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HF performance and its impact on qqH analysis (H->ZZ->llvv channel) A.Mestvirishvili

HF performance and its impact on qqH analysis (H->ZZ->llvv channel) A.Mestvirishvili University of Iowa FNAL VBF workshop, June 2009. HF for qqH.

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HF performance and its impact on qqH analysis (H->ZZ->llvv channel) A.Mestvirishvili

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  1. HF performance and its impact on qqH analysis (H->ZZ->llvv channel) A.Mestvirishvili University of Iowa FNAL VBF workshop, June 2009

  2. HF for qqH VBF – vector boson fusion processes are one the main processes of Higgs boson production – second largest cross section after gluon - gluon fusion Feature – two energetic forward jets, which can be tagged. Those usually are referred as TAG JETS HF covers pseudo rapidity range |η | 3 ÷ 5. Almost half of the forward TAG JETS falls into this region. No tracker on front of HF – not possible to perform track based corrections to jets It is important to understand how HF is able to measure jets. HF region Example of the forward TAG JET pseudo rapidity distribution

  3. Calibration • Few wedges of HF were placed into test beam and calibrated. • In addition all towers of HF+ and HF- were calibrated with radioactive source • Five to eight percent of calibration precision was achieved, depending on a tower type (HAD or EM, location) • But all of above is the case when (during test beams) single particle hits HF. • Jets needs little bit more. Usually jet energy resolution differs from those for single particles.

  4. Jet energy scale and energy resolution definition Several different methods will be developed for JES and jet energy resolution measurement when real data will be in our hands, but for now jets we have mainly in simulation. In simulation we can access reconstructed jets, as well as the generated jet energies. So best estimator for reconstructed jet energy is corresponding particle level (generated) jet energy. In this study Jet Energy Scale is defined as a ratio of Reconstructed Jet Transverse Energy (ETRec) to Generated Jet Transverse Energy (ETGen) (1) Jet energy resolution is defined as follows (2)

  5. Generated event samples used and jet selection • - generated and fully simulated events at 10TeV CM Energy • No specific selection – just those jets were taken into account which has |η| - 3 to 5 • with Etrec > 30GeV. • No sense to make any track based correction – no tracker after Eta=2.4 • No need to perform b tagging – for the same reason as above • GEN and REC jet association ΔR cut

  6. Reconstructed and generated jet Et Ratio for selected jets Generated Et Reconstructed Et

  7. JES These distributions were approximated with following function E0 =1GeV Fit gives similar values for parameters for both HF’s so it was decided to do not separate them in further studies

  8. JES E0 =1GeV

  9. Jet Et resolution M = 0.641 σ = 0.081 M = 0.675 σ = 0.077 M = 0.695 σ = 0.073 M = 0.713 σ = 0.072 M = 0.726 σ = 0.077 M = 0.733 σ = 0.069 Parameterization

  10. JEtS - corrected after correction a = 0 b = 0.585 ± 0.021 c = 0.0831± 0.003

  11. JES, Energies of reconstructed and generated jets • redefine JES , use Ej instead of Etj • correct Ej • go back to Etj E0 =1GeV After correction Red – Generated jet energy Black – Reconstructed jet energy

  12. Ratio Ratio is centered at 1 Width of this distribution can be assumed as uncertainty to the jet energy scale determination and it is at the level of 12%.

  13. Jet Et resolution a = 0 b = 0.585 ± 0.021 c = 0.083 ± 0.003 a = 0 b = 0.503 ± 0.022 c = 0.0923 ± 0.003

  14. Di jet Mass • To check performance of obtained corrections on a signal and • background events full forward jet tagging was performed in an • events from and signal samples (with small variations) • Two jet in opposite hemisphere • Pt>30GeV • Δη>4.5 • no central jet veto used (limited statistic in signal samples) • signal samples are: 250, 300, 400, 500 GeV mass Higgs Boson • Decay channel H->ZZ->llvv. • Thus jet energy scale correction in this particular case affects only • forward jets tagged and dijet mass

  15. DiJet Mass for signal Jet Et were corrected in forward region Di Jet mass was computed, in a similar way as for full qqH analysis is done. Plot shows two different distribution for Di Jet mass for signal events: Yellow – not corrected Blue - corrected

  16. ttbar and signal comparison green Di Jet Mass distribution blue Di jet Mass distribution from 250GeV Higgs samples brown Di Jet Mass distribution from 300GeV Higgs samples Because of very limited statistic in each signal sample (max 3000 before any selection) no conclusion can be made from this plots. Statistic increase in needed. Also, one have take into account, that corrections were applied only to jets in HF (|η| ÷ 3 to 5). But tag jets could fall out of this region as well

  17. Conclusion • HF JES studied and correction factors obtained. • JES systematic uncertainty in HF was found to be at the level of 12% • Corrections were applied to signal (H->qqZZ->qqllvv) and samples • After correction Stochastic term drops a bit, but we have increased constant term • Results are inconclusive because of limited statistic of signal events

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