Using direct photons to calibrate/monitor L1Calo

Hardeep BansilUniversity of Birmingham

L1Calo Joint Meeting, HeidelbergJanuary 11 – 13, 2010

Talk Outline

• Direct Photons• Motivation• Analysis• Results so far• Next steps• Data so far• Summary

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Direct Photons

• ‘Direct’ or ‘prompt’ photons originating directly from hard pp interaction

• Leading order processes – Compton (qg)

– Annihilation (qq)

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Francesca Bucci, 10/2008, Direct Photons at ATLAS

Direct Photons• Have a γj final state• Background from

‘fake’ photons created in the jet

• Long term strategy – Select events that were triggered by jet and get efficiency for γ (and vice versa)

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Direct photon event signature seen in ATLANTIS Event Display, Mark Stockton, Production of Direct Photons at ATLAS, 6-8/4/2009

Direct Photons• Jet and photon in event• Higher cross section than Z→ee (approx 2

orders of magnitude)

• γ complementary to e but still isolated5

Carminati, 28/8/2009

Motivation

• Using direct photons for:– Efficiency determination of electromagnetic and

jet triggers– Monitoring and calibration of L1Calo with physics

objects

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Analysis

• Using Athena version 15.5.1• Using Analysis package from John Morris

– with some modifications!

• Using MC Direct Photon data files– PYTHIA, √s = 10 TeV, pT > 150 GeV

• Get reconstructed offline photons in each event• Select the photon with highest ET

• Compare with EmTau RoIs

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Results so far• Distributions for highest ET offline reconstructed photons

• MC pT cut at 150 GeV – v. high

• Want to look at lower energies

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Results so far• Distributions for all EmTau RoIs• Not too different to offline photons

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Results so far

• Resolution in η, Δη = ηOfflinePhoton – ηEmTauRoI

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All Photons Direct Photons (> 50 GeV)

Results so far

• Resolution in φ, Δφ = φOfflinePhoton – φEmTauRoI

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All Photons Direct Photons (> 50 GeV)

Results so far• Calculate Δr = √((Δη)2+(Δφ)2) using offline photon and

EmTau RoI• Good photons have Δr < 0.4, ignore the rest (less than

5%)

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Results so far• Look at ‘triggered’ EmTau RoIs again (Δr < 0.4)• ET distribution matches offline highest ET

photon better

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• EmTau RoI v Offline Photon Energy– EmTau RoI energies seem higher than those for photons

Results so far

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Fake photons

Direct photons

Results so far• Resolution in ET = (ET,Phot- ET,RoI)/ET,Phot

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All Photons Direct Photons (> 50 GeV)

Results so far• Trigger Isolation Energy – observe ET behaviour when

isolation is / is not set for EmTau RoI thresholds• All γ

• Highest ET γ

Bit 01 – No Isolation, ET > 7 GeV Bit 05 – Isolation < 5 GeV, ET > 20 GeV

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Results so far• Efficiency in ET for EmTau RoIs =

RoI Δr < 0.4 & EM/TAU Threshold passedRoI Δr < 0.4

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Bit 06 – Isolation < 5 GeV, ET > 24 GeVBit 02 – No Isolation, ET > 14 GeV

Big loss at low ET

Results so far• Efficiency in ET – this time for offline photons

• Not as clean as for RoIs18

Bit 02 – No Isolation, ET > 14 GeV Bit 06 – Isolation < 5 GeV, ET > 24 GeV

Next steps

• Check code with other simulated direct photon datasets– Direct photons generated with lower ET threshold

• Comparisons of reconstructed offline photons with truth level

• Looking at real data!

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Data so far• Run 142193, 900 GeV, 152000 events in

dataset) – 101 medium offline electrons found• Still too low statistics to do proper analysis

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Juergen Thomas, 20/12/2009

Summary• Direct photons• Monitor / calibrate• Good results with current MC data• Look at more data

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Thank you for listening

Any questions / comments / suggestions?

Thanks to Paul Newman, Juraj Bracinik, Miriam Watson and Juergen Thomas for their help