# Presentation: 103205

## Study of the heavy flavor content of jets produced in association with W bosonsin pp collisions at  s=1.8 TeV.

**Fermilab**
**CDF Paper Seminar, September 2001**

## Introduction

*Production of W bosons in association with jets has been the subject of many studies at CDF*
*    **production studies*
*QCD studies*
*Previously all the excesses of tagged W + ****3 jets events have been attributed to tt production and used to measure **1 ** ** *
*	**	**SECVTX*
*	**	**JPB*
*	**	**SLT*
*	**	**	**	**	*
***	******	******	******	******	******This Study***
*Use theoretical value of *
*Test if Standard Model prediction is compatible with the observed yield of different tags as a function of jet multiplicity.*
*	**	**	**	*
*1   ****Phys. Rev. D64:032002, 2001***

##  Data sample : lepton + jet  events 

*Kinematic cuts:*
*One high E**t **lepton (e , **********) ***
*E**t **>20 GeV*
*Central ( ***
*Isolated *
*E**t **> 20 GeV*
* **at least 1 jet  with E**t **>15  GeV and **********************<2.0  *
*b-identification :                           **Efficiency*
*SECondary VerTeX** ** (**SECVTX**)         **	**50%*
*Jet-ProBability          (**JPB**)                   **	**50%*
*semileptonic decay   (**S**oft**L**epton**T**agging** )         **	**20%*

- ~

- ~

- ~

## W + jets  composition

***Source: Phys. Rev. D64:032002, 2001***

## W + jets after tagging

***Source: Phys. Rev. D64:032002, 2001***

## Various topological channels

## Correlation between SLT and SECVTX tags

*Begin study selecting W+jet events with both SECVTX and SLT tags*
*	**	**	**	**	**Observations*
*the  numbers of  events with SLT and no SECVTX  tags (mostly fakes) are consistent with the prediction. *
*The numbers of  observed and predicted  events with multitags, which are mostly contributed by real heavy flavor, are not very consistent with the prediction.*
*Since 70% of the events tagged by SECVTX contain b-jets (20% c-jets) we check the semileptonic BR in  heavy quark jets tagged by SECVTX.*

## Events with and w/o SECVTX and SLT tags in the same jet (superjet)

* **the complementary sample has 43 events and 43.6 *± *3.3 are expected*
*In the superjet sample, the probability of consistency with the SM in the 4 jet bins is 0.65%.*
*the “*a posteriori”* probability of observing 13 or more events with a superjet when 4.4  *± *0.6  are expected in the W+2,3 jets bin is  *P=*10**-3*

***Superjet Events***

***SECVTX Only Events***
***(Complementary Sample)***

## Additional SECVTX tags 

*If superjet events were “Complementary Sample-like”, we would expect  1.8 DT.*
*The likelihood of observing  5 additional SECVTX tags is 4.1x10**-2**.*

## Cross-check using generic-jet data 

*Herwig simulation*
*tuned by fitting the rates of SECVTX and JPB tags in Phys. Rev. D64:032002, 2001*

## Cross-check using generic-jet data

*The efficiency for finding supertags in the data is smaller than in the simulation (85±5)%*
* **	**note**: after tagging with SECVTX, the heavy flavor composition of generic-jets is similar to W + jet events*

## If  the 13 events are a statistical fluctuation,   the  kinematics of this sample will be consistent with the S.M. simulation and the C.S.
We  chose two sets of 9 variables to look for differences 

			First set 
studies d2dpT dfor every  different object in the final state (8 var.)
Replace ET with the system l+suj+b
Add the angle between the lepton and W (check if leptons are consistent with the decay of  W bosons)
This set of 9 variables fully describes the kinematics of the final state with modest correlations.

*We  chose two sets of 9 variables to look for differences *
*	**	**	*
*	**	**	**First set** *
*studies d**2****dp**T** d****for every  different object in the final state (8 var.)*
*Replace* ET* with the system l+suj+b*
*Add the angle between the lepton and *W* (check if leptons are consistent with the decay of  *W* bosons)*
*This set of 9 variables fully describes the kinematics of the final state with modest correlations.*

***Study of Kinematics***

## Each data distribution for a given variable xi is compared to the sum of various SM contributions using a K-S test.
Use the Kuiper’s definition of distance between the cumulative distributions of data and SM prediction

With Monte-Carlo pseudo experiments, randomly generate contributions of the various parent distributions. 
Determine the probability distribution of the K-S distance , Wi().
Define the probability Pi that the xi distribution in the data is consistent with the SM simulation as

*Use the Kuiper’s definition of distance between the cumulative distributions of data and SM prediction*
*With Monte-Carlo pseudo experiments, randomly generate contributions of the various parent distributions. *
*Determine the probability distribution of the K-S distance , W**i**(****).*
*Define the probability P**i **that the x**i** distribution in the data is consistent with the SM simulation as*

