Graviton Signals in Central Production at the LHC

In this paper, we study central production, in the inclusive case, to look for graviton signals in large extra dimensional model using dilepton and diphoton channels. We carefully analyze signal and possible Standard Model background processes and study the feasibility of such new physics searches in a relatively clean environment as in central production where the proton fragments are mostly emitted in the forward direction, and there is a clear rapidity gap between them and the centrally produced system. Our analysis shows that the LHC with 14 TeV center of mass energy and 100 fb$^{-1}$ (300 fb$^{-1}$) of integrated luminosity can probe the effective gravity scale up to 3.6 TeV (4.4 TeV) in both the dilepton and diphoton channels.Comment: 25 pages, 15 figure

Single Productions of Colored Particles at the LHC: An Example with Scalar Leptoquarks

Current LHC searches for new colored particles generally focus on their pair production channels and assume any single production to be negligible. We argue that such an assumption may be unnecessary in some cases. Inclusion of model dependent single productions in pair production searches (or vice versa) can give us new information about model parameters or better exclusion limits. Considering the example of the recent CMS search for first generation scalar leptoquarks in the pair production channel, we illustrate how single productions can be systematically included in the signal estimations and demonstrate how it can affect the mass exclusion limits and give new bounds on leptoquark-lepton-quark couplings. We also estimate the effect of the pair production in the more recent CMS search for scalar leptoquarks in single production channels.Comment: 11 pages, 6 figures, 2 tables. References added. Comments added on LQ single production search by CMS. Journal versio

Probing Compositeness with the CMS eejjeejj & eejeej Data

Quark-lepton compositeness is a well-known beyond the Standard Model (SM) scenario with heavy exotic particles like leptoquarks (LQs) and leptogluons (LGs) etc. These particles can couple to leptons and jets simultaneously. In this letter, we use the recent CMS scalar LQ search data in the $eejj$ and $eej$ channels to probe this scenario. We recast the data in terms of a color octet partner of the SM electron (or a first generation spin-1/2 LG) that couples to an electron and a gluon via a dimension five operator suppressed by the quark-lepton compositeness scale ($\Lambda$). By combining different production processes of the color octet electron ($e_8$) at the LHC, we use the CMS 8TeV data to obtain a simultaneous bound on $\Lambda$ and the mass of the $e_8$ ($M_{e_8}$). We also study the reach of the 13 TeV LHC to discover the $e_8$ and interpret the required luminosity in terms of $M_{e_8}$ and $\Lambda$.Comment: 7 pages, 6 figures, 3 tables. Minor changes, typos fixed. Matches with the published versio

The 750 GeV excess from photon-photon and quark-quark processes

The observed excess in the diphoton mass spectrum around 750 GeV at the 13 TeV LHC possibly indicates the presence of a photonphilic resonance. We show that the excess can be explained by a scalar of the type involved in Bekenstein's framework for varying electromagnetic coupling theories. The scalar, in our model, couples dominantly to photons and is mainly produced by the quark-quark fusion at the LHC. In addition, it can also be produced in photon-photon fusion. Our model has only two free parameters, the mass of the scalar and the scale of the new physics, which are fixed by the LHC excess to 750 GeV and 1.5 - 2 TeV, respectively. The scalar has a large three-body decay to a fermion pair and a photon, which provides an interesting search channel with a dilepton-photon resonance around 750 GeV.Comment: 4 pages, 2 figures, 4 tables. Presented at the 51st Rencontres de Moriond, QCD and High Energy Interactions, La Thuile, 19-26 March 201

Constraining minimal anomaly free U(1)\mathrm{U}(1) extensions of the Standard Model

We consider a class of minimal anomaly free $\mathrm{U}(1)$ extensions of the Standard Model with three generations of right-handed neutrinos and a complex scalar. Using electroweak precision constraints, new 13 TeV LHC data, and considering theoretical limitations such as perturbativity, we show that it is possible to constrain a wide class of models. By classifying these models with a single parameter, $\kappa$, we can put a model independent upper bound on the new $\mathrm{U}(1)$ gauge coupling $g_z$. We find that the new dilepton data puts strong bounds on the parameters, especially in the mass region $M_{Z'}\lesssim 3~ \mathrm{TeV}$.Comment: 23 pages, 4 figures. Modified model parametrization, exclusion limits with new dat