# Presentation: 415389

## Top group results for MoriondE. Shabalina (UIC)D0 Collaboration meeting, 02/14/2003 

*Outline*
***Introduction***
***Dilepton channels***
***Lepton+jets:***
*Topological analysis*
*Soft lepton tagging*
***Lifetime b-tagging***
***Top mass measurement ***
***Conclusions***

## Introduction

**Analysis Goals:**
**Demonstrate the existence of top quark in e, mu channels, including those with displaced vertex b-tagging of jets, and measure t- tbar production cross section at 1.96 TeV**
- (Recall that in 1995 we discovered the top quark with a similar amount of data. The production cross section is 35% higher now at 1.96 TeV and we have much better b-tagging capabilities)
**Show that we can model the data with a combination of top signal, W+jets and QCD background**
**Measure the top quark mass    **

## Introduction

**Thanks to:**
**Stefan Anderson, Ela Barberis, Ursula Bassler, Florian Beaudette,****Gregorio Bernardi, Dookee Cho, Regina Demina, Frank Fiedler, Cecilia Gerber, Tobias Golling, Jean-Francois Grivaz, Leslie Groer, Chunhui Han, Ann Heinson, Ia Iashvili, Aurelio Juste, Qizhong Li, Marumi Kado, Bob Kehoe, Alexander Khanov, Markus Klute, Joe Kozminzki, Arnulf Quadt, Breese Quinn, Prolay Mal, Dugan O'neil, Nirmalya Parua, Philip Perea, Lukas Phaf, Flera Ritzadinova,****Ariel Schwartzman, Reinhard Schwienhorst, Elizaveta Shabalina,****Jonas Strandberg, Daniel Whiteson, Marek Zielinski, Robert Zitoun Kevin Black, Sarosh Fatakia, Lars Sonnenschein, Ulrich Heintz**** **

## Top analysis channels 

**Top channels are determined by the decay modes of the two W bosons in        event:                                       , where *****l = e, ******μ***** or ****τ**
**Dilepton channel – **branching ratio: ee, μμ– 1.2%, eμ – 2.4%
**2 high pT leptons, 2 b-jets and large missing ET**
**large background from Z decays**
**Lepton + jets channel – **branching ratio: 30%
**1 high pT lepton, 4 jets (including 2 b-jets) and large missing ET**
**large background from Drell_Yan production of W with jets**
- Topological and kinematical cuts
- B-tag requirement
**All-jets channel  – ****branching ratio: 44%  **
**6 jets (including 2 b-jets) **
**Huge background from QCD multijet production**

|  |
| --- |

## ee, μμ dilepton channels: triggers 

| Trigger | Level 1 | Level 2 | Level 3 | total |
| --- | --- | --- | --- | --- |
| 2EM_HI | CEM(2,10) | none | ele (1,10) (old) 
ele (1,20) (new)  |  |
| efficiency | 95.2 ± 1.5 | - | Old: 100% for 20 GeV e
New – see the curve | 90.5 ± 2.9
 |
| 2MU_A_L2M0 | 2 tight scint muons | 1 Medium Muon | none |  |
| efficiency | 87 ± 2 | 97 ± 1 |  | 85 ± 2 |

|  |
| --- |

- μμ

*ee*

- 

**ee, ****μμ**** dilepton channels: event selection and signal efficiency**

|  |
| --- |

**Signal efficiency**

|  | ee | μμ |
| --- | --- | --- |
| _trigger | 90.5 ± 2.9 | 85 ± 2 |
| _ reco* _ acc* _ kin (MC) | 26.1 ± 0.3 |  |
| Tracking/ HM/ fiducial (ee)
Muon ID + isolation + match  | 46.279.2  77.1=28.2 | 
16±2 |
| total | 6.6 ± 0.7 | 6 ± 1 |

**Selection cuts:**
*   **2 tight electrons PT(EM) > 20 GeV and two track matches **(ee) ** *
*      **2 isolated muons with PT(**μ**) > 15 GeV and two track matches **(**μμ**)*
*  **MET > 25 GeV (outside Z window), MET > 40 GeV (inside Z window)*
*  **2 jets PT(jet) > 20 GeV, | ****|<2.5 *
*  **HTe (PT(e)+PT(j1)+PT(j2)) > 120 GeV **(ee)*
*     **HT > 100 GeV using jets with PT(jet) > 15 GeV,and | ****|<2.5 **(**μμ**)*

**ee, ****μμ**** dilepton channels: event selection and signal efficiency**

|  |
| --- |

**Signal efficiency**

**Selection cuts:**
*   **2 tight electrons PT(EM) > 20 GeV and two track matches **(ee) ** *
*      **2 isolated muons with PT(**μ**) > 15 GeV and two track matches **(**μμ**)*
*  **MET > 25 GeV (outside Z window), MET > 40 GeV (inside Z window)*
*  **2 jets PT(jet) > 20 GeV, | ****|<2.5 *
*  **HTe (PT(e)+PT(j1)+PT(j2)) > 120 GeV **(ee)*
*     **HT > 100 GeV using jets with PT(jet) > 15 GeV,and | ****|<2.5 **(**μμ**)*

