here are updated preliminary recommendations and associated tools from the egamma group for analyses using data up to TS3 (targeting more particularly HCP).

The use of the large data sample and the full set of MC12 events currently available has been allowing a thorough checks of the electron and photon performance. As it has been reported during the egamma plenary presentation at the ATLAS week, the current (ICHEP) recommendations are still found to adequately describe our understanding of the performance.

Therefore only few additions and changes are introduced w.r.t the ICHEP recommendations, mainly reflecting changes in conditions occurred after TS2 and some reduction of systematics derived from a better understanding, specifically:

1) Electron Trigger SF (accounting for new data periods and updates for the old ones)

2) Energy Scale in the crack region (accounting for the ITC cells recalibration in the Tile introduced after the TS2)

3) Photon Efficiency Systematics (improvement of 20-50% w.r.t. ICHEP, depending on the eta/Et region)

The tag including all these changes is egammaAnalysisUtils-00-03-55. Few extra information are added below for your convenience. All the relevant information can be reached from the twiki:
https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/Egamma2012Analyses

In addition, we would like to remind that at the end of August few refined recommendations concerning 2011 performance have been circulated, namely:

4) New Energy Scales with significantly improved associated systematics for both electrons and photons

5) Final photon efficiency measurements for cut-based PID with systematics at the level of 1-2% [ATLAS-CONF-2012-123]

*These recommendations should now be used by the analyses producing results with 2011 data.*

Once more, we would like to underline the dedicated and restless work of our egamma colleagues on understanding and improving the performance, only partially reflected on these recommendation updates. This effort is in fact still underway to provide more refined measurements and techniques ready to be exploited by the physics analyses producing results with the full Run I dataset.

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1) Electron Trigger SF

For 2012 we are adopting time-dependent trigger SF to account for the changes introduced online during the year, motivated by improvement in performance and/or rate. Trigger SF (G4 and AF2) for the new periods are provided, as well as updated SF for periods before TS2 are included on egammaAnalysisUtils-00-03-55 tag or above. More information and details can be found in the twiki: https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/EfficiencyMeasurements2012

2) ES for crack

The recalibration of the ITC cells (in particular E3/E4 used in the cluster energy calculation in the crack) prompted a 3% shift in the egamma energy response, as measured with Z events. The ES corrections (alphas) for the bin in eta corresponding to the crack is therefore different for data before and after TS2. The EnergyRescalerUpgrade tool for the tag egammaAnalysisUtils-00-03-55 or above, accept now a RunNumber as entry, based on which the correct ES for the crack region is returned.
More information and details can be found in the twiki:
https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/EnergyScaleResolutionRecommendations#2012_August_Recommendations

3) Improved systematics for photon ID efficiency

The new recommended systematics for 2012 photon efficiency measurement are reported in the twiki:
https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/PhotonID2012

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here are the preliminary recommendations and associated tools from the egamma group for 2012 data analyses, targeting more particularly ICHEP:

1. Generalities, electron and photon identification, technicalities
2. Electron efficiency measurements and associated systematics
3. Photon efficiency measurements and associated systematics
4. Electron and photon energy scale and resolution in the central region (|eta|<2.47)

These recommendations are preliminary and reflect the current understanding of the e/gamma performance on early 2012 data. A few pieces are missing (see below), while further cross-checks still need to be completed. Therefore, if necessary, updates are not excluded in the next few days and will be announced through the egamma HN.

As usual, more details are linked from the main egamma page: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/ElectronGamma under "Recommendations for data analysis", together with the other egamma recommendations.


Here is a brief summary:

1. Generalities, electron and photon identification, technicalities

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The released set of calibration and scale factors allows to concretize, for use in physics analyses, all the work made since several months to maintain/improve the egamma performance in the harsh pile-up conditions in 2012 data. To this effect, significant improvements have been incorporated at all levels (trigger, reconstruction, identification), reflecting for instance in:
- a higher reconstruction efficiency, thanks to the refitting with GSF of all tracks associated to electromagnetic clusters and a better track-cluster matching;
- a higher pile-up robustness of all reconstructed quantities and of the identification selection (PID) for both electrons and photons (online and offline).

