Exotics Papers

Recent ATLAS papers, tagged by links

[exoticpapers-blog]

Search for flavor-changing neutral currents in , with , and limit on the tcH coupling

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-081/

A search for flavour changing neutral currents in top quark decays , with  at  GeV, using 20 fb of = 8 TeV and 5 fb of  = 7 TeV data collected by the ATLAS experiment at the LHC, is reported. The analysis is based on  events in which one top decays to , the other decays to , and both the hadronic and the leptonic decay modes of the  are used and combined. No significant signal is observed and an upper limit on the branching ratio of 0.83% (0.53% expected) at the 95% confidence level is set. The corresponding limit on the  coupling is 0.17 (0.14 expected).

[exoticpapers-blog]

Search for a high-mass Higgs boson in the H->WW->lvlv decay channel with the ATLAS detector using 21 fb-1 of proton-proton collision data

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-067/

A search by the ATLAS experiment at the Large Hadron Collider for a Higgs boson in the  channel in the range 260 GeV  1 TeV is presented. The analysis uses proton-proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.7 fb. A Higgs boson with Standard Model-like couplings is excluded at 95\% confidence level in the mass range 260 GeV  642 GeV.

[exoticpapers-blog]

Search for charged Higgs bosons in the τ+jets final state with pp collision data recorded at s√=8 TeV with the ATLAS experiment

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-090/

The experimental observation of charged Higgs bosons, , which are predicted by many models with an extended Higgs sector, would indicate physics beyond the Standard Model. This note presents the results of a search for charged Higgs bosons in 19.5 fb of proton-proton collision data recorded at  TeV with the ATLAS experiment, using the  + jets channel with a hadronically decaying  lepton in the final state. For light charged Higgs bosons ( ), the  production mode is dominant, while for heavy charged Higgs bosons, associated production of  is dominant. No evidence for a charged Higgs boson is found. For the mass range 90 GeV  GeV, 95 confidence level upper limits on  are set in the range , and for the mass range 180 GeV  GeV, 95 confidence level upper limits are set on the production cross section of a charged Higgs boson in the range  pb, both with the assumption that .

[exoticpapers-blog]

Search for excited electrons and muons with 13/fb of proton-proton collisions at sqrt(s) = 8 TeV with the ATLAS detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2012-146/

The ATLAS detector at the LHC is used to search for excited leptons in the electromagnetic radiative decay channel . Results are presented based on the analysis of 13.0 fb of  collisions recorded in 2012 at a center-of-mass energy of 8 TeV. No evidence for excited leptons is found, and limits are set on the compositeness scale  as a function of the excited lepton mass . In the special case where , excited electron and muon masses below 2.2 TeV are excluded at 95% CL.

[exoticpapers-blog]

Search for New Phenomena in Monojet plus Missing Transverse Momentum Final States using 10/fb of pp Collisions at sqrt(s) = 8 TeV with the ATLAS detector at the LHC

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2012-147/

We report preliminary results on a search for new phenomena in monojet plus large missing transverse momentum final states. The analysis uses 10.5fb-1 of sqrt{s}=8TeV data collected in 2012 with the ATLAS detector. Good agreement is observed between the number of events in data and the Standard Model predictions. The results are translated into new limits on the production of light grativinos in association with gluinos or scalar quarks in a gauge-mediated supersymmetric model, leading to the best lower bound to date on the gravitino mass. Exclusion limits on models with large extra spatial dimensions and on pair production of weakly interacting dark matter candidates are also presented.

[exoticpapers-blog]

Search for New Phenomena in the Dijet Mass Distribution updated using 13/fb of pp Collisions at sqrt(s) = 8 TeV collected by the ATLAS Detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2012-148/

This note updates the results of ATLAS-CONF-2012-088, presented at the ICHEP 2012 conference. The dijet mass distribution produced in LHC proton-proton collisions at a center-of-mass energy sqrt{s}=8 TeV has been studied with the ATLAS detector using 2012 data with an integrated luminosity of 13.0 fb^{-1} including dijet masses up to ~ 4.69 TeV. No resonance-like features have been observed in the dijet mass spectrum. A new ATLAS exclusion limit has been set at 95% C.L. on the mass of excited quarks below 3.84 TeV. Model-independent limits on sigma cross A have also been extended.

[exoticpapers-blog]

Search for resonant ZZ production in the ZZ -> llqq channel with the ATLAS detector using 7.2/fb of sqrt(s) = 8 TeV pp collision data

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2012-150/

A search for a heavy particle that decays to a pair of Z bosons is presented, using events recorded by the ATLAS detector in proton-proton collisions at sqrt(s) = 8 TeV corresponding to an integrated luminosity of 7.2 fb-1. The analysis considers the llqq final state (l = e, mu) and uses the diboson mass reconstructed from the leptons and jets as the discriminating variable. No significant deviation in the mass distribution from a smoothly falling background distribution is observed. Upper limits on the production cross section times branching fraction into a ZZ boson pair are set for the bulk Randall-Sundrum graviton with coupling parameter kappa/bar{m}_Pl = 1.0, and the corresponding 95% credibility level observed (expected) lower limit on the mass for the graviton is 850 (870) GeV.

