Center Of Mass Energy Research Articles

Recent progress and future plan for STCF collider ring lattice design

The Super Tau-Charm Facility (STCF) is a proposed dual-ring electron–positron collider in China, designed to operate at a center-of-mass energy (CME) range of 2–7[Formula: see text]GeV with symmetric beam energies. The collider aims for a luminosity exceeding [Formula: see text] at the beam energy of 2.0[Formula: see text]GeV. This work presents the preliminary lattice design for the STCF collider ring, specifically optimized for the 2.0[Formula: see text]GeV beam energy. To improve the nonlinear dynamics performance, the optimization of lattice is carried out by adjusting the strengths of sextupole and octupole magnets following the tuning of phase advances.

Analysis of transverse momentum spectra of protons, deuterons, and tritons in symmetric heavy-ion collisions at √(s_NN ) = 200 GeV at the RHIC

Abstract The blast wave model with Tsallis statistics is used to analyze the transverse momentum spectra of the protons (p), deuteron (d), and triton (t) in √(s_NN ) = 200 GeV gold-gold (Au-Au) collisions at RHIC in various centrality bins. In particular transverse momentum ranges, model results closely match experimental data from the PHENIX (p) and STAR (d and t) Collaborations. The data is compared with protons obtained in Cu+Cu collisions and deuteron and triton in Ru+Ru collisions at 200 GeV, center of mass energy from STAR collaboration. Particle spectra are used to derive the kinetic freeze-out temperatures, transverse flow velocities, and freeze-out volumes. According to the findings, the kinetic freeze-out temperature rises as one goes from the central to peripheral collisions. In this transition, the transverse flow velocity and the freeze-out volume both drop. In the collisions of both Collaborations, this work reveals mass-dependent kinetic freeze-out temperature and differential volume possibilities. On the whole, the non-extensivity parameter q decreases with increasing centrality of the studied heavy-ion collisions, and heavier mass particles have smaller values of q, which implies higher degrees of thermalization and equilibrium in more central collisions and for heavier particles.

Dynamics and collision of particles in modified black-bounce geometry

In the present work, we first regularize a black hole spacetime in modified gravity (MOG) in the presence of the scalar-tensor-vector (STV) field, called the Schwarzschild MOG black hole, under the transformation r2→r2+a2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r^2 \\rightarrow r^2 + a^2$$\\end{document}, known as the Simpson–Visser (SV) spacetime (where a is regularization or black-bounce parameter). The spacetime can represent a black hole and a wormhole. We analyze horizon properties and calculate the effective mass of the spacetime. Also, we find black hole-wormhole regions in black-bounce and MOG parameter spacetime. We also analyze scalar invariants of spacetime, such as the Ricci scalar, the square of the Ricci tensor, and the Kretchmann scalar. We study test particle motion in the SV-MOG spacetime by considering the interaction between the particle and the STV field. We investigate how the STV fields change the innermost stable circular orbits (ISCOs), energy, and angular momentum of the test particle’s ISCO. It is shown that the ISCO decreases in the presence of the black bounce parameter and increases in the STV field. We also study the collisions of test particles and analyze how the MOG and black-bounce parameters influence the critical angular momentum of colliding particles and their center of mass energy.

Lepton flavour violation signal of the singly charged scalar singlet at the ILC

The singly charged SU(2) L singlet scalar is one of the very interesting new particles, as it can generate neutrino masses at loop level, produce contributions to various flavour observables. We study the possibility of detecting this kind of scalar predicted by the singly-charged scalar model at ILC via the lepton flavour violation process e+e−→S+S−→μe+E . Considering the constraints on the free parameters, we obtain the expected sensitivities of the ILC with the center of mass energy s=1TeV and the integrated luminosity L= 1.5 ab−1 to the parameter space of the singly-charged scalar model. The prospective excluded mass range at 95% C.L. is M S ≳ 470 GeV, 410 GeV for the branching ratio Bμe = 100% , 50%, respectively, while the scalar with M S ≳ 300 GeV is excluded at 95% C.L. for Bμe = 30%.

