Deep-elastic pp scattering at c.m. energy 14 TeV at LHC in the momentum transfer range 4 GeV*2 < |t| < 10 GeV*2 is planned to be measured by the TOTEM group. We study this process in a model where the deep-elastic scattering is due to a single hard collision of a valence quark from one proton with a valence quark from the other proton. The hard collision originates from the low-x gluon cloud around one valence quark interacting with that of the other. The low-x gluon cloud can be identified as color glass condensate and has size ~0.3 F. Our prediction is that pp differential cross section in the large |t| region decreases smoothly as momentum transfer increases. This is in contrast to the prediction of pp differential cross section with visible oscillations and smaller cross sections by a large number of other models.
We show estimates for shadowing of gluons at small values of $x$, appropriate to RHIC and LHC experiments using a new evolution equation which takes into account the effects of gluon recombination to all orders in gluon density. We show that there is a significant depletion in the gluon density of large nuclei.
We test several BFKL-like evolution equations for unintegrated gluon distributions against forward-central dijet production at LHC. Our study is based on fitting the evolution scenarios to the LHC data using the high energy factorization approach. Thus, as a by-product, we obtain a set of LHC-motivated unintegrated gluon distributions ready to use. We utilize this application by calculating azimuthal decorrelations for forward-central dijet production and compare with existing data.
Threshold resummation for gluon fusion $ZH$ production at the LHC
RWTH Aachen University（亚琛工业大学）；Indian Institute of Technology Kanpur（坎普尔印度理工学院）；Physical Research Laboratory（物理研究实验室）；Indian Institute of Technology Guwahati（古瓦哈提印度理工学院）；Durham University（杜伦大学）
Soft multiparticle production processes in hadronic collisions are considered in the framework of the Quark-Gluon Strings Model and the model predictions are compared with data from SppS and Tevatron. Predictions for LHC energies are given.
This note is a physics manual for a recent numerical implementation of k_t-factorization with running-coupling BK unintegrated gluon distributions. We also compile some results for Pb+Pb collisions at \sqrt{s} = 2.75 TeV, such as predictions for the centrality dependence of the charged particle multiplicity and transverse energy. The model can further be used to obtain initial conditions for hydrodynamic simulations of A+A collisions at the LHC.
We study a possibility of observation of the first Kaluza-Klein (KK) excitation of gluon in a warped extra dimension model at the LHC. In our analysis, we adopt the KK gluon mass and the b-quark coupling to the KK gluon as model parameters and study the sensitivity of the ATLAS experiment to observe the KK gluon through the two $b$-jets channel.
We study the role of the non-perturbative input to the transverse momentum dependent (TMD) gluon density in hard processes at the LHC. We derive the input TMD gluon distribution at low scale mu0^2 ~ 1 GeV^2 from the fit of the inclusive hadron spectra measured at low transverse momenta in pp collisions at the LHC and demonstrate that the best description of these spectra for larger hadron transverse momenta can be achieved by matching the derived TMD gluon distribution with the exact solution of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation obtained at low x and small gluon transverse mome…
The elastic scattering of gqq, gqqbar and gqbarqbar and the thermalization of quark-gluon matter are studied. According to Feynman diagrams at the tree level, squared amplitudes for the elastic gqq scattering and the elastic gqqbar scattering are derived in perturbative QCD. Transport equations including the squared amplitudes for the elastic gqq, gqqbar and gqbarqbar scattering are established. Corresponding to anisotropic gluon and quark distributions created in central Au-Au collisions at RHIC, solutions of the transport equations show that thermalization time of quark matter can be shorten…
Higgs production in association with three jets via gluon fusion (GF) is an important channel for the measurement of the CP-properties of the Higgs particle at the LHC. In this letter, we go beyond the heavy top effective theory approximation and include at LO the full mass dependence of the top- and bottom-quark contributions. We consider the dominant sub-channel gg -> H ggg which involves the manipulation of massive rank-5 hexagon integrals. Furthermore, we present results for several differential distributions and show deviations from the effective theory as large as 100% at high pT for lig…
Cross sections of the colored scalar particle production in $pp$-collisions are calculated and differential and total cross sections of the corresponding parton subprocesses are obtained. The total cross section of scalar gluon production in $pp$-collisions at the LHC is estimated and the dominant decays of scalar gluons are discussed. The production cross section of scalar gluons $F$ with masses $m_F\lesssim 1300$ GeV is shown to be sufficient for the effective production of these particles at the LHC.
