Discovery potential of toppartners in a realistic composite Higgs model with early LHC data

Transcription

1 Discovery potential of toppartners in a realistic composite Higgs model with early LHC data Günther Dissertori, Elisabetta Furlan, Filip Moortgat, JHEP09(20)019 Kick-off Meeting Of The LHCPhenoNet Initial Training Network Valencia, February 1st

2 composite Higgs model try to explain why the Higgs boson is light the Higgs boson is a composite state of some new, strongly interacting sector this new sector has a global SO(5) symmetry that is broken to SO(4) at the scale f get 4 real Goldstone bosons with the correct quantum numbers to be identified with the Higgs doublet the Higgs is the (pseudo) Goldstone boson associated to this symmetry breaking its mass is naturally light, as it is generated at loop level and not sensitive to radiative corrections above the compositeness scale Λ ~ 2 π f we choose f = 500 GeV in order not to have too large fine-tuning similar idea as for pions (π +, π -, π 0 ) in QCD!! 2

3 composite Higgs model we could also have other composite states of the new sector, for example new quarks! mixing of the top-quark with such new quarks could explain the large top-mass we consider the case of multiplets of new quarks that transform under the fundamental representation of SO(5) one multiplet contains three quarks of charge +2/3, one of charge -1/3, and one of charge +5/3 the new quarks can help in restoring the agreement of the model with electroweak precision tests... 3

4 composite Higgs model couplings of Higgs to gauge bosons are reduced w.r.t. the SM (shift of S and T parameters) the new quarks contribute to electroweak precision observables t 1 b Peskin-Takeuchi T Z t 1 b Z b L bl scan parameter space for points that are consistent with EWPT and CDF mass limits consider Peskin-Takeuchi S & T parameters and Z Z b L bl t 1 coupling Z the case of one multiplet of new quarks is very constrained the mass spectrum and possible decay chains are quite fixed 4

5 composite Higgs model for two multiplets of new quarks, the constraints are much weaker much richer collider phenomenology find large region of parameter space to be compatible with current electroweak precision data! focus on distinctive signatures of the two multiplet model either two charge 5/3 quarks below 500 GeV (XX signature) ν l + l W + b l + or t 1, t 2, x 1, and b 1 with Δm < 60 GeV below 500 GeV (4 of SO(4)) g g t 1 Z t upper mass bound of 500 GeV for early detection g t 1 W b we define 30 benchmark points that show these signatures q q 5

6 detector simulation & selection of jets and leptons implement the model consistently in the MadGraph event generator produce 5 events for pair-production of the new quarks for all 30 benchmark points fast detector simulation with Delphes using the CMS detector specifications searching for an excess over the SM expectation in multi-lepton final states select electrons and muons with p t > 20 GeV and η < 2.4 relative isolation P t p t,lept < 0.05 where P t = select cleaned jets with p t > 50 GeV and η < 3.0 (anti-k t with cone radius 0.5) tracks i=µ,e p t,i in cone R < 0.3 6

7 jet multiplicity final state selection lepton configuration vs. jet multiplicity for 200 pb -1 signal: benchmark point with cross section.78 pb -1 (LO) total SM background 9j 8j 7j # of events 9j 8j 7j 5 4 # of events 6j 6j 5j 1 5j 3 4j 3j 2j 1j 0j 2l SS 2l OS SF 2l OS OF 3l SS 3l OS 4l 5l -1-2 jet multiplicity 4j 3j 2j 1j 0j 2l SS 2l OS SF 2l OS OF 3l SS 3l OS 4l 5l 2 lepton configuration lepton configuration lower limit at 95% C.L. upper limit at 95% C.L. SF = same flavour, OF = opposite flavour, SS = same sign, OS = opposite sign (at least one lepton has a different sign) 7

8 final state selection & inclusive discovery potential number of signal events divided by the total number of background events from SM 9j 8j S/B j 6j most promising final states jet multiplicity 5j 4j 3j 2j 1j 0j 2l SS 2l OS SF 2l OS OF 3l SS 3l OS 4l 5l SS dilepton with 3 or 4 j OS trilepton with 2 or 3 j lepton configuration 8

9 two promising benchmark points robust, cut-based analysis for two benchmark points (BP) with a large total cross section both BPs show a 4 of SO(4) signature after preselection one BP has in addition two charge 5/3 quarks below 500 GeV both have a large cross section of 5.52 pb (4) and.78 pb (XX) events / 15 GeV 12-1 p L=200 pb T hardest jet for! lbp 18 BP SM background selection cuts: preselection: same-sign di-lepton cut 1: at least two jets with p t > 50 GeV cut 2: hardest jet p t > 90 GeV cut 3: h t > 300 GeV p (GeV) p t > 90 GeV T 9

10 two promising benchmark points for 200 pb -1 and our selection cuts 62 and 41 signal events 6.9 background events events / 30 GeV h T -1 for! L=200 pb lbp 18 BP SM background 5σ achieved with pb and only after requiring same-sign di-leptons LHC experiments have sensitivity already now ATLAS & CMS have collected about ~35 pb -1 in the 20 runs each first results will be public soon (GeV) h T