***ee*** :                     6.6 **±** 0.7 %
******_trigger                                           90.5 ± 2.9      **
******_ reco* ********_ acc* ********_ kin (MC):        26.1 ± 0.3**
**Tracking                                           46.2 ± 1.8 **
**HM                                                    79.2 ±** **1.3**
**fiducial                                              77.1 ± 1.4**

***μμ*****:                      6 ****±** **1 ****±**** 2%**
******_trigger                                        85 ± 2**
**Isolation (per muon)                    85 ± 5**
**Muon ID +isolation + match      16 ± 2 ±** **7**
**Jet  ID                                           82 ± 1**
**Preselection                                  79 ± 1 **

## ee, μμ dilepton channels: backgrounds

**Physics **
**WW -> e********e********       ******** = 0.03±0.012%    (from MC)  **
**          ****WW -> ****μ********μ********      ******** = 0.17%               (from MC)**
**Z->****ττ********ee************   ******** = 0.01%**
**          ****Z->****ττ******** μμ********   ******** = ??**
**Instrumental**
**“****fake” missing ET to pass cuts due to warm calorimeter region, misvertexing, mismeasured jets, detector resolution **
**          ****Z->ee(****μμ****) + 2jets + “fake MET”**
**QCD jets or photons look like electrons in cal if they catch a track ****(ee) ****or real muons from c or b pass isolation cut due to poor jet reconstruction ****(****μμ****)**
**         ****QCD multijet**
**         ****W->(****μ********) + jets ****(****μμ****)**** **
**         ****W+3jet->W+”fake e”+2 jets ****(ee) **

## eμ channel: trigger and event selection

**Trigger**
**Event selection**
*1 tight electrons with PT(EM) > 15 GeV and track match *
*1 medium muon with PT(**μ**) > 15 GeV and  track matches *
*MET > 10 GeV *
*2 jets PT(jet) > 20 GeV, | ****|<2.5 *
*HTe (PT(e)+PT(j1)+PT(j2)) > 120 GeV *

|  | Level 1 | Level 2 | Level 3 |
| --- | --- | --- | --- |
| MU_A_EM10 | CEM(1,5) 
1 tight scint muons | none | ele (1, 10) |
| efficiency | 95% |  | 100% for 
PT(EM) > 20 GeV  |

## eμ channel: acceptance and efficiency

**	**

** ****Local muon reconstruction efficiency**
**Find triggered medium local muon which forms Z when combined with a track matched calorimeter muon The second should have corresponding local muon**

** ****Central tracking + matching efficiency:****  79.6 ± 0.2%**
**Measure rate at which muons have central matches in clean sample (dimuon trigger, 2 isolated medium muons)**
** ****Isolation efficiency: ****91.5 ****±**** 0.5%**

**Geometrical acceptance :  74.2± 0.4 % (from tt->e****μ****jj MC)**

**82.9 ± 1.4 %**

## eμ channel: backgrounds

**Physics background**
**WW******** e****μ****: from MC  **
**Z ******** ****ττ****: from MC**
**Instrumental background:**
**Muon fakes (QCD muon which passes isolation cuts)**
**Electron fakes (QCD jet with a leading ********0 ****and a random track)**
**W -> ****μ**** + “fake *****e*****” (real muon and fake tight electron)**
**QCD  (fake tight electron and fake isolated muon)**

| Loose EM Muon0.12
 | Loose EM
Isolated Muon |
| --- | --- |
| 

Tight EM
Muon | 

         Tight EM
   Isolated Muon |

**0.11**

**0.02**

**0.36**

**0.067**

**0.007**

## eμ channel: data

**Njets, pT>15 GeV**

**Njets,  pT>20 GeV**

**HTe**

****** ****= 11%**

## Dilepton channels: summary

|  |  | ee | μμ | eμ |
| --- | --- | --- | --- | --- |
| Luminosity (pb-1) |  | 47.4 | 35 | 37.8 |
| N of signal events expected |  | 0.26 | 0.2± 0.01 ± 0.01 | 0.80 |
| N of background events

 | Instrum
(“fake”)
 | 0.48 ±0.18
 | 0.6 ± 0.2      (“fake” muon)
0.65 ± 0.13 ± 0.13 (Z->μμ) | 0.132 |
|  | Physics | 0.0016 (WW)
0.006 (Z->ττ) | 0.01 ± ?? (WW) | 0.002 (WW)
< 0.4 (Z->ττ) |
| Total background |  | 0.449 | 1.26 | 0.14 (no Z->ττ) |
| N of events observed |  | 2 | 2 | 1 |

