# Presentation: 425548

## Use of the D0 Central Preshower in Electron Identification

- John Gardner
*University of Kansas*
- APS   April 6, 2003

## Outline

- 1) Location of the Central Preshower
-    in the D0 Detector
- 2) Purpose & Design
- 3) Matching to particles
- 4) Electron id analysis

## The D0 Detector (central)

- The D0 Detector (central)

- Calorimeter

## The Central Preshower (CPS)

- -compensates for resolution
-  loss due to the solenoid
- -particles travel through two
-  radiation lengths of material
- -causes showering where
-   energy spreads out like a cone
- -the CPS provides both energy
-   and position measurements
-   while this cone is still small

- Sideview of a ttbar event going through the CPS

##    Design

- x u v

-  -provides coverage for  || < 1.25 (and  1.4 < || < 2.5 with FPS)
-        -three layers                           - divided into two halves at
-   (3 cm total thickness)                     positive and negative z

- 

- z

## CPS Layers

- x

- u

- v

- -  x strips run parallel to the
-    beam (z axis)
- -  (to get a z position)
-    have u and v layers
-    with a 23o slant to x
- - 7680 total scintillating fiber
-    strips (1280 per layer per side)
- - 4.9 mrad (or 3.6 mm)
-   strip separation
- - resolutions (will improve)
-      z: ~3mm ,   phi: ~1.5mm

## Clustering

- _single layer clusters (SLC's):_
-   formed when particles passing through the CPS deposit energy
-   in one or more adjacent strips
- _3D clusters:_
-   formed where SLC's  from all 3 layers intersect

- 3D cluster

- SLC centroid

- z

- 

## Ghosts

- - fake 3D clusters which occur where SLC's from
-   different particle tracks coincide
- - limit the number of 3D clusters which can share a SLC
- - use position an energy based matching qualities to
-   decide which are kept

- Example
- of a ghost

## CPS - Track Matching

- -a 3D cluster is a match to a particle track if
-  its distance (dr) is smaller than the dr_cut

- Example
- of track
- with one
- cps match

## Electron ID Analysis

- -_GOAL_:  demonstrate that the CPS can distinguish
-   between jets and electrons
- - use two types of data samples
-    1) fake electrons using back to back jets
-    2) good electrons from diem events
- - both fake and good electrons pass the  same
-    tight electron cuts (including a track match)
- - require a cps-track match and see what percent
-   of each is kept

## Data Samples

- _Fake electrons_:
- -  use qqbar events with back to  back jets where one
-    passes tight electron cuts
- - other jet must also pass
-   hard jet cuts

- _Diem electrons_:
- - events used are in this in
-   this Z-> ee peak

## Cut Parameters

- - keep a particle if these cuts are satisfied
- _dr_cut:_
-     - require at least one 3D cluster within dr_cut
-       distance from track
- _dr_iso:_
-     - must not have any 3D clusters between a
-       distance of dr_iso and 20 cm from the track
-     - this cut takes advantage of expectation that
-       diem electrons are isolated

## Quality

- - define a quality to decide
-    best choice of parameters:
- - vary the two parameters, dr_cut and dr_iso, while
-    keeping track of highest quality

-    (% diem kept)
-    (% fakes kept)

- =

- 2

-   - dr_cut comparison

- - dr_iso comparison

## Results and Conclusions

- - using the values 1.05 cm for dr_cut and 3.90 cm
-   for dr_iso yields the highest quality: 2.6 with
-      85% of diem electrons kept and
-      28% of fakes from jets kept
- -This demonstrates that the CPS can discriminate
-   between qcd jets and diem electrons
- -More work is needed to both improve this result
-   and demonstrate other cases where the CPS is useful