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The Higgs boson mass and σ(ZH) from the recoil mass with leptonic Z decays

Abstract

A precision on mH as small as 5 MeV can be achieved from a fit to the distribution of the mass recoiling to a leptonically-decaying Z boson (Z → e+e− or μ+μ−) in the e+e− → ZH process at √s = 240 GeV. The requirements on the detector design (electron energy and muon momentum resolution, in particular) to achieve this statistical precision will be checked with this channel in the FCC-ee context. The feasibility of a calibration of the method – to reduce systematic effects due to, e.g., momentum scale determination and stability – will be ascertained with the e+e− → ZZ → l+l−X process. The need for calibration data at the Z pole will also be estimated (frequency, number of events).

See also the determination of the centre-of-mass energy √s with a precision of O(1 MeV) which is a key ingredient for the determination of the recoil mass.

Contributors

  • Clement Helsens (CERN)
  • Ang Li, Gregorio Bernardi (LPNHE)
  • Sylvie Braibant, Valentina Diolaiti, Paolo Giacomelli (Bologna)
  • Markus Klute (MIT)

Preliminary analyses

  • Clement Helsens: Developer, Sample production, Preliminary FCCAnalyses design, Preliminary recoil fit analysis

To run the analysis, should use the corresponding FCCAnalyses configurations located in FCCAnalyses-config/mumu and FCCAnalyses-config/ee. This preliminary analysis i using the input files produced in the edm4hep data format, and produced with this sample production. FlatNtuples and histograms will be produced and used to fit the recoil mass. FCCAnalyses output files can also be directly accessed on eos /eos/experiment/fcc/ee/analyses/case-studies/higgs/mH-recoil/FlatNtuples/.

arguments and examples to run the fitting macro could be seen by running

python utils/massFit.py
usage:   python massFit.py BASEDIR HISTONAME SELECTION BINLOW=120 BINHIGH=140
example: python massFit.py /eos/experiment/fcc/ee/analyses/case-studies/higgs/mH-recoil/FlatNtuples/ZH_Zee/ leptonic_recoil_m_zoom3 sel1
example: python massFit.py /eos/experiment/fcc/ee/analyses/case-studies/higgs/mH-recoil/FlatNtuples/ZH_Zmumu/ leptonic_recoil_m_zoom4 sel0 122 128

As an example the fit result of running the following command

python utils/massFit.py /eos/experiment/fcc/ee/analyses/case-studies/higgs/mH-recoil/FlatNtuples/ZH_Zee/ leptonic_recoil_m_zoom4 sel1 123 127:

is shown below (to be re-done with including beam energy spread)

  EXT PARAMETER                                INTERNAL      INTERNAL  
  NO.   NAME      VALUE            ERROR       STEP SIZE       VALUE   
   1  alpha       -8.67272e-01   4.57686e-02   3.90224e-02   7.11703e-01
   2  cbmean       1.25094e+02   6.79656e-03   3.51532e-03   1.87562e-02
   3  cbsigma      2.81768e-01   6.89490e-03   5.74469e-02  -6.08122e-02
   4  lam         -3.43241e-06   1.01039e-02   3.40174e-01   1.56709e+00
   5  n            1.27209e+00   1.72834e-01   2.30740e-02  -1.34474e+00
   6  nbkg         7.59189e+03   2.15350e+02   1.34305e-03  -1.51568e+00
   7  nsig         9.05996e+03   2.19379e+02   1.28389e-03  -1.51059e+00

Bibliography