# Presentation: 868024

## B-tag Studies (SecVtx) for the All-hadronic top

**Introduction**
**Data Samples**
**Tag Rate**
**Parametrization **
**Systematics**
**... ****after kinematical selection**
**Conclusions**

- P. Azzi, A. Castro, G. Cortiana,T. Dorigo, **A. Gresele, **
-          J. Koningsberg, G. Lungu, A. Sukhanov
_**http://www-cdf.fnal.gov/internal/tthad/index.html**_

- Top Meeting 11-13-03

## Introduction: SecVtx tags ....

- We begin by studying **SecVtx tags** in our sample of multijet events
****** **using these tags we can define a **tag rate** and a **parametrization** which can provide a bckg estimate
- Our short-term goal (i.e. for low integrated luminosity,
-      165 pb-1 at present) is to follow Run I approach that it is compare **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 bckg evaluation
- Finally we apply a tight kinematical selection and look for an excess of tags w.r.t. the bckg as expected from top

- Top Meeting 11-13-03

## The datasets (data and MC)

- Dedicated trigger: TOP_MULTI_JET
- Requires: N(jet)>=4 with Et>=15 and Et>125 GeV
- Lint~ 165pb-1 with good run list and SVX requirement
-     (62 pb-1 before and 103 pb-1 after February shut down)
- 1880044 events
- Events processed through the “REMAKE” procedure used by the other Top analyses + 4.11.1 TopEventModule info
- RAW and CORRECTED JET energy information used
- Signal MC: ttopli
- Extra signal samples produced for systematic evaluation

- Top Meeting 11-13-03

## Tag Rate: as you know ...

- We define a POSITIVE Tag rate as:
**          **
**                  ****Number of Positive Tags / Number of Taggable Jets**
-   and the NEGATIVE Tag Rate (obviously!) as:
**                  ****Number of  Negative Tags / Number of Taggable Jets**
- where the jets are define taggable if Ntrk >= 2
- Tag rate shows strong dependence on **Et, Eta and Ntrk ****** we
- parametrize:
- Et in 8 bins (20-25,25-30,30-40,40-55,55-75,75-100,100-130, 130 GeV)
- Eta in 3 bins (||1, 1||1.2, ||1.2)
- Ntrk in 11 bins (2,3,...,>=12)

- Top Meeting 11-13-03

## Tag rate for gset09 and gset08: are they different?

- From the plots we can respond:                           NO!

**OK, we parametrize **
**the 2 samples toghether!**

- Top Meeting 11-13-03

## Positive Tag Rate vs Et, Eta and Ntrk 

- Top Meeting 11-13-03

## Negative Tag Rate vs Et, Eta and Ntrk 

- Top Meeting 11-13-03

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

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| Events | 450355 | 233466 | 64803 | 15395 |
| Taggable jets | 1079105 | 695647 | 231491 | 66197 |
| OBS (+ tags) | 33207 | 20190 | 6524 | 1768 |
| EXP (+ tags) | 33371178 | 20143140 | 639578 | 1777841 |
| OBS (- tags) | 8438 | 5318 | 1691 | 535 |
| EXP (- tags) | 876793 | 515471 | 161640 | 44621 |

- Top Meeting 11-13-03

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

- We plot the ratio:
**      **
**     ****(OBS – EXP) / EXP**
- as function of the jet
- multiplicity ( for 4, 5, 6 or  7)
- for positive tags Exp is consistent with OBS
- for negative tags EXP tends to underestimate OBS

- Top Meeting 11-13-03

## Conversions, rejections and parametrization in 

- To reject material interactions we ask positive tags to have Rxy  1.2 cm. To account for  assimetry we parametrize also in  (6 bins)

**pos**

**neg**

- Top Meeting 11-13-03

## Summary table for the parametrization (81136)

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| Events | 450355 | 233466 | 64803 | 15395 |
| Taggable jets | 1079105 | 695647 | 231491 | 66197 |
| OBS (+ tags) | 27855 | 17316 | 5625 | 1522 |
| EXP (+ tags) | 28063164 | 17201128 | 5513723 | 154038 |
| OBS (- tags) | 8438 | 5318 | 1691 | 535 |
| EXP (- tags) | 876993 | 515271 | 161740 | 445201 |

- Top Meeting 11-13-03

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

- We plot the ratio:
**          ****(OBS – EXP) / EXP**
- as function of the jet multiplicity
- ( for 4, 5, 6 or  7).
- Again:
- for positive tags Exp is consistent with OBS
- for negative tags EXP tends to underestimate OBS

- Top Meeting 11-13-03

## Systematics

- Systematics in the bckg parametrization come from biases due
- to the fact that we derive the matrix from events with  4 jets
- but eventually we want to apply it to events with:
- Njet  6
- (Apla+0.0025x3Et)0.65
- Centrality > 0.75
- SumEt > 350 GeV
- so we consider individually the possible bias of each request on
- the bckg estimate.
- Each one of these cuts increases the S/B ratio so we want to
- account also for tags from top ( = 6.7 pb, ttopli, tags degraded
- by the scale factor SF = 0.86  0.09)

