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---+ %$t\bar{t}$% sample validation

We compare the events produced by different Monte-Carlo generators in order to identify and characterize the main systematic errors relevant for the measurement of %$V_{tb}$%. Besides our Madgraph =All b= samples we make also use of the following signal samples:

%TABLE{ sort="off" tableborder="0" cellpadding="1" cellspacing="3" headerrows="2" footerrows="0"}%
| *TABLE 1 - SIGNAL SAMPLES USED FOR THIS STUDY* ||
| *Sample* | *Cross section (pb)* |
| =/tt0j_mT_70-alpgen/CMSSW_1_5_2-CSA07-2231/GEN-SIM-DIGI-RECO= | 334.51 |
| =/tt1j_mT_70-alpgen/CMSSW_1_5_2-CSA07-2211/GEN-SIM-DIGI-RECO= | 90.23 |
| =/tt2j_mT_70-alpgen/CMSSW_1_5_2-CSA07-2232/GEN-SIM-DIGI-RECO= | 18.75 |
| =/tt3j_mT_70-alpgen/CMSSW_1_5_2-CSA07-2212/GEN-SIM-DIGI-RECO= | 3.16 |

The comparison is done between inclusive distributions which means that a luminosity weighted sum of the %$t\bar{t}+Njets$% distributions is made for each different conditions (Alpgen, Alpgen-fastsim, Madgraph). For each sample the luminosity is computed as %$L_{sample}=\frac{N_{ev}(reco)}{\sigma_{process}}$%. For each variable the distributions is weighted by %$L^{-1}$% and acquires the dimensions of a cross section (pb).

---++ Top production kinematics
---+++ Cross sections

Below we compare the cross section yields, at the generator level, for our private Madgraph+PYTHIA 6 samples with other %$t\bar{t}$% samples. For completion we show the cross section obtained when the jet matching is done using %$p_{T}^{2}$% ordered showers. However in the plots shown in the subsequent paragraphs we shall make use of the samples obtained using jet matching with virtuality (%$Q^{2}$%) ordered showers.

| *Table 1.1- Cross section yields for %$t\bar{t}$% dilepton channel at generator level in pb* ||||||||
| Event type | =0 j= | =1 j= | =2 j= | =3 j= | =4 j= | ==Total== | ==K-factor== |
| Madgraph + PYTHIA 6 %$Q^{2}$% ordered showers w/ %$Q_{cut}=30 GeV/c$% | 11.00 | 7.97 | 3.53 | 2.10 | n.a. | <b>24.6</b> | <b> 1.54 %$\pm$% 0.03 </b> |
| Madgraph + PYTHIA 6 %$p_{T}^{2}$% ordered showers w/ %$Q_{cut}=20 GeV/c$% | 4.43 | 3.97 | 2.54 | 2.92 | n.a. | <b>13.86</b> | <b> 2.73 %$\pm$% 0.05 </b> |
| ALPGEN | 15.2 | 4.1 | 0.85 | 0.14 | 0.04 | <b>20.34</b> | <b> 1.86 %$\pm$% 0.03 </b> |

Note that despite the large differences in the cross sections for Madgraph+PYTHIA6 obtained with different methods of jet matching the inclusive kinematics distributions for %$t\bar{t}+Njets$% production is not affected, as it should. We also not that, depending on the parameters chosen for matching, the contribution of each jet multiplicity to the total cross section will be different. For more details see the sample validation [[PrivateSamplesValidationForVtbStudies][report]] from =MatchChecker= utility. 
Questions:
   * why does the cross section decrease so much when %$p_{T}^{2}$% ordered showers are used?  
   * how does the jet matching procedure efficiency affect the cross section?

---+++ Kinematics
We proceed to compare the top production kinematics. You can find the basic plots in the following table. We have normalized each distribution by the luminosity of the sample used to build it and, as so, the counts are shown in units of cross section (pb). 

%TABLE{ sort="off" tableborder="0" cellpadding="4" cellspacing="3" cellborder="0" columnwidths="150,150,150,150,150" }%
| *Table 2.1 - Top kinematics at MC level (GEN)* |||||
| %$p_{T}$% spectrum | %$\eta$% distribution | %$\sum p_{T}$% for the %$t\bar{t}$% pair | %$\Delta\phi$% between %$t$% and %$\bar{t}$% | invariant mass of the %$t\bar{t}$% pair |
| <img src="%ATTACHURLPATH%/ttbar_pT_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/ttbar_eta_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/ttbar_sumpT_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/ttbar_dphi_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/ttbar_minv_comp.png" width='150' height='150' /> |

