GeV Center Of Mass Energy Research Articles

Search for the production of dark matter in the framework of a mono- Z′ portal at the ILC with simulated electron-positron collisions at s=500 GeV

In the present work, we study the possible production of the light neutral gauge boson (Z′) candidates, which originated from a simplified-model scenario based on the mono-Z′ model, in association with dark matter. This study has been performed by studying events with dimuon plus missing transverse energy produced in the simulated electron-positron collisions at the foreseen International Linear Collider (ILC), operating at 500 GeV center of mass energy and integrated luminosity of 1000 fb−1. In case no new physics has been discovered, we set upper limits at 95% confidence level on the masses of various particles in the model as, spin-1 (Z′), as well as the fermionic dark matter. Published by the American Physical Society 2024

3D structure of anisotropic flow in small collision systems at energies available at the BNL Relativistic Heavy Ion Collider

We present (3+1)D dynamical simulations of asymmetric nuclear collisions at the Relativistic Heavy Ion Collider (RHIC). Employing a dynamical initial state model coupled to (3+1)D viscous relativistic hydrodynamics, we explore the rapidity dependence of anisotropic flow in the RHIC small system scan at 200 GeV center of mass energy. We calibrate parameters to describe central $^3$He+Au collisions and make extrapolations to d+Au and p+Au collisions. Our calculations demonstrate that approximately 50% of the $v_3(p_T)$ difference between the measurements by the STAR and PHENIX Collaborations can be explained by the use of reference flow vectors from different rapidity regions. This emphasizes the importance of longitudinal flow decorrelation for anisotropic flow measurements in asymmetric nuclear collisions, and the need for (3+1)D simulations. We also present results for the beam energy dependence of particle spectra and anisotropic flow in d+Au collisions.

Low Emittance Tuning of FCC-ee

The FCC-ee project studies the design of a future 100 km e+/e circular collider for precision studies and rare decay observations in the range of 90 to 350 GeV center of mass energy with luminosities in the order of 1035 cm–2 s–1. In order to reach these luminosity requirements, strong focusing is needed in the interaction regions. Large maximum beta values (of 7736 m for the Z energy) and the small beta star values, make the FCC-ee lattices particularly susceptible to misalignments and field errors. FCC-ee therefore presents an appreciable challenge for emittance tuning. In this paper, we describe a comprehensive correction strategy used for the low emittance tuning. The strategy includes programs that have been developed to optimise the lattice based on Dispersion Free Steering, linear coupling compensation based on Resonant Driving Terms and beta beat correction utilising response matrices. One hundred misalignment and field error random seeds were introduced in MAD-X simulations and the final corrected lattices are presented.

Multi-differential pattern of low-mass e+e− excess from [formula omitted] Au+Au collisions with HADES

The matter formed in central heavy-ion collisions at a few GeV per nucleon is commonly understood as resonance matter, a gas of nucleons and excited baryon states with a substantial contribution from mesonic, mostly pionic excitations. Yet, in the initial phase of the reaction the system is compressed to beyond nuclear ground state density and hence substantial modifications of the hadron properties are expected to occur. The spectral distribution of virtual photons measured in Au+Au collisions at 2.4 GeV center of mass energy indicates strong medium effects beyond pure superposition of individual NN collisions. We present multi-differential distributions of low-mass electron pairs. This radiation is remarkably well described assuming emission from a thermalized system. To gain deeper understanding of the microscopic origin of the radiation, we extracted the centrality dependent true (not blue-shifted) temperature, its azimuthal distribution, as well as mass-dependent effective slope parameter. Virtual photon spectra are confronted with available model calculations.

Probing the type-II seesaw mechanism through the production of Higgs bosons at a lepton collider

We investigate the production and decays of doubly-charged Higgs bosons for the Type-II seesaw mechanism at an $e^{+} e^{-}$ collider with two center of mass energies, $\sqrt{s}=380$ GeV and 3 TeV, and analyze the fully hadronic final states in detail. Lower mass ranges can be probed during the 380 GeV run of the collider, while high mass ranges, which are beyond the 13 TeV Large Hadron Collider discovery reach, can be probed with $\sqrt{s}=3$ TeV. For such a heavy Higgs boson, the final decay products are collimated, resulting in fat-jets. We perform a substructure analysis to reduce the background and find that a doubly-charged Higgs boson in the mass range 800-1120 GeV can be discovered during the 3 TeV run, with integrated luminosity $\mathcal{L} \sim 95\, \rm{fb}^{-1}$ of data. For 380 GeV center of mass energy, we find that for the doubly-charged Higgs boson in the range 160-172 GeV, a $5\sigma$ significance can be achieved with only integrated luminosity $\mathcal{L} \sim 24 \, \rm{fb}^{-1}$. Therefore, a light Higgs boson can be discovered immediately during the run of a future $e^{+} e^{-}$ collider.

