Center Of Mass Energy Research Articles

Quark-Hadron Model for Elastic scattering between two-composite systems at relativistic energies

We have previously developed formulas to calculate the full Glauber series of the elastic scattering between two composite systems their structures are pictured as bag of quarks or as cluster of nucleons. In this work, we have constructed a hybrid model in which the quark-hadron pictures are combined. The elastic cross sections of alpha-proton at center of mass energy √(s )=89 GeV and alpha-alpha at √(s )=126 GeV are evaluated by the hybrid model, the pure quark and conventional nucleon models. The results of different approaches are compared with the experimental data. The comparison shows that the predictions of the three model are identical at forward scattering angles and are significantly different at large momentum transfers. At large angles, the hybrid model calculation fits very well the experimental data than the calculations of quark and nucleon models. The nucleon model prediction provides better agreement with the data than the quark model calculation. The improvement achieved by hybrid model over the quark model at large scattering angles shows that the inclusion of quark–quark interactions is more consistently when the separation between the colliding nucleons is less than the hadron core.

A functional approach to the next-to-eikonal approximation of high energy gravitational scattering

The Fradkin–Schwinger functional methods to represent a Green function in an external gravitational field are used to study the eikonal and the next-to-eikonal limit, including the nonlinear gravitational interactions, of the scattering amplitudes of an ultra-relativistic scalar particle on a static super-massive scalar target in the nearly forward limit. The functional approach confirms the exponentiation of the leading eikonal which also applies to the first non-leading power in the energy of the light particle, moreover includes the interaction at impact parameter much larger than the Schwarzschild radius associated with the center of mass energy in the ultra-relativistic limit.

A genuine fermionic quintuplet seesaw model: phenomenological introduction

We study a model which generates Majorana neutrino masses at tree-level via low-energy effective operator with mass-dimension-9. Introduction of such a higher dimensional operator brings down the lepton number violating mass scale to TeV making such model potentially testable at present or near future colliders. This model possesses several new SU(2)L fermionic multiplets, in particular, three generations of triplets, quadruplets and quintuplets, and thus a rich phenomenology at the LHC. Noting that lepton flavour violation arises very naturally in such setup, we put constraints on the Yukawa couplings and heavy fermion masses using the current experimental bounds on lepton flavour violating processes. We also obtain 95% CL lower bounds on the masses of the triplets, quadruplets and quintuplets using a recent CMS search for multilepton final states with 137 inverse femtobarn integrated luminosity data at 13 TeV center of mass energy. The possibility that the heavy fermions could be long-lived leaving disappearing charge track signatures or displaced vertex at the future colliders like LHeC, FCC-he, MATHUSLA, etc. is also discussed.

Shadow cast and center of mass energy in a charged Gauss-Bonnet-AdS black hole

This work is devoted to the exploration of shadow cast and center of mass energy in the background of a 4-dimensional charged Gauss-Bonnet-AdS black hole. On investigating particle dynamics, we have examined black hole’s metric function. Whereas, with the help of null geodesics, we pursue to calculate the celestial coordinates and shadow radius of the black hole. We have made use of the hawking temperature to study the energy emission rate. Moreover, we have explored the center of mass energy and discussed its characteristics under the influence of spacetime parameters. For a better understanding, we graphically represent all of our main findings. The acquired result shows that both charge (Q) and AdS radius (l) decrease the shadow radius, while the Gauss-Bonnet coupling parameter (α) increases the shadow radius in AdS spacetime. On the other hand, both Q and α result in diminishing the shadow radius in asymptotically flat spacetime. Finally, we investigate the energy emission rate and center of mass energy under the influence of Q and α.

