# Presentation: 669541

## SAME SIDE TAGGINGfor B meson decays

**Avdhesh Chandra**
**James Fast**
**17-Oct-2003**

- TIFR

## Data Sample 

** ****Skim file of all the J/********candidate events for set 1-21, ****~**** 114 pb****-1****   **
** ****To get B******** vertex we used d0root_btag V7.0**
** ****Muon p****T**** ****cut is 1.5**
** ****New Branch ****ATRK ****added,**** ****which stores all track information **
** ****maximum 150 track per event, with p****T**** ****> 0.251 **
**                  **
**                                      **_**B**__****__**  **__**event selection**_
** ****After making B******** vertex using d0root_btag following additional cuts are applied**
** ****J/********Cuts:   ****p****T**** ******** 1.5,    # of SMT hits ******** 1 ( on both tracks ), **
**                                           ****2.8 < M********< 3.3 Gev, ****    ********2 ****< 10**
** ****K********  ****Cuts:     ****chi2vtx < 10,         # of hits ******** 0,          p****T**** ****> 1.0**
** ****B********  ****Cuts:      ********2 ****< 20,                  collin. > 0.9,       dl_sig > 4.5**

## B – mass plot after selection

- Signal/Total = 0.546

- Mean =  5.27429
- Sigma = 0.042442
-                        (Mean  2.5 Sigma)
-     Total  =  1852
-    Signal  =  1012
-      Bkgd  =  840
-       S/B    =  1.204
-       S/T     =  0.546

## Same Side Tagging 

***In same side tagging we exploit the flavor-charge correlation, to tag initial b-flavor.***
***Correlation of charged particles is expected to arise from pion, produced along with the B – meson, in the fragmentation chain, and from B** decay***

- Simple picture of fragmentation paths for a b-bar quark

## One can try many variables to tag initial b – flavor, in same side tagging method, based on fragmentation model
We tried following variables ( in the vicinity of B-meson ) to tag the event from the candidate tracks
Maximum  pT   track
Minimum  dR  between B – meson and the candidate track
Minimum  (B–meson + track) mass
Minimum of  pTrel  
Minimum of  pLrel    , where   pTrel    and   pLrel   are defined below

**We tried following variables ( in the vicinity of B-meson ) to tag the event from the candidate tracks**
**Maximum  p****T****   ****track**
**Minimum  dR  between B – meson and the candidate track**
**Minimum  (B–meson + track) mass**
**Minimum of  p****T****rel **** **
**Minimum of  p****L****rel  ****  , where ****  ****p****T****rel    ****and   p****L****rel   ****are defined below**

- Drawing of the momentum vectors determining pTrel    and   pLrel  of an SST candidate track

## Algorithm

**We start with all tracks in a event having B******** **
**Removing all the muon tracks, and K******** ****tracks (used to make B******** **** vertex ) from all track bank**
**Applying track quality cut, i.e. track must have atleast 2 SMT and 3 CFT hists**
**Choosing only those tracks which are inside dR < 0.7  cone, around  B-meson direction, these tracks are called candidate tracks**
**Among candidate tracks, selecting a track(tag track) for each method**
**Returning the charge of the tagged track, say  Q****t**
**If          Q****t****   =  - Q****k     ******** correctly  tagged  B,**
**                    ****Q****t****  =   Q****k       ********  wrong  tagged  B,            otherwise ******** untagged B**
**Filling the histos for each case, after fitting calculating total number of events, correct tagged events, wrong tagged events and untagged events (N****T****, N****C****, N****W**** & N****U****)**
**                                               ****Dilution(D) =  (N****C**** – N****W****) / (N****C**** + N****W****)   **
**                                             ****efficiency(********)  =  (N****C**** + N****W****) / N****T**
**                                 ****Tagging Power(TP)  =   ********D****2**
**                                                                            ****Merit          =  Sqrt( TP*S*S / (S+B) )**

