Production In High-energy Collisions Research Articles

Effect of the laser beam geometry on laser-assisted muon pair production process at collider

In this research paper, we have investigated the process of muon pair production in high energy collisions via the exchange of γ and Z-bosons in the presence of the laser field for different directions. Analytical calculations of the cross-section are done within the scattering matrix approach by using the Dirac-Volkov states for electron and positron. The numerical computation of the cross-section shows that it behaves differently by changing the laser wave direction. For a laser field propagating in parallel with the incident beam, the cross-section is strongly affected from low intensities. In addition, for a given laser field strength and frequency, the required number of photons to be transferred increases by increasing the centre of mass energy. Therefore, the acceleration gradient provided by a collinear laser field further enhances the centre of mass energy.

Probing strangeness canonical ensemble with K−, ϕ(1020) and Ξ− production in Au+Au collisions at [formula omitted

We report the first multi-differential measurements of strange hadrons of K−, ϕ and Ξ− yields as well as the ratios of ϕ/K− and ϕ/Ξ− in Au+Au collisions at sNN=3 GeV with the STAR experiment fixed target configuration at RHIC. The ϕ mesons and Ξ− hyperons are measured through hadronic decay channels, ϕ→K+K− and Ξ−→Λπ−. Collision centrality and rapidity dependence of the transverse momentum spectra for these strange hadrons are presented. The 4π yields and ratios are compared to thermal model and hadronic transport model predictions. At this collision energy, thermal model with grand canonical ensemble (GCE) under-predicts the ϕ/K− and ϕ/Ξ− ratios while the result of canonical ensemble (CE) calculations reproduce ϕ/K−, with the correlation length rc∼2.7 fm, and ϕ/Ξ−, rc∼4.2 fm, for the 0-10% central collisions. Hadronic transport models including high mass resonance decays could also describe the ratios. While thermal calculations with GCE work well for strangeness production in high energy collisions, the change to CE at 3 GeV implies a rather different medium property at high baryon density.

A Short Theoretical Review of Charmonium Production

In this paper, we review the current status of the phenomenological study of quarkonium production in high-energy collisions. After a brief introduction of several important models and effective field theories for quarkonium production, we discuss the comparisons between theoretical predictions and experimental measurements.

Jet-associated deuteron production in pp collisions at [formula omitted] TeV

Deuteron production in high-energy collisions is sensitive to the space–time evolution of the collision system, and is typically described by a coalescence mechanism. For the first time, we present results on jet-associated deuteron production in pp collisions at s=13 TeV, providing an opportunity to test the established picture for deuteron production in events with a hard scattering. Using a trigger particle with high transverse-momentum (pT>5 GeV/c) as a proxy for the presence of a jet at midrapidity, we observe a measurable population of deuterons being produced around the jet proxy. The associated deuteron yield measured in a narrow angular range around the trigger particle differs by 2.4–4.8 standard deviations from the uncorrelated background. The data are described by PYTHIA model calculations featuring baryon coalescence.

Charged particle production in pp collisions at s = 8, 7 and 2.76 TeV at the LHC-a case study

We analyze the charged-particle multiplicity distributions measured by the ALICE experiment, over a wide pseudorapidity range, for [Formula: see text] collisions at [Formula: see text], 7 and 2.76 TeV at the LHC. The analysis offers an understanding of particle production in high energy collisions in the purview of a new distribution, the shifted Gompertz distribution. Data are compared with the distribution and moments of the distributions are calculated. A modified version of the distribution is also proposed and used to improve the description of the data consisting of two different event classes: the inelastic and the nonsingle diffractive and their subsets in different windows of pseudorapidity, [Formula: see text]. The distribution used to analyze the data has a wide range of applicability to processes in different fields and complements the analysis done by the ALICE collaboration in terms of various LHC event generators and IP-Glasma calculations.

Beyond Color Glass Condensate: particle production at both low and high transverse momenta

We propose a new formalism for particle production in high energy collisions including both gluon saturation and large x gluons in the target.

Self-organized criticality: a new approach to multihadron production

We apply the concept of self-organized criticality in statistical physics to the study of multihadron production in high energy collisions.

Cosmological analogies in the search for new physics in high-energy collisions

In this paper, analogies between multiparticle production in high-energy collisions and the time evolution of the early universe are discussed. A common explanation is put forward under the assumption of an unconventional early state: a rapidly expanding universe before recombination (last scattering surface), followed by the CMB, later evolving up to present days, versus the formation of hidden/dark states in hadronic collisions followed by a conventional QCD parton shower yielding final-state particles. In particular, long-range angular correlations are considered pointing out deep connections between the two physical cases potentially useful for the discovery of new physics.

Rapidity loss, spin, and angular asymmetries in the scattering of a quark from the color field of a proton or nucleus

We calculate the helicity amplitudes for scattering of a quark from both large and small $x$ gluons of a target proton or nucleus using spinor helicity formalism. We show that scattering from large $x$ gluons of the target results in non-zero spin asymmetry at intermediate $p_t$ as well as rapidity loss of the projectile quark. We comment on how this can also generate angular asymmetries in particle production in high energy collisions.

