Gluon-gluon Collisions Research Articles

Particle production sources inpPb and PbPb at the LHC

Hadron production in relativistic heavy-ion collisions at LHC energies is investigated. After a brief consideration of stopping, particle production is accounted for in a nonequilibrium-statistical model with two fragmentation sources, and a central source that is mostly due to low-x gluon-gluon collisions. The particle content and energy dependence of the three sources is discussed for AuAu (RHIC) and PbPb (LHC). Results for asymmetric pPb collisions are compared with preliminary ALICE and ATLAS data. A brief survey of several features of hadron production in relativistic heavy-ion collisions at LHC energies is given in this article, which is essentially based on results pub- lished in (1), and obtained in (2, 3). The stopping process in the very first phase of the col- lision is mostly characterized by the interaction of fast va- lence quarks with low-x gluons in the respective other nu- cleus. The fragmentation peaks in net-proton (proton - antiproton) rapidity distributions are clearly visible in SPS and RHIC data (4-7). When considering rapidity or pseu- dorapidity distributions of produced charged particles, the fragmentation distributions also play a significant role, but since they shift to large values of rapidity at LHC, particle production near mid rapidity is almost exclusively deter- mined by the central low-x gluon-gluon source. This source cancels out in net-proton distributions, but in charged-hadron distributions its importance rises strongly with incident energy. In this note the relative im- portance of the three sources is investigated as function of energy from a direct comparison of the analytical solutions of a nonequilibrium-statistical relativistic diffusion model (RDM) (8) with PHOBOS (9) and recent ALICE data (10) data. This allows also for predictions at the LHC design energy, and for an analysis of the asymmetric pPb system at the current LHC energy of 5.02 TeV.

Hadron production and ϒ suppression at the LHC

Hadron production in relativistic heavy-ion collisions at LHC energies is investigated. After a brief consideration of stopping, particle production is accounted for in a nonequilibrium-statistical model with two fragmentation sources, and a central source that is mostly due to low-x gluon-gluon collisions. The particle content and energy dependence of the three sources is discussed for AuAu (RHIC) and PbPb (LHC). Results for asymmetric pPb collisions are compared with ALICE and preliminary ATLAS data. The suppression of ϒ-mesons in the hot quark-gluon medium in PbPb collisions as compared to pp at √sNN = 2.76 TeV is accounted for in a model that encompasses gluodissociation, collisional damping, screening, and reduced feed-down. Results are compared with CMS and ALICE data.

Hadron production and ϒ suppression at the LHC

Hadron production in relativistic heavy-ion collisions at LHC energies is in- vestigated. After a brief consideration of stopping, particle production is accounted for in a nonequilibrium-statistical model with two fragmentation sources, and a central source that is mostly due to low-x gluon-gluon collisions. The particle content and energy de- pendence of the three sources is discussed for AuAu (RHIC) and PbPb (LHC). Results for asymmetric pPb collisions are compared with ALICE and preliminary ATLAS data. The suppression of Y-mesons in the hot quark-gluon medium in PbPb collisions as compared to ppat √ sNN = 2.76 TeV is accounted for in a model that encompasses gluodissociation, collisional damping, screening, and reduced feed-down. Results are compared with CMS and ALICE data.

Hadron production and bottomia suppression at the LHC

Hadron production in relativistic heavy-ion collisions at LHC energies is in- vestigated. After a brief consideration of stopping, particle production is accounted for in a relativistic diffusion model with two fragmentation sources, and a central source that is mostly due to gluon-gluon collisions. The particle content and energy dependence of the sources is discussed. The suppression of Y-mesons in the hot quark-gluon medium in PbPb collisions as compared to pp at √ sNN = 2.76 TeV is accounted for in a model that encompasses gluodissociation, collisional damping, screening, and reduced feed-down. Model results are compared with CMS and ALICE data.