## Lepton + Jets channels:triggers

| Trigger | EM15_2JT15 | MU_JT20_L2M0 |
| --- | --- | --- |
| Level 1 | CEM(1,10), CJT(2,5) | 1 Muon All, CJT(1,5) |
| Level 2 | EM(1,10,0.85), JT(2,10) | 1 Medium Muon |
| Level 3 | 1 EM PT>15 GeV 
2 Jets PT>15 GeV | 1 Jet PT>20 GeV |
| efficiency | 88% | 84.3% |

**jet pt (GeV)**

*CJT(1,5)*

- 

**L1+L2+L3 jet turn-on**

*e+jets*

- μ+jets

**Lepton + Jets channels:****event selection**

| Selection | e+jets | μ+jets |
| --- | --- | --- |
| MET | MET > 20 GeV | MET > 15 GeV |
| Jets | PT(jet) > 15, | |< 2.0 | PT(jet) > 15, ||<2.5 |
| PT | PT(EM) > 15 | PT(μ) > 15 |
|  | D (e,MET) > 0.5 | dR( μ,jet) > 0.5 |
| Loose ID | Tight EM w/o track match | Medium muon with track match |
| Tight ID | Tight EM with track match | Isolated muon with track match |

_**Apply matrix method to estimate W and QCD content in the selected sample**_
******_qcd : ****efficiency to go from “loose” to “tight” in a background sample (MET < 15 GeV)**
******_sig:   ****same for signal sample**

**Nloose = N_W + N_QCD             **
**Ntight = ********_sig ******** N_W + ********_qcd ******** N_QCD**

**Solve equations for each jet  multiplicity bin**

## Lepton + Jets channels:trigger bias

***bias in 4******th****** bin for:***
***W+4 jet:******	******1.065+-0.01***
***ttbar:******	******	******1.001***

**Compare number of events selected by signal trigger and the one without jet requirement**

## μ+jets channel: Berends scaling

- μ+jets:
**N4 ****QCD ****      =   13.1 ± 6.0**
**N4 ****W         ****    =   24.2 + 14.2 -10.2**
**N4 ****observed  **** =   43**

**                   ****	****      ****Nobs****	****    Nbkg            Nw          Nqcd**
**MEt Cal > 15 GeV            29           30.0          **** 21.3         8.7****±****3.9**
**Jet Et > 55 GeV                13****	****     16.1 ****	****      12.1           4.0**
**A    > 0.065                         5****	****       4.4****	****        3.3            1.1**
**Ht > 220 GeV                     ****5****	****   2.9 ****±** **1.5      2.2 ****±** **1.3     0.7 ****±** **0.4**

- To improve S/B ratio use event topology:

- e+jets:
**N4 QCD       =   14.8 ± 6.8**
**N4 W             =   5.2 ± 2.7 **
**N4 observed   =   17**

- μ+jets

- μ+jets

- e+jets

**ET****W ****= pT(e)+MET>60**
**|********_W| < 2.0**
**A > 0.065**
**Ht > 180 GeV**

## Lepton+jets channels: summary

|  | e+jets | μ+jets |
| --- | --- | --- |
| Signal efficiency | 3.2% | 5.76 ± 0.18 ± 0.68 % |
| Luminosity (pb-1) | 40.7 | 41.7 |
| N of signal events expected | 1.5 | 2.4 |
| N of background events | 1.4 ± 0.6 | 2.9 ± 1.5 |
| N of events observed | 4 | 5 |

## Event Display	

**Event Display****	**

***run******	******167003***
***evt ******	******	******27714859***
********* ******pt******	******48 GeV***
***Met******	******55 GeV***
***Met c.******	******51 GeV***
***JetEt******	******154 GeV***
***Apla******	******0.160***
***Ht******	******	******517 GeV***

***two secondary vertex tags!!!***

## Individual and combined cross section

**Likelihood definition using Poisson statistic:**

**Cross section estimate using maximum Likelihood**

|  |  (pb) |
| --- | --- |
| ee |  |
| μμ |  |
| eμ |  |
| μ+jets |  |
| e+jets |  |

****** ****=**

-  (pb)

*-2 ln (L)*

## Soft-muon Tagger: Overview

**Definition: global medium muon (Saclay matching), p****T****>4 GeV and |********|<2;**
**                 ********R(muon-jet)<0.5 **
**                 ****no p****Trel**** cut**
**Tag Rate Function (TRF): determined from “all_jets” p13.05 skim; **
**                                          ********4 jets with p****T****>15 GeV and |********|<2**
**Assume same heavy flavor content in W+********3 jets (Run 1)**
**Backgrounds: **
**QCD: estimated by using the matrix method on the tagged sample                                                     (use of untagged sample and tag rate function yields consistent result)**
**W+top: estimated by using the matrix method on the untagged sample                                                  and applying the event mistag rate. **

