Randall-Sundrum Graviton Research Articles

A Search for Heavy Resonances in the Dilepton Channel

There are many extensions to the Standard Model of particle physics which predict the addition of a U(1) symmetry, and/or extra spatial dimensions, which give rise to new high mass resonances such as the Z' and Randall-Sundrum graviton. The LHC provides a unique opportunity to explore the TeV scale where these phenomena may become apparent, and can be searched for using the precision tracking and high energy resolution calorimetry of the ATLAS detector. This poster presents the search for high mass resonances in the dilepton channel, and was conducted with an integrated luminosity of 1.08/1.21 fb-1 in the dielectron/dimuon channel respectively, at a centre of mass energy \surd s = 7 TeV.

Search for Dilepton Resonances inppCollisions ats=7 TeVwith the ATLAS Detector

This Letter reports on a search for narrow high-mass resonances decaying into dilepton final states. The data were recorded by the ATLAS experiment in pp collisions at sqrt(s) = 7 TeV at the LHC and correspond to a total integrated luminosity of 1.08/fb (1.21/fb) in the ee (mumu) channel. No statistically significant excess above the Standard Model expectation is observed and upper limits are set at the 95% C.L. on the cross section times branching ratio of Z' resonances and Randall-Sundrum gravitons decaying into dileptons as a function of the resonance mass. A lower mass limit of 1.83 TeV on the Sequential Standard Model Z' boson is set. A Randall-Sundrum graviton with coupling k/M_Pl=0.1 is excluded at 95% C.L. for masses below 1.63 TeV.

Spin analysis ofs-channel diphoton resonances at the LHC

The high mass neutral quantum states envisaged by theories of physics beyond the standard model can at the hadron colliders reveal themselves through their decay into a pair of photons. Once such a peak in the diphoton invariant mass distribution is discovered, the determination of its spin through the distinctive photon angular distributions is needed in order to identify the associated nonstandard dynamics. We here discuss the discrimination of the spin-2 Randall-Sundrum graviton excitation against the hypothesis of a spin-0 exchange giving the same number of events under the peak, by means of the angular analysis applied to resonant diphoton events expected to be observed at the LHC. The spin-0 hypothesis is modelled by an effective interaction of a high mass gauge singlet scalar particle interacting with the standard model fields. The basic observable of our analysis is the symmetrically integrated angular asymmetry $A_{CE}$, calculated for both graviton and scalar s-channel exchanges to next-to-leading order in QCD.

Search for New Dielectron Resonances and Randall-Sundrum Gravitons at the Collider Detector at Fermilab

A search for new dielectron-mass resonances using data recorded by the CDF II detector and corresponding to an integrated luminosity of 5.7 fb(-1) is presented. No significant excess over the expected standard model prediction is observed. In this data set, an event with the highest dielectron mass ever observed (960 GeV/c(2)) was recorded. The results are interpreted in the Randall-Sundrum (RS) model. Combined with the 5.4 fb(-1) diphoton analysis, the RS-graviton lower-mass limit for the coupling k/M¯(Pl)=0.1 is 1058 GeV/c(2), making it the strongest limit to date.

Search for ResonantWWandWZProduction inpp¯Collisions ats=1.96 TeV

We search for resonant WW or WZ production using up to 5.4 fb-1 of integrated luminosity collected by the D0 experiment in Run II of the Fermilab Tevatron Collider. The data are consistent with the standard model background expectation, and we set limits on a resonance mass using the sequential standard model (SSM) W' boson and the Randall-Sundrum model graviton G as benchmarks. We exclude an SSM W' boson in the mass range 180 - 690 GeV and a Randall-Sundrum graviton in the range 300 - 754 GeV at 95% CL.

Spin identification of heavy nonstandard bosons in dilepton and diphoton events at the LHC

New Physics scenarios generally predict the existence of very heavy quantum states that can possibly manifest themselves as peaks in the cross sections at the LHC. For values of the parameters in certain domains, different nonstandard models can generate peaks with the same mass and same number of events. In this case, the spin determination of a peak, requiring the angular analysis of the events, becomes crucial in order to identify the relevant nonstandard source. We here discuss, using a particularly suitable symmetrically integrated angular asymmetry applied to Drell-Yan dilepton and diphoton events at LHC, the identification reach on the exchanges in these reactions of the following heavy bosons: spin-2 Randall-Sundrum graviton excitations; spin-1 heavy neutral gauge bosons Z′ and spin-0 SUSY R-parity violating sneutrinos.

