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

Papers:
http://arxiv.org/pdf/1107.3714.pdf  (Campbell et al.)

//If you are interested in contributing please subscribe to the [[https://e-groups.cern.ch/e-groups/EgroupsSearch.do?searchValue=houches-2015-topics-tools-vb|mailing list]]. You will be asked to log in with your CERN account. If you don't have a CERN account, please fill [[https://account.cern.ch/account/Externals/RegisterAccount.aspx|this form]] to create a lightweight account.//

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 [[http://arxiv.org/abs/1407.3643|arxiv:1407.3643]]

{{:2015:groups:tools:atlas_zbb.cc.txt|}}
{{:2015:groups:tools:atlas_zbb_el.yoda.txt|}}
{{:2015:groups:tools: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 [[http://arxiv.org/abs/1302.2929|arXiv:1302.2929]]

{{:2015:groups:tools:atlas_wbb.cc.txt|}}
{{:2015:groups:tools:atlas_wbb_el.yoda.txt|}}
{{:2015:groups:tools: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 
[[http://arxiv.org/abs/1310.1349|arxiv:1310.1349]]

{{:2015:groups:tools:cms_2013_i1256943.cc.txt|}}
{{:2015:groups:tools: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) MC@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 (aS(mZ)=0.118)
  * both parton and particle level
  * Possibly Wbb too if enough time
 
 4F Scheme Set Up:
  * b-Mass     = 4.72 GeV
  * Z-Mass     = 91.1876 GeV
  * PDF_Set    = NNPDF30_nlo_as_0118_nf_4
  * alphaS(mZ) = 0.118
  * Events     = 400M (Weighted)

 5F Scheme Set Up: (Both MEPS@LO and MEPS@NLO)
  * PDF_Set      = NNPDF30_nnlo_as_0118
  * alphaS(mZ)   = 0.118
  * QCUT merging = 10.0 GeV
  * Events       = 200M (LO) ~ 1B (NLO) (Weighted)

 Preliminary Plots (may still change):
  * ATLAS: https://users.hepforge.org/~dnapoletano/Lh_proceedings_Vbb/Zbb/ATLAS_2014_I1306294/index.html
  * CMS  : https://users.hepforge.org/~dnapoletano/Lh_proceedings_Vbb/Zbb/CMS_TEST/index.html
 
=== Powheg (Gionata, Carlo) === 

  * W+bb and W+bb+j
 4F scheme set up + matching with alphas and PDF with 5 flavours
  * b-Mass     = 4.75 GeV
  * Z-Mass     = 91.1876 GeV
  * W-Width    = 2.1054 GeV
  * CKM
     - Vud=0.97428
     - Vus=0.2253
     - Vub=0.00347
     - Vcd=0.2252
     - Vcs=0.97345
     - Vcb=0.0410
     - Vtd=0.00862
     - Vts=0.0403
     - Vtb=0.999152
      
  * PDF_Set  = MSTW2008  (21100 in the LHE numbering scheme)

  * Results for W+bb+j: 
     * {{:2015:groups:tools:powheg-wbbj-d01-x01-y01.pdf|}}
     * {{:2015:groups:tools:powheg-wbbj-d02-x01-y01.pdf|}}
     * {{:2015:groups:tools:powheg-wbbj-d02-x02-y01.pdf|}}

=== Herwig (Graeme, Christian) ===

Preliminary results for Zbb production in the 5FS can be found on http://www.hep.man.ac.uk/u/graeme/public/LH_Vbb/preliminary/Zbb/
  * Shown are the four matching-shower combinations of Herwig7, i.e.
    - NLO$\oplus$QTilde aka MCatNLO-based matching with the angular-ordered shower,
    - NLO$\oplus$Dipole aka MCatNLO-based matching with the dipole shower,
    - NLO$\otimes$QTilde aka Powheg-based matching with the angular-ordered shower,
    - NLO$\otimes$Dipole aka Powheg-based matching with the dipole shower.
  * The uncertainty bands are purely from scale variations with respect to all scales in the hard sub-processes and in the shower, i.e. muR, muF (and the corresponding scales of $\alpha_s$ and PDF arguments in the shower) and muQ (shower start scale).
  * The central scale choice is a fixed scale (Z mass) at the moment for muR=muF=muQ.
  * The PDF sets being used are the default PDF sets to which the showers are tuned, i.e. MMHT2014lo68cl and MMHT2014nlo68cl.
  * The underlying hard process is $p p \to e^+ e^- b \bar{b}$, with $b,\bar{b}\in p$ and we cut on the final state b quarks by requiring at least two jets, with a min. pT of 18 GeV and 15 GeV for the first and second jet respectively. 
  * Statistics: 40k, unweighted.


Preliminary results for Zb production in the 5FS can be found on http://www.hep.man.ac.uk/u/graeme/public/LH_Vbb/preliminary/Zb/
  * Description: see the first four main bullet points above.
  * The underlying hard process is $p p \to e^+ e^- {b,\bar{b}}$, with $b,\bar{b}\in p$ and we cut on the final state b quark by requiring at least one jet, with a min. pT of 18 GeV for the first jet.
  * We cut on the invariant mass of the charged-lepton pair, with a min. inv. mass of 60 GeV and a max. inv. mass of 120 GeV.
  * Statistics: 100k, unweighted.