## Slide 7

## Slide 8

## Cone size  -- 0.7

- _Cone size  -- 0.7_

| (Method)
 Tagged 
   with |  Total #
   Of  
 events | Correctly
  tagged
  events |   Wrong
  tagged
  events |      (%)
 ( error ) |  D  (%)
 ( error ) | D2(%)
 ( error )
                  |
| --- | --- | --- | --- | --- | --- | --- |
|    Max. 
 pT track |  1012 |  500 |  291 |  79.2
   (2.1) |  26.4
  (4.8) |  5.5
 (2.0) |
|     Min.
     dR |  1012 |  501 |  302 |  79.2
   (2.1) |  24.8
  (4.7) |  4.9
 (1.8) |
| Min. (B+ trk) mass |  1012 |  471
 |  329 |  79.2
   (2.1)          |   17.8
   (4.8) |  2.5
 (1.3) |
|    Min.
    pTrel |  1012 |  483 |  321 |  79.2
   (2.1) |   20.1
   (4.7) |  3.2
 (1.5) |
|     Max.
    pLrel |  1012 |  497 |  304 |  79.2
   (2.1) |   24.1
   (4.7) |  4.6
 (1.8) |

## Attempt to match the CDF analysis

** ****We are already applying following cuts**
** ****J/********Cuts:   ****p****T**** ******** 1.5,    # of SMT hits ******** 1 ( on both tracks ), **
**                                  ****2.8 < M********< 3.3 Gev, ****    ********2 ****< 10**
** ****K********  ****Cuts:     ****chi2vtx < 10,         # of hits ******** 0,             p****T**** ****> 1.0**
** ****B********  ****Cuts:      ********2 ****< 20,                  collin. > 0.9,       dl_sig > 4.5**
** ****On top of above cuts, we applied following additional cuts to match CDF cuts **
**J/********Cuts:    ****|********|**** **** of both the muons    < 1.1**
** ****K********  ****Cuts:     ****p****T**** ****> 1.75       &         |********|**** **** < 1.1**
** ****B********  ****Cuts:      ****p****T**** ****> 4.5**
** ****All tracks:****   must  have      p****T**** ****> 0.4       &       |********|**** **** < 1.1**

_***Attempt to match the CDF analysis***_

## “CDF Cuts” results

- _Cone size  -- 0.7_

| (Method)
 Tagged 
   with |  Total #
   Of  
 events | Correctly
  tagged
  events |   Wrong
  tagged
  events |      (%)
 ( error ) |  D  (%)
 ( error ) | D2(%)
 ( error )
                  |
| --- | --- | --- | --- | --- | --- | --- |
|    Max. 
 pT track |  296 |  157 |  64 |  75.3
  (3.7) |  41.9
 (7.4) |  13.2
  (4.7) |
|     Min.
     dR |  296 |  149 |  77 |  75.3
  (3.7) |  31.5
 (7.4) |   7.5
  (3.5) |
| Min. (B+ trk) mass |  296 |  148
 |  73 |  75.3
  (3.7) |  33.9
 (7.2) |   8.7
  (3.7) |
|    Min.
    pTrel |  296 |  151 |  74 |  75.3
  (3.7) |   33.8
 (7.4) |   8.6 
  (3.8) |
|     Max.
    pLrel |  296 |  149 |  75 |  75.3
  (3.7) |   32.8
 (7.2) |   8.1
  (3.8) |

- “CDF Cuts” results

## “CDF cuts” B mass

- “CDF cuts” B mass

## Recent Work on the Analysis

**We were running d0root_btag V7**
**Some known problems**
******=79.4%, D****1****=26.4%, ********D****2****=5.5%**
**Ran with V8 of d0root_btag **
******=84.0%, D****1****=25.8%, ********D****2****=5.6%**

**With dca/sigdca<4, zca<5cm**
**Really a 2.3 sigma cut (see plot)  **
******=76.1%, D****1****=26.8%, ********D****2****=5.5%**

## Summary/Outlook

**We are getting good efficiency (~79%) with 0.7 cone size and ********D****2 ****  is ~3.0 % (average of all method) **
**We need  to understand, why there is a significant difference between tagging with (B+track) mass and other methods**
**High p****T**** tags are more effective, as expected**
**Maximum p****L**** rel. should in theory be best, but max p****T**** is better**
**We need to understand “CDF Run I cuts” results – Why so much better?**
**Refining analysis**
**Ran with V8 of d0root_btag: ********=84.0%, D****1****=25.8%, ********D****2****=5.6%**
**With dca/sigdca<4, zca<5cm:  ********=76.1%, D****1****=26.8%, ********D****2****=5.5%**
**Code is being integrated into bflavor_tag package**
**Working on Monte Carlo**
**B spectrum is too soft**
**Tag track spectrum is too soft**

## Mean ~ 4.3

- Mean ~ 3.4

- Mean ~ 6.4

- Mean ~ 5.3

## Slide 16

## Slide 17

## Slide 18

## Slide 19