Compared to the first PID optimisation put at the trigger level and in offline release 17.2, the first 2012 data have shown that a further tuning was necessary (mainly due to changes in some shower shapes variables at high eta implied by the use of new LAr optimal filtering coefficients) to preserve a high identification efficiency. As a consequence, until an AODFix accounting for these changes will be deployed, the offline PID for central electrons and photons in both AOD and D3PDs are not up-to-date and therefore should NOT be used. Instead, the correct electron/photon identification MUST be retrieved with a macro applied at analysis level
--> electron PID: egammaAnalysisUtils-00-03-16 (or higher), IsEMPlusPlusDefs for loose++, medium++, tight++ and MultiLeptonDefs for MultiLepton menu
--> photon PID: PhotonIDTool-00-01-06, tight tune 2012. This applies to both data and MC. This also applies if you skim your analysis ntuples.

Moreover, the z-vertex spread being different between data and MC, a tool is provided in the egammaAnalysisUtils package to reweight the MC z-vertex distribution.

More details, useful for 2012 data analyses (including event/object selections, trigger, isolation usage recommendations, ...) are given here: https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/Egamma2012Analyses

2. Electron efficiency

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Preliminary scale factors for reconstruction and identification efficiencies have been measured for central (|eta|<2.47) isolated (DeltaR(e,jet)>0.4) electrons with ET>7 GeV, using 2012 data and MC12a fully simulated samples.

As usual, C++ macros are provided to apply these scale factors and their uncertainties, using a factorisation of the measured SF dependencies along eta and Et.

Identification SF are provided for the four recommended operating points (loose++, medium++, tight++ and MultiLepton), using 20 eta bins from -2.47 to 2.47 (including the crack region). The typical uncertainties are of the order of <1% at high Et (>30 GeV), ~2% for [15-20] GeV bin and ~7% for ET<15 GeV.

Scale factors and associated uncertainties for reconstruction efficiency are also provided in the same 20 eta bins (no Et dependency).

All these preliminary scale factors and associated uncertainties have been incorporated in the egammaSFclass package of egammaAnalysisUtils-00-03-18.

Trigger efficiency SF will be made available for the recommended single electron (e24vhi_medium1 || e60_medium1) and di-electron (2e12Tvh_loose1) triggers. As the online trigger criteria have been changed twice at high eta (to mitigate the problem described in point 1., see above), time dependent trigger efficiency/SF are necessary and will be given as soon as feasible.

More details: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/EfficiencyMeasurements2012

3. Photon efficiency

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The use of the efficiency values from Monte Carlo corrected by Fudge-Factor method is the recommended option for ICHEP results. The Fudge Factors have been computed by comparing all shower shapes observed in 2012 data and JF17+JF35+JF70+JF140 MC12a samples. --> Use FudgeMCTool (tag FudgeMCTool-00-00-16) with the preselection 13

The preliminary systematic uncertainty on efficiency to be considered for photons above 30 GeV is 5% in the barrel calorimeter region (|eta|<1.37) and 7% in the endcaps (1.52<|eta|<2.37). This is based on very first results on data-driven measurements from electron extrapolation with Z to ee Tag&Probe. More data driven measurements with 2012 data are underway to better constrain these systematics.

More details: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/PhotonFudgeFactors

4. Calibration

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Calibration studies have been performed from 2012 Z to ee data vs. MC12a comparison. The use of new LAr Optimal Filtering coefficients in 2012 data induces an eta-dependent few per mill change in the energy scale as compared to 2011. Therefore, the intercalibration factors, to be applied to data, have been updated in the EnergyRescalerTool (in egammaAnalysisUtils-00-03-18) for central electrons, using 34 eta bins from -2.47 to 2.47 (including the crack region). The Monte Carlo smearing has also been updated and is now provided using a finer granularity (12 eta-bins), to better take into account that the larger resolution observed in data is mostly coming from the 1.5<|eta|<1.8 region of the end-caps.

The systematics on energy scale and smearing are unchanged w.r.t last round, while functions have been added to access separately the three components of energy scale uncertainties (material, presampler energy scale and the rest). As a reminder, the calibration of the crack region has been reoptimised at the reconstruction level, so the ad-hoc function provided for 2011 MC/data should not be used anymore for 2012 MC/data.

More details: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/EnergyScaleResolutionRecommendations

We would like to underline the hard and dedicated work of our egamma colleagues, allowing to get these preliminary results ready in time for ICHEP, despite the very challenging schedule. This effort is still underway to provide more refined measurements and improved performance.