We address aspects of jet physics at the Large Hadron Collider focusing on features of recent jet measurements which challenge the theory. We discuss examples illustrating the role of QCD parton showers, nonperturbative corrections, soft multi-gluon emission.
The early thermalization is crucial to the quark-gluon plasma as a perfect liquid and results from many-body scattering. We calculate squared amplitudes for elastic parton-parton-parton scattering in perturbative QCD. Transport equations with the squared amplitudes are established and solved to obtain the thermalization time of initially produced quark-gluon matter and the initial temperature of quark-gluon plasma. We find that the thermalization times of quark matter and gluon matter are different.
In this paper, we study the sensitivity of the fraction of $t\bar{t}$ events arising from gluon-gluon fusion to the chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) as well as the total and differential $t\bar{t}$ cross sections at the LHC and Tevatron. The sensitivity of measured charged asymmetry at the LHC to CEDM and CMDM is also studied. We find that at the Tevatron and the LHC, non-zero values of CMDM could suppress the $t\bar{t}$ production rate. It is shown that the ratio of $σ(gg\rightarrow t\bar{t})/σ(p\bar{p}\rightarrow t\bar{t})$ at the Tevatron is more sensitive to…
The hadroproduction of lepton pairs with mass $Q$ and finite transverse momentum $Q_T$ is dominated by quark-gluon scattering in the region $Q_T > Q/2$. This feature provides a new independent method for constraining the gluon density with data at hadron collider energies. Predictions are provided at the energy of the LHC.
A new geometrical scaling method with gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate the net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net-baryon rapidity distribution…
I present a calculation of soft-gluon corrections to single top quark production in pp collisions at the LHC via the Standard Model partonic processes in the t and s channels and associated top quark and W boson production. Higher-order soft-gluon corrections through next-to-next-to-next-to-leading order (NNNLO) are calculated at next-to-leading logarithmic (NLL) accuracy. The soft-gluon corrections in the s channel and in tW production are large and dominant, while in the t channel they are not a good approximation of the complete QCD corrections.
We present our results on soft gluon resummation in the invariant mass threshold applied to the associated production of a top quark pair with a W boson at the LHC in the Mellin space formalism.
We calculate the unintegrated gluon distribution at low intrinsic transverse momenta and its parameters are found from the best description of the SPS and LHC data on the $pp$ collision in the soft kinematical region. It allows us to study the saturation of the gluon density at low $Q^2$ more carefully and find the saturation scale.
We investigate the importance of unitarity corrections to parton evolution in heavy flavor production at the LHC. The gluon distribution is determined with a fit to HERA data applying a unified BFKL-DGLAP approach, in which the non-linear evolution is described by the Balitsky-Kovchegov equation. First we estimate b anti-b production at CDF and D0. Then, cross sections for heavy quark production at various LHC experiments are estimated, tracing the impact of the unitarity corrections.
Understanding the pattern of gluon radiation in $t \bar t$ production and decay processes is important for making an accurate determination of the top mass from the momenta of its decay products. The larger energy of the LHC $pp$ collider boosts the top cross section by a factor of 100 compared to that at the Tevatron, but it also increases the amount of additional gluon radiation. We calculate the cross section for gluon radiation in top production and decay at the LHC. The distributions of this radiation are presented and the exact matrix-element results are compared with results from the HE…
The pseudorapidity distribution of centers of dense isolated groups of particles in HIJING model is determined. It can be considered as the background for Cherenkov gluons. If peaks over this background were found in experiment, they would indicate the onset of new collective effects.