Charged Particles Multiplicity and Scaling Violation of Fragmentation Functions in Electron-Positron Annihilation

By the use of data from the annihilation process of electron-positron in AMY detector at 60 GeV center of mass energy, charged particles multiplicity distribution is obtained and fitted with the KNO scaling. Then, momentum spectra of charged particles and momentum distribution with respect to the jet axis are obtained, and the results are compared to the different models of QCD; also, the distribution of fragmentation functions and scaling violations are studied. It is being expected that the scaling violations of the fragmentation functions of gluon jets are stronger than the quark ones. One of the reasons for such case is that splitting function of quarks is larger than splitting function of gluon.

The Italian Tau/charm project

A τ/charm Factory, an e + e- collider with very high luminosity at the 2–4.6 GeV center of mass energy, to be built on the Rome University at Tor Vergata campus, was studied by the Consortium Nicola Cabibbo Laboratory and the INFN Frascati Laboratories. This project is the natural evolution of the flagship Italian project SuperB Factory, funded by the Italian Government in 2010 with a budget that turned out to be insufficient to cover the total costs of the project. The study of rare events at the τ/charm energy was already planned as a Phase-II of SuperB [1]. This design keeps all the unique features of SuperB, including the polarization of the electron beam, with the possibility to take data in a larger energy range, with reduced accelerator dimensions and construction and operation costs. A Report on the accelerator design has been published in September 2013 [2].

Beam energy scan results from PHENIX

Probes like J/ψ and π0 production are very important for studying the properties of the strongly interacting partonic medium created in heavy ion collisions. Their production is strongly suppressed in =200 GeV Au + Au collisions, in comparison to the expectation from binary collision scaled p + p collisions. The recent low-energy scan at RHIC provided the PHENIX collaboration with an opportunity to study the evolution of the suppression at =39 and 62.4 GeV center of mass energies in order to disentangle multiple contributing mechanisms. The suppression of J/ψ observed is similar to those previously measured at 200 GeV. In contrast neutral pion suppression shows a distinct energy dependence at moderate pT region of the central collisions.

“T-odd effects” in unpolarized Drell–Yan scattering

We consider the leading twist “T-odd” contributions as the dominant source of the cos2ϕ azimuthal asymmetry in unpolarized pp¯→μ−μ+X di-lepton production in Drell–Yan scattering. This asymmetry contains information on the distribution of quark transverse spin in an unpolarized proton. In a parton-spectator framework we estimate these asymmetries at 50 GeV center of mass energy. This azimuthal asymmetry is interesting in light of proposed experiments at GSI, where an anti-proton beam is ideal for studying the transversity properties of quarks due to the dominance of valence quark effects.

Charm meson spectra ine+e−annihilation at 10.5 GeV center of mass energy

Using the CLEO detector at the Cornell Electron-positron Storage Ring, we have measured the scaled momentum spectra, dsigma/dx_p, and the inclusive production cross sections of the charm mesons D+, D0, D*+, and D*0 in e+e- annihilation at about 10.5 GeV center of mass energy, excluding the decay products of B mesons. The statistical accuracy and momentum resolution are superior to previous measurements at this energy.

Hunting radions at linear colliders

We investigate the possibility to disentangle the radions in the Randall–Sundrum scenario from Higgs boson at the next generation high energy e+e− linear colliders. Due to trace anomaly, the radion coupling (and in turn the branching ratio) to gluons is enhanced over the same for the Standard Model (SM) higgs. We study the radion φ production at electron–positron colliders, via the process e+e−→νν̄φ, and propose to investigate radion decay to a pair of gluons. At 500 GeV center of mass energy, our signal is not very promising. We find our results are encouraging for finding radion and differentiating it from higgs for center of mass energies of 1 TeV and above.

