A new LHC Run 1 search for di-Higgs resonances in the 4b decay channel has now been submitted to Eur. Phys. J. C, see http://arxiv.org/abs/1506.00285. The data sample corresponds to about 20 inverse femtobarns of proton-proton collisions collected by the ATLAS detector in 2012 at a collision energy of 8 TeV. Prof. Willocq and postdoctoral Research Associate Bellomo had responsibility for the statistical analysis and editing of the paper for the so-called boosted analysis. This boosted analysis features the first application of b-tagging to track-jets associated with large-radius jets in ATLAS. Such a novel approach is required for tagging of high-momentum Higgs bosons decaying in the dominant bbbar mode and is expected to have broad application in searches involving Higgs bosons in Run 2 of the LHC.
Invariant mass distribution for pairs of large-radius jets with 4 associated b-tagged track-jets
See the mass distribution for pairs of large-radius jets (figure on the right) with dashed curves showing the expected deviations in the presence of Kaluza-Klein excitations of the graviton, as predicted by the Randall-Sundrum model with one warped extra spatial dimension. Interpretations were also made in the context of Two-Higgs Doublet models.
The latest LHC Run 1 search for contact interactions and large extra dimensions with dielectrons and dimuons is now published in Eur. Phys. J. C, see EPJC 74 (2014) 3134 or http://arxiv.org/abs/1407.2410. The data sample corresponds to about 20 inverse femtobarns of proton-proton collisions collected by the ATLAS detector in 2012 at a collision energy of 8 TeV. Prof. Willocq and Graduate Student Varol have led the analysis of the dimuon channel. Varol completed her dissertation on this topic and earned her Ph.D. degree in 2014.
Dimuon invariant mass distribution
See the dimuon mass distribution (first figure on the right) with colored curves showing the expected distributions in the presence of new phenomena from contact interactions or large extra dimensions.
Dimuon invariant mass distribution
A novel aspect of this search is the inclusion of the muon angular distribution (second figure on the right) for the first time at the LHC, in addition to the dimuon mass distribution, as an independent observable sensitive to new phenomena in the dimuon final state.
The latest search for contact interactions and large extra dimensions with dielectrons and dimuons is now published in Phys. Rev. D, see http://prd.aps.org/abstract/PRD/v87/i1/e015010. The data sample corresponds to about 5 inverse femtobarns of proton-proton collisions collected by the ATLAS detector in 2011. Prof. Willocq and Graduate Student Varol have led the analysis of the dimuon channel.
Dimuon invariant mass distribution
See the dimuon mass distribution with colored curves showing the expected distributions in the presence of new phenomena from contact interactions or large extra dimensions.
Graduate student Tülin Varol and Prof. Willocq have led an update to the search for contact interactions in the dilepton channel at the LHC. The new results have been submitted to the new Physical Review X online journal and the preprint can be seen at http://arxiv.org/abs/1112.4462. This new search was carried out with about 1 fb-1 of proton-proton collisions data, corresponding to a factor 25 increase in statistics over the previous results. The new search adds the dielectron channel to the dimuon channel and excludes the existence of contact interactions up to scales of about 10 TeV.
Tülin Varol presented those results at CERN on Dec 8 in the context of the “Implications of LHC results for TeV-scale physics” workshop, see her talk in the agenda.
Graduate student Emily Thompson and Professor Stéphane Willocq performed the first search for contact interactions at the LHC in the dimuon channel using data collected with the ATLAS detector during the 2010 pp collision run. The results of this search have been published in the July 1st edition of Physical Review D Rapid Communications: Phys. Rev. D 84, 011101 (2011), arXiv:1104.4398 [hep-ex]. The limits placed on the compositeness scale Lambda are the most stringent to date.
Emily Thompson earned her PhD in June 2011 and is currently working as a postdoctoral research associate for Columbia University. She continues to work on ATLAS at CERN, focusing on boosted top quarks.