Vector-boson pair production is an important background for Higgs boson and new physics searches at the Large Hadron Collider LHC. We have calculated the loop-induced gluon-fusion process gg -> WW -> leptons, allowing for arbitrary invariant masses of the intermediate W bosons. This process contributes at O(alpha_s^2) relative to quark-antiquark annihilation, but its importance is enhanced by the large gluon flux at the LHC and by experimental cuts employed in Higgs boson searches. We find that gg -> WW provides only a moderate correction (ca. 5%) to the inclusive W-pair production cross secti…
We report calculations of the gluon induced Zg and Zgg productions in the Standard Model at the LHC operating at both 7 TeV and 14 TeV collision energy. We present total cross sections and differential distributions of the processes and compare them with the leading and next-to-leading order QCD pp -> Z+1 jet, Z+2 jets results. Our results show that the gluon induced Zg and Zgg productions contribute to pp -> Z+1 jet, Z+2 jets at 1% level.
The application of a modified gluon propagator and an infrared frozen running co upling constant in the description of the proton-proton elastic scattering is in vestigated. The model based on the exchange of the Pomeron as a pair of non-pert urbative gluons is modified to include the frozen coupling constant in the infra red kinematic region. A good fit to the data of the differential cross section f or different center of mass energies (53 GeV and 1.8 TeV) is obtained.
Transverse momentum dependent (TMD) parton distributions in a proton are important in high energy physics from both theoretical and phenomenological points of view. Using the latest RHIC and LHC data on the inclusive soft hadron production in $pp$ and $AA$ collisions at small transverse momenta, we determine the parameters of the initial TMD gluon density, derived in the framework of quark-gluon string model at the low scale $μ_0 \sim 1 - 2$ GeV and refine its large-$x$ behaviour using the LHC data on the $t \bar t$ production at $\sqrt s = 13$ TeV. Then, we apply the Catani-Ciafaloni-Fiorani-…
We have calculated one-loop amplitudes for the production of Higgs boson in association with two electroweak bosons ($H,γ,Z$) via gluon-gluon fusion. We present preliminary results for the total cross section at 8, 13 and 100 TeV center-of-mass energies at $pp$ colliders. We study the interference effect and, also comment on the effect of new physics in terms of anomalous couplings of the Higgs boson in these processes.
We compute the next-to-leading order (NLO) QCD corrections to the gluon-fusion subprocess of diphoton-plus-jet production at the LHC. We compute fully differential distributions by combining two-loop virtual corrections with one-loop real radiation using antenna subtraction to cancel infrared divergences. We observe significant corrections at NLO which demonstrate the importance of combining these corrections with the quark-induced diphoton-plus-jet channel at next-to-next-to-leading order (NNLO).
Higher-dimensional multi-gluon interactions affect essentially all effective Lagrangian analyses at the LHC. We show that, contrary to common lore, such operators are best constrained in multi-jet production. Our limit on the corresponding new physics scale in the multi-TeV range exceeds the typical reach of global dimension-6 Higgs and top analyses. This implies that the pure Yang-Mills operator can safely be neglected in almost all specific higher-dimensional analyses at Run II.
Transverse momentum dependent gluon distributions encode fundamental information on the structure of the proton. Here we show how they can be accessed in heavy quarkonium production in proton-proton collisions at the LHC. In particular, their first determination could come from the study of an isolated J/psi or Upsilon particle, produced back to back with a photon.
In this talk we report on recent calculation of high energy baryon scattering amplitudes in QCD. Elastic baryon impact factors for two, three and four gluons are presented and their energy evolution is described that incorporates unitarity corrections. We find that the baryon couples directly to the BFKL Pomeron, to the BKP odderon and to a new state, a three-gluon BKP Pomeron. The new state may decay into four gluons with a new 3 -> 4 transition vertex. This vertex defines the transition amplitude of the three-gluon BKP Pomeron state into two BFKL Pomerons.