- Top Meeting 11-13-03

## Systematics on Njet

- If we compare OBS and EXP for Njet  6 we see that:
-                          **(OBS – EXP) / EXP ******** + 1.5 %**
- However if we remove the expected contribution from top (OBS’  173 tags and EXP’ 35 tags) we have
-      (OBS” = OBS –OBS’ , EXP”=EXP –EXP’):
-                          **(OBS”-EXP”) / EXP” ******** –1%**
****** ****We consider a systematic uncertainty on Njet = ******** 1.5 %**

- Top Meeting 11-13-03

## Systematics on Fake tags

- We do not use negative tags, and their prediction is off by about 8 %:
-                       **(OBS – EXP) / EXP ******** + 8 %**
**    **we still study this ...
- However negative tags (i.e. fakes) are about 30%  of all positive tags so we include a systematic in the positive prediction of 2.5% (= 0.3*8%)
**We consider a systematic uncertainty **
**             ****due to fake tags in positive tags= ******** 2.5 %**
- We are being conservative because this should be already accounting
- for in the previous systematic

- Top Meeting 11-13-03

## Systematics on Et, Centr and (Apla+0.0025x3Et) 

- We use events with 5 jets, where the S/B is smaller than in 6 jets. We
- do not use 4 jets to have larger statistics for high values of Et,Centr
- and (Apla+0.0025x3Et):
- we consider the cumulative distribution of Et, Centr and (Apla+0.0025x3Et) for OBS tags and EXP tags obtained by weigthing the taggable jets with the tag rate
- we subtract from the OBS distribution the presence of tags from top and renormalize the integral of OBS and EXP to be the same
- from the ratio of the two cumulative distributions we derive the systematic uncertainty around the specific value of the cut

- Top Meeting 11-13-03

## Systematics on Et

- At most, around the cut at 350 GeV, there is a difference between OBS and EXP of:
-                     **2%**

- Top Meeting 11-13-03

## Systematics on Centrality

- At most, around the cut at 0.75, there is a difference
-     between OBS and EXP of:
-                     **1%**

- Top Meeting 11-13-03

## Systematics on (Apla+0.0025x3Et) 

- We consider an intermidiate situation between removing and not removing top.
-      In this way the difference
-      between OBS and EXP of:
-                     **8 %**

- Top Meeting 11-13-03

## Total Systematic uncertainty ...

- We now combine all systematics (sum in quadrature):
-  **Njet :                 1.5 %**
** ****Fakes                  2.5% (some already included above)**
** ****SumEt :               2%**
** ****Centrality :           1%**
** ****(Apla+0.0025x********3****Et): 8% (probably overestimate)**
-         **Total systematic uncertainty:   9 %**

- Top Meeting 11-13-03

## Kinematical Selection (reminder ...)

|  Pre-requisites (|Zvert|<60,    |Zvert|<5, MET/Et  6 GeV1/2) |
| --- |
|  Njet  6 |
|  (Apla+0.0025x3Et)0.65 |
|  Centrality > 0.75 |
|  SumEt > 350 GeV |

**Using :**

** ****S/B = 1/18**
** ********K ****= 7.0 ******** 2.2**
** ****S = 77.5 in 165pb****-1**

- Top Meeting 11-13-03

## Summary table for the parametrization (81136) after KIN SEL

|  | 4 jets | 5 jets | 6 jets |  7 jets |
| --- | --- | --- | --- | --- |
| Events | 45 | 252 | 505 | 704 |
| Taggable jets | 133 | 962 | 2238 | 3761 |
| OBS (+ tags) | 5 | 35 | 96 | 108 |
| EXP (+ tags) | 4.42.0 | 28.95.2 | 64.97.9 | 103.69.9 |
| top MC fakes | 0.05 | 1.2 | 4.9 | 6.4 |

- Top Meeting 11-13-03

## ... some preliminary results

- For Njet  6 jets (SIGNAL REGION) we see :
- OBS = 96 + 108 = 204 tags
- EXP = 65  8 (stat) + 104  10 (stat) = 169  13 (stat)  15(syst)
**              **
**                ****OBS – EXP = 35 ( about 2 sigma excess)**
- We compare this to the expectation from top ( = 6.7 pb):
-                     OBS’ = 52      and       EXP’ = 11.3  0.2
- so one needs to remove EXP’ from EXP in order to compare to
- the real top signal:
-      OBS – (EXP – EXP’) = 204 – (169-11) = 46 tags
- which is quite close to the 52 tags expected from top.

- Top Meeting 11-13-03

## Conclusions

- In this analysis we have :
- studied SecVtx tags on  multijet events
- derived a tag rate parametrization
- evaluated bckg and systematics
- Once we apply the kinematical selection we see a top signal as
- expected ...
-              ... from this we are going to measure the cross section!

- Top Meeting 11-13-03