Absolute Calibration of Electromagnetic Calorimeter at LHC with Physics Processes

1. Absolute Calibration of Electromagnetic Calorimeter at LHC with Physics Processes Tao Hu, Lei Xia, Ren-yuan Zhu California Institute of Technology Pasadena, CA 91125, USA Calor 2002March 25 – 29, Pasadena, USA

2. Introduction • Absolute calibration of electromagnetic calorimeter is provided by physics processes with: • Clean final states with electrons (positrons) and/or photons • Clear physical constrains • Example: • Final state with 2 energetic electrons, constrains on Z mass and width • Using an algorithm of fitting the Z mass and line shape Calor 2002March 25 – 29, Pasadena, USA

3. Introduction: as an example • The algorithm converges after several iterations • The precision of this calibration is limited by statistics. • In the given plot, shows a statistics of 100 electrons per crystal. Calibration precision is better than 0.4% • To achieve better than 1%, a statistics of 25 electrons per crystal is needed Calor 2002March 25 – 29, Pasadena, USA

4. Introduction: useful processes at LHC • Z production: • Ideal final state and physics constrains for calibration, however has limited cross section • W production: • Need E/P matching, relies on the performance of the tracker • J/ψ and Υ(1s) production: • Advantage: both processes have large cross sections and clear physics constrains • Disadvantage: require a very low PT cut at level-1 trigger Calor 2002March 25 – 29, Pasadena, USA

5. Production Cross Sections: Z • CDF gave the cross section of inclusive Z production, followed by decay to muon pair • PYTHIA6.136: corresponding cross section at 1.8TeV • Compare the above two, we get k factor to Z production cross section is 1.35. We use it to estimate the cross section at LHC (14TeV) • PYTHIA: • Apply k factor: Calor 2002March 25 – 29, Pasadena, USA

6. Production Cross Sections: Z Calor 2002March 25 – 29, Pasadena, USA

7. Production Cross Sections: W • CDF gave the cross section of inclusive W production, followed by decay to an electron and a neutrino • PYTHIA6.136: corresponding cross section at 1.8TeV • Compare the above two, we get k factor to W production cross section is 1.33. We use it to estimate the cross section at LHC (14TeV) • PYTHIA: • Apply k factor: Calor 2002March 25 – 29, Pasadena, USA

8. Production Cross Sections: W Calor 2002March 25 – 29, Pasadena, USA

9. Production Cross Sections: J/ψ • CDF gave the cross section of inclusive J/ψ production, followed by decay to muon pair • PYTHIA6.136: corresponding cross section at 1.8TeV • Compare the above two, we get k factor to J/ψ production cross section is 4.62. We use it to estimate the cross section at LHC (14TeV) • PYTHIA: • Apply k factor: Calor 2002March 25 – 29, Pasadena, USA

10. Production Cross Sections: J/ψ Calor 2002March 25 – 29, Pasadena, USA

11. Production Cross Sections: Υ • CDF gave the cross section of inclusive Υ production, followed by decay to muon pair • PYTHIA6.136: corresponding cross section at 1.8TeV • Compare the above two, we get k factor to Υ production cross section is 2.41. We use it to estimate the cross section at LHC (14TeV) • PYTHIA: • Apply k factor: Calor 2002March 25 – 29, Pasadena, USA

12. Production Cross Sections: Υ Calor 2002March 25 – 29, Pasadena, USA

13. Trigger Efficiency & Event Rate • The key issue of using J/ψ or Υ channels is the level-1 trigger efficiency • Using CMS ECAL as an example, we can estimate the trigger efficiency and event rate • The level-1 trigger rate was calculated by using signal events generated by using CMSIM 121 for CMS detector response • ORCA_4_4_0_optimized was used to generate level-1 ntuples for each physics process • The level-1 trigger ntuples of QCD background for total trigger rate calculation was provided by Dr. P. Chumney and S. Dasu • We assume that the maximum acceptable total trigger rate is about 7.5 kHz Calor 2002March 25 – 29, Pasadena, USA

14. Trigger Efficiency & Event Rate Trigger efficiency and event rate for Z Trigger efficiency and event rate for W Calor 2002March 25 – 29, Pasadena, USA

15. Trigger Efficiency & Event Rate Trigger efficiency and event rate for J/Ψ Calor 2002March 25 – 29, Pasadena, USA

16. Trigger Efficiency & Event Rate Trigger efficiency and event rate for Y Calor 2002March 25 – 29, Pasadena, USA

17. Time needed for calibration • Time needed to reach a sub percent precision Calor 2002March 25 – 29, Pasadena, USA

18. Summary • Four physics processes has been studied for calibration of electromagnetic calorimeter at LHC • By using CDF data corrections factors, cross section of these processes were determined • As an example, level-1 trigger efficiency and event rate has been studied using CMS detector simulation • By using channel, about 1(0.5) year of data taking is needed at • A combination of all physics processes is needed at the beginning… Calor 2002March 25 – 29, Pasadena, USA