Preliminary results for Zbb production in the 4FS can be found on http://www.hep.fsu.edu/~creuschle/public/.Plots_2016_LHVbb_Preliminary/plots_Zbb_4FS_MMHTnf5_BnotinJ_0Jet_NoBCut_WeightedOff_FixedScale/
  * Shown is NLO$\oplus$QTilde (MCatNLO-DefaultShower) and NLO$\otimes$QTilde (Powheg-DefaultShower).
  * Scale choices, scale variations and choice of PDF sets as described above.
  * The underlying hard process is $p p \to e^+ e^- b \bar{b}$, with $b,\bar{b}\notin p$. There are no cuts on the b quarks.
  * We cut on the invariant mass of the charged-lepton pair, with a min. inv. mass of 60 GeV and a max. inv. mass of 120 GeV.
  * We cut slightly on the charged leptons, with a min. pT of 5 GeV and a rapidity range between -4 and 4.
  * Statistics: 100k, unweighted.


Preliminary results for Wbb production in the 4FS can be found on http://www.hep.fsu.edu/~creuschle/public/.Plots_2016_LHVbb_Preliminary/plots_Wbb_4FS_MMHTnf5_BnotinJ_0Jet_NoBCut_WeightedOff_FixedScale/
  * Shown is NLO$\oplus$QTilde (MCatNLO-DefaultShower) and NLO$\otimes$QTilde (Powheg-DefaultShower).
  * The central scale choice is a fixed scale (W mass) at the moment for muR=muF=muQ.
  * Scale variations and choice of PDF sets as described above.
  * The underlying hard process is $p p \to l \nu b \bar{b}$, considering $e^{\pm},\mu^{\pm}\in l$. There are no cuts on the b quarks.
  * We cut on the transverse mass of the W, with a min. trans. mass of 20 GeV.
  * We cut slightly on the charged lepton, with a min. pT of 5 GeV and a rapidity range between -4 and 4.
  * Statistics: 100k, unweighted.


Further studies on Zbb production in the 4FS, for a different PDF choice, can be found on https://www.itp.kit.edu/~reuschle/.Plots_2016_LHVbb_Preliminary/Zbb4FS/plots_NNPDFnf4_BnotinJ_0Jet_MCatNLO-DefaultShower_WeightedOn_Central/
  * Shown is the NLO$\oplus$QTilde aka MCatNLO-based matching with the angular ordered shower.
  * No scale variations.
  * The central scale choice is a fixed scale (Z mass) at the moment for muR=muF=muQ.
  * The PDF set being used is NNPDF30_nlo_as_0118_nf_4.
  * Statistics: 1M, weighted.


Further studies on Wbb production in the 4FS, for varying PDF choices, can be found on https://www.itp.kit.edu/~reuschle/.Plots_2016_LHVbb_Preliminary/Wbb4FS/plots_AllPDFs_BinJ_1Jet_MCatNLO-DefaultShower_WeightedOff_Central/ or similarly for on https://www.itp.kit.edu/~reuschle/.Plots_2016_LHVbb_Preliminary/Wbb4FS/plots_AllPDFs_BnotinJ_0Jet_MCatNLO-DefaultShower_WeightedOff_Central/
  * The difference between the two is that for one we require one jet (which may contain a b quark) with a certain min pT (first link), for the other we don't cut on the b quarks at all (second link).
  * Shown is the NLO$\oplus$QTilde aka MCatNLO-based matching with the angular ordered shower.
  * No scale variations.
  * The central scale choice is a fixed scale (W mass) at the moment for muR=muF=muQ.
  * There is a choice of different PDF sets being used, i.e.
    - MMHTnf5: MMHT2014lo68cl and MMHT2014nlo68cl,
    - MMHTnf4: MMHT2014nlo68cl_nf4,
    - NNPDFnf5: NNPDF30_lo_as_0118 and NNPDF30_nlo_as_0118,
    - NNPDFnf4: NNPDF30_lo_as_0118_nf_4 and NNPDF30_nlo_as_0118_nf_4.
  * Statistics: 100k, unweighted.


The remaining parts of the description of the run setups can be found in the vbb.pdf file in the draft for the proceedings.
==== github instructions ====

To setup your local repository
  - go to github.com and get an account
  - log in, go to https://github.com/vciulli/leshouches_vbb
  - In the top-right corner of the page, click Fork
  - open a shell where git is available
  - clone the repository with the command: git clone git@github.com:your_git_username/leshouches_vbb.git
    - if you have problems with ssh publickey try: git clone https://github.com/your_git_username/leshouches_vbb.git
  - enjoy

To start contributing
  - modify/add a file
  - add file(s) to local repository: git add filename.bla
  - commit file(s) to local repository: git commit -m "commit messate" filename.bla
  - "push" modifications to your remote (i.e. github) repository : git push
  - inform Vitaliano to include your modifications to the main repositiry

To synch your repository with the main repository
  - git pull https://github.com/vciulli/leshouches_vbb master
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