---++ Jets
---+++ Kinematics

%TABLE{ sort="off" tableborder="0" cellpadding="4" cellspacing="3" cellborder="0" columnwidths="150,150,150" }%
| *Table 3.1 - Jet kinematics at RECO level* |||
| Variable | RECO | RECO + matched to b-parton from top decay |
| Jet multiplicity | <img src="%ATTACHURLPATH%/jets_multiplicity_comp.png" width='150' height='150' /> | n.a. |
| %$p_{T}$% | <img src="%ATTACHURLPATH%/jets_pT_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/jets_matched_pT_comp.png" width='150' height='150' /> | 
| %$\eta$% | <img src="%ATTACHURLPATH%/jets_eta_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/jets_matched_eta_comp.png" width='150' height='150' /> | 
| emf (electromagnetic fraction of the energy deposit of the jets) | <img src="%ATTACHURLPATH%/jets_emf_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/jets_matched_emf_comp.png" width='150' height='150' /> | 
| %$\Delta_{2}$% (b-tag discriminant for the high efficiency track counting algorithm | <img src="%ATTACHURLPATH%/jets_trkCountHighEff_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/jets_matched_trkCountHighEff_comp.png" width='150' height='150' /> | 

There is an overall good agreemenent between jet multiplicities generated by =Alpgen= and =Madgraph=. The main differences are seen in the electromagnetic fraction distribution and are most likely due to =FastSim=.

---++ Leptons

%TABLE{ sort="off" tableborder="0" cellpadding="4" cellspacing="3" cellborder="0" columnwidths="100,150,150,150,150" }%
| *Table 4.1 - Lepton kinematics at RECO level for the tt~0j samples* ||||||||
| Lepton | Electron || Muon ||
| Variable | RECO | RECO + matched | RECO | RECO + matched |
| Lepton multiplicity | <img src="%ATTACHURLPATH%/e_multiplicity_comp.png" width='150' height='150' /> | n.a. |  <img src="%ATTACHURLPATH%/mu_multiplicity_comp.png" width='150' height='150' /> | n.a. | 
| %$p_{T}$% | <img src="%ATTACHURLPATH%/e_pT_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/e_matched_pT_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_pT_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_matched_pT_comp.png" width='150' height='150' /> | 
| %$\eta$% | <img src="%ATTACHURLPATH%/e_eta_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/e_matched_eta_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_eta_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_matched_eta_comp.png" width='150' height='150' /> |
| %$\frac{E}{p}$% | <img src="%ATTACHURLPATH%/e_EoverP_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/e_matched_EoverP_comp.png" width='150' height='150' /> | n.a. | n.a. |
| tracker iso | <img src="%ATTACHURLPATH%/e_trackerIso_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/e_matched_trackerIso_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_trackerIso_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_matched_trackerIso_comp.png" width='150' height='150' /> |
| calo iso | <img src="%ATTACHURLPATH%/e_caloIso_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/e_matched_caloIso_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_caloIso_comp.png" width='150' height='150' /> | <img src="%ATTACHURLPATH%/mu_matched_caloIso_comp.png" width='150' height='150' /> |

From this plots we conclude that there's a good agreement between the samples. Some comments:
   * there are some differences in lepton multiplicities
   * the low %$\p_{T}$% electronic spectrum is understimated by =FastSim=
   * for the %$\eta$% distribution of electrons we can clearly see similar drops in =FullSim= and =FastSim= in the ECAL barrel to endcap transition (%$1.479\leq\eta\leq1.653$%)
   * there's an underestimation of the the low E/p values for electrons in =FastSim=

---++ MET
Below we show the comparison of the MET.  The main conclusion is that =FastSim= yields a softer spectrum than full simulation but is in good agreement in the region %$30 < E_{T} <100 GeV$%.

<center>
<img src="%ATTACHURLPATH%/met_comp.png" alt="met.png" width='200' height='200' /> |
</center>


