electron/ g physics in cms

HIP CMS Software and Physics project evaluation 1/2222.5.2006

Kati Lassila-Perini/HIP

Electron/ physics in CMS

Kati Lassila-PeriniHIP

• Activities in the e/ working group and connected physics analysis.

– electron HLT: jet rejection by pixel matching– electron isolation studies– simulation and reconstruction validation– fast simulation validation– photon position and energy corrections– error estimates in photon energy measurement.

• Test beam studies of ECAL module– cluster containment as a function of

• Online selection and pilot run physics.• New: HIP involvement in User Support.

Motivation and goals



Activities in e/ group:Motivation and goals

• The participation to the e/ activities motivated by:– experience in the previous H studies– possibility of an efficient and visible contribution– connection to the tracker activities (converted photons,

electrons)– possibility of participating in beam studies before the LHC

start-up.

• We have achieved – wide recognition of the quality of our work– understanding of the e/ physics in the CMS environment– thorough knowledge of the photon and electron reconstruction

and online selection.



Jet rejection for electrons at HLT

• The event rate of electron at the High Level Trigger (HLT) is dominated by neutral pions from jets– An algorithm developed and optimized by us for an early and

quick identification of electron by looking at the corresponding hit in the inner tracking system.

Electron efficiency vs accepted jets

Each point:different search areasin pixel layers



Validation of the new G4 simulation

• We have validated the electromagnetic part of the new G4 simulation in CMS– at the transition phase GEANT3 (cmsim) GEANT4 (OSCAR)– at several OSCAR releases.

OSCAR_3_6_0

OSCAR_2_4_5



Validation tools for fast simulation

• A tool was developed for an easy comparison between full (OSCAR) and fast (FAMOS) simulation– E and pos. resolution– shower shape variables.



Photons

• Several items studied:– converted photons– photon energy corrections– photon position measurement– photon energy uncertainties and their impact on H

mass resolution– implementations of these items in the PhotonCandidate

class in the reconstruction software.

• People involved:– KLP– Jukka Nysten, graduate student– former members:

• Mikko Voutilainen, summer student, Masters’ thesis • Timo Aaltonen, summer student.



Energy corrections

• The correction logic:– First, shift the peak to Erec/Etrue = 1 (a single scaling factor).

– The corrections bring the tail in, but should not move the peak

Photons (5x5) barrelwith E9/Esc > 0.937

away from module borders

eff = 0.99% eff = 0.96%

eff = 0.87%



Energy resolution for corrected energies

• Photons from H, pt > 40, 25 GeV/c

• Photons at the module borders excluded



Position measurement

• The position optimized for electrons gave a visible shift for unconverted photons.

• The depth parameter T0 was optimized for photons.

• The position of photon candidates is now recalculated with the new value.



Endcap: unconverted photons, position

Eff.RMS = 3.66% Eff.RMS = 2.88% Eff.RMS = 1.18% Eff.RMS = 1.80%



Module border corrections• The measured energy is reduced

at the module borders as the particle goes through less material.

Module

Module borders

E1 E2



Module border corrections

• Corrections defined• Exclusion region where the spread is so large that correction

cannot be made



Supe

r cl

uste

rs

Correction functions

Overall scale“ADC to GeV”

r9 = E9/ESC

Containmentr1 = E1/E9

Containment log(E1/E2) +Module borders

Module borders

5x5

Overall scale“ADC to GeV”

r9 = E9/ESC

Containmentr1 = E1/E9 or log(E1/E2)

Module borders

Old

Now

• Correction logic was implemented in the PhotonCandidate class• The implementation was streamlined with the transfer of the code to the

new CMSSW in mind: readability of the code, no fancy technicalities.



Error estimate for photon E measurement

• The precision of the photon energy measurement is crucial for an early discovery of the H signal.

• Photon energy measurement may be degraded due to several factors:

– shower shape (due to the conversions in the tracker material)– shower position with respect to the crystal boundaries and module boundaries– shower position in (due to different geometrical shape of the crystal array)– shower energy (a feature of the calorimeter).

