# Presentation: 832299

## Status of the Hadronic Top Search

**The all hadronic channel**
**Samples: data and MonteCarlo**
**Kinematical Selection**
**Tag Rate**
**Background and Systematics**
**Btagging Efficiency**
**Cross section**
**Conclusions**

- P. Azzi, A. Castro, G. Cortiana,T. Dorigo, **A. Gresele, **
-          J. Konigsberg, G. Lungu, A. Sukhanov

- Top Meeting 11-13-03

## Dataset and kinematical selection optimization 

**Dedicated trigger: ****N(jet)>=4 with Et>=15 and ********Et>125 GeV**
******L****int****~ 165pb****-1**** with all relevant subdetectors on and ok**
**RAW and CORRECTED (L7) JET energy information used **
**Signal MC: ****Herwig + Detector Simulation + TrigSim**
**We apply some pre-requisites for a minimal clean-up of the sample (see CDF Note 6808) **
**Optimization of S/********B**** ****for jet multiplicity >=6 and for the following quantities (see CDF Note 6808) with these results: **** **
******Et ******** 320 GeV **
******Et/********ŝ (centrality) ******** 0.77**
**(Aplanarity + 0.0037 x ********3****Et)** ****** 0.85**

- Top Meeting 11-13-03

## Summary table of kinematical selection using at least 6 jets

| Cut | ttbar evt
(165 pb-1) | MJ evt | Eff.(%)
(inclusive ttbar) | S/B |
| --- | --- | --- | --- | --- |
| Pre-requisites | 631 | 1134030 | 54.7 | 1/2000 |
| 6  Njet  8 | 244 | 83219 | 22.0 | 1/340 |
| (Apla+0.0037x3Et)0.85 | 97 | 4221 | 8.7 | 1/43 |
| Centrality > 0.77 | 72.0 | 1930 | 6.5 | 1/26 |
| SumEt > 320 GeV | 69.0 | 1237 | 6.3 | 1/23 |

- Top Meeting 11-13-03

## Systematics on the kin. selection

| Source | what | / (%) |
| --- | --- | --- |
| Fragmentation | HERWIG vs PYTHIA | 1 |
| ISR modeling | PYTHIA vs PY.noISR | 13 |
| FSR modeling | PYTHIA vs PY.noFSR | 5 |
| Energy scale | Change by  1  | 26 |
| Total | All contributions | 30 |

******incl ****= (6.3 ******** 0.04 (stat) ******** 1.9 (syst)) %**

- Top Meeting 11-13-03

## Secondary Vertices (btags) ....

**We use SECVTX (Summer 2003) in a method 1 line approach:**
**define a ****tag rate**** and a ****parametrization**** which can provide a bgr estimate**
**compare positive ****OBS****erved tags to ****EXP****ected tags from the tag rate parametrization**
**We do so before the application of any ****kinematical selection**** and derive a systematic uncertainty on the bgr evaluation**
**Finally we apply a tight kinematical selection and look for an excess of tags w.r.t. the bgr as expected from top**

- Top Meeting 11-13-03

## Tag Rate vs Et, Eta, Ntrk and Apla

-   Et
- 8 bins

-   **Ntrk **
**11 bins**

-   **Eta **
**3 bins**

-  **Apla **
**8 bins**

- Top Meeting 11-13-03

## Summary table for the parametrization (81133)

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| Events | 532634 | 249573 | 66807 | 15599 |
| Taggable jets | 1274233 | 742349 | 238532 | 67039 |
| OBS (+ tags) | 38421 | 21313 | 6680 | 1708 |
| EXP (+ tags) | 38421191 | 21150116 | 652446 | 1733.518 |
| Nobs-Nexp/Nexp(%) | 0  0.8 | 0.3  0.9 | 2.3  1.4 | -1.4  2.6 |

- Top Meeting 11-13-03

## (OBS – EXP) / EXP vs Jet Multiplicity

- If we plot the ratio:
**      **
**     ****(OBS – EXP) / EXP**
- as a function of the jet
- multiplicity ( for 4, 5, 6 or  7)
- Tags EXP is consistent with OBS

- Top Meeting 11-13-03

## Systematics uncertainties on the bgr estimate 

- Different control samples :
**pick events with the SMALLEST  possible presence of ttbar events**
**highly populated**
- Three cases:
**2 with reverse cuts**
**1 check stability**