The hybrid N=1/N=2 supersymmetric model predicts scalar gluons (sgluons) as SUSY partners of the Dirac gluino. Their strikingly distinct phenomenology at the CERN Large Hadron Collider is discussed.
In Randall-Sundrum models, the Kaluza-Klein (KK) excitations of the gluon, g_{KK} have enhanced couplings to the right-handed quarks. In the absence of a gg g_{KK} coupling in these models, the single production of a g_{KK} from an initial gg state is not possible. The search for other production mechanisms at the LHC, therefore, becomes important. We suggest that the associated production of a g_{KK} with a t t(bar) pair is such a mechanism. Our study shows that through this process the LHC can probe KK gluon masses in the range of 2.8 -- 2.9 TeV.
Heavy charged lepton productions via gluon fusion at the LHC are revisited. Full loop calculations are adopted with an updated parton distribution function and electroweak data. Including contribution from new generation quarks in the loop, pair production of the sequential heavy lepton via gluon fusion at the LHC dominates over that via the Drell-Yan mechanism in some heavy lepton mass range. Exotic lepton single production of vector-like lepton extended models is also calculated. In the later case, the gluon fusion mechanism via the Higgs exchange is emphasized. Our numerical results for bot…
We study the unintegrated, or transverse momentum dependent (TMD) gluon distribution obtained from the best description of the LHC data on the inclusive spectra of hadrons produced in the mid-rapidity region and low transverse momenta at starting scale Q0^2 = 1 GeV^2. To extend this gluon density at higher Q^2 we apply the Catani-Ciafoloni-Fiorani-Marchesini (CCFM) evolution equation. The influence of the initial (starting) non-perturbative gluon distribution is studied. The application of the obtained gluon density to the analysis of the ep deep inelastic scattering allows us to get the resul…
We present results of QCD corrections to Higgs boson production at the CERN Large Hadron Collider. Potentially large logarithmic contributions from multiple soft-gluon emission are summed up to all order in the strong coupling. Various kinematical distributions, including the Higgs transverse momentum, are predicted with O(alpha_s^3) precision. Comparison is made to outputs of the popular Monte Carlo event generator PYTHIA.
The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at SSC and LHC energies.
We calculate the transverse momentum distribution of low-mass Drell-Yan pairs in QCD perturbation theory with all-order resummation. We demonstrate that the transverse momentum distribution of low-mass Drell-Yan pairs is an advantageous source of constraints on the gluon distribution and its nuclear dependence. With the reduction in background, we argue that low-mass Drell-Yan pairs in the forward region provide a good and clean probe of small-x gluons at RHIC and LHC.
A model for total cross-sections incorporating QCD jet cross-sections and soft gluon resummation is described and compared with present data on $pp$ and ${\bar p}p$ cross-sections. Predictions for LHC are presented for different parameter sets. It is shown that they differ according to the small x-behaviour of available parton density functions.
We extend the methods of Yennie, Frautschi and Suura (YFS) to compute, via Monte Carlo methods, the effects of multiple gluon emission in the processes $q+q'\to q''+q'''+n(G)$, where $G$ is a soft gluon. We show explicitly that the infrared singularities in the respective simulations are canceled to all orders in $α_s$. Some discussion of this result from the standpoint of confinement is given. More importantly, we present, for the first time ever, sample numerical Monte Carlo data on multiple soft gluon emission in the rigorously extended YFS framework. We find that such soft gluon effects mu…
It is shown that the amplitude for the scattering of a heavy quarkonium system from a nucleon near threshold is completely determined by the fraction of angular momentum, as well as linear momentum, carried by gluons in the nucleon. A form for the quarkonium-nucleon non-relativistic potential is derived.
I review the color dipole formulation of heavy quark production in the light of recent RHIC data. Since charm and bottom production directly probe the gluon density, these processes allow one to study shadowing and parton saturation at RHIC and LHC. The dipole approach provides a convenient framework to calculate these nuclear effects. I present numerical results for open charm and bottom production in proton-proton and proton-nucleus collisions and discuss transverse momentum broadening of heavy quarkonia.