-- Main.PedroSilva - 04 Apr 2008

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Topic attachments
I	Attachment	History	Action	Size	Date	Who
png	e_EoverP_comp.png	r4 r3 r2 r1	manage	16.4 K	2008-04-28 - 11:52	PedroSilva
png	e_caloIso_comp.png	r3 r2 r1	manage	16.3 K	2008-04-28 - 11:52	PedroSilva
png	e_eta_comp.png	r4 r3 r2 r1	manage	14.0 K	2008-04-28 - 11:53	PedroSilva
png	e_matched_EoverP_comp.png	r4 r3 r2 r1	manage	16.7 K	2008-04-28 - 11:53	PedroSilva
png	e_matched_caloIso_comp.png	r3 r2 r1	manage	18.1 K	2008-04-28 - 11:53	PedroSilva
png	e_matched_eta_comp.png	r4 r3 r2 r1	manage	14.5 K	2008-04-28 - 11:54	PedroSilva
png	e_matched_pT_comp.png	r4 r3 r2 r1	manage	16.1 K	2008-04-28 - 11:55	PedroSilva
png	e_matched_trackerIso_comp.png	r4 r3 r2 r1	manage	18.3 K	2008-04-28 - 11:54	PedroSilva
png	e_multiplicity_comp.png	r4 r3 r2 r1	manage	12.1 K	2008-04-28 - 11:55	PedroSilva
png	e_pT_comp.png	r4 r3 r2 r1	manage	16.7 K	2008-04-28 - 11:56	PedroSilva
png	e_trackerIso_comp.png	r4 r3 r2 r1	manage	17.6 K	2008-04-28 - 11:56	PedroSilva
png	jets_emf_comp.png	r5 r4 r3 r2 r1	manage	14.6 K	2008-04-28 - 11:24	PedroSilva
png	jets_eta_comp.png	r6 r5 r4 r3 r2	manage	12.7 K	2008-04-28 - 11:24	PedroSilva
png	jets_matched_emf_comp.png	r5 r4 r3 r2 r1	manage	15.3 K	2008-04-28 - 11:24	PedroSilva
png	jets_matched_eta_comp.png	r5 r4 r3 r2 r1	manage	12.6 K	2008-04-28 - 11:25	PedroSilva
png	jets_matched_pT_comp.png	r5 r4 r3 r2 r1	manage	16.8 K	2008-04-28 - 11:25	PedroSilva
png	jets_matched_trkCountHighEff_comp.png	r5 r4 r3 r2 r1	manage	14.9 K	2008-04-28 - 11:26	PedroSilva
png	jets_multiplicity_comp.png	r5 r4 r3 r2 r1	manage	14.8 K	2008-04-28 - 11:26	PedroSilva
png	jets_pT_comp.png	r5 r4 r3 r2 r1	manage	16.9 K	2008-04-28 - 11:28	PedroSilva
png	jets_trkCountHighEff_comp.png	r5 r4 r3 r2 r1	manage	14.8 K	2008-04-28 - 11:28	PedroSilva
png	met_comp.png	r4 r3 r2 r1	manage	16.9 K	2008-04-28 - 11:42	PedroSilva
png	mu_EoverP_comp.png	r2 r1	manage	13.6 K	2008-04-28 - 12:07	PedroSilva
png	mu_caloIso_comp.png	r3 r2 r1	manage	15.6 K	2008-04-28 - 12:09	PedroSilva
png	mu_eta_comp.png	r3 r2 r1	manage	14.3 K	2008-04-28 - 12:08	PedroSilva
png	mu_matched_EoverP_comp.png	r2 r1	manage	13.4 K	2008-04-28 - 12:08	PedroSilva
png	mu_matched_caloIso_comp.png	r3 r2 r1	manage	16.8 K	2008-04-28 - 12:09	PedroSilva
png	mu_matched_eta_comp.png	r3 r2 r1	manage	14.2 K	2008-04-28 - 12:09	PedroSilva
png	mu_matched_pT_comp.png	r3 r2 r1	manage	16.9 K	2008-04-28 - 12:10	PedroSilva
png	mu_matched_trackerIso_comp.png	r3 r2 r1	manage	18.2 K	2008-04-28 - 12:11	PedroSilva
png	mu_multiplicity_comp.png	r3 r2 r1	manage	11.8 K	2008-04-28 - 12:11	PedroSilva
png	mu_pT_comp.png	r3 r2 r1	manage	16.9 K	2008-04-28 - 12:10	PedroSilva
png	mu_trackerIso_comp.png	r3 r2 r1	manage	17.6 K	2008-04-28 - 12:10	PedroSilva
png	ttbar_dphi_comp.png	r4 r3 r2 r1	manage	16.7 K	2008-04-28 - 11:37	PedroSilva
png	ttbar_eta_comp.png	r4 r3 r2 r1	manage	15.8 K	2008-04-28 - 11:37	PedroSilva
png	ttbar_minv_comp.png	r3 r2 r1	manage	17.7 K	2008-04-28 - 11:38	PedroSilva
png	ttbar_pT_comp.png	r4 r3 r2 r1	manage	17.8 K	2008-04-28 - 11:38	PedroSilva
png	ttbar_sumpT_comp.png	r4 r3 r2 r1	manage	19.8 K	2008-04-28 - 11:38	PedroSilva

Topic revision: r13 - 2008-06-26 - PedroSilva

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