- Top Meeting 11-13-03

## Systematics on Njet

- If we compare OBS and EXP for Njet  6,
- (Apla+0.0037x3Et)  0.85, Centrality  0.77 and Et  320 GeV we
- see that:
**N****obs**** = 3542**
**N****exp**** = 3550 ******** 47**
**(N****obs**** – N****exp****)/N****exp**** = (0.2 ******** 0.1)%**
****** ****We consider a systematic uncertainty on Njet = 0.2 %**

- Top Meeting 11-13-03

## Systematics on Et, ...

- We consider all events
- with 5 jets and
- (Apla+0.0037x3Et)  0.85,
- Centrality  0.77.
-      **Systs. on ********Et **
**       ****1.4 %**** **

- ALLOW SLOPE

- CONVOLUTION

**0.6**

**1.6**

- Top Meeting 11-13-03

## ... on (Apla+0.0037x3Et) and on Centr.

**Syst. (Apla+0.0037x********3****Et) = 4.7 %**

**Syst. Centr. = 0.3%**

**0.6**

**1.4**

**0.8**

**1.2**

- Top Meeting 11-13-03

## Systematics on Inst.Luminosity, ...

- We consider as a
- control sample
- all events with 4 jets.
**Syst. Inst. Lum. << 1 %**

- Top Meeting 11-13-03

## ... on Run # and on jet-

**Syst. Run # << 1%**

**Syst. jet-******** << 1%**

- Top Meeting 11-13-03

## Total Systematic uncertainty ...

- We now combine all systematics (sum in quadrature):
-  **Njet :                          0.2 %**
** ****SumEt :                        1.4 %**
** ****Centrality :                    0.3 %**
** ****(Apla+0.0037x********3****Et):          4.7 % **
** ****Inst. Luminosity:          << 1.0 %**
** ****Run #:                     << 1.0 %**
** ****Jet-******** :                     << 1.0 %**
-         **Total systematic uncertainty:  ~ 5 %**

- Top Meeting 11-13-03

## Background estimate after KIN SEL

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| Events | 60 | 420 | 773 | 883 |
| EXP (+) | 7.90.40.4 | 62.91.43.1 | 126  2  6 | 152  2  7.6 |
| OBS (+) | 11 | 70 | 170 | 156 |
| Nobs- Nexp | 3.1  0.6 | 7.1  3.4 | 44  6 | 4  8 |

- Top Meeting 11-13-03

## ... some preliminary results

- For Njet  6 jets
- (SIGNAL REGION) we see :
- Nobs = 326 tags
- Nexp(bgr) = 278.0  2.8 (stat)
-                        13.9(syst) tags
**              **
****** ****N****obs****–N****exp**** = 48.0 ******** 14.0 tags**

- Top Meeting 11-13-03

## Btagging Efficiency

**We can follow two methods:**
- factorization method where
-       ******overall,ev****btag  ****= ******** ****evt**** ****btag**** + (1 - ********evt**** ****btag****) **** ********evt**** ****mistag**
- with  evt btag = F2b  btag  SF  (2- btag  SF) + F1b  btag  SF
- and SF = 0.86  0.07.
**We have done a cross-check with the single lepton analysis **
**(following CDF Note 6598) **
- counting method where we degrade the tagged jets with the SF
- If we compare the two methods they give consistent results.

- Top Meeting 11-13-03

## Btagging efficiency per event and per jet 

| Njet |   evtbtag(%)
 |
| --- | --- |
| 4j | 53.1  3.5 |
| 5j | 53.6  3.5 |
| 6j | 54.7  3.5 |
| >=6j | 54.9  3.5 |
| >=6j+kin | 59.3  3.7 |

| Njet |   jetbtag (%)
 |
| --- | --- |
| 4j | 63.5  5.1 |
| 5j | 64.4  5.2 |
| 6j | 66.6  5.5 |
| >=6j | 66.6  5.5 |
| >=6j+kin | 73.7  6.0 |

**Eff. b-evt = (****59.3 ******** 3.7) %**** **

**Eff. b-jet = (****73.7 ******** 6.0) %**** **

- If NO matching with b-jet:**  Eff. jet = (****83.7 ******** 8.2) %**

- Top Meeting 11-13-03

## Efficiencies plot

- Top Meeting 11-13-03

## Cross Section

- The presence of tt events in the pretag sample leads to an
- overestimate of the background. We  account for it with an
- iterative procedure and then we rescale the background:
- Nexp’ = Nexp  ((N – Ntt) / N)pretag = 266.1
- and the corrected excess would be:
- Nobs-  Nexp ‘ = 326 – 266.1 = 60