Search for Randall-Sundrum gravitons in the diphoton channel at CDF

We report on a search for new particles in the diphoton channel using a data sample of $p\bar p$ collisions at $\sqrt{s} = 1.96$ TeV collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of 5.4 fb$^{-1}$. The diphoton invariant mass spectrum of the data agrees well with the standard model expectation. We set upper limits on the production cross section times branching ratio for the Randall-Sundrum graviton, as a function of diphoton mass. We subsequently derive lower limits on the graviton mass of 459 GeV$/c^{2}$ and 963 GeV$/c^{2}$, at the 95% confidence level, for coupling parameters ($k/\bar{M}_{Pl}$) of 0.01 and 0.1 respectively.

Sneutrino identification in dilepton events at the LHC

Heavy neutral resonances appearing in the clean Drell-Yan channel may be the first new physics to be observed at the proton-proton CERN LHC. If a new resonance is discovered at the LHC as a (narrow) peak in the dilepton invariant mass distribution, the characterization of its spin and couplings will proceed via the measurement of production rates and angular distributions of the decay products. We discuss the discrimination of a spin-0 resonance (sneutrino) predicted by supersymmetric theories with R-parity breaking against the spin-1 of Z^\prime bosons and the Randall-Sundrum graviton resonance (spin-2) with the same mass and producing the same number of events under the observed peak. To assess the region of sneutrino parameters (couplings and masses) where the spin determination can be performed to a given confidence level, we focus on the event rate and the angular distributions of the Drell-Yan leptons, in particular using the center-edge asymmetry, A_{\rm CE}. We find that although the measured event rate permits solving the above problem partially, the center-edge asymmetry, on the contrary allows to differentiate the various spins entirely with a minimal number of events around 200.

Search forWWandWZResonances Decaying to Electron, MissingET, and Two Jets inpp¯Collisions ats=1.96 TeV.

Using data from 2.9/fb of integrated luminosity collected with the CDF II detector at the Tevatron, we search for resonances decaying into a pair of on-shell gauge bosons, WW or WZ, where one W decays into an electron and a neutrino, and the other boson decays into two jets. We observed no statistically significant excess above the expected standard model background, and we set cross section limits at 95% confidence level on G*(Randall-Sundrum graviton), Z', and W' bosons. By comparing these limits to theoretical cross sections, mass exclusion regions for the three particles are derived. The mass exclusion regions for Z' and W' are further evaluated as a function of their gauge coupling strength.

Search for High-Masse+e−Resonances inpp¯Collisions ats=1.96 TeV

A search for high-mass resonances in the $e^+e^-$ final state is presented based on 2.5 fb$^{-1}$ of $\sqrt{s}=$1.96 TeV $p\bar{p}$ collision data from the CDF II detector at the Fermilab Tevatron. The largest excess over the standard model prediction is at an $e^+e^-$ invariant mass of 240 GeV/$c^2$. The probability of observing such an excess arising from fluctuations in the standard model anywhere in the mass range of 150--1,000 GeV/$c^2$ is 0.6% (equivalent to 2.5 $\sigma$). We exclude the standard model coupling $Z'$ and the Randall-Sundrum graviton for $k/\overline{M}_{Pl}=0.1$ with masses below 963 and 848 GeV/$c^2$ at the 95% credibility level, respectively.

Search for new heavy particles decaying toZ0Z0→eeeeinpp¯collisions ats=1.96 TeV

We report the results of a search for the anomalous production of a massive particle decaying to four electrons via two Z^0 bosons in 1.1 fb^{-1} of p-pbar collisions at sqrt(s)=1.96 TeV collected by the CDF II detector at Fermilab. We employ optimized electron identification criteria to maximize acceptance and efficiency. We estimate the backgrounds in the invariant mass range 500 - 1000 GeV/c^2 to be 0.028 +/- 0.009 (stat) +/- 0.011 (syst) events. We observe zero events in this search region. Assuming a Randall-Sundrum graviton production model, we set 95% CL limits on \sigma times BF(G -> Z^0 Z^0) < 4 - 6 pb, depending on the graviton mass.

Heavy resonance searches at tevatron

We present a selection of beyond-the-standard-model searches of heavy resonances from the CDF and D0 experiments at the Tevatron collider. The data used are part or all of the Run Ha Tevatron data giving more than 1 fb-1 per experiment. The searches have been performed for spin 0, spin 1/2, spin 1 and spin 2 resonances. All the searches and the limits on the different cross section times branching fractions are model independent. They have been interpreted using different models, such as: spin 0 third-generation neutrino, spin 1/2 excited quark, spin 1 W' and Z' and also spin 2 Randall-Sundrum graviton. No evidence of new physics or deviations from the standard model were observed. Limits on particle masses are thus extracted.