Two paths towards precision at a very high energy lepton collider

We illustrate the potential of a very high energy lepton collider (from 10 to 30 TeV center of mass energy) to explore new physics indirectly in the vector boson fusion double Higgs production process and in direct diboson production at high energy. Double Higgs production is found to be sensitive to the anomalous Higgs trilinear coupling at the percent level, and to the Higgs compositeness ξ parameter at the per mille or sub-per mille level thanks to the measurement of the cross-section in the di-Higgs high invariant mass tail. High energy diboson (and tri-boson) production is sensitive to Higgs-lepton contact interaction operators at a scale of several tens or hundred TeV, corresponding to a reach on the Higgs compositeness scale well above the one of any other future collider project currently under discussion. This result follows from the unique capability of the very high energy lepton collider to measure Electroweak cross-sections at 10 TeV energy or more, where the effect of new physics at even higher energy is amplified. The general lesson is that the standard path towards precision physics, based on measurements of high-statistics processes such as single and double Higgs production, is accompanied at the very high energy lepton collider by a second strategy based on measurements at the highest available energy.

Study of Dependence of Kinetic Freezeout Temperature on the Production Cross-Section of Particles in Various Centrality Intervals in Au-Au and Pb-Pb Collisions at High Energies.

Transverse momentum spectra of , p, , or , or and deuteron (d) in different centrality intervals in nucleus–nucleus collisions at the center of mass energy are analyzed by the blast wave model with Boltzmann Gibbs statistics. We extracted the kinetic freezeout temperature, transverse flow velocity and kinetic freezeout volume from the transverse momentum spectra of the particles. It is observed that the non-strange and strange (multi-strange) particles freezeout separately due to different reaction cross-sections. While the freezeout volume and transverse flow velocity are mass dependent, they decrease with the resting mass of the particles. The present work reveals the scenario of a double kinetic freezeout in nucleus–nucleus collisions. Furthermore, the kinetic freezeout temperature and freezeout volume are larger in central collisions than peripheral collisions. However, the transverse flow velocity remains almost unchanged from central to peripheral collisions.

Measurement of theH2(p,γ)He3Sfactor at 265–1094 keV

Recent astronomical data have provided the primordial deuterium abundance with percent precision. As a result, Big Bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave background. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the $^2$H($p,\gamma$)$^3$He cross section is reported. This nuclear reaction dominates the error on the predicted Big Bang deuterium abundance. A proton beam of 400-1650keV beam energy was incident on solid titanium deuteride targets, and the emitted $\gamma$-rays were detected in two high-purity germanium detectors at angles of 55$^\circ$ and 90$^\circ$, respectively. The deuterium content of the targets has been obtained in situ by the $^2$H($^3$He,$p$)$^4$He reaction and offline using the Elastic Recoil Detection method. The astrophysical S-factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for Big Bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher S-factor at Big Bang temperatures than previously assumed, reducing the predicted deuterium abundance.

Particle dynamics and geometric optics in Chern–Simons black holes

In this paper we study the effects of the coupling constant of the Chern–Simons modified gravity on some physical properties of black holes. The Hawking mass is one of the proposed definitions of quasilocal mass. We find that, for slowly rotating Chern–Simons black holes, the Hawking mass is independent of the coupling constant. Next, we show the dependence on the centre of mass energy, for two neutral colliding particles, of coupling constant and the rotation parameter. We also investigate energy extraction through Penrose process and find that the energy gain and efficiency of the Penrose process are independent of this coupling constant. Rotation of the polarization vector is also studied for dependence on the Chern–Simons coupling constant.

Identifying heavy-flavor jets using vectors of locally aggregated descriptors

Jets of collimated particles serve a multitude of purposes in high energy collisions. Recently, studies of jet interaction with the quark-gluon plasma (QGP) created in high energy heavy ion collisions are of growing interest, particularly towards understanding partonic energy loss in the QGP medium and its related modifications of the jet shower and fragmentation. Since the QGP is a colored medium, the extent of jet quenching and consequently, the transport properties of the medium are expected to be sensitive to fundamental properties of the jets such as the flavor of the parton that initiates the jet. Identifying the jet flavor enables an extraction of the mass dependence in jet-QGP interactions. We present a novel approach to tagging heavy-flavor jets at collider experiments utilizing the information contained within jet constituents via the model architecture. We show the performance of this model in proton-proton collisions at center of mass energy √(s) = 200 GeV as characterized by common metrics and showcase its ability to extract high purity heavy-flavor jet sample at various jet momenta and realistic production cross-sections including a brief discussion on the impact of out-of-time pile-up. Such studies open new opportunities for future high purity heavy-flavor measurements at jet energies accessible at current and future collider experiments.

