@article{9c8a0f8e98f4495789c124b0c3a3441d,

title = "Search for pair production of up-type vector-like quarks and for four-top-quark events in final states with multiple b-jets with the ATLAS detector",

abstract = "A search for pair production of up-type vector-like quarks (T) with a significant branching ratio into a top quark and either a Standard Model Higgs boson or a Z boson is presented. The same analysis is also used to search for four-top-quark production in several new physics scenarios. The search is based on a dataset of pp collisions at s=13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb-1. Data are analysed in the lepton+jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets, as well as the jets + ETmiss final state, characterised by multiple jets and large missing transverse momentum. The search exploits the high multiplicity of jets identified as originating from b-quarks, and the presence of boosted, hadronically decaying top quarks and Higgs bosons reconstructed as large-radius jets, characteristic of signal events. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross sections for the different signal processes considered. These cross-section limits are used to derive lower limits on the mass of a vector-like T quark under several branching ratio hypotheses assuming contributions from T ? W b, Zt, Ht decays. The 95% CL observed lower limits on the T quark mass range between 0.99 TeV and 1.43 TeV for all possible values of the branching ratios into the three decay modes considered, significantly extending the reach beyond that of previous searches. Additionally, upper limits on anomalous four-top-quark production are set in the context of an effective field theory model, as well as in an universal extra dimensions model.[Figure not available: see fulltext.].",

keywords = "Beyond Standard Model, Hadron-Hadron scattering (experiments), vectorlike quarks",

author = "{The ATLAS collaboration} and M. Aaboud and G. Aad and B. Abbott and O. Abdinov and B. Abeloos and Abidi, {S. H.} and AbouZeid, {O. S.} and Abraham, {N. L.} and H. Abramowicz and H. Abreu and Y. Abulaiti and Acharya, {B. S.} and S. Adachi and L. Adamczyk and J. Adelman and M. Adersberger and T. Adye and Affolder, {A. A.} and Y. Afik and C. Agheorghiesei and Aguilar-Saavedra, {J. A.} and F. Ahmadov and G. Aielli and S. Akatsuka and {\AA}kesson, {T. P.A.} and E. Akilli and Akimov, {A. V.} and Alberghi, {G. L.} and J. Albert and P. Albicocco and {Alconada Verzini}, {M. J.} and S. Alderweireldt and M. Aleksa and Aleksandrov, {I. N.} and C. Alexa and G. Alexander and T. Alexopoulos and M. Alhroob and B. Ali and M. Aliev and G. Alimonti and J. Alison and Alkire, {S. P.} and C. Allaire and Allbrooke, {B. M.M.} and Allen, {B. W.} and Allport, {P. P.} and A. Aloisio and A. Alonso and F. Alonso and C. Alpigiani and Alshehri, {A. A.} and Alstaty, {M. I.} and {Alvarez Gonzalez}, B. and {{\'A}lvarez Piqueras}, D. and Alviggi, {M. G.} and Amadio, {B. T.} and {Amaral Coutinho}, Y. and L. Ambroz and C. Amelung and D. Amidei and {Amor Dos Santos}, {S. P.} and S. Amoroso and Amrouche, {C. S.} and C. Anastopoulos and Ancu, {L. S.} and N. Andari and T. Andeen and Anders, {C. F.} and Anders, {J. K.} and Anderson, {K. J.} and A. Andreazza and V. Andrei and S. Angelidakis and I. Angelozzi and A. Angerami and Anisenkov, {A. V.} and A. Annovi and C. Antel and Anthony, {M. T.} and M. Antonelli and Antrim, {D. J.A.} and F. Anulli and M. Aoki and {Aperio Bella}, L. and G. Arabidze and Y. Arai and Araque, {J. P.} and {Araujo Ferraz}, V. and {Araujo Pereira}, R. and Arce, {A. T.H.} and Ardell, {R. E.} and Arduh, {F. A.} and Arguin, {J. F.} and S. Argyropoulos and Armbruster, {A. J.} and Armitage, {L. J.} and O. Arnaez and H. Arnold and M. Arratia and O. Arslan and A. Artamonov and G. Artoni and S. Artz and S. Asai and N. Asbah and A. Ashkenazi and Asimakopoulou, {E. M.} and L. Asquith and K. Assamagan and R. Astalos and Atkin, {R. J.} and M. Atkinson and Atlay, {N. B.} and K. Augsten and G. Avolio and R. Avramidou and B. Axen and Ayoub, {M. K.} and G. Azuelos and Baas, {A. E.} and Baca, {M. J.} and H. Bachacou and K. Bachas and M. Backes and P. Bagnaia and M. Bahmani and H. Bahrasemani and Bailey, {A. J.} and Baines, {J. T.} and M. Bajic and Baker, {O. K.} and Bakker, {P. J.} and {Bakshi Gupta}, D. and Baldin, {E. M.} and P. Balek and F. Balli and Balunas, {W. K.} and E. Banas and A. Bandyopadhyay and Sw Banerjee and Bannoura, {A. A.E.} and L. Barak and Barbe, {W. M.} and Barberio, {E. L.} and D. Barberis and M. Barbero and T. Barillari and Barisits, {M. S.} and Barkeloo, {J. T.} and T. Barklow and N. Barlow and R. Barnea and Barnes, {S. L.} and Barnett, {B. M.} and Barnett, {R. M.} and Z. Barnovska-Blenessy and A. Baroncelli and G. Barone and Barr, {A. J.} and {Barranco Navarro}, L. and F. Barreiro and {Barreiro Guimar{\~a}es da Costa}, J. and R. Bartoldus and Barton, {A. E.} and P. Bartos and A. Basalaev and A. Bassalat and Bates, {R. L.} and Batista, {S. J.} and S. Batlamous and Batley, {J. R.} and M. Battaglia and M. Bauce and F. Bauer and Bauer, {K. T.} and Bawa, {H. S.} and Beacham, {J. B.} and Beattie, {M. D.} and T. Beau and Beauchemin, {P. H.} and P. Bechtle and Beck, {H. P.} and Beck, {H. C.} and K. Becker and M. Becker and C. Becot and Beddall, {A. J.} and A. Beddall and Bednyakov, {V. A.} and M. Bedognetti and Bee, {C. P.} and Beermann, {T. A.} and M. Begalli and M. Begel and A. Behera and Behr, {J. K.} and Bell, {A. S.} and G. Bella and X. Zhao",

note = "Publisher Copyright: {\textcopyright} 2018, The Author(s).",

year = "2018",

month = jul,

day = "1",

doi = "10.1007/JHEP07(2018)089",

language = "English",

volume = "2018",

journal = "Journal of High Energy Physics",

issn = "1126-6708",

number = "7",

}