• These uncertainties have been estimated from simulated data and parameterized as functions of r9 = E9/Esc, r1 = E1/E9, , ln(E1/E2) at module borders and E.

• The total uncertainty is taken as a maximum of different estimates:– take = max(r9,r1,mod.borders,E)

• Each photon is given an uncertainty estimate which can be used in the event selection.



Example: uncertainty due photon energyBarrel Endcap

Number of events in each bin

E<60GeV excluded

E<30GeV excluded from

further fits

Divide Emeas/Egen in bins of E

For each bin,compute eff. RMS



Higgs mass resolution

Select events with the combined uncertainty

below a threshold.



ECAL test beam studies

• Motivation:– many energy correction have only been studied with simulated

data, now, there is a chance to validate them with real data.

• Goals:– study the effect of shower position in to the energy

containment in a limited size cluster.– comparison with the simulation.

Simulation Test beam data



Activities in e/ group:Conclusions

• We have contributed to many areas in the photon and electron reconstruction.

• Many of the items we have been active in do not produce publications

– this is a known risk career-wise (and for evaluations…)– we feel that our choice has been correct and our engagement to not so

grateful tasks has been highly valued in the collaboration.• The physical ideas have been turned to software, now in CMS we

are transferring this knowledge to a new software system (ORCA CMSSW).

• We have decided to reduce our activities in the area of reconstruction software development

– as a small institute and as physicists (and not sw engineers) we think that rewriting the same code is not where we can best contribute.

• But: we will continue test beam analysis and connected studies in other areas such as online selection at the LHC start-up .



Online selection

• Motivation:– data-taking is approaching: quick involvement with the early

LHC data.

• Goals:– get a thorough understanding of the triggering process and its

impact on the physics analysis.

• Projects:– cross-trigger studies– e/ connected items:

• rate studies for start-up run• minimum bias signal from ECAL.



Cross-trigger studies: L1 rates (kHZ) , L = 2.1033cm-2s-1

Muon + Jet Et > 60 GeV

Jet Et > 100 GeV

METEt > 40 GeV

METEt >60 GeV

pt >5 GeV/c 0.38 0.15 0.033 0.0

0.21 0.025 0.008 0.001

pt >10 GeV/c 0.23 0.10 0.017 0.0

0.044 0.005 0.0015 0.0002

Electron + Jet Et > 60 GeV

Jet Et > 100 GeV

METEt > 40 GeV

METEt >60 GeV

pt >10 GeV/c 9.6 1.3 1.1 0.05

pt >15 GeV/c 1.9 0.42 0.77 0.03

pt >20 GeV/c 0.48 0.15 0.70 0.03

Muon + Electron pt > 10GeV/c

Electronpt > 15GeV/c

pt >5 GeV/c 3.8 0.63

0.32 0.1

pt >10 GeV/c 0.79 0.18

0.065 0.02

Muon from another eventin the same bunch crossing



User support

• CMS has opened Computing positions inviting contributions from participating countries.

• We have decided to contribute ½FTE to the post of CMS User Support Coordinator starting from May, the 1st, 2006.

– to supervise the documentation for computing and software processes– to setup a unified user support gateway– to continue analysis in order to be well familiar with the tools.

• Our proposal has been accepted by the CMS management– the experience with the CMS software and analysis and the background

as a physicist and user were especially appreciated.

• Motivation:– possibility of a visible and useful contribution – user support knowledge in an institute is valuable.

• Goals:– to understand the needs of the user support for a collaboration like CMS– to build a user-friendly and up-to-date documentation system– to monitor the evolution of the user support needs in time.



Conclusions and plans

• We have had a fruitful and long-term involvement in the e/ working group.

• With the data-taking approaching, we are modifying our priorities– reduced activities in the electron and photon reconstruction software

development– continuing involvement in the ECAL test beam analysis– new activities in the online selection.

• New engagement as a CMS User Support Coordinator.• We are looking forward to the start of the data-taking!

electron/ g physics in cms

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