electron/ g physics in cms
DESCRIPTION
Electron/ g physics in CMS. Kati Lassila-Perini HIP Activities in the e/ g working group and connected physics analysis. electron HLT: jet rejection by pixel matching electron isolation studies simulation and reconstruction validation fast simulation validation - PowerPoint PPT PresentationTRANSCRIPT
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
HIP CMS Software and Physics project evaluation 2/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 3/2222.5.2006
Kati Lassila-Perini/HIP
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
HIP CMS Software and Physics project evaluation 4/2222.5.2006
Kati Lassila-Perini/HIP
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
HIP CMS Software and Physics project evaluation 5/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 6/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 7/2222.5.2006
Kati Lassila-Perini/HIP
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%
HIP CMS Software and Physics project evaluation 8/2222.5.2006
Kati Lassila-Perini/HIP
Energy resolution for corrected energies
• Photons from H, pt > 40, 25 GeV/c
• Photons at the module borders excluded
HIP CMS Software and Physics project evaluation 9/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 10/2222.5.2006
Kati Lassila-Perini/HIP
Endcap: unconverted photons, position
Eff.RMS = 3.66% Eff.RMS = 2.88% Eff.RMS = 1.18% Eff.RMS = 1.80%
HIP CMS Software and Physics project evaluation 11/2222.5.2006
Kati Lassila-Perini/HIP
Module border corrections• The measured energy is reduced
at the module borders as the particle goes through less material.
Module
Module borders
E1 E2
HIP CMS Software and Physics project evaluation 12/2222.5.2006
Kati Lassila-Perini/HIP
Module border corrections
• Corrections defined• Exclusion region where the spread is so large that correction
cannot be made
HIP CMS Software and Physics project evaluation 13/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 14/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 15/2222.5.2006
Kati Lassila-Perini/HIP
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
HIP CMS Software and Physics project evaluation 16/2222.5.2006
Kati Lassila-Perini/HIP
Higgs mass resolution
Select events with the combined uncertainty
below a threshold.
HIP CMS Software and Physics project evaluation 17/2222.5.2006
Kati Lassila-Perini/HIP
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
HIP CMS Software and Physics project evaluation 18/2222.5.2006
Kati Lassila-Perini/HIP
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 .
HIP CMS Software and Physics project evaluation 19/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 20/2222.5.2006
Kati Lassila-Perini/HIP
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
HIP CMS Software and Physics project evaluation 21/2222.5.2006
Kati Lassila-Perini/HIP
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.
HIP CMS Software and Physics project evaluation 22/2222.5.2006
Kati Lassila-Perini/HIP
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!