Dark matter production at the LHC from black hole remnants

We study dark matter production at CERN LHC from black hole remnants (BHR). We find that the typical mass of these BHR at the LHC is ∼5–10 TeV which is heavier than other dark matter candidates, such as axion, axino, neutralino, etc. We propose the detection of this dark matter via single jet production in the process pp → jet + BHR (dark matter) at CERN LHC. We find that for zero impact parameter partonic collisions, the monojet cross section is not negligible in comparison to the standard model background and is much higher than the other dark matter scenarios studied so far. We also find that dσ/dp _T of jet production in this process increases as p _T increases, whereas in all other dark matter scenarios the dσ/dp _T decreases at CERN LHC. This may provide a useful signature for dark matter detection at the LHC. However, we find that when the impact parameter dependent effect of inelasticity is included, the monojet cross section from the above process becomes much smaller than the standard model background and may not be detectable at the LHC.     

Inelastic dark matter at the LHC

The dark matter sector may be more complicated than anticipated. An inelastically scattering dark matter with a mass splitting above one MeV will make direct detection experiments hopeless, and render LHC the primary chance for discovery. We perform a model-independent study of inelastic dark matter at the LHC, concentrating on the parameter space with the mass splitting between the excited and ground states of dark matter above a few hundred MeV. The generic signatures of inelastic dark matter at the LHC are displaced pions together with a monojet plus missing energy, and can be tested at the 7 TeV LHC.     

Prospects for discovering supersymmetry at the LHC

Supersymmetry is one of the best-motivated candidates for physics beyond the standard model that might be discovered at the LHC. There are many reasons to expect that it may appear at the TeV scale, in particular because it provides a natural cold dark-matter candidate. The apparent discrepancy between the experimental measurement of g _μ −2 and the standard-model value calculated using low-energy e ⁺ e ⁻ data favours relatively light sparticles, accessible to the LHC. A global likelihood analysis including this, other electroweak precision observables and B decay observables suggests that the LHC might be able to discover supersymmetry with 1/fb or less of integrated luminosity. The LHC should be able to discover supersymmetry via the classic missing-energy signature, or in alternative phenomenological scenarios. The prospects for discovering supersymmetry at the LHC look very good. CERN-PH-TH/2008-208.     

MSSM Higgs boson searches at the Tevatron and the LHC: Impact of different benchmark scenarios

The Higgs boson search has shifted from LEP2 to the Tevatron and will subsequently move to the LHC. The current limits from the Tevatron and the prospective sensitivities at the LHC are often interpreted in specific MSSM scenarios. For heavy Higgs boson production and subsequent decay into or τ⁺τ^–, the present Tevatron data allow one to set limits in the M_A–tan β plane for small M_A and large tan β values. Similar channels have been explored for the LHC, where the discovery reach extends to higher values of M_A and smaller tan β. Searches for MSSM charged Higgs bosons, produced in top decays or in association with top quarks, have also been investigated at the Tevatron and the LHC. We analyze the current Tevatron limits and prospective LHC sensitivities. We discuss how robust they are with respect to variations of the other MSSM parameters and possible improvements of the theoretical predictions for Higgs boson production and decay. It is shown that the inclusion of supersymmetric radiative corrections to the production cross sections and decay widths leads to important modifications of the present limits on the MSSM parameter space. The impact on the region where only the lightest MSSM Higgs boson can be detected at the LHC is also analyzed. We propose to extend the existing benchmark scenarios by including additional values of the higgsino mass parameter μ. This affects only slightly the search channels for a SM-like Higgs boson, while having a major impact on the searches for non-standard MSSM Higgs bosons.     

Working group report: Dictionary of Large Hadron Collider signatures

We report on a plan to establish a ‘Dictionary of LHC Signatures’, an initiative that started at the WHEPP-X workshop in Chennai, January 2008. This study aims at the strategy of distinguishing 3 classes of dark matter motivated scenarios such as R-parity conserved supersymmetry, little Higgs models with T-parity conservation and universal extra dimensions with KK-parity for generic cases of their realization in a wide range of the model space. Discriminating signatures are tabulated and will need a further detailed analysis.      

