Electron/ g physics in CMS

1. Electron/g physics in CMS Kati Lassila-Perini HIP Activities in the e/g working groupand 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 h Online selection and pilot run physics. New: HIP involvement in User Support.  Motivation and goals HIP CMS Software and Physics project evaluation

2. Activities in e/g group:Motivation and goals • The participation to the e/g activities motivated by: • experience in the previous H gg 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/g physics in the CMS environment • thorough knowledge of the photon and electron reconstruction and online selection. HIP CMS Software and Physics project evaluation

3. 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. Each point: different search areas in pixel layers Electron efficiency vs accepted jets HIP CMS Software and Physics project evaluation

4. 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. 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. Photons • Several items studied: • converted photons • photon energy corrections • photon position measurement • photon energy uncertainties and their impact on Hgg 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. 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) barrel with E9/Esc > 0.937 away from module borders seff = 0.99% seff = 0.96% seff = 0.87% HIP CMS Software and Physics project evaluation

8. Energy resolution for corrected energies • Photons from Hgg, pt > 40, 25 GeV/c • Photons at the module borders excluded HIP CMS Software and Physics project evaluation

9. 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. 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. Module Module borders Module border corrections • The measured energy is reduced at the module borders as the particle goes through less material. E1 E2 HIP CMS Software and Physics project evaluation

12. 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. Correctionfunctions Overall scale “ADC to GeV” r9 = E9/ESC Old Overall scale “ADC to GeV” Now h h Super clusters r9 = E9/ESC 5x5 Containment r1 = E1/E9 Containment r1 = E1/E9 or log(E1/E2) Containment log(E1/E2) +Module borders Module borders Module borders • 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. Error estimate for photon E measurement • The precision of the photon energy measurement is crucial for an early discovery of the Hgg 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 h(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, h, ln(E1/E2) at module borders and E. • The total uncertainty is taken as a maximum of different estimates: • take s = max(sr9,sr1,smod.borders,sE) • Each photon is given an uncertainty estimate which can be used in the event selection. HIP CMS Software and Physics project evaluation

15. Example: uncertainty due photon energy Barrel Endcap Divide Emeas/Egen in bins of E Number of events in each bin E<60GeV excluded For each bin, compute eff. RMS E<30GeV excluded from further fits HIP CMS Software and Physics project evaluation

16. Higgs mass resolution Select events with the combined uncertainty below a threshold. HIP CMS Software and Physics project evaluation

17. 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 h 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. Activities in e/g 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. 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/g connected items: • rate studies for start-up run • minimum bias signal from ECAL. HIP CMS Software and Physics project evaluation

20. Cross-trigger studies: L1 rates (kHZ) , L = 2.1033cm-2s-1 Muon from another event in the same bunch crossing HIP CMS Software and Physics project evaluation

21. 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. Conclusions and plans • We have had a fruitful and long-term involvement in the e/g 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! HIP CMS Software and Physics project evaluation