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Boosted Higgs and jet substructure

Boosted Higgs and jet substructure. Mrinal Dasgupta The University of Manchester Atlas-UK Higgs Workshop, Birmingham, 25 September, 2014. Overview. Quick introduction to jet substructure and boosted particle searches/studies. E xamples of recent (and not so recent) Higgs studies.

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Boosted Higgs and jet substructure

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  1. Boosted Higgs and jet substructure Mrinal Dasgupta The University of Manchester Atlas-UK Higgs Workshop, Birmingham, 25 September, 2014

  2. Overview • Quick introduction to jet substructure and boosted particle searches/studies. • Examples of recent (and not so recent) Higgs studies. • Introduction to substructure tools, challenges and open questions. • Understanding substructure better. • The future: creating robust tools for future applications (LHC run 2 and beyond)

  3. Introduction Period since 2008 has seen emergence of a vibrant research area dedicated to use of jet substructure for LHC discoveries. Basic idea goes back to 1993 and work by Seymour.

  4. It all started with the Higgs…. The famous 2008 “BDRS” paper. Discovery potential for Higgs ~ 120 GeV in VH production with H to bb.

  5. Basic ideas

  6. Signal vs background : tagging and grooming How to tell signal (e.g. jet originating from a Higgs decay) from “boring” QCD jets i.e. tagging signal? • Exploit differences in “energy-sharing”. Cut on z discriminates against background. • No large-angle soft radiation from colour singlet Higgs. How to clean signal from contamination i.e. ISR, UE pile-up? Removal of soft large angle junk. We have 10-20 different methods invented for this with > 100 papers over 5 years!

  7. Since BDRS • LHC Run 1 has shown that these methods actually work. Run 2 with higher energies will mean they become very important methods. • And if the future holds 100 TeV colliders everything will be boosted!

  8. Examples: ttH Higgs production in association with tt was taken off list of promising discovery channels due to poor S/B. Important also for direct access to top Yukawa coupling. Using fat jet methods and top+Higgs tagging Plehn, Spannowsky Salam turned S/B ~1/9 to S/B ~ 1/2 for same significance.

  9. Examples: Boosted Higgs pair production Presented by J.Rojo at BOOST 2014

  10. Examples: hhvv coupling F Requires a combination of resolved and boosted analysis. Also work on SM hh production with h to bb by Konstantinides et. al

  11. Examples: CP properties Uses jet substructure to reconstruct Higgs and study angular variables that discriminate between SM and BSM structure of HVV vertex. BSM contributions from higher dimensional operators enhanced by selection cuts in boosted analysis. Godbole, Miller, Mohan White 2013 and 2014

  12. So what is left to do? The techniques are valuable in a variety of contexts and viable. However a number of open questions remain: • There are numerous tools (Taggers/groomers). Which one to pick? • How do we compare tools? How do results obtained depend on many parameters of the taggers? Optimal values? • How do we know we have made a discovery and have not unearthed a feature of the taggers? • How to quantify theory uncertainties in substructure studies? What tools to use? MC? Fixed-order? Combinations thereof? • Can results depend on shower models, tunes, jet algorithms? What we need are formulae….

  13. QCD jet mass

  14. Comparison of taggers Taggers look similar…..

  15. Comparison of taggers But only for a limited mass range. How to understand what we are seeing? Position of kinks etc? Calls for analysis and calculation.

  16. Analytical vs MC : trimming MD FregosoMarzani and Salam 2013

  17. Analytical vs MC: pruning MD FregosoMarzani and Salam 2013

  18. Analytical vs MC mMDT (BDRS)

  19. Non perturbative effects

  20. Tagger performance We now have a much better idea of the factors behind tagger performance and are using this to develop better tools

  21. Outlook • Boosted object techniques have already been demonstrated to be of great value for several Higgs studies. Many examples of previously unfavourable channels being converted to promising avenues. • The focus now is on understanding the tools both in and beyond perturbation theory. • The focus is on performance i.esignal significance but also on robustness and reliability. • The understanding of substructure is still in its infancy.

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