Search for microscopic black holes and string balls in final states with leptons and jets with the ATLAS detector at s $$ \sqrt{s} $$ = 8 TeV

Abstract

A search for an excess of events with multiple high transverse momentum objects including charged leptons and jets is presented, using 20.3 fb −1 of proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2012 at a centre-of-mass energy of √ s = 8 TeV. No excess of events beyond Standard Model expectations is observed. Using extra-dimensional models for black hole and string ball production and decay, exclusion contours are determined as a function of the mass threshold for production and the fundamental gravity scale for two, four and six extra dimensions. For six extra dimensions, mass thresholds of 4.8-6.2 TeV are excluded at 95% confidence level, depending on the fundamental gravity scale and model assumptions. Upper limits on the fiducial cross-sections for non-Standard Model production of these final states are set. 6 Event selection 8 7 Background estimation 9 7.1 Prompt background estimation from control regions 9 7.2 Backgrounds from misidentified objects and non-prompt leptons 13 7.3 Background smoothing with fits 148 Systematic uncertainties 159 Results and interpretation 17 Summary 25The ATLAS collaboration 32 IntroductionA long-standing problem in particle physics is the very large difference between two apparently fundamental energy scales: the electroweak scale at O(0.1 TeV) and the gravitational (Planck) scale M Pl = O(10 16 TeV). Models postulating extra spatial dimensions into which the gravitational field propagates attempt to address this hierarchy problem [1][2][3][4]. In most of these models, the Standard Model (SM) fields are constrained to the one time and three spatial dimensions of our universe, whilst the gravitons also propagate into the n "bulk" extra dimensions. In these models, the fundamental gravitational scale in the full (n + 4) space-time dimensions, M D , is dramatically lower than M Pl , and represents an effective scale appropriate for probes of the gravitational interactions at low energies. A value of M D in the TeV range would allow for the production of strong gravitational states such as microscopic black holes at energies accessible at the Large Hadron Collider (LHC) [5][6][7]. Two well-motivated extra-dimensional models are those with large flat extra dimensions -1 - JHEP08(2014)103(ADD models [2,3]) and those with small, usually warped, extra dimensions (RS models [4]). This analysis considers ADD models, for which the n = 1 case is ruled out and the n = 2 case is disfavoured by current astrophysical and tabletop experiments [8]. Thus, benchmark models with two, four and six additional spatial dimensions are considered.Estimates of the black hole production cross-sections invoke semiclassical approximations, the validity of which require the production centre-of-mass energy to be significantly above M D . This motivates the introduction of a production mass threshold M th , well above M D . In the black hole formation stage, some energy is expected to be lost to gravitational or SM radiation. This has recently been calcu...

Search for black holes and sphalerons in high-multiplicity final states in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV

“…The observed number of events with S T values above a chosen threshold is compared with the background and signal+background predictions to either establish a signal or to set limits on the signal production. This approach does not rely on the Monte Carlo (MC) simulation of the backgrounds, and it also has higher sensitivity than exclusive searches in specific final states, e.g., lepton+jets [66,67].…”

Exotics Searches at ATLAS

“…[13]). The fundamental Planck scale M D is then related to the usual Planck scale M Pl via M Pl = M n+2 D R n .…”

“…This means, that the fundamental Planck scale could be of the order of TeV, which in turn allows for the production of black holes at LHC energies with some production mass threshold M th . The ATLAS collaboration has used events with at least three objects (electron, muons or jets) with a p T above 100 GeV, at least one of which has to be a lepton, to search for evidence of black hole production [13]. The discriminant variable is the scalar p T sum of the leptons and jets in the event and is shown in the left …”

Collider searches for nonperturbative low-scale gravity states

“…Thermal gravity states such as GR black holes and string balls have been searched for by ATLAS [20] and CMS [21,22,23] in multi-jet events. In addition, ATLAS has search for the same states in +jets events [24,25], and same-sign dimuon events with a large number of tracks [26,27].…”