In this work we study the collider phenomenology of a compressed supersymmetric model with the gluino (g) and the lightest neutralino (χ 0 1 ). All other sparticles are assumed to be heavy. We consider gluino pair production at the 14 TeV LHC and present the mass reach of the gluino as a function of mass splitting between the gluino and the lightest neutralino. We find that the gluino mass below 1 TeV can be excluded at 95% C.L. with an integrated luminosity of 100 fb −1 for the extreme degenerate case where the mass separation between the gluino and the lightest neutralino is about 20 GeV. On the other hand, the lower bound on the mass of the gluino increases to 1.2-1.3 TeV if the mass splitting between the gluino andχ 0 1 is about 200 GeV. This result shows that for a degenerate gluino, the current mass limit may approximately extend up to 400-500 GeV at the 14 TeV LHC.The constrained minimal supersymmetric standard model (cMSSM) [1] is one of the supersymmetric (SUSY) models which draws much attention to the particle physics community due to its small number of parameters which make this model highly predictive. For this reason, two major collaborations of the LHC, ATLAS and CMS, have searched for the cMSSM from the very beginning of the LHC run in many different final states. In the R-parity conserving model, SUSY particles (sparticles) are produced in pairs and the lightest supersymmetric particle (LSP) must be stable. In most of the cases, the lightest neutralino (χ 0 1 ), being the LSP can be a good candidate for cold dark matter. The generic signature of a SUSY search is comprised of multijets þ leptons þ large amount of missing transverse energy (E T ) which arises due to cascade decays of squarks and gluino into jets, leptons andχ 0 1 . Hereχ 0 1 is the primary source of E T which escapes the detector like neutrinos.In cMSSM, the gluino is generally much heavier than the LSP (mg ∼ 6m~χ0 1 ) and jets produced from the decay ofg, i.e.,g → qqχ 0i are very energetic resulting in signatures having a sufficient amount of E T as well as effective mass (M eff ). Here M eff is defined as the scalar sum of P T of jets, P T of leptons (wherever leptons are present) and E T . These two kinematic variables ðE T ; M eff Þ can be efficiently used to discriminate SUSY signals from the SM backgrounds. The CMS [2] and ATLAS [3] Collaborations have searched for SUSY in the jets þ leptons þ E T channel and in the absence of a significant excess of signal events over the SM backgrounds, they put stringent bounds on the masses of squarks and the gluino in the framework of cMSSM using 7=8 TeV data. For example, with an integrated luminosity ðLÞ ¼ 20.3 fb −1 , equal masses of squarks and gluino are excluded below 1.7 TeV in the cMSSM scenario from 8 TeV LHC data [3]. 1

The idea of left-right symmetry with mirror fermions is very appealing from the symmetry point of view. In this picture, unlike the Standard Model, the symmetry is not only left-right symmetric, but each left handed fermion multiplet is accompanied by new right handed fermion multiplet of opposite chirality. In this work, we consider a gauge symmetry, SU (3) c ⊗ SU (2) L ⊗ SU (2) R ⊗ U (1) Y ′ supplemented by a discrete Z 2 symmetry. Instead of having right handed multiplets for each left handed multiplets of the same fermions as in the usual left-right model, the mirror model include right handed doublets involving new fermions (called mirrors), and similarly for each right handed singlet, there are corresponding mirror singlets. Thus the gauge anomaly is naturally absent in this model, and the model also provide a solution for the strong CP problem because of parity conservation. The first stage of symmetry breaking is achieved by a doublet mirror Higgs with a vacuum expectation value ≃ 10 7 GeV, needed to explain the neutrino mass ≃ 10 −11 GeV. The mirror fermions can mix with the ordinary fermions via a scalar which is singlet under the gauge symmetry. In this model, only light mirror particles, having masses in the few hundred GeV range areê,û,d with well-defined spectrum.û andd can be pair produced at the LHC, and can be detected as (u Z) and (d Z) resonances. We discuss the signals of these mirror fermions at the LHC, and find that the reach at the LHC can be as large as mq ≃ 800 GeV.

Observation of non-zero neutrino masses at a scale ∼ 10 −1 − 10 −2 eV is a major problem in the otherwise highly successful Standard Model. The most elegant mechanism to explain such tiny neutrino masses is the seesaw mechanism with right handed neutrinos. However, the required seesaw scale is so high, ∼ 10 14 GeV, it will not have any collider implications. Recently, an explicit model has been constructed to realize the seesaw mechanism with the right handed neutrinos at the electroweak scale. The model has a mirror symmetry having both the left and right lepton and quark doublets and singlets for the same SU (2) W gauge symmetry. Additional Higgs multiplets have been introduced to realize this scenario. It turns out that these extra Higgs fields also help to satisfy the precision electroweak tests, and other observables. Because the scale of the symmetry breaking is electroweak, both the mirror quark and mirror leptons have masses in the electroweak scale in the range ∼ 150 − 800 GeV. The mirror quarks / leptons decay to ordinary quarks /leptons plus very light neutral scalars. In this work, we calculate the final state signals arising from the pair productions of these mirror quarks and their subsequent decays. We find that these signals are well observable over the Standard Model background for 13 TeV LHC. Depending on the associated Yukawa couplings, these decays can also give rise displaced vertices with long decay length, very different from the usual displaced vertices associated with b decays.

The Universal Extra Dimension (UED) model is one of the popular extension of the standard model (SM) which offers interesting phenomenology. In the minimal UED (mUED) model, Kaluza-Klein (KK) parity conservation ensures that n ¼ 1 KK states can only be pair produced at colliders and the lightest KK particle is stable. In most of the parameter space, first KK excitation of SM hypercharge gauge boson is the lightest one and it can be a viable dark matter candidate. Thus, the decay of n ¼ 1 KK particles will always involve missing transverse energy (E T ) as well as leptons and jets. The production cross sections of n ¼ 1 KK particles are large and such particles may be observed at the Large Hadron Collider (LHC). We explore the mUED discovery potential of the LHC with ffiffi ffi s p ¼ 7 TeV in the multileptonic final states.Since in the early LHC run, precise determination of E T may not be possible, we examine the LHC reach with and without using E T information. We observe that E T cut will not improve mUED discovery reach significantly. We have found that opposite-sign di-lepton channel is the most promising discovery mode and with first fb À1 of collected luminosity, LHC will be able to discover the strongly interacting n ¼ 1 KK particles with masses up to 800 $ 900 GeV.

No abstract