Optimization of design parameters for SPPC longitudinal dynamics

As the second stage of the CEPC-SPPC project, SPPC (Super Proton-Proton Collider) aims at exploring new physics beyond the Standard Model. The key design goal for the SPPC accelerator complex is to reach 75 TeV in center of mass energy with a circumference of 100 km for the collider and an injector chain of four accelerators in cascade to support the collider. As an important part of the SPPC conceptual study, the longitudinal beam dynamics was studied systematically, which includes the dynamics in the collider and its complex injector chain. First, the bunch filling scheme of the SPPC complex was designed on the basis of various constraints such as the technical challenges of the kicker magnets, limited extraction energy per injection and so on. Next, the study on the longitudinal dynamics in the collider focused on the RF scheme to meet the requirements for luminosity and mitigate relevant instabilities. A higher harmonic RF system (800 MHz) together with the basic RF system (400 MHz) to form a dual-harmonic RF system was employed to mitigate collective instabilities and increase the luminosity by producing shorter bunches. In addition, the longitudinal matchings between the bunches in the different accelerator stages were studied, with special attention to the space charge effects and the beam loading effect in the two lower energy rings (p-RCS and MSS), which result in an optimization of the RF schemes. A set of self-consistent beam and RF parameters for the SPPC complex was obtained. The collider and the three proton synchrotrons of the injector chain have unprecedented features, thus this study demonstrates how a future proton-proton collider complex looks like.

The see-saw portal at future Higgs Factories

We consider an extension of the Standard Model with two right-handed singlet fermions with mass at the electroweak scale that induce neutrino masses, plus a generic new physics sector at a higher scale Λ. We focus on the effective operators of lowest dimension d = 5, which induce new production and decay modes for the singlet fermions. We assess the sensitivity of future Higgs Factories, such as FCC-ee, CLIC-380, ILC and CEPC, to the coefficients of these operators for various center of mass energies. We show that future lepton colliders can test the cut-off of the theory up to Λ ≃ 500–1000 TeV, surpassing the reach of future indirect measurements of the Higgs and Z boson widths. We also comment on the possibility of determining the underlying model flavor structure should a New Physics signal be observed, and on the impact of higher dimensional d = 6 operators on the experimental signatures.

Dependence of related parameters on centrality and mass in a new treatment for transverse momentum spectra in high energy collisions

We collected the experimental data of transverse momentum spectra of identified particles produced in proton-proton ($p$-$p$), deuteron-gold ($d$-Au or $d$-$A$), gold-gold (Au-Au or $A$-$A$), proton-lead ($p$-Pb or $p$-$A$), and lead-lead (Pb-Pb or $A$-$A$) collisions measured by the ALICE, CMS, LHCb, NA49, NA61/SHINE, PHENIX, and STAR collaborations at different center-of mass energies. The multisource thermal model at the quark level or the participant quark model is used to describe the experimental data. The free parameters, the effective temperature $T$, entropy index-related $n$, and revised index $a_{0}$, in the revised Tsallis--Pareto-type function are extracted at the quark level. In most cases, $T$ and $n$ in central collisions are larger than those in peripheral collisions, and $a_0$ does not change in different centrality classes. With the increase in the mass of produced particle or participant quark, $T$ and $a_0$ increase, and $n$ does not change significantly. The behaviors of related parameters from $p$-$p$, $p(d)$-$A$, and $A$-$A$ collisions are similar.