Lepton decay channels of egret gluinos at the LHC

Prospects for observing a SUSY-like signal from two gluinos are investigated within a certain region of the mSUGRA parameter space, where the cross section of the two gluino production in pp collisions at the LHC ( = 14 TeV) via gluon-gluon fusion (gg → ) is estimated at a rather high level of 17.3 pb. In this so-called EGRET region, the lightest stable neutralinos can serve as cold dark matter particles and are natural explanations of the excess of diffuse galactic gamma rays observed by the EGRET space apparatus. The -event selection relies on a very clear signature when decay products of each gluino contain one b-anti-b pair, one or two lepton-antilepton pair(s) and a neutralino. Rather high transverse-missing energy, carried away by the two neutralinos, is an essential signature of the events and also allows the relevant Standard Model background to be reduced significantly. In particular, it was found that the clear signatures of the selected processes demonstrate good prospects discovering the EGRET gluinos at the LHC. Furthermore, these signatures allow one to distinguish different mSUGRA parameters m _1/2 inside the EGRET region. The text was submitted by the authors in English.     

Stop the top

The UA1 Collaboration has seen striking monojet events, and events consistent with a W → $\text{tb}$ interpretation. We investigate whether supersymmetric scenarios invented to explain the monojet events can also explain the top candidate events. This is found to occur only for the squark pair production scenario. In a minimal N = 1 supergravity model, both events occur only if parameters of the theory are chosen to be in certain ranges. Further implications and predictions are made.     

Heavy-flavor tagging and the supersymmetry reach of the CERN Large Hadron Collider

The branching fraction for the decays of gluinos to third generation quarks is expected to be enhanced in classes of supersymmetric models where either third generation squarks are lighter than other squarks, or in mixed-higgsino dark matter models constructed so as to be in concordance with the measured density of cold dark matter. In such scenarios, gluino production events at the CERN Large Hadron Collider should be rich in top and bottom quark jets. Requiring b jets in addition to E _T ^miss should, therefore, enhance the supersymmetry signal relative to Standard Model backgrounds from V + jet, VV and QCD backgrounds (V=W,Z). We quantify the increase in the supersymmetry reach of the LHC from b-tagging in a variety of well-motivated models of supersymmetry. We also explore “top tagging” at the LHC. We find that while the efficiency for this turns out to be too low to give an increase in reach beyond that obtained via b-tagging, top tagging can indeed provide a confirmatory signal if gluinos are not too heavy. We also examine c jet tagging but find that it is not useful at the LHC. Finally, we explore the prospects for detecting the direct production of third generation squarks in models with an inverted squark mass hierarchy. This is signaled by b jets + E _T ^miss events being harder than in the Standard Model, but softer than those from the production of gluinos and heavier squarks. We find that while these events can be readily separated from the SM background (for third generation squark masses ∼300–500 GeV), the contamination from the much heavier gluinos and squarks remains formidable if these are also accessible.     

Prospects for identification the direct and indirect effects of extra spatial dimensions at the Large Hadron Collider

The existence of massive graviton states, that may be produced as real and virtual particles in high-energy proton collisions, is predicted by the modern developments of Kaluza–Klein models with extra spatial dimensions. The direct and indirect signatures of large and warped extra spatial dimensions may be revealed by analyzing the specific characteristics of dilepton and diphoton final states formed in proton–proton collisions at the Large Hadron Collider (LHC). Virtual effects in the Kaluza–Klein models with large extra spatial dimensions can be discovered by the specic behavior of the dilpton and diphoton invariant-mass distributions, and their identication (in case of discovery) can be performed by the analysis of their angular distributions with integrated center-edge asymmetry. Assuming the nominal values of the LHC collision energy (14 TeV) and luminosity (100 fb^–1), for the models with large extra spatial dimensions we find that the sensitivity to the cutoff parameter M _S will extend up to 8.5 and 7.6 TeV for their discovery and identification, respectively. For the Randall–Sundrum model with a warped extra dimension, the LHC experiments will be sensitive to the graviton resonance with mass up to 4.4 and 3.1 TeV for its discovery and identification, respectively.     

The Higgs mass beyond the CMSSM

The recent discovery of a new boson at the LHC, which resembles a SM-like Higgs boson with m _h =125 GeV, is starting to provide strong guidelines into SUSY model building. For instance, the identification of such a state with the lightest CP-even Higgs boson of the MSSM (h ⁰), requires large values of tanβ and/or heavy sfermions. One outcome of this result is the possibility to solve the SUSY flavor and CP problems by decoupling, which points towards some realization of Split-inspired SUSY scenarios, in which scalars are much heavier than gauginos and higgsinos. However, we argue here that the remaining Higgs bosons of the MSSM (H ⁰, A ⁰, H ^±) do not have to be as heavy as the sfermions, and having them with masses near the EW scale does not pose any conflict with current MSSM constraints. We discuss then some SUSY scenarios with heavy sfermions, from a bottom-up approach, which contain the full Higgs sector, as well as a possible dark matter candidate, with masses near the EW scale, and identify distinctive signals from these scenarios that could be searched at the LHC.     