Curvature-bias corrections using a pseudomass method

Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy √(s)=13 TeV during 2016, 2017 and 2018. The biases are determined using Z→μ + μ - decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10-4 GeV-1 level, improves the Z→μ + μ - mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass.

Searching for singlet vector-like leptons via pair production at ILC

Vector-like leptons (VLLs) as one kind of the most intriguing particles, have been widely concerned in several extensions of the Standard Model (SM). In this work, we explore the discovery potential of VLLs via pair production in the context of models that satisfy asymptotic safety at the International Linear Collider (ILC). The expected sensitivities of the ILC with the center of mass energy s=1 TeV and the integrated luminosity L=1 ab−1 to the parameter space of this kind of VLL models are derived. The results we obtained show that, for the VLL with mass MF in the region of MF∈[101 GeV,463 GeV], the Yukawa coupling κ can be as low as κ∈[0.032,0.098].

Search for the light hadron decay χc1(3872)→π+π−η

With a data sample corresponding to an integrated luminosity of 11.5 fb−1 collected with the BESIII detector operating at the BEPCII storage ring, for the first time the light hadron decay χc1(3872)→π+π−η is searched for. While no significant signal is observed, the upper limits at the 90% confidence level for σ[e+e−→γχc1(3872)]B[χc1(3872)→π+π−η] at center of mass energies from 4.13 GeV to 4.34 GeV are determined. By normalizing to the χc1(3872)→π+π−J/ψ decay channel, a 90% confidence level upper limit for the branching fraction ratio R=B[χc1(3872)→π+π−η]/B[χc1(3872)→π+π−J/ψ]<0.12 is given. These measurements provide important inputs for understanding the internal structure of the χc1(3872) resonance. Published by the American Physical Society 2024

Exclusive diffractive J/ψ and ψ(2S) production in dipole model using a holographic AdS/QCD light-front wavefunction with longitudinal confinement

We use anti-de Sitter/quantum chromodynamics based holographic light-front wavefunction (LFWF) for vector meson, in conjunction with the dipole model to investigate the cross sections data for the diffractive and exclusive J/ψ and ψ(2S) production. We confront the experimental data using a new explicit form of the holographic LFWF, where the longitudinal confinement dynamics in the light-front Schrödinger equation is captured by the ’t Hooft equation of (1+1)-dim, in large Nc approximation, in addition to the transverse confinement dynamics governed by the confining mass scale parameter κ in vector mesons. We obtain the LFWF parameters from fitting to the exclusive J/ψ electroproduction data from the electron-proton collision at the Hadron Electron Ring Accelerator collider for mc=1.27 GeV. Our results suggest that the dipole model together with holographic meson LFWFs with longitudinal confinement is able to give a successful description for differential scattering cross section for exclusive J/ψ electroproduction for H1 and ZEUS data. We also predict the rapidity distributions of differential scattering cross section and total photoproduction of J/ψ and ψ(2S) states in proton-proton ultraperipheral collisions (UPCs) at center of mass energy s=7,13 TeV. Using the minimum set of parameters, our predictions for the UPCs are in good agreement with the recent experimental observations of UPCs at ALICE and LHCb Collaborations. Published by the American Physical Society 2024

Empirical model for fusion cross sections of Ca-induced reactions

A new empirical formula for the astrophysical S-factor has been suggested as a function of the Coulomb interaction parameter, center of mass energy, and barrier height. About 22 fusion reactions with 40,48Ca as projectiles were considered for different targets, leading to compound nuclei with atomic and mass numbers varying between 40 112 and , respectively. The fusion cross-sections have been estimated using the geometric factor, the Gamow-Sommerfield factor, and the empirical formula for the S-factor. This study's findings showed better agreement with those of available experiments when compared to Wong's formula. The present work leads to a smaller standard deviation value than Wong's formula when used to correlate the experimental data of calcium-induced fusion reactions. Wong's formula provides a good approximation of fusion cross-sections when the center of mass energy is below the fusion barrier when compared to above the fusion barrier.