We study open b\bar{b} production at large rapidity at the LHC in an attempt to pin down the gluon distribution at very low x. For the LHC energy of 7 TeV, at next-to-leading order (NLO), there is a large factorization scale uncertainty. We show that the uncertainty can be greatly reduced if events are selected in which the transverse momenta of the two B-mesons balance each other to some accuracy, that is |\vec p_{1T}+\vec p_{2T}| < k_0. This will fix the scale μ_F \simeq k_0, and will allow the LHCb experiment, in particular, to study the x-behaviour of gluon distribution down to x ~ 10^{-5}…
Predictions of the elastic proton-proton cross sections at energies of LHC are calculate on the base of the high energy dynamical model. The growth of $ds/dt$ at fixed transfer momenta are shown. The form of eikonal of elastic hadron scattering at super high energies is discussed.
Starting from an unintegrated gluon distribution which satisfies a `unified' equation which embodies both BFKL and DGLAP behaviour, we compute the shadowing corrections to the integrated gluon in the small x domain that will be accessible at the LHC. The corrections are calculated via the Korchegov equation, which incorporates the leading ln(1/x) triple-Pomeron vertex, and are approximately resummed using a simple Pade technique. We find that the shadowing corrections to xg(x,Q^2) are rather small in the HERA domain, but lead to a factor of 2 suppression in the region x \sim 10^-6, Q^2 \sim 4 …
Higgs boson production in association with two tagging jets will be mediated by electroweak vector boson fusion and by gluon fusion processes at the CERN LHC. The characteristic distributions for the gluon fusion process are analyzed for the $H\to W^+W^-$ signal at $m_H=160$ GeV, with subsequent leptonic decay of the $W$-pair. The dominant backgrounds from top-quark pair production, $WWjj$ production and vector boson fusion processes can be suppressed to a level of $S/B\approx 1/4$, yielding a highly significant gluon fusion signal with 30 fb$^{-1}$. Analysis of the azimuthal angle correlation…
Photon-pair direct or jet-associated productions are important for relevant standard model measurement, Higgs and new physics searches at the LHC. The loop-induced gluon-fusion process gg -> γγg, which although formally contributes only at the next-to-next-to-leading order to γγj productions, may get enhanced by the large gluon flux at the LHC. We have checked and confirmed previous results on gg -> γγ, γγg at one loop, using now the traditional Feynman diagram based approach and taking into account the quark mass effects, and further updated them for the 7 and 14 TeV LHC with new inputs and s…
We perform resummation of soft gluon corrections to the total cross section for the process $pp \to t\bar{t}H$. The resummation is carried out at next-to-leading-logarithmic (NLL) accuracy using the Mellin space technique, extending its application to the class of $2 \to 3$ processes. We present an analytical result for the soft anomalous dimension for a hadronic production of two coloured massive particles in association with a colour singlet. We discuss the impact of resummation on the numerical prediction for the associated Higgs boson production with top quarks at the LHC.
We propose a simple way to test the Abelian decomposition of QCD, the existence of two types of gluons, experimentally at LHC. The Abelian decomposition decomposes the gluons to the color neutral neurons and colored chromons gauge independently. This refines the Feynman diagram in a way that the color conservation is explicit, and generalizes the quark model to the quark and chromon model. We predict that the neuron jet has the color factor 3/4 and has a sharpest jet radius and smallest particle multiplicity, while the chromon jet with the color factor 9/4 remains the broadest jet. Moreover, t…
We present results for a combined resummation of soft and Coloumb gluon corrections in squark-antisquark production at the LHC, including the non-trivial interference of the two effects and the contribution of squark-antisquark bound states below threshold. The total correction to the next-to-leading order approximation is found to be sizeable, and amounts to 5-14 % in the squark mass region 200 GeV-2 TeV. The scale dependence of the total cross section is also reduced.