Top squark and neutralino decays in a <Emphasis Type="Italic">R</Emphasis>-parity violating model constrained by neutrino oscillation data

In a R-parity violating (RPV) model of neutrino mass with three bilinear couplings μ _i and three trilinear couplings λ′ _i33, where i is the lepton index, we find six generic scenarios each with a distinctive pattern of the trilinear couplings consistent with the neutrino oscillation data. These patterns may be reflected in direct RPV decays of the lighter top squark or in the RPV decays of the lightest superparticle, assumed to be the lightest neutralino. Typical signal sizes at the Tevatron RUN II and the LHC have been estimated and the results turn out to be encouraging.      

On the LHC observation of gluinos from the Egret-preferred region

Prospects for observation of a SUSY-like signal from two gluinos are investigated within a certain region of the mSUGRA parameter space, where the cross section of the two-gluino production in pp-collisions at the LHC ( = 14 TeV) is estimated at a rather high level of 17.3 pb. In this so-called EGRET-preferred region, the lightest stable neutralinos χ ₁⁰ can serve as cold-dark-matter particles and can naturally explain the excess of diffuse Galactic gamma rays observed by the EGRET space apparatus. The -event selection relies on a clear signature when decay products of each gluino contain one b pair, one or two l pair(s) or one or two light q pair(s), and a neutralino. Rather high transverse missing energy carried away by the two neutralinos is the essential signature of the events using of which allows the relevant Standard Model background to be reduced significantly. Furthermore, distributions of the reconstructed invariant masses of two opposite-charged-lepton or light-jet pairs produced by the χ ₂⁰ → χ ₁⁰ l ⁺ l ⁻ and χ ₂⁰ → χ ₁⁰ q three-body decays have kinematic end points which measure the difference between masses of χ ₂⁰ and χ ₁⁰. In particular, it was found that these signatures of selected processes demonstrate good prospects for discovery of gluinos at the LHC. These signatures allow one to distinguish different mSUGRA parameters m _1/2 within the EGRET-preferred region (at a higher than 6σ confidence level with 300 fb⁻¹ data). The text was submitted by the authors in English.     

On radiative QCD backgrounds to exclusive H→bb̄ production at the LHC and a photon collider

Central exclusive Higgs boson production, pp→p⊕H⊕p, at the LHC and s-channel resonant Higgs production in the photon-collider option of the ILC can provide a very important contribution to the comprehensive study of the Higgs sector. Especially attractive is the bb̄ Higgs decay mode, which for certain MSSM scenarios may become the discovery channel in exclusive Higgs production at the LHC and the photon collider (PC). Strongly suppressed and controllable backgrounds is an obvious requirement for the success of these exclusive measurements. One of the main sources of background comes from additional gluon radiation which leads to a three-jet bb̄g final state. We perform an explicit calculation of the subprocesses gg→qq̄g and γγ→qq̄g, where the incoming particles are required to be in a J_z=0 state and the two gluons form a colour singlet, and investigate the salient properties of these potentially important background processes.     

Discovery potential of R-hadrons with the ATLAS detector

The production of exotic heavy hadronic particles arises in several models for physics beyond the standard model. The focus is on R-hadrons, which are stable hadronized gluinos, predicted by certain supersymmetric models. Interactions and signatures of single R-hadrons are studied with the ATLAS simulation and reconstruction framework. The ATLAS fast simulation framework has been extended to include parameterizations for R-hadrons. Based on topological and kinematic variables only, the discovery potential of the ATLAS detector for R-hadron events produced in , is studied for masses below 2 TeV/c². R-hadrons with masses as predicted by standard SUSY scenarios would be discovered already in the very early stages of the running of the LHC. The discovery reach of heavy gluinos, predicted by for example split supersymmetry models, extends up to at least 1.8 TeV/c² for three years running of the LHC at low luminosity.     

