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2015:groups:tools:vbb

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A comparison of generators/fixed order predictions for Z+b(b) and W+b(b) among them and against data

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Gavin Hesketh, Vitaliano Ciulli, Rikkert Frederix, Marek Schoenherr, Paolo Francavilla, Gionata Luisoni, Davide Napoletano, Carlo Pandini, Frank Krauss, Carlo Oleari, Stefano Pozzorini, …

This study includes both comparison at particle level (after hadronization) and at parton level (either before or after the parton shower). One of the goal is comparing results in 5-flavour vs 4-flavour scheme. Some Rivet routine have been provided based on measurements of ATLAS and CMS. At particle level this plugins allows comparison to the results of the measurement on 7 TeV data, so we should use this center-of-mass energy.

ATLAS Rivet routines:

Measurement of differential production cross-sections for a Z boson in association with b-jets in 7 TeV proton-proton collisions with the ATLAS detector arxiv:1407.3643

atlas_zbb.cc.txt atlas_zbb_el.yoda.txt atlas_zbb_el.plot.txt

Measurement of the cross-section for W boson production in association with b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector arXiv:1302.2929

atlas_wbb.cc.txt atlas_wbb_el.yoda.txt atlas_wbb_el.plot.txt

Center-of-mass energy: 7 TeV

Run the analyses over Z→ee or W→enu events. The .yoda file is also needed to define the binning for some plots, and for data comparison.

The routine will work with either a pure parton level hepmc file, or a full particle level file. It will reconstruct anti-kT 0.4 jets with rapidity < 2.4 (2.1 for W) and pT>20 GeV (25 for W), and label as b-jets based on matching Delta R(jet, quark/hadron) < 0.3. The quarks are taken at the end of the shower (no b-quark daughters), and the weakly decaying b-hadrons are used (no b-hadron daughters).

Makes the following plots:

  • quarklev_b_quark_pT : pT of all b quarks with rapidity<2.7
  • quarklev_b_quark_pT_matching_jet : pT of all b quarks with rapidity<2.7, matching a jet
  • quarklev_bjet_number_matching_b_quarks : number of b-quarks matching each jet
  • quarklev_bjet_number_matching_b_quarks_5GeV : number of b-quarks with pT>5 GeV matching each jet
  • quarklev_bjet_pT_single_quark_0GeV : pT of bjets containing a single b quark (no cut on quark pT)
  • quarklev_bjet_pT_double_quark_0GeV : pT of bjets containing at least two b quarks (quark pT>5 GeV)
  • quarklev_bjet_pT_single_quark_5GeV : pT of bjets containing a single b quark (no cut on quark pT)
  • quarklev_bjet_pT_double_quark_5GeV : pT of bjets containing at least two b quarks (quark pT>5GeV)
  • quarklev_bjet_bb_over_b_quarks : ratio of jets with >=2/==1 matched b quarks, vs jet pT
  • quarklev_bjet_bb_over_b_quarks_5GeV : ratio of jets with >=2/==1 matched b-quarks with pT>5GeV, vs jet pT.

If the full particle level is present in the events, the routine will also make the same plots at the hadron level (titles are “hadlev_…”), as well as the standard plots from the Z+b ATLAS analysis (with data comparison).

CMS Rivet routine:

Cross-section and angular correlations in $Z$ boson with $b$-hadrons events at $\sqrt{s} = 7$ TeV arxiv:1310.1349

cms_2013_i1256943.cc.txt cms_2013_i1256943.yoda.txt

Center-of-mass energy: 7 TeV

Run the analysis CMS_2013_I1256943 over Z→ee and Z→mumu events. The relevant files have been uploaded for reference, but the routine is available as standard analysis in Rivet. Events with exactly two $b$-hadrons and an $e^+e^-$ or $\mu^+\mu^-$ lepton pair from the Z boson decay are selected. Each lepton has $p_T > 20$ GeV and $|\eta| < 2.4$ and the dilepton invariant mass is $81 < M_{\ell\ell} < 101$ GeV. The $b$-hadrons have $p_T > 15$ GeV and $|\eta| < 2$. The differential cross sections are measured for $p_T > 0$ and $p_T > 50$ GeV.

The analysis works only if full particle level is present in the events, because weakly decaying b-hadrons are used (no b-hadron daughters), without clustering jets. Which permitting the study of $b$-hadron pair production at small angular separation.

The routine will make the standard plots of the Z+BB CMS analysis with data comparison.

List of plots:

  • _h_min_ZpT: total cross section for different Z boson $p_T$ thresholds

Histograms in non-boosted region of $Z$ $p_T$

  • _h_dR_BB: Differential cross section as a function of the angular variable $\Delta R_{\mathrm{BB}}$
  • _h_dphi_BB: Differential cross section as a function of the angular variable $\Delta \phi_{\mathrm{BB}}$
  • _h_min_dR_ZB: Differential cross section as a function of the angular variable $\mathrm{min}\Delta R_{\mathrm{ZB}}$
  • _h_A_ZBB:Differential cross section as a function of the angular variable $\mathrm{A}_{\mathrm{ZBB}}$

Histograms in boosted region of $Z$ $p_T$ ($p_T > 50$ GeV)

  • _h_dR_BB_boost: Differential cross section as a function of the angular variable $\Delta R_{\mathrm{BB}}$
  • _h_dphi_BB_boost: Differential cross section as a function of the angular variable $\Delta \phi_{\mathrm{BB}}$
  • _h_min_dR_ZB_boost: Differential cross section as a function of the angular variable $\mathrm{min}\Delta R_{\mathrm{ZB}}$
  • _h_A_ZBB_boost: Differential cross section as a function of the angular variable $\mathrm{A}_{\mathrm{ZBB}}$

Ongoing work and planned contributions:

Sherpa (Davide, Frank)

Samples:

  • 4F MC@NLO (pp→Zbb)
  • 5F MEPS@LO (pp→Z + pp→Zj+ pp→ Zjj + pp → Z jjj) all processes at LO,
  • 5F MEPS@NLO (pp→Z + pp→Zj+ pp→ Zjj) @NLO + (pp → Z jjj) at LO.

Notes:

  • For the 5F_LO scheme different choices of mass treatment in the ME
  • PDF variations: NNPDF30, CT14, MMHT14
  • both parton and particle level
  • Possibly Wbb too if enough time

Powheg (Gionata, Carlo)

  • W+bb only (?)

Herwig (Christian)

  • Z+bb
  • W+bb(?)
2015/groups/tools/vbb.1446877923.txt.gz · Last modified: 2015/11/07 07:32 by vitaliano.ciulli