***Study of Kinematics (cont.)***

## Primary lepton

## Primary lepton

***Primary lepton***

## Superjet

***Superjet***

## Superjet

***Superjet***

## Additional jets (b-jets)

***Additional jets (b-jets)***

## Additional jets (b-jets)

***Additional jets (b-jets)***

## “ET“ or ETl+b+suj

***“******E******T******“ or E******T******l+b+suj***

## “Longitudinal E” or y l+b+suj 

## Azimuthal Angle (l,E)

***Azimuthal Angle (l,E)***

## The binomial probability that the vertex asymmetry and the -asymmetries are due to a equal or larger statistical fluctuation is P=1.6•10-4 (3.8 )
 we know of no such physics process
It may be a low probability statistical fluctuation
 obscure detector effect; such asymmetries are not visible in any other control sample

* **we know of no such physics process*
*It may be a low probability statistical fluctuation*
* **obscure detector effect; such asymmetries are not visible in any other control sample*

***Event Vertex***

## Summary of the Probabilities

***Summary of the Probabilities***

## Additional probabilities

*	**	**	*
*	**	**	**	**Second Set *
*The first set of 9 kinematic variables were part of a larger set of 18 variables used to study the events.*
*The remaining 9 variables study the combination of the various objects in the superjet events*

## 18 Kinematical variables

- < P>=0.13 RMS=0.11

- < P>=0.50 RMS=0.24

## Superjet Event properties:Primary Lepton distributions 

*Superjet Sample*

*Superjet Sample*

*Complementary *
*Sample*

*Complementary *
*Sample*

***Superjet Event properties:******Primary Lepton distributions ***

## Superjet Event properties:Soft Lepton distributions 

* **Soft leptons*
*  **not prompt*
* **in 8 cases are part of the SECVTX tag*
* **emitted along the superjet axis*

## Superjet properties:Lifetime

*Lifetime*
*pseudo-***
*The pseudo-****distribution does not account for neutral particles emitted in the heavy flavor decays (boost factor ~1.1 in b and c decays)*

## Superjet properties:Lifetime

***ip** *
* **define R****= ****ip**/pseudo-***
* **compare data to the SM simulation with a K-S test*
* **control sample  **	*P*=0.35*
* **b-jets         **	*P*=0.47*
* **superjets:   **	*P*=0.05*

## Check of R with generic-jet data

- Data

- Herwig

## Superjet Properties:SECVTX tag Invariant Mass

## Superjet properties:Soft Lepton pT

*Compare to a SM simulation, in which the superjet transverse momentum distribution in each SM process has been sculpted to reproduce the data*
* **the usual K-S test yields  P= 9•10**-4*

## Check of the fragmentation (control sample)

- 13 events

- Complementary  sample

## Check of the fragmentation (generic-jet data)

* **550,000 generic-jet events in the data and in the Herwig simulation  (JET20, JET50, and JET100). *
*1324 supertags in the data*
*1342 simulated supertags*

## Studies of the primary lepton

- 0.1 < *I* <0.2

## Studies of the primary lepton

* **The p**T** of the primary leptons has a cluster at the 20 GeV/c threshold*
* **lower the theshold in the  high-p**T** lepton sample to 18 GeV/c*
*No events with a superjet found*
* **Search in the low-p**T** lepton sample with a 10 GeV/c threshold*
*This sample is prescaled by a factor of  about 1.3*
*Smaller integrated luminosity (Run 1B only); it corresponds to 8 of the 13 events with a superjet*
*We find 6 of the 8 events, and an additional one containing a primary lepton with  p**T**=17.7 GeV/c*

## Primary lepton trigger studies

*We require that the primary leptons fired the L2 trigger *
*For muons the L2 trigger efficiency is about 70% *
*If superjets are real, we expect to have lost 2 muon events with a superjet because of this request*
* **as seen before, 85% of the superjets contain a soft muon above the L2 trigger theshold*
* **we then expect to recover **1 or 2 *W*+2,3 jet events** **with a supertag removing the L2 request*
*If  superjet events are a fluctuation of SM processes, we expect to recover*
*3 *W*+1 jet, 1.1 *W*+2,3 jet events** (all without supertags)  *
* **We find **3 *W*+1 jet events** with no supertags, and             **1* W*+2 jet & 1 W+3 jet events**  (both with a supertag)*

## Plug electrons

## Conclusions

*Comparison of observed rates of SECVTX and SLT tags  with SM predictions, including NLO calculation of single and pair produced top quarks are generally in good agreement.*
*However, we find an excess of events which have jets with both SECVTX and SLT heavy flavor tags.*
*Detailed examinations of these events find them difficult to reconcile with a simulation of SM processes, which well reproduces closely related data samples.*
*Extensive studies of these events and investigations of larger samples of generic jet data have not revealed any effect which indicates the existence of detector problem or simulation deficiencies.*

## Prospects for Run II

*Run II will have the potential to confirm these observations and allow a highly detailed study of this class of events.*
*Run II Advantage*
*All probability measurement will be performed “a priori” thanks to the pioneering work performed on the Run I data.*