[exoticpapers-blog]

Search for resonant WZ -> lnu ll production using sqrt(s) = 8 TeV pp collisions with ATLAS

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-015/

A search is presented for a resonant state decaying to WZ in a fully leptonic channel,lvl'l' (l, l'=e, mu). The data represent an integrated luminosity of 13 fb-1 recorded by the ATLAS detector in sqrt{s} = 8 TeV pp collisions at the LHC. No significant localized excess is observed in the reconstructed WZ invariant mass distribution. Upper limits on the production cross section times branching ratio are derived and bounds on the resonant mass are obtained in the context of benchmark Extended Gauge and Low Scale Technicolor models.

[exoticpapers-blog]

Search for high-mass dilepton resonances in 20/fb of pp collisions at sqrt(s) = 8 TeV with the ATLAS experiment

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-017/

The ATLAS detector is used to search for heavy neutral gauge bosons () decaying to an electron-positron pair or a muon-antimuon pair. Results are presented based on the analysis of  collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of approximately 20 . A  with Standard Model  couplings to fermions is excluded at 95\% C.L. for masses below 2.79 TeV in the electron channel, 2.48 TeV in the muon channel, and 2.86 TeV in the two channels combined. Limits on other model interpretations are also presented, including a Grand Unification model based on the  gauge group, a Randall-Sundrum graviton and a technicolor model with a composite Higgs boson.

[exoticpapers-blog]

Search for heavy top-like quarks decaying to a Higgs boson and a top quark in the lepton plus jets final state in pp collisions at sqrt(s) = 8 TeV with the ATLAS detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-018/

A search is presented for production of a heavy up-type quark ( ) together with its antiparticle, assuming a significant branching ratio for subsequent  decay into a Standard Model Higgs boson and a top quark, as predicted by vector-like quark models. The search is based on 14.3 fb of  collisions at  TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton+jets final state, characterised by an isolated electron or muon with moderately high transverse momentum, significant missing transverse momentum, and at least six jets. The search exploits the high total transverse momenta of all final state objects and the high multiplicity of  jets characteristic of signal events with at least one Higgs boson decaying into , to discriminate against the dominant background from top quark pair production. No significant excess of events above the Standard Model expectation is observed, and upper limits are derived for vector-like quarks of various masses in the two-dimensional plane of  versus , where  is the Standard Model Higgs boson, assumed to have a mass of  GeV. Under the branching ratio assumptions corresponding to a weak-isospin doublet (singlet) scenario, a  quark with mass lower than 790 (640) GeV is excluded at the 95\% confidence level.

[exoticpapers-blog]

Search for Type III Seesaw Model Heavy Fermions in Events with Four Charged Leptons using 5.8/fb of sqrt(s) = 8 TeV Data with the ATLAS Detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-019/

A search for Type III Seesaw model heavy fermions is presented. The search is performed in a data sample corresponding to 5.8 fb of integrated luminosity collected in 2012 in  collisions at ~TeV by the ATLAS detector at the LHC. Charged heavy fermions, , are reconstructed in the channel  together with an additional charged lepton from the decay of a partner heavy fermion, , where . No evidence of the  is observed. Upper limits at 95\% confidence level are set on the production cross section of  times the branching fraction to the examined four lepton final states. When interpreted in the context of the Type III Seesaw model, the results translate into a lower limit on the mass of the  states of 245 GeV at 95\% confidence level.

[exoticpapers-blog]

Search for W' → tb in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 8 TeV with the ATLAS detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-050/

A search for  bosons is performed with the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of = 8 TeV, using a dataset corresponding to an integrated luminosity of 14.3 . This analysis searches for  bosons in the  decay channel in final states with electrons or muons, using a multivariate method based on boosted decision trees. The search range covers  -boson masses between 0.5 and 3.0 TeV, with right-handed or left-handed -boson chiralities. No significant deviation from the Standard Model expectation is observed and upper limits are set on the  cross-section times branching ratio and on the -boson effective couplings as a function of the -boson mass, using the CLs procedure. For a left-handed (right-handed)  boson, masses below 1.74 (1.84) TeV are excluded at 95% confidence level.

