# Presentation: 378455

## Jet Studies

- 1. Changes in seed finding for cone jets reconstruction
- 2. t42 and jets

- Emmanuel Busato

## 1. Changes in seed finding for cone jets 		reconstruction

- - technical description
- - effect on cone R=0.5 jets reconstruction
- - what's the best value for the new parameter « n »
- - conclusion

## Technical description

- Go to clustering around T
- (with  R=coneSize=0.3).
- Remove progressively towers
- from the list.

-  yes

- no

- Stop preclustering

- Current preclustering
- (Simple Cone)

- _Technical description_

## ?

- no

- Stop preclustering

- List of towers (pT ordered)

- Go to clustering around T
- (with  R=coneSize=0.3).
- Remove progressively towers
- from the list.

- pT > seedET =500MeV

-  Yes

- yes

- no

- Modified preclustering

## Effect on cone R=0.5 jets reconstruction

- Data sample :
-  Run #169894 (30 Dec)  and #172603 (16 feb)
- Reconstrution version : p13.06.01
-  Quality cuts :
- 		0.05<emf<0.95
- 		chf<0.4
- 		hotf<10
- 		n90>1
-  No trigger selection

-  5.1% of events have more jets with old seeding
- 1.4% of events have more jets with new seeding

## Jets not found with new seeding (R>0.5)

- Jet not found with new seeding :
- 	- mostly low pT jets
- 	- in ICR
- 	- big number of merge

_*Jets not found with new seeding*_* (****R>0.5)*

## New Jets found with new seeding (R>0.5)

- - First, an example :

##  Look like low pT good jets

-  Look like low pT good jets

- - What are those jets ?

## What's the best value for the new parameter « n » ?

- nb1

- nb2

- nb1

- nb2

- _What's the best value for the new parameter « n » ?_

## Conclusion

- - Jets not found with new seeding look like noise jets
- - New jets found with new seeding look like low pT good jets
- Looking at f90 distribution as a function of n, we decided to remove all CH seed (n=1000sigma)
- This new seeding scheme is in p14 with n=1000sigma

## 2. t42 and jets

- - jets properties (emf, chf, f90 ...) without and with t42
- - jets reconstruction without and with t42

## Jets properties (emf, chf, f90 ...) without and with t42

- Top group’s alljets skim (reco version p13.06.01) :
-   	  * Passes the 4JT10 trigger.
- 	   * At least 4 jets (JCCB).
- 	   * HT > 100 GeV (just plain sum of uncorrected JCCB jets).
-                         **20000 events**

- Jets are JES corrected.
- No quality cuts applied because jet id distributions change significantly.

- _Jets properties (emf, chf, f90 ...) without and with t42_

## New seeding not applied, its effect 

- New seeding not applied, its effect
- is small once t42 is applied

## Warm zone around phi ~ 0.8 

- Warm zone around phi ~ 0.8
- disappears with new seeding !

## Summary

- - id distributions change significantly with t42
- - t42 reduces the number of jets by ~ 11%
-  	- mostly in -2 < eta < 2
- 	- mostly low pt jets
- 	- mostly high f90 jets
- 	- merge > 0
- - t42 doesn’t affect jets with 0 merge

## Jets reconstruction without and with t42

-  There are jets, close to a track jet (R<0.5) ( probably good), not found with t42 !
-  Part of  these jets can be explained simply
-      • low pT jets : - *threshold effect (the same jet is less energetic with t42)*
-     •* *high pT jets :    there is still 0.9 of jets with                                              not found with t42
-                               *- threshold effect up to 25 GeV*
*	**	**                **- unphysical cases :*
*	**	**	**	**  **- split/merge effect :*
- 		- split/merge effect :

- _Jets reconstruction without and with t42_

***R(cal jet, track jet) < 0.5*
*pT> 25*

## This particular example is not isolated, approximately 40 of high pT jets close 

- This particular example is not isolated, approximately 40 of high pT jets close
- a track jet not found with t42 can be explained by this effect.

##  Reduction of 8

- Look at MC sample without noise :
- 	  -  no calorimeter noise
- 	  -  no minimum bias
- 			Single top events – schannel production mode

- JETS

- without t42  :  Number of jets = 3568
- with t42  : Number of jets = 3540

-  Reduction of 8

## Same number of Ws !

- ELECTRONS

- W selection :
-           Electrons :
- 	        Hmx8 < 20
- 	        isolation < 15
- 	        EMF>0.9
- 	        no track match

-       PT (electron)>20 Gev and MET>20 GeV

## Conclusion and to do

-  Looking at single top events without noise reconstructed without and
-    with t42, we find that the number of jets is reduced by 8
- 		  look what happens on a QCD sample without noise
- 		  understand lost jets
-    Number of Ws not reduced with t42
-  In data, good jets (and all objects) are polluted with noise, we saw that            split/merge effects changes jets multiplicity.
- 		  make sure that it goes in the good direction