Light- and hyper-nuclei collectivity in Au+Au collisions at RHIC-STAR

We report the first results on collision energy and particle mass dependence of directed flow v1 of light- and hyper-nuclei in mid-central Au+Au collisions at center of mass energies per nucleon pair of 3.0, 3.2, 3.5, and 3.9 GeV. All data have been collected by the STAR experiment in the fixed-target mode during the second phase of the RHIC beam energy scan. The mid-rapidity v1 slope, dv1/dy|y=0, of hyper-nuclei shows a similar energy and particle mass dependence to that of light-nuclei. The results suggest that the coalescence mechanism plays a dominant role in the formation of light- and hyper-nuclei.

Measurements of (anti)(hyper)nuclei with ALICE

The investigation of the production mechanism of light (anti)(hyper)nuclei in ultrarelativistic hadronic collisions is one of the main topics in modern nuclear physics. The ALICE Collaboration has significantly contributed to this specific field of research with systematic measurements of the production of (anti)(hyper)nuclei in different collision systems and centre-ofmass energies provided by the Large Hadron Collider. Measurements of the properties of hypernuclei, such as their lifetimes and binding energies, provide information on the hadronic interaction between hyperons and nucleons, which is complementary to that obtained from correlation measurements. In this contribution, recent results on the production of (anti)(hyper)nuclei measured with ALICE during the LHC Run 2 in different collision systems will be presented. These results will be discussed within the context of the statistical hadronization model and baryon coalescence. For the first time, the observations of the (anti)hyperhydrogen-4 and (anti)hyperhelium-4 in Pb–Pb collisions at 5.02 TeV will be shown. Moreover, new results on (anti)(hyper)nuclei measurements obtained using the LHC Run 3 data will be presented.

Event-by-event investigation of the two-particle source function in [formula omitted] TeV PbPb collisions with EPOS

The investigation of the two-particle source function in lead-lead collisions simulated by the EPOS model at a center of mass energy per nucleon pair of sNN=2.76 TeV is presented. The two-particle source functions are reconstructed directly on an event-by-event basis for pions, kaons and protons separately, using the final stage of EPOS. A Lévy source shape is observed for all three particle species in the individual events, deviating significantly from a Gaussian shape. The source parameters are extracted as functions of collision centrality and pair average transverse mass (mT). The Lévy exponent is found to be ordered accordingly to particle mass. The Lévy scale parameter is found to scale for all particle species with mT according to Gaussian hydrodynamic predictions; however, there is no mT-scaling found across these species. In case of pions, the effects of the decay products and hadronic rescattering are also investigated. The Lévy exponent is decreased when decay products are also included in the analysis. Without hadronic rescattering and decay products, the source shape is close to a Gaussian.

(γ, χcJ(J = 0,1)) and (γ, ηc) production in electron-positron annihilation at [formula omitted] GeV and 4.6 GeV in the framework of Bethe-Salpeter equation

In present work we study the production of ground and excited charmonium states in e−e+→γχcJ(nP)(J=0,1), and e−e+→γηc(nS), through leading order (LO) diagrams, which proceed through exchange of a virtual photon that couples to γ and ηc/χcJ through the triangular quark loop diagram, in the framework of 4×4 Bethe-Salpeter equation (BSE), at center of mass energies s=10.6 GeV (Belle energy), and 4.6 GeV (BESIII energy). The amplitude simplifies to a general form required by Lorentz-covariance, in terms of its form factors. The cross sections for these processes with leading order diagrams alone at s=10.6 GeV provide a sizable contribution, which might be mainly due to the BSE being a fully relativistic approach that incorporates the relativistic effect of quark spins and can also describe internal motion of constituent quarks within the hadron in a relativistically covariant manner. Our results are compared with recent Belle data at 10.6 GeV, and BESIII data at 4.6 GeV, as well as other models. Plots of cross sections versus the center-of mass energy, s reveal mild fluctuations in their behaviour for all the three processes in the low energy (s=4–6 GeV) region, and are analyzed in terms of the form factors.