Measurement of the CKM angle \u03b3 in B\xb1 \u2192 DK\xb1 and B\xb1 \u2192 D\u03c0\xb1 decays with D \u2192 {K}_{mathrm{S}}^0 h+h\u2212

A measurement of CP-violating observables is performed using the decays B± → DK± and B± → Dπ±, where the D meson is reconstructed in one of the self-conjugate three-body final states {K}_{mathrm{S}}^0 π+π− and {K}_{mathrm{S}}^0 K+K− (commonly denoted {K}_{mathrm{S}}^0 h+h−). The decays are analysed in bins of the D-decay phase space, leading to a measurement that is independent of the modelling of the D-decay amplitude. The observables are inter- preted in terms of the CKM angle γ. Using a data sample corresponding to an integrated luminosity of 9 fb−1 collected in proton-proton collisions at centre-of mass energies of 7, 8, and 13 TeV with the LHCb experiment, γ is measured to be left({68.7}_{-5.1}^{+5.2}right){}^{circ} . The hadronic parameters {r}_B^{D K},{r}_B^{Dpi},{delta}_B^{D K},kern0.5em mathrm{and}kern0.5em {delta}_B^{Dpi} , which are the ratios and strong-phase differences of the suppressed and favoured B± decays, are also reported.

Discrimination between the final state of tH and tA using neural network

The Higgs Boson discovered in 2012 at the Large Hadron Collider (LHC) is still assumed to be the Standard Model Higgs Boson -a scalar particle. But there are still possibilities for a pseudo-scalar Higgs Boson. Currently, LHC has not been able to discriminate whether the particle is a scalar, pseudo-scalar, or mixed-scalar-pseudoscalar particle. The focus of this research is in the formulation of the neural network algorithm to discriminate between event signals from a scalar Higgs Boson and pseudo-scalar Higgs Boson in the Higgs production channel of associate production of Higgs Boson with a pair of top-antitop quark in a proton-proton collision pp → tH with center of mass energy with only Higgs decaying to a pair of bottom-antibottom quark had been considered. The set of discriminating variables used is the 3-momentum of all the final state particles. Discriminating efficiency of 0.412 was obtained which showed relatively small discriminating power.

The rates of charmonium dissociation and recombination in heavy-ion collisions at [formula omitted] TeV using Bateman equation

The charmonium states with their different binding energies and radii dissolve at different temperatures of the medium produced in relativistic heavy-ion collisions. Relative yields of charmonium and thus their survival have potential to map the properties of Quark Gluon Plasma. In this study, we estimate the combined effect of color screening, gluon-induced dissociation and recombination on charmonium production in heavy-ion collisions (Pb+Pb ions) at center of mass energy (sNN)=5.02 TeV. The rate equations of dissociation and recombination are solved separately with a 2-dimensional accelerated expansion of fireball volume. To solve the recombination rate equation, we have used an approach of Bateman solution which ensures the dissociation of the recombined charmonium in the QGP medium. The modifications of charmonium states are estimated in an expanding QGP with the conditions relevant for Pb+Pb collisions at LHC.

