Update on Higgs self-coupling

1. Update on Higgs self-coupling Tomáš Laštovička FZÚ AV ČR WG6 Meeting 24/01/2012

2. Brief summary from the last presentation • Cross-check uncertainty relating factor (for hhνν channel): It turns out it is rather around 1, when including Z-diagrams(checked with CalcHEP2.4) • Unfortunately, @ 3TeV the situation is worse and the factor is around 1.6 • The best achieved cross-section uncertainty around 14.6%-16% depending on the neural net training and the uncertainty evaluation method. • This would lead to λhhh uncertainty of around 23.4%-25.6%, i.e. not as good as we hoped for. @ 1TeV

3. More on uncertainty ratio • Previous results based on CalcHEP 2.4, no ISR, no beamstrahlung • Moving to the last version of CalcHEP 3.2: • ISR presence has changed the behavior of the cross section slope • It’s increasing when the coupling is rising (?) • Uncertainty ratio factor is getting higher (we started at 0.85…) • Might need an independent cross check from a volunteer • In analysis chain Whizard’shhνν cross section is much lower, around 0.622fb • should be checked in CalcHEP with beamstrahlung on

4. Jet reconstruction with secondary vertices I • Jet reconstruction and γγ overlay is an issue… • The Idea: • make sure that tracks, composing secondary vertices, will not be split into different jets • If they do, one would loose these vertices (vertex finding is performed within jets) • One might improve jet finding, flavour tagging, analysis results (acc. to ILC 500GeV) Should not happen: vtx IP

5. Jet reconstruction with secondary vertices II • Not as (relatively) straightforward as for the ILC - due to γγ overlay • Algorithm: • Find 4 jets + “beam jet” • Merge 4 jets into 1 fat jet (not the same as asking FastJet for 1 jet!) • Run LCFI’s secondary vertexing on this jet (slow…) • Merge particles corresponding to each vertex into one particle per vertex • Find 4 jets + “beam jet” once again • Recover “merged” particles in jets and go back to original particles • Run LCFI’s secondary vertices (not the same as step 3) • Run LCFI’s flavour tagging inputs evaluation • Run analysis processor and write all needed for the subsequent analysis chain

6. Jet reconstruction with secondary vertices III • The algorithm was implemented via a new processor VertexTracks • It’s SLOW • LCFI runs twice • much more combinatorics for vertex finding in the first step with 1 jet ► Step 1 ► ► Step 2

7. Jet reconstruction with secondary vertices IV • I did not manage to run all the samples for today’s presentation • and some jobs were cancelled • Sufficient for a rough first estimates • No improvement observed • Cross section uncertainty around 16% • i.e. as in the previous case before playing with NN training and flavour tags

8. Summary • @ 3TeV, 120GeV Higgs the hhνν cross section uncertainty remains at around 15% • We are unlucky with the uncertainty ratio factor • increasing with every cross-check (from 0.85 to 1 to 1.6 to 1.8) • Could we use different topological features of hhh diagrams in hhνν events, compared to other contributions? • What is needed: • Samples for mh = 125GeV • We may skip 130, 140 GeV Higgs • Remaining 4q backgrounds • Table with required statistics per sample 8

9. BACKUPS

10. Illustration of jet shapes (from MCParticles) • Red and green are particles from different Hs, blue squares are secondary vertices and black points are directions of Hs (no RPs and jets overlaid) φ η