Dead cone effect in charm and bottom quark jets

The evolution of a heavy quark initiated jet is mainly ruled by gluon bremsstrahlung. As a consequence of the dead-cone effect, this radiation is suppressed in the forward direction at angles smaller than that proportional to the heavy quark mass MQ, i.e. Θ0=MQ/EQ at energy EQ of the primary quark. In this paper, we unveil this effect in charm and bottom quark jets using DELPHI and OPAL data from Z0 boson decays in e+e− annihilation at center of mass energy 91.2 GeV. The analysis of the reconstructed heavy quark fragmentation function in momentum space shows the strong suppression of hadrons at high momenta in such events compared to light quark fragmentation by a factor ≲1/10. The amount of this suppression is well reproduced by perturbative QCD (pQCD) within the Modified Leading Logarithmic Aproximation and the compact scheme of Local Parton Hadron Duality (MLLA-LPHD). As a new result, we obtain an almost perfect agreement between the light quark fragmentation functions expected at W0∝MQ from DELPHI and OPAL data with Pythia8 and shed light on the reasons for the existence of the ultra-soft gluon excess at small momentum fraction in comparison with pQCD predictions.

The Influence of the Scalar and Vector Anomalous Couplings on the Z-production at ILC in the Randall - Sundrum Model

An attempt is made to present the effect of the scalar and vector anomalous couplings on scattering process with polarized initial beams in the Randall-Sundrum model. We have studied the contribution of radion, Higgs and gauge bosons on the Z-production cross-section at International Linear Colliders (ILC). The cross-section depends strongly on the polarization of initial beams, the center of mass energy and model interaction parameters. The obtained results indicate that with the vector anomalous couplings included Z boson and photon, the cross-sections for the Z production are much larger than that with the scalar couplings included radion and Higgs under the same conditions.

Search for the signal of vector-like bottom quark at LHeC in the final state with 3 b-jets

Vector-like quarks arise in many new theories beyond the Standard Model, which is driven by several theoretical issues. In a framework of the Standard Model simply extended by an SU(2) singlet vector-like bottom quark, we present a study of single production of such vector-like bottom quark at the LHeC. The work is preformed with assuming the LHeC with center of mass energy s=1.98 TeV and an integrated luminosity L=1000fb−1. We focus on the process e−p→νeB→νebH(orZ)→νebbb¯. The signal is searched in events with three b-jets within final state. Exclusion (discover) capability of the LHeC for the signal of the vector-like bottom quark are obtained at 2 σ (5 σ) confidence level. Our result demonstrates a significant improvement compared to previous relevant researches. We also discuss the capability of LHeC for the singlet B search with combined analysis from other experiments.

Dissociation rates and recombination likelihood of bottomonium states in heavy-ion collisions at sNN=5.02 TeV

In the medium of relativistic heavy-ion collisions, dissociation of the quarkonium and its survival have been studied to understand the properties of Quark Gluon Plasma (QGP). The coupled rates of dissociation and recombination reactions in QGP are commonly solved with the Boltzmann transport equation in which the formation and dissociation reactions compete with each other. Since the dissociation of newly formed bound-states is not accounted in the Boltzmann equation, a framework of decoupled rates is developed to assess the combined effect of gluon-induced dissociation and recombination (though it is small for [Formula: see text]) together with color screening on bottomonium production in heavy-ion collisions at center of mass energy [Formula: see text][Formula: see text]TeV. To calculate the recombination rates, we have employed an effective method of Bateman solution which ensures the correlated effect between the recombination and the dissociation of the newly combined bottomonium in the QGP medium. The modifications of bottomonium have been estimated in an inflating QGP with the constraints matching with the dynamics of [Formula: see text] collision events at LHC.