The proton in high definition: revisiting photon-initiated production in high energy collisions

We re-examine the current state of the art for the calculation of photon- initiated processes at the LHC, as formulated in terms of a photon PDF in the proton that may be determined rather precisely from the known proton structure functions. We in particular demonstrate that a by construction more precise calculation is provided by a direct application of the structure function approach, best known from the case of Higgs Boson production via vector boson fusion. This avoids any artificial scale variation uncertainties, which can otherwise be rather significant for processes calculated within the standard approach thus far. To understand the source of these, we present a detailed comparison of the structure function approach and its relation to the photon PDF. We then provide precise predictions for the photon-initiated contribution to lepton pair production at the LHC, including the lepton pair transverse momentum distribution. Thus, by a direct application of the structure function formalism we show how the contribution from initial-state photons at the LHC may for the first time be included with high precision in a universal and straightforward way, providing a high definition picture of the photon content of the proton.

Interpretation of Yb(10750) as a tetraquark and its production mechanism

Recently, the Belle Collaboration has updated the analysis of the cross sections for the processes e+e−→ϒ(nS)π+π− (n=1,2,3) in the e+e− center-of-mass energy range from 10.52 to 11.02 GeV. A new structure, called here Yb(10750), with the mass M(Yb)=(10752.7±5.9−1.1+0.7) MeV and the Breit-Wigner width Γ(Yb)=(35.5−11.3−3.3+17.6+3.9) MeV was observed [1]. We interpret Yb(10750) as a compact JPC=1−− state with a dominant tetraquark component. The mass eigenstate Yb(10750) is treated as a linear combination of the diquark-antidiquark and bb¯ components due to the mixing via gluonic exchanges shown recently to arise in the limit of large number of quark colors. The mixing angle between Yb and ϒ(5S) can be estimated from the electronic width, recently determined to be Γee(Yb)=(13.7±1.8) eV. The mixing provides a plausible mechanism for Yb(10750) production in high energy collisions from its bb¯ component and we work out the Drell-Yan and prompt production cross sections for pp→Yb(10750)→ϒ(nS)π+π− at the LHC. The resonant part of the dipion invariant mass spectrum in Yb(10750)→ϒ(1S)π+π− and the corresponding angular distribution of π+-meson in the dipion rest frame are presented as an example.

Light hidden photon production in high energy collisions

The visible and dark sectors of particle physics can be connected via the kinetic mixing between the ordinary (γ) and hidden photon (γ′). If the latter is light its production in high energy collisions of ordinary particles occurs via the γ − γ′ oscillations similarly to the neutrino processes. Generically, the experiments are insensitive to mass of the hidden photon, if it is lighter than 1 MeV, and it does not decay into e+e−-pair. Still, one can use the missing energy and scattering off the detector as signatures to search for light hidden photon. Presence of media suppresses production of the light vectors making the experiments insensitive to the entire model. In media the light hidden photon production is typically suppressed due to the dump of the γ − γ′ oscillations making the experiments insensitive to the entire model. We present analytic formulas for the light hidden photon production, propagation and detection valid for searches at colliders and beam-target experiments and apply them to estimate the impact on the sensitivities of NA64, FASER, MATHUSLA, SHiP, T2K, DUNE and NA62 for the background-free case.

Particle Production at High Energy: DGLAP, BFKL and Beyond

Particle production in high energy hadronic/nuclear collisions in the Bjorken limit Q 2 , s → ∞ can be described in the collinear factorization framework of perturbative Quantum ChromoDynamics (QCD). On the other hand in the Regge limit, at fixed and not too high Q 2 with s → ∞ , a k ⊥ factorization approach (or a generalization of it) is the appropriate framework. A new effective action approach to QCD in the Regge limit, known as the Color Glass Condensate (CGC) formalism, has been developed which allows one to investigate particle production in high energy collisions in the kinematics where collinear factorization breaks down. Here we give a brief overview of particle production in CGC framework and the evolution equation which governs energy dependence of the observables in this formalism. We show that the new evolution equation reduces to previously known evolution equations in the appropriate limits.

Particle production in high energy collisions: from high to low pt and back

We outline a new formalism which aims to unify different approaches to particle production in high energy collisions. The most common approach is that of collinear factorization valid at high pt while the so-called kt factorization is used for low pt particle production. The proposed formalism includes both low and high x gluon degrees of freedom in the hadron/nucleus wave function and thus can be applied to particle production in both low and high pt kinematic regions.

Resonance production in high energy collisions from small to big systems

The aim of this paper is to understand resonance production (and more generally particle production) for different collision systems, namely proton-proton (pp), proton-nucleus (pA), and nucleus-nucleus (AA) scattering at the LHC. We will investigate in particular particle yields and ratios versus multiplicity, using the same multiplicity definition for the three different systems, in order to analyse in a compact way the evolution of particle production with the system size and the origin of a very different system size dependence of the different particles.

