Itamar Roth, Ehud Duchovni Group meeting 19/01/15 1

 Several SM extensions predict particles that decay rapidly to many colored particles.  Observables at the LHC: large jet multiplicity at high H T.  The result could be interpreted within RPV SUSY, micro Black Holes, etc.  The multi-jet final state may be the outcome of multi-body decays or long sequential cascade decays.  The analysis has reached to the unblinding stage. 2

 Signals manifest as threshold effects.  Classical black holes evaporate thermally through Hawking radiation.  Density of states in hadronic sector implies “decay” is dominated by jets  Characteristic signature is large multiplicity, high p T jet production 3

 Trigger: Event pass EF_j170_a4tchad_ht700.  Track Quality: At least 1 primary vertex, ≥ 2 tracks sourced to it.  Jets Selection: Select Jets for which p T > 50 GeV and |  | < 2.8.  Up to date event cut flow as is for 20.3 fb data:  ~700 million raw events, ~30 million events accepted for analysis. 4

5

6  Main background is QCD.  Many jets implies many partons, which lead to multitude of difficult high order matrix calculations.  Simulated using parton showers algorithms.  Hard to estimate the effect of the jet-reconstruction algorithm.  Uncertainty is large and hard to estimate. Needs a data-driven background estimation method

 The parameter space (N jet, H T ) is broken up into inclusive N jet ≥ X slices.  The slices are further divided into two exclusive H T regions.  Control region (CR): 1.5 < H T < 2.9 TeV  An H T region where no new physics is found.  Signal region (SR): H T > 3.0 TeV. 7

 A carefully chosen function is fitted to the CR and extrapolated into the SR.  We use a three-parameter empirical function:  This function was used to fit dijet at LHC and Tevatron.  The extrapolation is taken as the central value of the background estimation.  The background estimation method is inspired by a CMS search for mBH (arXiv: [hep-ex] (2012)). 8

 The method was validated on Pythia, Herwig and Alpgen MC: 9

 We predict the shape and normalization of the H T with accuracy as follows: 10

 Lower possible limit: Trigger is fully efficient for events with H T > 1.2 TeV.  Upper possible limit: the fit becomes sensitive to mBH contamination above 3.0 TeV.  The CR range with the most stable fit extrapolation was found to be: 1.5 < H T < 2.9 TeV. 11

 A number of functional forms with common characteristics were evaluated, best extrapolation chosen based on  2 / NDF.  Alternate forms are taken as a uncertainty based on criteria:  Reasonably Fit CR in data and MC;  Must always monotonically fall as a function x;  Demonstrate reasonably good extrapolation based on QCD MC. 12

 In the absence of new physics, model independent limits on observed multi-jet production as a function of H T Min will be set, where 13

 The results are interpreted in terms of exclusion contours in the space of (M TH, M D ) for various microscopic black holes.  Signal parameter space: 1.5 TeV ≤ M D ≤ 4 TeV, 4.5 TeV ≤ M TH ≤ 6.5 TeV. 14

15  A data driven search for new physics in the multi-jet channel is presented.  A fit and extrapolate method is used to estimate the shape and normalization of the H T distribution in slices of inclusive N jet.  The associated ambiguities on the choice of functional form, CR and statistics are studied and taken into account as systematic uncertainties  The SR in the 2012 data is still blinded.  In the absence of statistically significant excess the results are interpreted in the context of model independent limits on the multi-jet production cross section and model dependent exclusion contours in the (M TH, M D ) space.

16

18

19 Spin No. of Gen ColorTotal q(u,c,t) q(d,s,b) W31126 Z g The probability to emit is 8/117~7%