Production of multiple charged Higgs bosons in 3-3-1 models

We undertake the study of the charged Higgs bosons predicted by the model with gauge symmetry $SU(3{)}_{c}\ensuremath{\bigotimes}SU(3{)}_{L}\ensuremath{\bigotimes}U(1{)}_{X}$. By considering Yukawa mixing couplings between small ($\ensuremath{\sim}\text{ }\text{ }\mathrm{GeV}$) and large ($\ensuremath{\sim}\text{ }\text{ }\mathrm{TeV}$) scales, we show that the hypercharge-1 (${H}_{1}^{\ifmmode\pm\else\textpm\fi{}}$) and hypercharge-2 (${H}_{2}^{\ifmmode\pm\else\textpm\fi{}}$) Higgs bosons predicted by the model can be simultaneously produced in $pp$ collisions at different production rates. At low energy, the ${H}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ bosons exhibit the same properties as the charged Higgs bosons from a two Higgs doublet model, while ${H}_{2}^{\ifmmode\pm\else\textpm\fi{}}$ are additional like-charged Higgs bosons from the underlying 3-3-1 model. Thus, the identification of multiple like-charged Higgs boson resonances may test the compatibility of theoretical models with experimental data. We study ${H}_{1,2}^{\ifmmode\pm\else\textpm\fi{}}$ pairs and associated $tb{H}_{1,2}^{\ifmmode\pm\else\textpm\fi{}}$ productions at the CERN LHC. In particular, we obtain that pair production can be as large as the single production in gluon-gluon collisions due to the interchange of a heavy neutral ${Z}^{\ensuremath{'}}$ gauge boson predicted by the model. By considering decays to leptons ${H}_{1,2}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}\ensuremath{\tau}{\ensuremath{\nu}}_{\ensuremath{\tau}}$, we obtain scenarios where small peaks of ${H}_{2}^{\ifmmode\pm\else\textpm\fi{}}$-boson events in transverse mass distributions can be identified over the ${H}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ background.

Does the ‘Higgs’ have Spin Zero?

Abstract The Higgs boson is predicted to have spin zero. The ATLAS and CMS experiments have recently reported of an excess of events with mass ~ 125 GeV that has some of the characteristics expected for a Higgs boson. We address the questions whether there is already any evidence that this excess has spin zero, and how this possibility could be confirmed in the near future. The excess observed in the γγ final state could not have spin one, leaving zero and two as open possibilities. We review the angular distribution of γγ pairs from the decays of a graviton-like spin-two boson produced in gluon-gluon collisions, which is well-defined and distinct from the spin-zero case. We also calculate the distributions for lepton pairs that would be produced in the W W * decays of a spin-two boson, which are very different from those in Higgs decays, and note that the kinematics of the event selection currently used in the analysis of the W W * final state have reduced efficiency for spin two.

Multiple particle production in proton-proton collisions at energies available at the Large Hadron Collider

A shift three-source model is used in this paper to describe the multiplicity and the pseudorapidity distributions of final-state charged particles produced in proton-proton collisions at energies available at the Large Hadron Collider (LHC). The three kinds of sources are central sources arising from gluon-gluon collisions, target fragmentation sources arising from gluon- or quark-induced collisions with target quarks, and projectile fragmentation sources arising from gluon- or quark-induced collisions with projectile quarks. The central, target fragmentation, and projectile fragmentation sources each have shifts around their centers. The results calculated by using the shift three-source model are in agreement with the experimental data of the ALICE (A Large Ion Collider Experiment) and the CMS (Compact Muon Solenoid experiment) Collaborations.