Search for New Physics in High-Mass Electron-Positron Events inpp¯Collisions ats=1.96 TeV

We report the results of a search for a narrow resonance in electron-positron events in the invariant mass range of 150-950 GeV/c(2) using 1.3 fb(-1) of pp[over] collision data at square root s = 1.96 TeV collected by the CDF II detector at Fermilab. No significant evidence of such a resonance is observed and we interpret the results to exclude the standard-model-like Z' with a mass below 923 GeV/c(2) and the Randall-Sundrum graviton with a mass below 807 GeV/c(2) for k/M[over](pl) = 0.1, both at the 95% confidence level. Combining with diphoton data excludes the Randall-Sundrum graviton for masses below 889 GeV/c(2) for k/M[over](pl) = 0.1.

Search for High-Mass Diphoton States and Limits on Randall-Sundrum Gravitons at CDF

We have performed a search for new particles which decay to two photons using 1.2 fb(-1) of integrated luminosity from pp[over] collisions at square root s = 1.96 TeV collected using the CDF II detector at the Fermilab Tevatron. We find the diphoton mass spectrum to be in agreement with the standard model expectation, and set limits on the cross section times branching ratio for the Randall-Sundrum graviton, as a function of diphoton mass. We subsequently derive lower limits for the graviton mass of 230 GeV/c(2) and 850 GeV/c(2), at the 95% confidence level, for coupling parameters (k/M[over](Pl)) of 0.01 and 0.1, respectively.

Holographic mixing quantified

We compute the precise elementary/composite field content of mass eigenstates in holographic duals of warped models in a slice of AdS{sub 5}. This is accomplished by decomposing the bulk fields not in the usual Kaluza-Klein basis, but rather into a holographic basis of 4D fields, corresponding to purely elementary source or conformal field theory (CFT) composite fields. Generically, this decomposition yields kinetic and mass mixing between the elementary and composite sectors of the holographic theory. Depending on where the bulk zero mode is localized, the elementary/composite content may differ radically, which we show explicitly for several examples including the bulk Randall-Sundrum graviton, bulk gauge boson, and Higgs boson.

Probing a Very NarrowZ′Boson with CDF and D0 Data

The CDF and D0 data of nearly 475 pb(-1) in the dilepton channel is used to probe a recent class of models, Stueckelberg extensions of the standard model (StSM), which predict a Z' boson whose mass is of topological origin with a very narrow decay width. A Drell-Yan analysis for dilepton production via this Z' shows that the current data put constraints on the parameter space of the StSM. With a total integrated luminosity of 8 fb(-1), the very narrow can be discovered up to a mass of about 600 GeV. The StSM Z' will be very distinct since it can occur in the region where a Randall-Sundrum graviton is excluded.

Emergent gravity from a mass deformation in warped spacetime

We consider a deformation of five-dimensional warped gravity with bulk and boundary mass terms to quadratic order in the action. We show that massless zero modes occur for special choices of the masses. The tensor zero mode is a smooth deformation of the Randall-Sundrum graviton wavefunction and can be localized anywhere in the bulk. There is also a vector zero mode with similar localization properties, which is decoupled from conserved sources at tree level. Interestingly, there are no scalar modes, and the model is ghost-free at the linearized level. When the tensor zero mode is localized near the IR brane, the dual interpretation is a composite graviton describing an emergent (induced) theory of gravity at the IR scale. In this case Newton's law of gravity changes to a new power law below the millimeter scale, with an exponent that can even be irrational.

Search for Randall-Sundrum Gravitons in Dilepton and Diphoton Final States

We report the first direct search for the Kaluza-Klein (KK) modes of Randall-Sundrum gravitons using dielectron, dimuon, and diphoton events observed with the D0 detector operating at the Fermilab Tevatron pp(-) Collider at sqrt[s]=1.96 TeV. No evidence for resonant production of gravitons has been found in the data corresponding to an integrated luminosity of approximately equal to 260 pb(-1). Lower limits on the mass of the first KK mode at the 95% C.L. have been set between 250 and 785 GeV, depending on its coupling to standard model particles.

Search for new particles or gauge bosons decaying into dileptons/dijets at the tevatron

The existence of new particles decaying in a jet or lepton pair is probed with the Run II data collected by the Tevatron ${\rm{p}}\bar{\rm{p}}$ collider at $\sqrt{s}\!=\!1.96\,{\rm{TeV}}$ . Searches performed on both jet and lepton data collected by the CDF and DO detectors do not show signs of any new resonance within the considered mass range. The sensitivity achieved by these searches leads to 95% C.L. limits on the production cross-section times branching ratio for axigluons, flavour universal colorons, excited quarks, colour octet techni-ρ, E6 diquarks, new gauge bosons and Randall-Sundrum gravitons. Excluded mass regions for these models are also computed. PACS 13.85.Rm Limits – 14.80.-j Other gauge bosons – 14.70.Pw Other particles – 12.60.-i Models