Asymptotes of multiplicity and transverse momentum correlation coefficients at large string density

The multiple hadron production in high energy collisions is studied in the model with string fusion on transverse lattice. In the framework of the model the asymptotes of the correlation coefficients between the mean transverse momentum and the multiplicity and between the mean transverse momenta for realistic case of non-uniform string distribution in transverse plane were calculated. The results were obtained by two different methods using the alternative definitions of the correlation coefficients. It is shown that the asymptotes of the correlation coefficients obtained by these two methods coincide in the leading approximation. The examples with non-uniform string distribution in transverse plane were considered. Strong dependence of the correlation coefficient between the transverse momentum and a multiplicity on non-uniformity in the distribution of the strings was found. In particular it is shown that there are distributions of strings for which this coefficient becomes negative. For the correlation coefficient between transverse momenta its dependence on the scaled variance of the number of particles produced from a single string, which disappears in the case of a homogeneous string distribution, is analyzed. The analytical asymptote for the correlation coefficient between transverse momenta obtained at large string density are compared with the results of the MC numerical calculations of this coefficient.

Multifractal characteristics of multiparticle production in heavy-ion collisions at SPS energies

Entropy, dimensions and other multifractal characteristics of multiplicity distributions of relativistic charged hadrons produced in ion–ion collisions at SPS energies are investigated. The analysis of the experimental data is carried out in terms of phase space bin-size dependence of multiplicity distributions following the Takagi’s approach. Yet another method is also followed to study the multifractality which, is not related to the bin-width and (or) the detector resolution, rather involves multiplicity distribution of charged particles in full phase space in terms of information entropy and its generalization, Rényi’s order-[Formula: see text] information entropy. The findings reveal the presence of multifractal structure — a remarkable property of the fluctuations. Nearly constant values of multifractal specific heat “[Formula: see text]” estimated by the two different methods of analysis followed indicate that the parameter “[Formula: see text]” may be used as a universal characteristic of the particle production in high energy collisions. The results obtained from the analysis of the experimental data agree well with the predictions of Monte Carlo model AMPT.

Strangeness production in high-energy collisions and Hawking–Unruh radiation

The assumption that the production of quark–antiquark pairs and their sequential string-breaking takes place, likely as a tunneling process, through the event horizon of the color confinement determines the freezeout temperature and gives a plausible interpretation for the thermal pattern of elementary and nucleus–nucleus collisions. When relating the black-hole electric charges to the baryon-chemical potentials, it was found that the phenomenologically deduced parameters from the ratios of various particle species and the higher-order moments of net-proton multiplicity in the statistical thermal models and Polyakov linear-sigma model agree well with the ones determined from the thermal radiation from charged black hole. Accordingly, the resulting freezeout conditions, such as normalized entropy density [Formula: see text] and average energy per particle [Formula: see text][Formula: see text]GeV, are confirmed at finite chemical potentials as well. Furthermore, the problem of strangeness production in elementary collisions can be interpreted by thermal particle production from the Hawking–Unruh radiation. Consequently, the freezeout temperature depends on the quark masses. This leads to a deviation from full equilibrium and thus a suppression of the strangeness production in the elementary collisions. But in nucleus–nucleus collisions, an average temperature should be introduced in order to dilute the quark masses. This nearly removes the strangeness suppression. An extension to finite chemical potentials is introduced. The particle ratios of kaon-to-pion ([Formula: see text]), phi-to-kaon ([Formula: see text]) and antilambda-to-pion ([Formula: see text]) are determined from Hawking–Unruh radiation and compared with the thermal calculations and the measurements in different experiments. We conclude that these particle ratios can be reproduced, at least qualitatively, as Hawking–Unruh radiation at finite chemical potential. With increasing energy, both [Formula: see text] and [Formula: see text] keep their maximum values at low SPS energies. But the further energy decrease rapidly reduces both ratios. For [Formula: see text], there is an increase with increasing [Formula: see text], i.e., no saturation is to be observed.

Particle production in high-energy collisions beyond the shockwave limit

We compute next to eikonal (NE) and next to next to eikonal (NNE) corrections to the Lipatov vertex due to a finite target thickness. These arise from electric field insertions into the eikonal Wilson lines. We then derive a $k_T$-factorization formula for single inclusive gluon production at NNE accuracy and find that nuclear effects are absent. We also analyze NNE corrections to two-gluon production where some of the contributions are found to exhibit corrections proportional to $A^{2/3}$.

Strangeness production in AA and pp collisions

Boost-invariant hadron production in high energy collisions occurs in causally disconnected regions of finite space-time size. As a result, globally conserved quantum numbers (charge, strangeness, baryon number) are conserved locally in spatially restricted correlation clusters. Their size is determined by two time scales: the equilibration time specifying the formation of a quark-gluon plasma, and the hadronization time, specifying the onset of confinement. The expected values for these scales provide the theoretical basis for the suppression observed for strangeness production in elementary interactions ($pp$, $e^+e^-$) below LHC energies. In contrast, the space-time superposition of individual collisions in high energy heavy ion interactions leads to higher energy densities, resulting in much later hadronization and hence much larger hadronization volumes. This largely removes the causality constraints and results in an ideal hadronic resonance gas in full chemical equilibrium. In the present paper, we determine the collision energies needed for that; we also estimate when $pp$ collisions reach comparable hadronization volumes and thus determine when strangeness suppression should disappear there as well.