Measurement of the trilinear Higgs self-couplings at 1.4 TeV (update)

1. Measurement of the trilinear Higgs self-couplings at 1.4 TeV(update) Tomáš Laštovička (IoP AC, Prague) Jan Strube (Tohoku, Japan) CLICdp WG Analysis Meeting 25 February 2014

2. Introduction • Higgs self-coupling analysis @ 1.4 TeV was done a while (>year) ago • mH = 120 GeV • 2000 fb-1 accumulated luminosity • Temporary qq̅qq̅eν backgrounds • difficult to produce these @ 1.4 TeV • No eγ, γe, γγbackgrounds (but γγ→had. overlay included) • The uncertainty of the self-coupling was 28% • The HHνν̅ cross section at 1.4 TeV is smaller compared to 3 TeV • 0.149 fb vs. 0.588 fb for 126 GeV Higgs • We expect 223 (1180) events at 1.4 TeV (3 TeV) in 1.5 ab-1(2ab-1 )

3. Introduction II • The self-coupling analysis redone in last weeks with • mH = 126 GeV • Lower cross section: 0.149fb vs 0.164fb (0.91x) • Lower BR(H→bb̅) 56%(55.1%) vs 64.6% • Similar uncertainty relating factor: 1.22 vs. 1.20 (or 1.17?) • 1500 fb-1 acc. lumi - factor of √(2/1.5) = 1.15 degradation • About 4-5% on the coupling uncertainty • New qq̅qq̅eν background sample (prodID 1085) • Replaced private samples produced by Jan. • Missing piece for completing the Higgs picture at CLIC. • Still includes broken SiD reconstruction – small effect @ 1.4 TeV, unlike 3 TeV We are already at 37% at this place just by simply scaling up the “old” results (28%)

4. Samples 1535: HHNUNU_ 27260 Signal 1652: HHNUNU_0.8_ 64258 Modified coupling 1648: HHNUNU_1.2_ 57383 1081: QQQQNUNU_ 218563 4Q backgrounds 1097: QQQQ_ 246612 1089: QQQQLL_ 162046 1085: QQQQENU_ 116082 2364: AE_EQQQQ1_ 121000 eγand γe 4Q backgrounds 2355: EA_EQQQQ2_ 99637 2358: EA_EQQQQ1_ 125700 2361: AE_EQQQQ2_ 91322 2643: AA_QQQQ11_ 193544 γγ 4Q backgrounds 2637: AA_QQQQ21_ 128576 2640: AA_QQQQ12_ 81311 2634: AA_QQQQ22_ 63965 =========== 1.8M events

5. Neural net inputs

6. Neural net classifier qq̅qq̅eν qq̅qq̅νν̅ signal Relevant part of the neural net classifier in a fine binning. Signal is constant by construction. 100 bins per 0.1

7. CS err Results qq̅qq̅eν events • Cut-and-count • Best significance at 4% signal selection eff. (!!), i.e. 9 signal and 1 bkg event (??) 35.5% x 1.22 = 43.3%(one really should not use 1.22 here) • Template fitting λHHH directly 37-38% • Template fitting σHHνν 29-32% x 1.22 = 35.5-39% (consistent) • Reminder: In the old analysis we quote 28% on λHHHand 23% on σHHνν Sig eff

8. Summary • The new qq̅qq̅eν background samples contribute significantly • cross-check with older qq̅qq̅eν samples produced by Jan. • New beam induced backgrounds contribute less than expected. • Change in accumulated luminosity alone would change the λHHHuncertainty from 28% to 32%. Combined with lower cross section, lower BR, slightly worse unc. rel. factor it gets down to 37%. • Jet optimization a la Jan’s work for the 3 TeV case was not done, we do not expect a dramatic effect (was ~1% at 3 TeV).

9. Outlook • Improving the Higgs self-coupling analyses may take significant time. • Manpower issues [Jan Strubeat Tohoku, TL working for ELI] • Results from the 3 TeV analysis look reasonable (16-18% without polarisation) • However, 1.4 TeV CLIC should not do much worse than 1 TeV (or even 500 GeV) ILC. • Polarisation improves the result to 28% (-80,0) or to 25% (-80,30) TODO: Jet optimization, investigating the new qq̅qq̅eν background, anything else?

10. Backups

11. Double Higgs and tt̅H Production at CLIC tt̅Hproduction Double Higgs production Higgs self-coupling Quartic HHWW coupling Unpolarised cross sections HHνν̅ signal increased by a factor of 1.8 (2.34) for P(e-) = -80% ( P(e-) = -80%, P(e+) = 30% )