments of the octet and the decuplet using different limits of the SU(3) flavor group

Working within the non relativistic quark model a two parameter fit to the magnetic moments of baryons is presented. The fit has an excellent $χ^2$. The model is based on taking different flavor groups to describe the different magnetic moments. The selection of which group to assign to each baryon is guided by the structure of its wavefunction. The model corresponds to assigning different effective masses to a quark depending on which baryon is being considered. Using the values extracted from the fit, the magnetic moments of the $Ω^-$ and the $Δ^{++}$ have been predicted and the comparison to the existing experimental values is quite satisfactory.

hep-ph↗
arXiv2000

A new determination of the Pomeron intercept in hard processes

A method allowing for a direct comparison of data with theoretical predictions is proposed for forward jet production at HERA. It avoids the reconstruction of multi-parton contributions by expressing the experimental data directly as correction factors on the QCD forward jet cross-section. An application to the determination of the effective Pomeron intercept in the BFKL-LO parametrization from dsigma/dx data at HERA leads to a good fit with a significantly higher effective intercept, alpha_P = 1.43 \pm 0.025(stat.) \pm >.025(syst.), than for proton (total and diffractive) structure functions. It is however less than the value of the Pomeron intercept using dijets with large rapidity intervals obtained at Tevatron. We also evaluate the rapidity veto contribution to the higher order BFKL corrections. The method can be extended to other theoretical inputs.

hep-ph↗
arXiv1998

The intercept of the BFKL pomeron from Forward Jets at HERA

Recently the H1 and ZEUS collaborations have presented cross sections for DIS events with a forward jet. The BFKL formalism is able to produce an excellent fit to these data. The extracted intercept of the hard pomeron suggests that when all higher order corrections are taken into account the cross section will still rise very rapidly as expected for low $x$ dynamics.

hep-ph↗
arXiv1997

Semi-inclusive asymmetries with polarized proton beams at HERA

The prospects of semi-inclusive measurements with polarized proton beams at HERA are discussed. Detailed simulations show that one can disentangle the valence-quark and sea-quark contribution to the polarized structure function g_1(x) in the small x-domain, if the equivalent of 1000 pb-1 of data are collected. It is also shown how semi-inclusive charged- current events can provide information on the relative importance of the spin contribution of the anti-s and anti-d sea quarks. Moreover, various methods to determine the fragmentation functions in this kinematical domain are presented.

hep-ph↗
arXiv1997

Fast simulation of a HERA--like detector

A set of FORTRAN routines to perform a fast simulation of a HERA--like detector including the smearing of the $z$ coordinate of the interaction vertex, the simulation of a tracker system, of an electromagnetic and of a hadronic calorimeter is presented.

hep-ph↗