# Presentation: 381521

## Photon Efficiencies

- Photon Selection
- Present Central Photon Cuts
- Differences to electrons
- Shape of cuts
- Measurement of Efficiencies
- Proposed Plug Photon Cuts

- Tracey Pratt

**http://www-cdf.fnal.gov/internal/physics/photon/photon.html**

## Photons Selection

- Aim is to select photon cuts which
- efficiently select ’s – so need to define what a photon is
- effectively distinguish ’s from backgrounds (mainly 0’s, also jets)

## Photon IdentificationVariables

- ’s deposit energy in the calorimeter
- Had/Em cut - not too much leakage into had calorimeter - distinguish from  a jet
- Isolated in calorimeter – distinguish from  a jet
- EM shower-shape (CES chi2) consistent with a  - distinguish from background 0
- <=1 track with pT<1 GeV pointing to EM cluster –
-     distinguish from *e*
- Track Isolation around  	- distinguish from jets
- 2nd CES cut to reject 0 → background

## Position of Photon CutsBaseline Analysis Cuts for High Pt Photons V2.1 

_**Variable **_			_**Cut **_
**Et ****	****	****	****	****> 7**
**Had/Em****	****	****	****< 0.125 || < 0.055 + 0.00045 * ECorr **
**Chi2 (Strips+Wires)/2.0****	****< 20 ****	***(unbiased cluster)*
**N track (N3D) ****	****	****<=1**
**Track Pt ****	****	****	****< 1+0.005*EtCorr GeV**
**Cone 0.4 IsoEtCorr ****	****        ****  EtCorr<20: < 0.1*EtCorr ****                                   ****	****EtCorr>20: < 2.0+0.02*(EtCorr-20.0) **
**Cone 0.4 Track Iso  ****	****	****< 2.0+0.005*EtCorr **
**2nd CES cluster E*sin(theta) (strip and wire) **
**	****	****	****	****EtCorr<18: < 0.14*EtCorr ****	****	****	****EtCorr>18: < 2.4+0.01*EtCorr **
**Fiducial****	****	****	****Ces |X|<21 cm, 9< Ces |Z|<230 cm **

**is this to allow for an underlying event?**

**what if higher E/had – a jet?**

**(new correction- see notes)**

*corrected for **** boundary leakage *

*and N**vertices*

##  Cuts, Different to e

_**Variable **_			_**Cut **_
**Et ****	****	****	****	****> 7**
**Had/Em****	****	****	****<**** 0.125**** || < 0.055 + 0.00045 * ECorr **
**Chi2 (Strips+Wires)/2.0****	****< 20 *****Cut on strips and wires separately******	******	******      ************ use unbiased cluster,****** e use track-seeded CES cluster***
**N track (N3D) ****	****	****<=1 *****require a track***
**Track Pt ****	****	****	****< 1+0.005*EtCorr GeV**
**Cone 0.4 IsoEtCorr ****	****             EtCorr<20: < 0.1*EtCorr                                 *****corrected for N******vert*****	****	****EtCorr>20: < 2.0+0.02*(EtCorr-20.0) **
**Cone 0.4 Track Iso  ****	****	****< 2.0+0.005*EtCorr **
**2nd CES cluster in same wedge (strip and wire)  *****no cut***
**	****	****	****	****EtCorr<18: < 0.14*EtCorr ****	****	****	****EtCorr>18: < 2.4+0.01*EtCorr **
**Fiducial****	****	****	****Ces |X|<21 cm, 9< Ces |Z|<230 cm **

**is this to allow for an underlying event?**

**what if higher E/had – a jet?**

- E*sin(theta)

- e cut on chis2 strips and wires separately –
- want a track
- iso not change above 20 GeV
- no 2nd CES cut

## Had/Em Sliding

**Expected had/EM from naïve shower model **

**systematic range**

**fake-event photons**

**fake-event electrons**

- Had/Em < 0.125 || < 0.055 + 0.00045 * ECorr

- CDF6560

- Sliding Had/Em : was imposed at trigger level, now <0.125
- 		  as E increases  shower length increases
- 			→ larger leakage into Had. cal.
- Or Had/Em < 0.125 : some evidence that  shower later than e
- 		→  deposit slightly higher Had/Em at low energies