Gluino polarization at the LHC

Gluinos are produced pairwise at the LHC in quark-antiquark and gluon-gluon collisions: $q\overline{q}$, $gg\ensuremath{\rightarrow}\stackrel{\texttildelow{}}{g}\stackrel{\texttildelow{}}{g}$. While the individual polarization of gluinos vanishes in the limit in which the small mass difference between $L$ and $R$ squarks of the first two generations is neglected, nonzero spin-spin correlations are predicted within gluino pairs. If the squark/quark charges in Majorana gluino decays are tagged, the spin correlations have an impact on the energy and angular distributions in reconstructed final states. On the other hand, the gluino polarization in single gluino production in the supersymmetric Compton process $gq\ensuremath{\rightarrow}\stackrel{\texttildelow{}}{g}{\stackrel{\texttildelow{}}{q}}_{R,L}$ is predicted to be nonzero, and the polarization affects the final-state distributions in super-Compton events.

Jet angular correlation in vector-boson fusion processes at hadron colliders

Higgs boson and massive-graviton productions in association with two jets via vector-boson fusion (VBF) processes and their decays into a vector-boson pair at hadron colliders are studied. They include scalar and tensor boson production processes via weak-boson fusion in quark-quark collisions, gluon fusion in quark-quark, quark-gluon and gluon-gluon collisions, as well as their decays into a pair of weak bosons or virtual gluons which subsequently decay into $\ell\bar\ell$, $q\bar q$ or $gg$. We give the helicity amplitudes explicitly for all the VBF subprocesses, and show that the VBF amplitudes dominate the exact matrix elements not only for the weak-boson fusion processes but also for all the gluon fusion processes when appropriate selection cuts are applied, such as a large rapidity separation between two jets and a slicing cut for the transverse momenta of the jets. We also show that our off-shell vector-boson current amplitudes reduce to the standard quark and gluon splitting amplitudes with appropriate gluon-polarization phases in the collinear limit. Nontrivial azimuthal angle correlations of the jets in the production and in the decay of massive spin-0 and -2 bosons are manifestly expressed as the quantum interference among different helicity states of the intermediate vector-bosons. Those correlations reflect the spin and the CP nature of the Higgs bosons and the massive gravitons.

Effects ofR-parity violation in the minimal supersymmetric standard model on dilepton pair production at the CERN LHC

We investigate in detail the effects of the R-parity lepton number violation in the minimal supersymmetric standard model (MSSM) on the parent process $pp \to e^+ e^- + X$ at the CERN Large Hadron Collider (LHC). The numerical comparisons between the contributions of the R-parity violating effects to the parent process via the Drell-Yan subprocess and the gluon-gluon fusion are made. We find that the R-violating effects on $e^+ e^-$ pair production at the LHC could be significant. The results show that the cross section of the $ e^+ e^-$ pair productions via gluon-gluon collision at the LHC can be of the order of $10^2$ fb, and this subprocess maybe competitive with the production mechanism via the Drell-Yan subprocess. We give also quantitatively the analysis of the effects from both the mass of sneutrino and coupling strength of the R-parity violating interactions.

Charged Higgs Boson Pair Production via Gluon-Gluon Collisions in MSSM with CP Violation**The project supported in part by National Natural Science Foundation of China (19875049), a grant from the Education Ministry of China and the State Commission of Science and Technology of China, and the Youth Science Foundation of the University of Science and Technology of China

The CP-violating effects to the subprocess are studied in the mSUGRA scenario at the CERN large hadron collider, by taking into account the experimental bounds of electron and neutron electric dipole moments. The CP-violating effects in this process are related to the complex phases of and in the mSUGRA scenario. In our calculation we consider small CP phases of and and neglect the effects of neutral Higgs boson mixing. In this case the CP effects to the process mainly come from the complex couplings of Higgs-squark-squark. We find a strong dependence of charged Higgs boson pair production rate on the complex couplings in the parameter space of minimal supersymmetric standard model.

Single charginoproduction via gluon-gluon fusion in a supersymmetric theory with anexplicit R-parity violation

We studied the production ofa single chargino χ̃1±accompanied by a µ∓ lepton via gluon-gluon fusion at the LHC.The numerical analysis of their production rates was carried out in themSUGRA scenario with some typical parameter sets. The results showquantitativelythat the cross sections of the χ̃1±µ∓productions via gluon-gluon collision are of the order of 1-102 fb at the CERN LHC, and can be competitive with theproduction mechanism via thequark-antiquark annihilation process.

