1 / 7

Thoughts to get started on combination of Higgs-like boson properties measurements

Thoughts to get started on combination of Higgs-like boson properties measurements. Marco Zanetti (MIT). Intro and goal. The existence of a new narrow higgs-like resonance at 125 GeV is well established by both experiments.

kosey
Download Presentation

Thoughts to get started on combination of Higgs-like boson properties measurements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Thoughts to get started on combination of Higgs-like boson properties measurements Marco Zanetti (MIT)

  2. Intro and goal • The existence of a new narrow higgs-like resonance at 125 GeV is well established by both experiments. • Combining ATLAS and CMS observations to better constrain its properties makes a lot of sense • We have endorsed a document recommending the framework to explore the coupling structure • Regardless the time scale, we need to implement those recommendations in such a way to enable the ATLAS and CMS datasets combination • Disclaimer: what follows is a (non exhaustive) core dump of items we need to discuss/address

  3. Basics • The aim is to provide estimates for the Mass and the Coupling structure • The latter according to arXiv:1209.0040 • Signal strength k2 • Other quantum numbers (JCP) not addressed at the moment • Test workspaces corresponding to the ICHEP dataset (10/fb): • Hgg+HZZ as a benchmark? • Ok for CMS to use actual workspaces (or simplified/cleaned-up versions) • In specific cases (eventually) we may want to use more channels and combine them individually, e.g. for the signal strength or for the mass

  4. Mass • Mass should be address first, used then as input for the coupling measurement (baseline) • In CMS Hgg and HZZ have a parametric dependency of the signal modifier(s) on the mass. “MH” is a RooRealVar we can fit for • Being implemented for VHbb, Htt and HWW too. Probably not worth considering them for the combination • Any subtle correlation? • Investigate effect of floating mass in the coupling fit, checking for possible biases (e.g. on Hgg)

  5. Variable and nuisances • Agree on the naming convention for the POI and nuisances • Agree on the ranges • Possibly different for different integrated luminosities • Address degeneracies as in the case of CVCF • Thorough review of the theoretical uncertainties • Jet bins migrations, VBF/ggH contamination, mass line-shape, etc • Nuisances PDFs

  6. Fits (CMS case) • Python classes (interfaced to RooFit) to map parameters to signal and background yields (physics models) • We perform multidimensional (profiled) likelihood fits (default) and bayesian fits. • Uncertainties/contours: • Simple Minos for each parameter (works in any dimension, Δχ2=1) • Grid scan: perform a likelihood scan (profiling or not the other POI/nuisances) on a 1D or 2D grid. Errors/contours from the assumption of asymptotic c2 behavior of -2DLogL (robust, split in several jobs)

  7. Fits (CMS case) • Possible to let MH floating in the fit (as additional POI) • Need to study possible biases: • E.g. Hgg is expected to be biased in signal strength -> in other couplings • Toss frequentist toys? • How to treat/communicate correlations between POIs? • In the case of 2D fits, issue the 2D contour (1s and 2s bands) • For n>2 we don’t have yet means to get the n-dim ellipsoid • Ideally we should provide the full covariance matrix..

More Related