- Top Meeting 11-13-03

## Final summary table

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| Events | 60 | 420 | 773 | 883 |
| Backg. | 7.90.40.4 | 62.91.43.1 | 126  2  6 | 152  2  7.6 |
|   Backg. corrected |  |  | 266.1  16.7 |  |
| Top MC
(6.7 pb) | 0.3  0.1 | 6.5  2.0 | 51.3  15.9 |  |

| OBS (+) | 11 | 70 | 170 | 156 |
| --- | --- | --- | --- | --- |

|    Tags     Expected | 8.2 | 69.4 | 317.4 |
| --- | --- | --- | --- |

- Top Meeting 11-13-03

##  We build the following likelihood function:

-  We build the following likelihood function:

- with the following input values:

| Lumin | L | 165+-10 pb-1 |
| --- | --- | --- |
| Obs tags | n | 326 |
| Exp tags | b | 278+-14 |
| Exp tags corr | b’ | 266.1+-16.7 |
| Kin eff. | ek | 6.3+-1.9% |
| Tag eff. | eb | 83.7+-8.2% |

- b’=b*(N-Ntt)/N
- N=pretag events
- Ntt=pretag tt events

- Top Meeting 11-13-03

##  The cross section (iterative) amounts to:

-  The maximization of the likelihood gives, as central value:

-  The cross section (iterative) amounts to:

- Top Meeting 11-13-03

## Conclusions

**First full pass with Run I method top cross **
**section.**
**                ****To do next ...**
**  **
**brush up the systematic especially jet energy scale and state of the cut PSR, FSR and PDF**
**Seek preblessing next March ...**

- Top Meeting 11-13-03

## Kinematic cuts optimization: Apla vs 3Et 

- Aplanarity

- SumEt3

- Projection

- Optimization

**We reject the bottom left corner.**
**By cutting on ****Aplanarity + K x ********3****Et****. We pick up the best value for k and look for the maximum of S/********B**

**mj**

**tt**

- Top Meeting 11-13-03

## Kinematic cuts optimization: Centrality

- After the cut (Aplanarity + 0.0037 x 3Et)  0.85 we
- find the best value to cut on the **Centrality**

**S/B**

**S/********B**

**mj**

- Top Meeting 11-13-03

## Kinematic cuts optimization: Et 

- After the cut (Aplanarity + 0.0037 x 3Et)  0.85  and
- Centrality  0.77 we find the best value to cut on ******Et**** **

**mj**

**tt**

**S/B**

**S/********B**

- Top Meeting 11-13-03

## Parametrization using matrix of Jet50

- As a cross-check , we apply the matrix of Jet50 on our data
- sample even if it is not much appropriate because:
- it comes from a sample with 2 jets and low SumEt and we use a data with at least 6 jets at higher SumEt
- the statistic of the Jet50 sample is very small in our signal region
-  and this is reflected in the bigger **N****obs****-N****exp****/N****exp **

| Nobs-Nexp/Nexp(%) | 4.0  0.7 | 4.7  0.9 | 7.0  1.4 | 4.6  1.5 |
| --- | --- | --- | --- | --- |

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |

- Top Meeting 11-13-03

## Negative Tags before and after kin. sel.

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| OBS (- tags) | 9774 | 5593 | 1745 | 515 |
| EXP (- tags) | 977498 | 523258 | 159323 | 4209 |
| OBS–EXP/EXP(%) | - | 7 | 9 | 22 |
| EXP(JET50) (-tags) | 10508107 | 571572 | 174826 | 4629 |

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| OBS (- tags) | 5 | 15 | 42 | 52 |
| EXP (- tags) | 3  0.4 | 18.1  0.6 | 34.4  1.0 | 39  1.0 |
| EXP(JET50) (-tags) | 3.40.2 | 21.40.8 | 39.21.0 | 44.11.3 |

- Top Meeting 11-13-03

## Cross Check with matrix from Jet50

- Top Meeting 11-13-03

## Systematics on Et, Centr and (Apla+0.0037x3Et) 

- for events passing the kin. sel., we drop the 6th jet and  reconstruct new Et, Centr and (Apla+0.0037x3Et) distributions (“6-to-5,, distributions)
- in the corresponding control sample we fit the distributions of the Nobs/Nexp ratio with a first degree polynomial
- convolute the polynomial function with the corresponding  “6-to-5,, normalized distribution
- the integral of the convolution  gives the total systematic uncertainty

- Top Meeting 11-13-03