- LOOK UP ECORR!! ASK RAY ***

- 4.9.1MC

- E GeV

- Had/Em

## Track Cuts
N track (N3D) 		<=1
Track Pt 			< 1+0.005*EtCorr GeV
Cone 0.4 Track Iso  		< 2.0+0.005*EtCorr 
Sliding Et cut from underlying event studies. Underlying Et in the event grows as the collision becomes more energetic.
Calorimeter Isolation Cuts
Cone 0.4 IsoEtCorr 	  
EtCorr<20: < 0.1*EtCorr
EtCorr>20: < 2.0+0.02*(EtCorr-20.0) 

- N track (N3D) 		<=1
- Track Pt 			< 1+0.005*EtCorr GeV
- Cone 0.4 Track Iso  		< 2.0+0.005*EtCorr
- Sliding Et cut from underlying event studies. Underlying Et in the event grows as the collision becomes more energetic.
- _Calorimeter Isolation Cuts_
- Cone 0.4 IsoEtCorr
- EtCorr<20: < 0.1*EtCorr
- EtCorr>20: < 2.0+0.02*(EtCorr-20.0)

**Track  & Caliso Sliding Cuts**

- >20: 2% from leakage correction as Energy increases, fluctuation in calorimeter energy increases: depends on √N

- <20: loose efficiency to reject bkgd,
- 	gain in signal/bkgd

## Measure Efficiencies

- Unlike *e* (which use* Z**→**ee*) can’t so easily study pure  data sample
*→ *Use  MC to determine efficiencies, then correct for differences between MC to data
- Corrections from:
*Z**→**ee *MC to data comparisions
- (for  cuts similar to electrons)
- Conversion MC to data comparisons
- (to study low energy ’s)
- Underlying event corrections

- Take an average

- average taken in CDF 6857 for W+gamma analysis

## Z→ee Efficiencies

*e*

*e*

*Z*

- Select *Z→ee* sample
- use 2nd leg to study efficiencies
- for  cuts applicable to electrons

- CDF 6857

- Use conversions to similarly study low energy 

-  Conlcude  data well described by the simulation

## Underlying Event Studies

- Look in random cone in the event (perpendicular to leading object in the event), see if cut is passed randomly
- Only calorimeter isolation f(ET) and 2nd CES cluster cut need to be corrected for UE
- additional studies as function of Nvertices (luminosity)

- CDF 6608, 6560

- Calorimeter isolation

**V****corr****=0.28*(N****vert****-1)**

-  (data
- 4.10.4)

- RAY – is this corrected in the IsoCorr code?

## Overall corrections

- CDF 6857

- Combination of the corrections:    	*Z**→**ee*                   	conversion                	underlying event studies
- Depends on QCD environment

- W corrections:  (relatively clean events)

## Proposed Plug Photon Cuts

_**Other potential cuts: **_
**delta-r PES-PEM **
**reject phoenix track **
**cut on number of Si hits in a cone **
**isolation in PES **

- Ask RAY PES 5/9?

- Ask RAY Why log E cut for had/EM

- _Differences to Central_
- No N3D track cut
- No 2nd PES cut
- PES 5/9

**Discussion?!**

## Notes on Plug photons

- Notes:
- The functions in the _[HLO photon library](http://cdfcodebrowser.fnal.gov/CdfCode/source/HighLevelObjects/src/Photon)__ and the __[Stntuple](http://ncdf41.fnal.gov/murat/Stntuple/Stntuple.html)__ determine the details. _
- To find Et, PPR energy is added to PEM, then corrected with em_alg::pemcorr. Et is then found using the vertex and PES position at PES z. Result is EtCorr.
- iso energy is corrected to the photon sin theta, corrected for leakage in phi and eta direction, and for number of vertices (from class>=12 ZVertexModule vertices).
- track iso is sum over all defTracks with z within 5cm of vertex and delta-R with photon <0.4.
- if a lepton is part of the analysis, and there is a vertex within 5cm the lepton, use the vertex, otherwise use the lepton z. If leptons are not an integral part of the analysis, use highest-sumPt z vertex (ZVertexModule).

## Conversion Studies

- Compare conversion MC to data similar to* Z**→**ee*
- Identify 2 legs of conversions, if one randomly chosen EmObject passes L3 trigger cuts, then use other leg from conversion as unbiased *e* to study efficiency
- Don’t study calorimeter isolation, N3D or track isolation with this sample, because most of 2 conversion legs falls into the neighbour CES wedge

*e*+

*e*-

- CDF 6857

## High Mass photon issues

- Do we need all of the cuts ?
- 		can we remove some to make efficiency higher?
- 		- e.g. allow conversions – loose 10 % eff. per photon

- code 4.11

- CDF 6560