[exoticpapers-blog]

Search for anomalous production of events with same-sign dileptons and b jets in 14.3/fb of pp collisions at sqrt(s) = 8 TeV with the ATLAS detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-051/

A search is presented for exotic processes that result in final states containing jets including at least one  jet, sizable missing transverse momentum, and a pair of leptons with the same electric charge. There are several models that predict an enhanced rate of production of such events beyond the expectations of the Standard Model (SM); the ones considered in this note are pair production of chiral  quarks, pair production of vector-like quarks, enhanced four top quark production and production of two positively-charged top quarks. Using a sample of 14.3 fb of  collisions at  TeV recorded by the ATLAS detector at the Large Hadron Collider, with selection criteria optimised for each signal, no significant excess of events over the background expectation is observed. This observation is interpreted as constraining the signal hypotheses, and it is found at 95% confidence level that: the mass of the , assuming 100% branching fraction to , must be  TeV; the mass of a vector-like  () quark, assuming branching ratios to , , and  decay modes consistent with the  or  being a singlet, must be  0.59 (0.54) TeV; the four top production cross section must be  fb in the SM and  fb for production via a contact interaction; the mass of an sgluon must be  TeV; in the context of models with two universal extra dimensions the inverse size of the extra dimensions must be  TeV; and the cross section for production of two positively-charged top quarks must be  fb.

[exoticpapers-blog]

A search for tt resonances in lepton plus jets events with ATLAS using 14/fb of proton-proton collisions at sqrt(s) = 8 TeV

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-052/

A search for new particles that decay into top quark pairs ( ) is performed with the ATLAS experiment at the LHC using an integrated luminosity of 14 fb of proton-proton collision data collected at center-of-mass energy  TeV. The lepton plus jets final state is used, where the top-pair decays as  with one  boson decaying leptonically and the other hadronically. The  system is reconstructed using both a conventional resolved jet analysis and a large-radius jet substructure analysis. The  invariant mass spectrum is searched for local excesses deviating from the Standard Model prediction. No evidence for a  resonance is found and 95% CL limits on the production rate are determined for massive states in two benchmark models. The upper limits on the cross section times branching ratio of a narrow  boson decaying to top pairs range from 5.3 pb for a resonance mass of 0.5 TeV to 0.08 pb for a mass of 3 TeV. A narrow leptophobic topcolor  boson with a mass below 1.8 TeV is excluded. Upper limits are set on the cross section times branching ratio for a broad color-octet resonance with 15.3% decaying to . These range from 9.6 pb for a mass of 0.5 TeV to 0.152 pb for a mass of 2.5 TeV. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.0 TeV.

[exoticpapers-blog]

Search for pair production of new heavy quarks that decay to a Z boson and a third generation quark in pp collisions at sqrt(s)=8 TeV with the ATLAS detector

A search is presented for the production of a new heavy quark with its antiparticle, assuming the new quark has a significant branching ratio to decay into a  boson and a third generation Standard Model quark. In the case of a new charge  quark () the decay targeted is , while for a new charge  quark () the decay targeted is . The search uses a dataset corresponding to  of  collisions at  TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Selected events contain a high transverse momentum  boson candidate reconstructed from a pair of oppositely charged electrons or muons. Additionally, the presence of at least two jets possessing properties consistent with the decay of a  hadron is required, as well as large total transverse momentum of all central jets in the event. No significant excess of events above the Standard Model expectation is observed, and upper limits are derived for vector-like quarks of various masses in a two-dimensional plane of branching ratios. Under branching ratio assumptions corresponding to a weak-isospin singlet scenario, a  () quark with mass lower than 585 (645) GeV is excluded at the 95% confidence level. Under branching ratio assumptions corresponding to a particular weak-isospin doublet scenario, a  () quark with mass lower than 680 (725) GeV is excluded at the 95% confidence level.

[exoticpapers-blog]

Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state in pp collisions at sqrt(s) = 8 TeV with the ATLAS detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-060/

A search is presented for production of a heavy top-like quark () together with its antiparticle, assuming a significant branching ratio for subsequent decay into a  boson and a  quark. The search is based on 14.3 fb of  collisions at  TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton+jets final state, characterised by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least four jets, with at least one of them  tagged. The analysis strategy relies on the substantial boost of the  bosons in the  signal when  GeV. No significant excess of events above the Standard Model expectation is observed. For a chiral fourth generation quark, and under the assumption of a branching ratio , a mass lower than 740 GeV is excluded at 95% CL. For vector-like  quarks, and under the assumption that only the ,  and  decay modes contribute, 95% CL upper limits are derived for various masses in the two-dimensional plane of  versus , where  is the Standard Model Higgs boson. These limits are significantly improved by combining this search with a previous search for , with .

[exoticpapers-blog]

A search for high-mass ditau resonances decaying in the fully hadronic final state in pp collisions at √s=8 TeV with the ATLAS detector

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-066/

This note presents a search for high-mass ditau resonances decaying in the fully hadronic final state using proton-proton collisions at  TeV produced by the Large Hadron Collider. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 19.5 fb. No statistically significant excess above the Standard Model expectation is observed; 95% credibility upper limits are set on the cross section times branching fraction of  resonances decaying into  pairs as a function of the resonance mass. As a result,  bosons of the Sequential Standard Model with masses less than 1.90 TeV are excluded at 95% credibility.