The problems linked with the extraction of the basic parameters of the hadron elastic scattering amplitude at the LHC are explored. It is shown that one should take into account the saturation regime which will lead to new effects at the LHC.
We show that the production of a Higgs boson in association with a jet in proton-proton collisions is sensitive to the linear polarization of gluons inside unpolarized protons. We present the analytical expressions, at leading order in perturbative QCD, for various transverse momentum dependent observables, which can be measured at the LHC. Since there are no experimental constraints on the linearly polarized gluon distribution, its effects are studied by adopting two different models. In particular, we find that the $\cos2ϕ$ azimuthal asymmetry is a very promising observable because it could …
We examine a possibility to discover a Kaluza-Klein (KK) excitation of gluon in a warped extra dimension model at the Large Hadron Collider focusing on a decay channel of the KK gluon into a $b$-quark pair. It is known that, in a certain extension of the warped extra dimension model, the third generation quarks could strongly couple to the KK gluon owing to appropriate bulk fermion mass parameters. Taking account of kinematical cuts to reduce background events, we show the model parameter space which leads to a significance larger than 5$σ$ with the integrated luminosity of 10 (100) ${\rm fb}^…
The problems linked to the extraction of the basic parameters of the hadron elastic scattering amplitude at the LHC are explored. The impact of the Black Disk Limit (BDL)$-$ which constitutes a new regime of the scattering processes - on the determination of these values is examined.
The T-odd top-quark chromoelectric dipole moment, $d_t$, is probed through top-quark-pair production via gluon fusion at the CERN LHC with the possibility of having polarized proton beams in account. At 1-$σ$ level, the typical CP-odd lepton energy and tensor correlations enable us to measure $Re(d_t)$ and $Im(d_t)$ up to the order of 10$^{-18}$ ($g_scm$) in the unpolarized case and the initial CP-odd gluon spin correlation allows us to probe $Im(d_t)$ up to the order of 10$^{-20}$ ($g_scm$) for $\sqrt{s}=14$ TeV and the integrated luminosity $L_{pp}=10 fb^{-1}$.
Pair production of W bosons constitutes an important background to Higgs boson and new physics searches at the Large Hadron Collider LHC. We have calculated the loop-induced gluon-fusion process gg -> W*W* -> leptons, including intermediate light and heavy quarks and allowing for arbitrary invariant masses of the W bosons. While formally of next-to-next-to-leading order, the gg -> W*W* -> leptons process is enhanced by the large gluon flux at the LHC and by experimental Higgs search cuts, and increases the next-to-leading order WW background estimate for Higgs searches by about 30%. We have ex…
Using the recently published model for the collisional energy loss of heavy quarks (Q) in a Quark Gluon Plasma (QGP), based on perturbative QCD (pQCD) with a running coupling constant, we study the interaction between heavy quarks and plasma particles in detail. We discuss correlations between the simultaneously produced $c$ and $\bar{c}$ quarks, study how central collisions can be experimentally selected, predict observable correlations and extend our model to the energy domain of the large hadron collider (LHC). We finally compare the predictions of our model with that of other approaches li…
We study the effect of soft gluon emission in the hadroproduction of gluino-gluino and squark-antisquark pairs at the next-to-leading logarithmic (NLL) accuracy within the framework of the minimal supersymmetric model. We present the calculation of the one-loop soft anomalous dimension matrices controlling the colour evolution of the underlying hard-scattering processes. The numerical results for resummed cross sections for proton-proton collisions at the Large Hadron Collider are discussed in detail.
Linearly polarized gluons inside an unpolarized proton contribute to the transverse momentum distributions of (pseudo)scalar particles produced in hadronic collisions, such as Higgs bosons and quarkonia with even charge conjugation ($η_c$, $η_b$, $χ_{c0}$, $χ_{b0}$). Moreover, they can produce azimuthal asymmetries in the associated production of a photon and a $J/ψ$ or a $Υ$ particle, in a kinematic configuration in which they are almost back to back. These observables, which can be measured in the running experiments at the LHC, could lead to a first extraction of both the polarized and the …