- 44% of top events are expected to have soft muon

## Soft-muon Tagger: e+jets channel

**Start from Lukas’ skimmed root-tuples:**

_**Background estimate**_
**QCD (tagged sample):**
**W+top (untagged sample):**

- s   = 0.880.04
- qcd = 0.430.03

- Nloose = 2
- Ntight  = 2

- Nqcd = -0.230.67

- Nloose = 64
- Ntight  = 26

- NW+top = -0.05 0.12

- Nbckg+top = -0.3 0.7   => Ntop = 2.1 1.9

- Ntop(expected) = 51 pb-1 x 0.72 x 0.147 x 0.214 x 0.146 x 8 pb = 1.3

- in 4th jet bin

## Soft-muon Tagger: e+jets candidate

**Electron: p****T****= 67.4 GeV, ******** = -0.8**
**Jets:  (*)  p****T**** = 150.8 GeV, ******** = -0.14**
**                ****p****T**** = 80.7 GeV, ******** = -0.04**
**                ****p****T**** = 33.1 GeV, ******** = 0.52**
**	****         ****p****T**** = 33.9 GeV, ******** = 0.96**
**Muons:    p****T**** = 5.3 GeV, ******** = -0.18**
**H****T**** = 298.5 GeV**
**Apla = 0.071**

## Lifetime b-tagging: ingredients of the analysis

- Input:
***number of W and non-W events after preselection***
***Efficiency for signal preselection***
- Calculate number of expected tagged events in each jet multiplicity bin
***Flavour composition of the sample (ALPGEN MC)***
***Efficiency to tag b- jet (from data and MC)***
***Efficiency to tag c-jet***
***A probability to tag a background (QCD) event  (positive tag rate determined from EMqcd or generic jets sample)***
***A probability to tag a light jet (negative TRF) to estimate mistags in W+jets component***
***Scale factor between data and MC (determine as a ratio of b-tagging efficiency in data and MC)***
***Taggability  ***
** **

## SVT rates in latest W()+jets sample

- SVT rates in latest W()+jets sample

**After event preselection in W(********)+jets sample (w/o soft-muon veto + 0.77 pb****-1****):**
**Caveats:**
- not requiring events with good lumi blocks (Markus does)
- QCD prediction based on preselection with soft-muon veto.

- Exclusive jet multiplicity

- Double tagged

- Tagged

## CSIP Tag rates in W()+jets sample

- CSIP Tag rates in W()+jets sample

## Top mass analysis in the dilepton channel

**matrix element method from PRD60, 052001 (1999).**
**two neutrinos but only measure missing p****T**** (=********pT********)**
- four unknowns
- four mass constraints (two W bosons and two top quarks)
**for each value of the top quark mass**
- quartic equation  0, 2, or 4 possible top/antitop momenta
**assign weight to each solution and sum over all solutions for both lepton-jet assignments **

- Fatakia, Heintz, Sonnenschein – 2/14/03

## e- candidate event

- weight curve

- peak

- median

- weight

- median-peak

- Fatakia, Heintz, Sonnenschein – 2/14/03

## Top mass in lepton+jets channel

- Mass reconstruction
**1 unknown (p****z********) and 3 constraints**
***m*****(*****l***********) = *****m*****(*****q***********) = *****m******W***
***m*****(*****l************b*****) = *****m*****(*****q***********)**
**2C kinematic fit**
- Complications
**12 possible assignments of the 4 jets to the 4 quarks; 6 if one of the jets is b-tagged; radiation can add extra jets**
**Choose combination with minimal **
- where *X *is vector of measured quantities, *G *– inverse error matrix
- Event selection
**the same preselection as for Xsection (kinematic cuts on lepton, jets and missing ET)**
**Use topological variables with small correlation with top mass to construct event discriminant**

## Top mass in lepton+jets channel

**Reconstructed mass **

**discriminant for candidate events**

- e+jets channel
**40  events  before LB discr. Cut**
**24 events with discr. > 0.3**
- mu+jets channel
**42 events before LB discr. Cut**
**16 events with discr > 0.3**

**bkgd-rich**

**signal-rich**

- Run 167003, ev 27714859
- Double b-tagged event
- Discr ≈ 0.95
- Fitted Mass ≈ 230 GeV

- discr > 0.3

## Conclusions

**Lots of work was done to obtain the results we are presenting today**
**To better understand results and do detailed systematic studies we need stable data, stable Ids**
**Where do we loose efficiency: **
**Data quality: loose a lot of luminosity due to bad runs**
**Noise in calorimeter**
**Level 1 muon trigger**
**Tracking**
**A lot of room for improvement and exciting results in the near future... if we have sufficient manpower!**
**There are almost no people working on top properties and mass...**