Pair production of charged Higgs bosons in the left–right twin Higgs model at the ILC and LHC

The left–right twin Higgs (LRTH) model predicts the existence of a pair of charged Higgs bosons φ^±. In this paper, we study the production of the charged Higgs boson pair φ^± at the international linear collider (ILC) and the CERN large hadron collider (LHC). The numerical results show that the production rates are at the level of several tens fb at the ILC, and the process e⁺e^-→φ⁺φ^- can produce adequately distinct multi-jet final states. We also discuss the charged Higgs boson pair production via the process qq̄→φ⁺φ^- at the LHC and estimate in this case the production rates. We find that, as long as the charged Higgs bosons are not too heavy, they can be abundantly produced at the LHC. The possible signatures of these new particles might be detected at the ILC and LHC experiments. PACS 12.60.Fr; 14.80.Mz; 14.65.Ha; 12.15.Lk     

Theoretical expectations for σtot at the large hadron collider

In this note, we summarize and compare various model predictions forpp total cross-section σ _tot ^pp , giving an estimate of the range of predictions for the total cross-section, σ _tot ^pp expected at the LHC. We concentrate on the results for σ _tot ^pp obtained in a particular QCD based model of the energy dependence of the total cross-section, including the effect of soft gluon radiation. We obtain the range of predictions in this model by exploring the allowed range of model parameters. We further give a handy parametrisation of these results which incidentally spans the range of various other available predictions at the LHC as well     

The productions of the top-pions and top-Higgs associated with the charm quark at the hadron colliders

In the topcolor-assisted technicolor (TC2) model, the typical physical particles, top-pions and top-Higgs, are predicted and the existence of these particles could be regarded as robust evidence for the model. These particles are accessible at the Tevatron and LHC, and furthermore the flavor-changing (FC) feature of the TC2 model may provide us with a unique opportunity to probe them. In this paper, we study some interesting FC production processes of top-pions and top-Higgs particles at the Tevatron and LHC, i.e., cΠ_t ^- and cΠ_t ⁰(h_t ⁰) productions. We find that the light charged top-pions are not favorable by the Tevatron experiments, and the Tevatron has little capability to probe the neutral top-pion and top-Higgs particles via these FC production processes. At LHC, however, the cross section can reach the level of 10–100 pb for cΠ_t ^- production and 10–100 fb for cΠ_t ⁰(h_t ⁰) production. So one can expect that enough signals could be produced at the LHC experiments. Furthermore, the SM backgrounds should be clean due to the FC feature of the processes, and the FC decay modes Π_t ^-→bc̄, Π_t ⁰(h_t ⁰)→tc̄ can provide us with the signal typical for the detection of the top-pions and top-Higgs particles. Therefore, one may have hope to find the signal of top-pions and top-Higgs particles with the running of LHC via these FC processes. PACS 12.60.Nz; 14.80.Mz; 12.15.LK; 14.65.Ha     

R-宇称破缺的相互作用研究

在LHC上,最小超对称标准模型中R-宇称破缺相互作用使LHC上tt对的产生有两种过程,一种是交换slepton粒子的t道的d_Rd_R→t_Lt_L过程,一种是交换squark粒子的u道的d_Rd_R→t_Rt 关键词： 最小超对称标准模型 R-宇称破缺相互作用 top夸克极化     

Constraints on the MSSM from the Higgs sector

We discuss the constraints on supersymmetry in the Higgs sector arising from LHC searches, rare B decays and dark matter direct detection experiments. We show that constraints derived on the mass of the lightest h ⁰ and the CP-odd A ⁰ bosons from these searches are covering a larger fraction of the SUSY parameter space compared to searches for strongly interacting supersymmetric particle partners. We discuss the implications of a mass determination for the lightest Higgs boson in the range 123<M _h <127?GeV, inspired by the intriguing hints reported by the ATLAS and CMS Collaborations, as well as those of a non-observation of the lightest Higgs boson for MSSM scenarios not excluded at the end of 2012 by LHC and direct dark matter searches and their implications on LHC SUSY searches.     

Can we get deeper inside the pion at the LHC?

We propose a measurement of leading neutrons spectra at LHC in order to extract inclusive π ⁺ p and π ⁺ π ⁺ cross-sections with high p _T jets production. The cross-sections for these processes are simulated with the use of parton distributions in hadrons. In this work we estimate the possibility to extract parton distributions in the pion from the data on these cross-sections and also search for signatures of fundamental differences in the pion and proton structure.