Searching for the Higgs boson in the VH and VBF channels at ATLAS and CMS Dr. Adrian Buzatu Research Associate

We need to study the Higgs couplings to all particles. A straight line (SM) or a curve (SUSY)? The Higgs boson (SM) or a Higgs boson (SUSY)? arXiv: W Z Data Standard Model (SM) Supersymmetry (SUSY) ? ? --- Subtle differences ---

Higgs bosons can be produced by coupling with bosons (VH, VBF) or with fermions (ggF, ttH).

ggF cross-section is ~13x that of VBF, which in turn is ~2x that of WH and ~4x that of ZH. σ at 7 TeV [pb]σ at 8 TeV [pb] ggF15.0 +/ /- 2.0 VBF1.22 +/ / WH0.57 +/ / ZH0.33 +/ /- 0.01

Higgs bosons at 125 GeV decay in many ways.

ATLAS and CMS studied almost all combinations of Higgs boson production and decay channels. DecayggFVBFVHPapers H to bb Yes JHEP 1501, 0692 (2015) Phys. Rev. D89, (2014); Phys. Rev. D92, (2015) H to ττYes JHEP 1504, 117 (2015) JHEP 05, 104 (2014) H to WWYes Phys. Rev. D92, (2015); JHEP 08, 137 (2015) JHEP 01, 096 (2014) H to ZZYes Phys. Rev. D91, (2015) Phys. Rev. D89, (2014) H to γγYes Phys. Rev. D90, (2014) Eur. Phys. J. C74, 3076 (2014) H to μμYes - Yes Phys. Lett. B738, 68 (2014) Phys. Lett. B744, 184 (2015) H to inv---- Yes Eur. Phys. J. C75, 337 (2015); arXiv: Eur. Phys. J. C74, 2980 (2014)

VH+VBF Higgs production H to bbH to ττH to WWResults

VH and VBF production signatures reject most of the QCD jet background, especially needed for H to bb and H to ττ. W or Z boson, decaying to leptons. Two forward jets with Large |Δη| between them.

This increases the S/B ratio from roughly 1 to 1 million to roughly 1 to 1 thousand.

VH+VBF Higgs production H to bbH to ττH to WWResults

ATLAS and CMS have three VH channels based on number of leptons. In addition, CMS has WH->τ h bb. To increase the sensitivity even more, the analysis channels are split further by p T V. ATLAS also splits further by the number of jets and b-tagging discriminant.

The event selection is chosen for each category. CMS signal region.

The best single S to B discriminant is m bb, improved by b-jet specific energy corrections. 12% of b jets contain a muon ATLASMuon-in-jet pT spectrum or Kinematic Likelihood Fit CMSMVA-based regression

The main backgrounds are ttbar, V+jets and QCD. The search sensitivity increases with the P T V bin. ttbar and V+jets have shapes taken from simulation and normalization from data. QCD jets background is fully data driven. ATLAS m bb 0 leptons, 2 jets, 2 b-tags, different p T V bins.

m bb and other event quantities are used to train an MVA S to B discriminant, which is used for limits. BDT trained for each lepton category. BDT trained for each P T V category.

Both ATLAS and CMS experiments see signal strengths consistent to one.

Only CMS has a VBF H to bb channel. It’s the first LHC result using only a jet final state.

There are two trigger categories: Higgs-signal specific and general-purpose VBF.

m bb, best S to B discriminant, is improved with b-jet-specific energy corrections, and used for limits. The largest background is by far the QCD multi jet.

There is an excess observed of 2.2σ while 0.8σ is expected. The signal strength is μ=

VH+VBF Higgs production H to bbH to ττH to WWResults

There are many many H to ττ final states. All are covered by both ATLAS and CMS. ATLAS CMS newly published Two categories: VBF and ggF (boosted). VBF: 2 jets, pT j1 > 50 GeV, pT j2 > 30 GeV, |Δη(j1,j2)| is large Three categories: 0, 1, or 2 jets. VBF: 2 jets, m j1j2 > 500 GeV |Δη(j1,j2)| > 3.5

The VBF channel has better resolution than the ggF. At ATLAS μ=1.4+/-0.4, while at CMS μ=0.78+/-0.27.

The new ATLAS VH H to ττ result is μ=2.3+/-1.6.

VH+VBF Higgs production H to bbH to ττH to WWResults

Only ATLAS has a VH with H to WW channel. It reveals the tree-level H to V coupling strength. Event selection is optimised for each category based on lepton multiplicity and electric charge.

There is an excess observed of 2.5σ while 0.9σ is expected. The signal strength is μ=

VH+VBF Higgs production H to bbH to ττH to WWResults

VH and VBF channels are in agreement with the SM.

ATLAS compare coupling strengths with bosons (VH+VBF) and fermions (ggF+ttH).

CMS splits each decay channel in production modes.

VH H to bb is expected to improve after 10 years of High Luminosity LHC L=3000fb -1 & μ=140. CERN-LHCC ; CERN-LHCC

Conclusion VH VBF Reject a lot of QCD bkg for H to bb and H to ττ Access coupling of H and V Part of measuring every single production and decay pairing

Research Associate Peter Higgs

Backup slides

I have been analyzing CDF and ATLAS data for H->bb. MSc, PhD Postdoc

ATLAS VH H to WW event selection as a function of categories based on lepton multiplicity and charge.

W/Z boson production is rare, so we reject a lot of background by asking for Higgs + W/Z bosons. Colliding particles Virtual particles Decay products seen in detector Signal to Background is about 1 / 1 thousand.

It’s easier to identify electrons and muons than jets originating from quarks.

Main background processes have a W boson and jets. Reducible in time with more work on detector understanding Different final state particles Irreducible Same final state particles

Invariant mass of the two b jets has different shape between signal and backgrounds. Higgs mass 125 GeV gluon mass 0 GeV We measure Higgs candidate mass better by measuring jet energies better, aka calibrating our detector better.

Mbb is the best signal discriminant between the Higgs signal and the backgrounds, top and W+jets.

b-jets need extra energy calibrations to account for muons, neutrinos, non closure, jet pT spectrum. 12% have muon

In Run I VH, after a muon-in-jet corr, PtReco was used in vvbb and lvbb, and a Kinematic Fit in llbb.

2012, Higgs boson; 2013, Nobel Prize Bowl space-time + new field Ingredients elementary particles Recipe 4 +1 elementary forces