Signatures of α -clustering in O16 by using a multiphase transport model

$\alpha$-clustered structures in light nuclei could be studied through "snapshots" taken by relativistic heavy-ion collisions. A multiphase transport (AMPT) model is employed to simulate the initial structure of collision nuclei and the proceeding collisions at center of mass energy $\sqrt{s_{NN}}$ = 6.37 TeV. This initial structure can finally be reflected in the subsequent observations, such as elliptic flow ($v_{2}$), triangular flow ($v_{3}$) and quadrangular flow ($v_4$). Three sets of the collision systems are chosen to illustrate system scan is a good way to identify the exotic $\alpha$-clustered nuclear structure, case I: $\mathrm{^{16}O}$ nucleus (with or without $\alpha$-cluster) + ordinary nuclei (always in Woods-Saxon distribution) in most central collisions, case II: $\mathrm{^{16}O}$ nucleus (with or without $\alpha$-cluster) + $\mathrm{^{197}Au}$ nucleus collisions for centrality dependence, and case III: symmetric collision systems (namely, $^{10}$B + $^{10}$B, $^{12}$C + $^{12}$C, $^{16}$O + $^{16}$O (with or without $\alpha$-cluster), $^{20}$Ne + $^{20}$Ne, and $^{40}$Ca + $^{40}$Ca) in most central collisions. Our calculations propose that relativistic heavy-ion collision experiments at $\sqrt{s_{NN}}$ = 6.37 TeV are promised to distinguish the tetrahedron structure of $\mathrm{^{16}O}$ from the Woods-Saxon one and shed lights on the system scan projects in experiments.

Light singlino dark matter at the LHC

The light singlino-like neutralino is expected to be a promising candidate for DM in the allowed parameter space of the NMSSM. The DM annihilation process takes place via the light Higgs bosons which are natural in this model. Identifying the allowed region of parameter space including various constraints, the detection prospect of such light DM candidate and Higgs bosons are explored at the LHC with its high luminosity options. Light Higgs bosons and the DM candidate, the lightest singlino-like neutralino are indirectly produced at the LHC via the SM Higgs production and its subsequent decays. Jet substructure techniques are used to tag boosted Higgs. It is found that the favourable range of masses of Higgs bosons and neutralino, compatible with a low mass DM solution, can be discovered with a reasonable signal significance ($\sim 5 \sigma$) at the LHC, with the center of mass energy $\sqrt{s}=14$ TeV and integrated luminosity options $\rm{\cal L}=300~fb^{-1}$ and 3000 $\rm fb^{-1}$.

Particle collisions near static spherically symmetric black holes

It has been shown by Bañados, Silk and West (BSW) that the center of mass energy (Ecm) of test particles starting from rest at infinity and colliding near the horizon of a Schwarzschild black hole is always finite. In this short note, we extent the BSW scenario and study two particles with different energies colliding near the horizon of a static spherically symmetric black hole. Interestingly, we find that even for the static spherically symmetric (i.e., Schwarzschild like) black holes it is possible to obtain an arbitrarily high Ecm from the two test particles colliding near but outside of the horizon of a black hole, if one fine-tunes the parameters of geodesic motion.

Coulomb dissociation of 16O into 4He and 12C

We measured the Coulomb dissociation of 16O into 4He and 12C at the R3B setup in a first campaign within FAIR Phase 0 at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The goal was to improve the accuracy of the experimental data for the 12C(α,γ)16O fusion reaction and to reach lower center-ofmass energies than measured so far.The experiment required beam intensities of 109 16O ions per second at an energy of 500 MeV/nucleon. The rare case of Coulomb breakup into 12C and 4He posed another challenge: The magnetic rigidities of the particles are so close because of the same mass-to-charge-number ratio A/Z = 2 for 16O, 12C and 4He. Hence, radical changes of the R3B setup were necessary. All detectors had slits to allow the passage of the unreacted 16O ions, while 4He and 12C would hit the detectors’ active areas depending on the scattering angle and their relative energies. We developed and built detectors based on organic scintillators to track and identify the reaction products with sufficient precision.

QCD and electro-weak corrections to the production of Higgs+2 jets at the LHC

We present complete next-to-leading-order (NLO) QCD correction and electro-weak (EW) correction to the production cross section of Higgs–Boson in association with two hard quark jets by using Monte-Carlo numerical calculation program, HAWK, for various photon parton distribution functions at the Large Hadron Collider with center of mass energy 7, 8, 13, and 14 TeV without and with typical vector-Boson-fusion cuts on the tagging jets. In our calculation we include complete contribution from the full set of t-channel, u-channel and s-channel Feynman diagrams, and corresponding interferences as well as NLO QCD and EW corrections.