Measuring the Higgs boson's parity using τ→ρν

We present a very promising method for a measurement of the Higgs boson parity using the H/A→τ+τ−→ρ+ν̄τρ−ντ→π+π0ν̄τπ−π0ντ decay chain. The method is both model independent and independent of the Higgs production mechanism. Angular distributions of the τ decay products which are sensitive to the Higgs boson parity are defined and are found to be measurable using typical properties of a future detector for an e+e− linear collider. The prospects for the measurement of the parity of a Higgs boson with a mass of 120 GeV are quantified for the case of e+e− collisions of 500 GeV center of mass energy with an integrated luminosity of 500 fb−1. The Standard Model Higgsstrahlung production process is used as an example.

Distinguishing Higgs models in →ττ

We analyze the ratio of branching ratios R=BR(H→bb̄)/BR(H→τ+τ−) of Higgs boson decays as a discriminant quantity between supersymmetric and nonsupersymmetric models. This ratio receives large renormalization-scheme independent radiative corrections in supersymmetric models at large tanβ, which are absent in the Standard Model or Two-Higgs-doublet models. These corrections are insensitive to the supersymmetric mass scale. A detailed analysis in the effective Lagrangian approach shows that, with a measurement of ±21% accuracy, the Large Hadron Collider can discriminate between models if the CP-odd Higgs boson mass is below 900 GeV. An e+e− Linear Collider at 500 GeV center of mass energy can discriminate supersymmetric models up to a CP-odd Higgs mass of ∼1.8 TeV.

Multidimensional binning techniques for a two parameter trilinear gauge coupling estimation at LEP II

This paper describes two generalization schemes of the Optimal Variables technique in estimating simultaneously two Trilinear Gauge Couplings. The first is an iterative procedure to perform a two-dimensional fit using the linear terms of the expansion of the probability density function with respect to the corresponding couplings, whilst the second is a clustering method of probability distribution representation in five dimensions. The pair production of W's at 183 GeV center of mass energy, where one W decays leptonically and the other hadronically, was used to demonstrate the optimal properties of the proposed estimation techniques.

The first measurement of the neutron electromagnetic form factors in the time-like region

The detection of the e +e − → nn reaction at the Adone collider by the Fenice Collaboration has allowed to measure for the first time the neutron electromagnetic form factors in the time-like region, from threshold to 2.44 GeV center of mass energy. After a brief description of apparatus and data reduction, the new data are presented and compared to the proton results. Possible future perspectives are also discussed.

Search for lepton flavor violation in $ep$ collisions at 300 GeV center of mass energy

Using the ZEUS detector at the HERA electron-proton collider, we have searched for lepton flavor violation in ep collisions at a center-of-mass energy (root s) of 300 GeV. Events of the type e + p --> l + X with a final-state lepton of high transverse momentum, l = mu or tau, were sought. No evidence was found for lepton flavor violation in the combined 1993 and 1994 data samples, for which the integrated luminosities were 0.84 pb(-1) for e(-)p collisions and 2.94 pb(-1) for e(+)p collisions. Limits on coupling vs. mass are provided for leptoquarks and R-parity violating squarks, For flavor violating couplings of electromagnetic strength, we set 95% confidence level lower limits on leptoquark masses between 207 GeV and 272 GeV, depending on the leptoquark species and final-state lepton. For leptoquark,masses larger than 300 GeV, limits on flavor-changing couplings are determined, many of which supersede prior limits from rare decay processes.

Measurement of the total photon proton cross section and its decomposition at 200 GeV centre of mass energy

Measurement of the total photon proton cross section and its decomposition at 200 GeV centre of mass energy

Measurement of the total photon proton cross section and its decomposition at 200 GeV centre of mass energy

We present a new measurement of the total photoproduction cross section performed with the H1 detector at HERA. For an average centre of mass energy of 200 GeV a value of σtotλp=165±2±11µb has been obtained. A detailed analysis of the data in adequate kinematic regions enabled a decomposition of the total cross section in its elastic, single diffractive dissociation and remaining non-diffractive parts, based on safe assumptions on the double diffractive dissociation contribution.

Measurement of total and partial photon proton cross sections at 180 GeV center of mass energy

Photon proton cross sections for elastic light vector meson production, σelνp, inelastic diffractive production, σndνp, non-diffractive production, σdνp, as well as the total cross section, σtotνp, have been measured at an average υp center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are σelνp = 18 ± 7 μb, σdνp = 33 ± 8 μb, σndνp = 91 ± 11 μb, and σtotνp 143 ± 17 μb, where the errors include statistical and systematic errors added in quadrature.

Study ofpp and ΛΛ production ine + e − annihilation at 10 GeV center of mass energy

Study ofpp and ΛΛ production ine + e − annihilation at 10 GeV center of mass energy