Search for a Light Higgs Boson Decaying to Long-Lived Weakly Interacting Particles in Proton-Proton Collisions ats=7  TeVwith the ATLAS Detector

Abstract

A search for the decay of a light Higgs boson (120-140 GeV) to a pair of weakly interacting, long-lived particles in 1:94 fb À1 of proton-proton collisions at ffiffi ffi s p ¼ 7 TeV recorded in 2011 by the ATLAS detector is presented. The search strategy requires that both long-lived particles decay inside the muon spectrometer. No excess of events is observed above the expected background and limits on the Higgs boson production times branching ratio to weakly interacting, long-lived particles are derived as a function of the particle proper decay length. This Letter presents the first ATLAS search for the Higgs boson decay, h 0 ! v v , to two identical neutral particles ( v ) that have a displaced decay to fermionantifermion pairs. As a benchmark, we take a HV model [9] in which the SM is weakly coupled, by a heavy communicator particle, to a hidden sector that includes a pseudoscalar, the v . Because of the helicity suppression of pseudoscalar decays to low-mass f " f pairs, the v decays predominantly to heavy fermions, b " b, c " c, and þ À in the ratio 85:5:8%. The weak coupling between the two sectors leads the v to have a long lifetime. Other, non-HV, models with the identical signature, where the v is replaced with another weakly interacting scalar or pseudoscalar particle, are discussed in Refs. [4,10]. Both Tevatron experiments, CDF and D0, performed similar searches for displaced decays in their respective tracking volumes, which limited the proper decay length range they could explore to a few hundred millimeters [11,12].In many of these beyond-the-SM scenarios, the lifetime of the neutral states is not specified and can have a very large range. The current search covers a range of expected proper decay lengths extending to about 20 m by exploiting the size and layout of the ATLAS muon spectrometer.

Displaced vertices and long-lived charged particles in the NMSSM with right-handed sneutrinos

“…The resolution of the vertices in the pixel tracker for both ATLAS and CMS detectors is of the order of hundred µm, however as the displaced vertices must be distinguished from primary ones, usually |d 0 | 2 − 4 mm and L xy 4 − 8 mm is imposed [68][69][70][71]. These cuts also remove completely the SM background, as it was shown in refs.…”

“…[71] it was shown through MC simulation studies that the selection on |d 0 | > 2mm can remove 98% of all tracks from the primary pp vertices. Although in their searches for displaced vertices ATLAS and CMS use the whole detector volume, the identification of a displaced vertex decreases when d 0 grows [68,69,71]. In our analysis we will therefore restrict our searches to the inner detector 4 and for each simulated event we impose impose a cut on the decay length of the RH neutrino, 10 mm< cτ N <100 cm.…”

“…[68][69][70][71] are the present constraints from the LHC on displaced vertices. Some of these searches share the same signatures with this model.…”

Exotic decays of the 125 GeV Higgs boson

“…These signatures offer opportunities for LHCb [76,77] as well as ATLAS and CMS, but we do not cover them here. A number of relevant experimental searches have already been performed [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95]. In the following sections we examine most of the above decay modes in detail, outline their theoretical motivations, and review existing collider studies and relevant experimental searches.…”

Search for New Physical Phenomena via Displaced Muon Signatures with the CMS Detector at the LHC

“…The ATLAS Collaboration has performed searches that are sensitive to decay lengths up to about 20 m by exploiting the ATLAS muon spectrometer [9,10], using di↵erent decay channels from those considered in this analysis. In order to stop electrons and photons, the electromagnetic calorimeter is placed on the periphery of the silicon tracker.…”