Pair production of the lightest chargino via gluon-gluon collisions

The production of the lightest chargino pair from gluon-gluon fusion is studied in the minimal supersymmetric standard model (MSSM) at proton-proton colliders. We find that with the chosen parameters, the production rate of the subprocess can be over 2.7 fb when the chargino is Higgsino-like, and the corresponding total cross section in proton-proton colliders can reach 56 fb at the CERN Large Hadron Colider (LHC) in the $\mathrm{CP}$-conserving MSSM. It shows that this loop mediated subprocess can be competitive with the standard Drell-Yan subprocess in proton-proton colliders, especially at the LHC. Furthermore, our calculation shows it would be possible to extract information about some $\mathrm{CP}$-violating phase parameters if we collected enough chargino pair events.

Production of charged Higgs-boson pairs in gluon-gluon collisions

The search for charged Higgs bosons, which are predicted in supersymmetric theories, is difficult at hadron colliders if the mass is large. In this paper we present the theoretical set-up for the production of charged Higgs-boson pairs at the LHC in gluon-gluon collisions: pp → gg → H + H −. When established experimentally, the trilinear couplings between charged and neutral CP-even Higgs bosons, H +H −H 0 and H +H −H 0 , can be measured.

Diffractive mass spectra at DESY HERA in the interacting gluon model

We have successfully applied the interacting gluon model to calculate diffractive mass spectra measured recently in $e\ensuremath{-}p$ collisions at DESY HERA. We show that it is possible to treat them in terms of gluon-gluon collisions in the same way as was done before for hadronic collisions. An analysis of available data is performed.

Diffractive dissociation in the interacting gluon model

We have extended the Interacting Gluon Model (IGM) to calculate diffractive mass spectra generated in hadronic collisions. We show that it is possible to treat both diffractive and non-diffractive events on the same footing, in terms of gluon-gluon collisions. A systematic analysis of available data is performed. The energy dependence of diffractive mass spectra is addressed. They show a moderate narrowing at increasing energies. Predictions for LHC energies are presented.

Pair production of neutral Higgs particles in gluon-gluon collisions

Pair production processes of neutral Higgs particles will allow us to study the trilinear Higgs couplings at future high-energy colliders. Several mechanisms give rise to multi-Higgs final states in hadron interactions. In the present paper we investigate Higgs pair production in gluon-gluon collisions. After recapitulating pair production in the Standard Model, the analysis of the cross sections is carried out in detail for the neutral Higgs particles in the minimal supersymmetric extension.

Multiplicity gluon production in QCD

We compute the approximate cross section σ (0) n for producing n−2 resolved in a gluon-gluon collision, using the Parke-Taylor formula regularized in a Lorentz invariant manner. We find, in double leading logarithm approximation, that, for 1⪡n∼ ln( S S cut ) , σ n (0)≈ 1 s N cα s 2π 12 1n 2(s/s cut ) n−2 where s cut is the minimum invariant mass for a resolved glupn pair. Tbuilthere is no factor of 1 (n−2) ! multiplying the expression. We briefly discuss the relation of our result to perturbative of n-jet cross sections at coliders.

Gluon fusion: A probe of Higgs sector CP violation.

We demonstrate that CP violation in the Higgs sector, \eg\ of a multi-doublet model, can be directly probed using gluon-gluon collisions at the SSC. % requires phyzzx.tex macro package

First quantum corrections to gluon-gluon collisions in the one-instanton sector

The first quantum correction is calculated for 2 gluons→ n gluons in the presence of an instanton. The correction is found to be negative and proportional to αsϱ 2 with ϱ the instanton size. A physical picture is given both for the semi-classical scattering and for the first quantum corrections.