11 x 1 mass reconstruction how to reconstruct the mass of a charge 5/3 quark? x 1 t W + traditional method (e.g. CMS PAS EXO ) g W + ν t l + W + ν b l + x 1 x 1 g x 1 identify the decay using the same-sign di-leptons from the decay of the one quark g x 1 W t reconstruct the mass of the other, hadronically decaying quark q q W b q q 11

12 x 1 mass reconstruction how to reconstruct the mass of a charge 5/3 quark? x 1 t W + traditional method (e.g. CMS PAS EXO ) g W + ν t l + W + ν b l + x 1 x 1 g x 1 identify the decay using the same-sign di-leptons from the decay of the one quark g x 1 W t reconstruct the mass of the other, hadronically decaying quark q q W b q q our idea: use the invariant mass distribution of the SS di-leptons to reconstruct the x 1 mass in the decay x 1 tw + bw + W + bl + l + ν l ν l 11

13 x 1 mass reconstruction with 200 pb -1 selecting signal events with our selection cuts kinematic configuration of x 1 decay is identical to g t t 1, t 1 c χ 0 1 Kraml & Raklev: analytic expression for M lc in gluino decay events / 28 GeV M ll for -1 L=200 pb signal + SM SM m fit = ± 33.4 GeV m x1 = 365 GeV fit tail of SS di-lepton inv mass distribution to reconstruct x 1 mass! pb -1 is sufficient to get x 1 mass within ~ 30 GeV (GeV) M ll 12

14 applying the method to the benchmark points for both discussed signatures of the model, the excess of SS di-lepton events is produced by the contributions of various new quarks t 1 and x 1 are the lightest new quarks: x 1 gives the largest contribution! Q: is 200 pb -1 (~50 events) enough to reveal the presence of new quarks in addition to x 1? 13

15 applying the method to the benchmark points for both discussed signatures of the model, the excess of SS di-lepton events is produced by the contributions of various new quarks t 1 and x 1 are the lightest new quarks: x 1 gives the largest contribution! Q: is 200 pb -1 (~50 events) enough to reveal the presence of new quarks in addition to x 1? idea: if only x 1 is present, a fit of the tail of M ll leads to a fairly accurate estimate of the x 1 mass. with a given mass hypothesis, we can calculate the pair production cross section for the heavy top-partner knowing mass and cross section, we can use MC to compare the observation with the expected distribution due to x 1 with the fitted mass. if various quarks are present, the above leads to a discrepancy between the single x 1 hypothesis and the observation. 13

16 applying the method to the benchmark points SS di-lepton invariant mass of signal + SM (red) signal produced by t 1, x 1, t 2, b 1, t 3, x 2, t 4 62 signal and 7 SM events for 200 pb -1 m x1 = 365 GeV, fit gives m fit =395 ± 25 GeV events / 28 GeV 12 M ll -1 for L=200 pb BP + SM expectation for x 1 only + SM blue distributions due to pair-produced x 1 with fitted mass ± error on mass. 8 expect 11 ± 3 events from x1 only with fitted mass 6 large discrepancy of 51 unexplained signal events! evidence for contribution of additional quarks M ll (GeV) 14

17 conclusions composite Higgs models are attractive solutions to the hierarchy problem large top mass explained by mixing of top with heavy top-partners SS di-lepton and tri-lepton final states were found to be promising for a potential discovery outlined new method to reconstruct the mass of a charge 5/3 top-partner via its leptonic decay does not rely on jets the method can be used to judge if the signal is compatible with the presence of one charge 5/3 quark only 15

18 Backup 16

19 analogy to pions the three pions have the same problem as the Higgs: they are light scalars explanation: the pions are composite states of up- and down-quarks the quark Lagrangian has a global SU(2) L x SU(2) R symmetry that is (spontaneously) broken to SU(2) V get three light, real Goldstone bosons, the pions! composite Higgs: adopt solution from pions 17

20 the quark multiplets we consider vector-like multiplets of top partners Ψ that transform under the fundamental representation of SO(5) Ψ=(Q, X, T ) Q: SU(2) L doublet with the same quantum numbers as q L = (t L, b L ) X: SU(2) L doublet with hypercharge 7/6 its upper component is a charge 5/3 quark T: singlet with hypercharge 2/3 same quantum numbers as t R 18

21 electroweak precision tests reduction of W-h couplings UV physics S 19

22 two promising benchmark points # of jets after preselection cut we require # jets 2 events 2-1 number of jets for! L=200 pb lbp 18 BP SM background N jets 20

23 x 1 mass reco using the endpoint the x 1 mass can be extracted from the endpoint of the SS di-lepton invariant mass distribution via: m x1 = M max l 1 l m 2 M max 2 t l 1 l 2 + m 2 W M max l 1 l 2 events / 28 GeV M ll for -1 L=200 pb signal + SM SM m fit = ± 33.4 GeV m x1 = 365 GeV (GeV) M ll M max l 1 l 2 = 308 GeV 21