Excitation Function of Freeze-Out Parameters in Symmetric Nucleus–Nucleus and Proton–Proton Collisions at the Same Collision Energy

We analyze the transverse momentum (pT) spectra of π+, π−, K+, K−, p, p¯, Λ, Λ¯, Ξ, Ξ¯, Ω−, Ω¯+ or Ω−+Ω¯+ in different centrality intervals in gold–gold (Au–Au) and lead–lead (Pb–Pb) symmetric collisions at 200 GeV and 2.76 TeV, respectively, by Tsallis–Pareto-type function. Proton–proton collisions at the same centre of mass energies are also analyzed for these particles to compare the results obtained from these systems. The present work extracts the effective temperature T, non-extensivity parameter (q), the mean transverse momentum spectra (⟨pT⟩), the multiplicity parameter (N0), kinetic freeze-out temperature (T0) and transverse flow velocity (βT). We reported a plateau structure of pT, T, T0, βT, pT and q in central collisions. Beyond the plateau region, the excitation function of all the above parameters decreases towards the periphery, except q, which has a reverse trend. The multiplicity parameter is also extracted, which is found to be decreasing towards the periphery from the central collisions. In addition, we observed that the excitation function of pp collisions is nearly the same to that of the most peripheral symmetric nucleus–nucleus collisions at the same colliding energy. Throughout the analyses, the same multiplicity parameters for particles and their antiparticles have been reported, which show the symmetric production of particles and their antiparticles.

Charged particles and Penrose process near charged black holes in Einstein–Maxwell-scalar theory

We study the dynamics of charged test particles around an electrically charged black hole in Einstein–Maxwell-scalar (EMS) gravity. The event horizon properties of the spacetime around the black hole are explored and the upper limit for the EMS theory parameters corresponding to extreme charge and minimal value of the event horizon are found. The effective potential for the radial motion of the charged particles at the equatorial plane is investigated. Specific energy and angular momentum of the particles corresponding to circular stable orbits are also studied. We also investigate the effects of the EMS parameter and the black hole charge on innermost stable circular orbits (ISCOs). We also investigate synchrotron radiation of charged particles in the spacetime of the charged black hole in EMS gravity. We also explore electric Penrose and Bañados–Silk–West processes near the black hole horizon, where we analyse in detail the effects of EMS parameters on energy efficiency in the Penrose process and critical angular momentum that allows colliding particles near the horizon, together with the center of mass energy in charged particles collisions.

Exploring light nuclei production at RHIC and LHC energies with A Multi-Phase Transport model and a coalescence afterburner

In heavy-ion collisions, understanding how light nuclei species are produced can provide insight into the nature of hadronic interactions in extreme conditions. It can also shed light on understanding the matter-antimatter asymmetry and dark matter searches in astrophysical processes. To investigate the production mechanism of light nuclei such as deuteron, triton, and helium-3, we use a naive coalescence afterburner coupled to the well-known “A Multi-Phase Transport model” (AMPT). We focus on studying the production of light nuclei in central Au+Au collisions at different center of mass energies (sNN = 19.6, 39, and 200 GeV) and in Pb+Pb collisions at sNN = 2.76 TeV, at mid-rapidity. We generate events with the string melting version of AMPT, and feed the information of the nucleons with spatial and momentum conditions into the coalescence afterburner. Our study reports differential and integrated yields in transverse momentum (pT) of the light nuclei in different center of mass energies. We also estimate the coalescence parameters (BA) as a function of pT and collision energy for (anti-)deuterons, tritons and helium-3s for Au+Au and Pb+Pb collisions, which are compared to other light nuclei production studies. All results are compared with measurements from the STAR and ALICE experiments.