Table of Contents

Inclusive direct photon measurements using 2011 data

R.Blair, S.Chekanov, R.Norberg, M.Stockton, plus the Direct Photon group

Public results ATLAS-CONF-2013-02

Current CDS note: http://cdsweb.cern.ch/record/1453853

ATLAS note using 4.9 fb-1

The current note is located here: https://svnweb.cern.ch/trac/atlasphys/browser/Physics/StandardModel/PromptPhotons/Notes/InclusivePhotons3fb How to get and work with it:

Outside CERN:

/usr/kerberos/bin/kinit   <username>@CERN.CH

(or just kinit <username>@CERN.CH). Then find the note:

export SVNROOT="svn+ssh://svn.cern.ch/reps/atlasphys/Physics/StandardModel/PromptPhotons/Notes/InclusivePhotons3fb"

Getting the note:

svn co $SVNROOT

This will create a directory “InclusivePhotons3fb”. “cd” into it and compile the package “make”. Always make sure that you keep the most recent directory “svn update”.

Modify a file, then do “svn ci” and put notes. To remove a file, use “svn remove file”. To add file, use “svn add file”.

Read here howto use SVN: https://twiki.cern.ch/twiki/bin/viewauth/Atlas/SoftwareDevelopmentWorkBookSVN

Old instruction:

The current note is located here: 
[[https://svnweb.cern.ch/trac/atlasusr/browser/chekanov/Physics/Photons/Notes/InclusivePhotons2011]]
How to get and work with it:
Outside CERN: 
/usr/kerberos/bin/kinit   <username>@CERN.CH
export SVNUSR="svn+ssh://svn.cern.ch/reps/atlasusr/chekanov"
Getting the note: 
svn co $SVNUSR/Physics//Photons/Notes/InclusivePhotons2011
This will create a directory "InclusivePhotons2011". 
"cd" into it and compile the package "make". Always make sure that you keep the most recent directory "svn update".
Modify a file, then do "svn ci" and put notes. To remove a file, use "svn remove file". To add file, use "svn add file".
Read here howto use SVN: [[https://twiki.cern.ch/twiki/bin/viewauth/Atlas/SoftwareDevelopmentWorkBookSVN]]

Status of the final results

Systematical and statistical errors added in guadrature.

Green bads shows the renormalisation scale uncertanty plus PDF uncertainties from 52 eigenvectors of CT10 PDF. Yellow-gray band shows the renormalisation uncertanty only.

Here is a plot with 2010 cross sections (extended to 25 GeV)

Selection cuts, data and Monte Carlo models

We follow the general recommendations described here

Current selection cuts:

2011 data:

iLumiCalc.exe –lumitag=OflLumi-7TeV-002 –livetrigger=L1_EM14 –trigger=None –xml=/tmp/lumifiles/795b77/data11_7TeV.periodAllYear_DetStatus-v18-pro08-05_CoolRunQuery-00-03-98_GammaJet.xml

  1. Total Luminosity: 1.072 fb-1
  2. NTUPLE_PHOTON sample
  3. Event selection: 1 PV having at least 3 tracks and EF_g80_loose trigger. See: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/CaloIsolationCorrections

Photon selection:

  1. ph_goodOQ rejection
  2. isEM & 0x800000 – AR cut (missing B-layer)
  3. if ( !( (ph_OQ&34214)==0) )
  4. if ( ( (ph_OQ&134217728)!=0 && (ph_reta>0.98||ph_rphi>1.0||(ph_OQ&67108864)!=0)))
  5. pT(γ)>100 GeV and |η (γ)|<1.37  and  1.52<|η (γ)|<2.37
  6. Isolation cut at 7 GeV. We use Etcone40_corrected that has both the leakage and ambient energy density pileup corrections applied.
  7. Pile-up reweighting using the standard PileupReweighting tool

PYTHIA  simulation

  1. Signal gamma+jet: 108082 (70 GeV),   108083 (140 GeV), 108084 (280 GeV), 119079 (500 GeV)
  2. QCD  (JF sample): 105814 (70 GeV),    105815 (140 GeV),  105812 (240 GeV)

HERWIG simulation (only for systematics on efficiency)

  1. Signal gamma+jet: 108092 (70 GeV), 108093 (140 GeV), 108094 (280 GeV), 119078 (500 GeV)

All samples are weighted according to their cross sections and generated efficiencies

General MC status is given here

Pile up

MC simulations include pile-up as shown in this figure: det_nPV.eps.png

Isolation plots

Isolation in bins of pT

Isolations for signal and background

Detector-level distributions

Detector level pT in the region A and D

Look also at the background region:

Detector level pT after the side-band backgroud subtraction. We use a simple backgrown subtraction (non-correlated) due to small statistics for MC. We use correlated quadrant method as systematics.

Systematical uncertainties so far

  1. Isolation cut is changed by - 1 GeV
  2. Isolation cut is changed by + 1 GeV
  3. Photon energy scale is propogated for converted and non-converted photons (separately). *Down variation*
  4. Photon energy scale is propogated for converted and non-converted photons (separately). *UP variation*
  5. HERWIG for efficiency correction - next
  6. Using a simple data-driven approach without assumptions on correlations between A,B,C,D regions
  7. Using alternative pile-up reweighting based on comparing nPV with the data

The tables below show the contributions of each systematic variation in % to the total cross section:

The total systematic uncertainty is calculated by addeding all uncertainties in quadrature.

Bin-by-bin corrections for the central cuts and for systematical uncertainties

Bin-by-bin correction factors are defined as C= N(true photons after isolation)/N(reconstructed in the region A). The efficiency is 1/C.

Purity calculations

Purity is defined as N(after bkg subtraction)/N(region A).

Gamma plus jet measurements

This measurement is based on the inclusive analysis above by adding a antiKT4 jet.

* det_gamma_jet_mass.eps.png - M(gamma+jet) using the quadrand A for photons

JETPHOX predictions

The JETPHOX predictions are based on the JETPHOX V1.3 (ROOT-based) generating ROOT ntuples using the pT ranges as for the final plots. This technique is descibed on the CERN Twiki

4 different JETPHOX ntuples were generated. First sample has 44 PDF sets, 2 other are used to estimate PDF and scale variations, changing one scale at the time. Additional sample was generated by changing the scale and PDF scales coherently.

PDF uncertainties are calculated by taking a max deviation from the central value.

Scale uncertanties were estimated by considering the largest deviation from the central value using different combinations of the scale and PDF uncertainties.

Here are the cuts:

ROOT files and figures

All figure are here: All figures

Root files and tables are available here: All root files

Jetphox prediction: here

Direct-photon group: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/SMDirectPhotons

Our wiki: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/PhotonJetAtANL

JetPhox wiki: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/SMDirectPhotonsPhotonJetCS

Theory papers: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/SMDirectPhotonsBiblio


Sergei Chekanov 2011/09/02 22:07