TOWARDS PARAMETRIZATION OF DETECTOR BACKGROUND

1. Fermilab Accelerator Physics Center TOWARDS PARAMETRIZATION OF DETECTOR BACKGROUND Sergei Striganov Fermilab MAP 2012 Winter Meeting SLAC March 8, 2012

2. Motivation To obtain current background files we need about 7 days x 24 CPU. This files are about 2 Gb size. To calculate background from one bunch in exclusive approach we need to simulate 23 times more decays. To study bunch-to-bunch simulations we need at least 100 bunches. So, we need increase 2300 times our CPU and memory consumption. Is it real in near future? “Parameterization” of background can be convenient way to resolve this problem. “Parameterization” does not mean set of fits, but some algorithm which provide possibility to extrapolate background properties studied in large number of decays to huge number of decays equivalent to 100 bunches.

3. Background simulation Black hole - interface surface Muon decay points are simulated randomly from -200 to 200 m from IP. Muon position and angle is sampled from precalculated accelerator structure functions. Electron/positron has large momentum and small angle relatively muon trajectory, so it could flight inside beam pipe few meters before start shower in accelerator elements. Simulation is stopped at interface surface – entrance to detector. Following results were obtained with cutoff energies (±25 m from IP): gamma, e± - 200 keV neutron - 100 keV muon, charged hadron – 1 MeV. Towards Parametrization of Detector Background - S. Striganov

4. Where is Background Produced?Number of Particles Entering Detector Towards Parametrization of Detector Background - S. Striganov

5. Where is Background Produced?Energy Flow Entering Detector Towards Parametrization of Detector Background - S. Striganov

6. Fluctuation of background energy coming into detector : for bunch Ndec = 1.1128 107 Background sample contains results of 480000 decays from 26 meters. To estimate energy fluctuation lets look at distribution of 1000 energies coming from 480 decays, 100 energies coming from 4800 ... Other way – calculate energy distribution from ONE decay. One can use RMS of this distribution to calculate width of energy distribution from large enough numbers of decays. For bunch decaying along 26m fluctuation of background energy coming into detector are not large => RMS=1500 GeV Small subbunch # Towards Parametrization of Detector Background - S. Striganov

7. Fluctuation of number of background particles coming into detector: for bunch Ndec = 1.1128 107n gamma e+- ch hRMS/MEAN= .001 0.003 0.003 0.009 Small subbunch # Towards Parametrization of Detector Background - S. Striganov

8. Correlation between different particle type (10x4.8 10^4 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

9. Correlation between different particle type (30x1.6 10^4 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

10. Correlation between different particle type (30x1.6 10^4 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

11. Energy fluctuation vs number of particle fluctuations (10x4.8 10^4 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

12. Energy per particles vs number of particles (10x4.8 10^4 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

13. Energy per particles vs number of particles (30x1.6 10^4 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

14. Correlations in background muon production Background muons are coming from -200 to 200 m from IP. This background is produced in 1.71 108 decays. Total number of muon entering into detector is small – 8 103 ( 23 GeV/muon): Background muons are produced in independent decays, so there are no correlation between background muons. Background muons are produced in very small number of decyas, therefore correlation between muons and other background particles produced in large number of decays are negligible. MAP 2012, SLAC, March 8, 2012 Towards Parametrization of Detector Background - S. Striganov

15. Hadrons, gammas and electrons production Average number of decays which produce other background particles from one side (mostly in muon decays from 25 to -1 m) is 1.11 10 7 Only 17% of decays produce background, products of other decay are stopping in accelerator component, shielding, rock. “Successful” decay produce in average: 47 gammas (0.9 MeV per gamma) 0.27 electron/positron (5.7 MeV per electron) 1.8 neutrons (4.2 MeV/neutron) 2.1 10-3 charged hadrons ( 257 MeV/hadron) MAP 2012, SLAC, March 8, 2012 Towards Parametrization of Detector Background - S. Striganov

16. Event display: background particles at detector entrance:gammas, neutrons andelectrons MAP 2012, SLAC, March 8, 2012 Towards Parametrization of Detector Background - S. Striganov

17. Spatial Distribution at Detector Entrance Most of particles come to detector through nozzle surface (±6m) ; for muons this fraction is 30% Background (except muons) on nozzle surface weakly depends on azimuthal angle m+ beam MAP 2012, SLAC, March 8, 2012 Towards Parametrization of Detector Background - S. Striganov

18. Entrance point of gammas vs number of gammas (3x3.2 10^5 decays from 25 to -25 m) Towards Parametrization of Detector Background - S. Striganov

19. Entrance point of neutrons vs number of neutrons (3x3.2 10^5 decays from 25 to -25 m) Towards Parametrization of Detector Background - S. Striganov

20. Entrance point of electrons vs number of electrons (3x3.2 10^5 decays from 25 to -25 m) Towards Parametrization of Detector Background - S. Striganov

21. Entrance point of charged hadrons vs number of charged hadrons (3x3.2 10^5 decays from 25 to -25 m) Towards Parametrization of Detector Background - S. Striganov

22. Spectra of gammas vs number of gammas (3x1.6 10^5 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

23. Spectra of electrons vs number of electrons (3x1.6 10^5 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

24. Spectra of neutrons vs number of neutrons (3x1.6 10^5 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

25. Spectra of ch hadrons vs number of ch hadrons (3x1.6 10^5 decays from 25 to -1 m) Towards Parametrization of Detector Background - S. Striganov

26. Space and momentum distribution vs number of particle It look likes that space/momentum distributions do not depend on number produced particles ( at least at current statistical accuracy). Background particles even in small spots (about 10 cm radius on interface surface) are produced in hundreds-thousands independent decays, so there are no correlation between them. We do not need expensive “exclusive” simulation to calculate space-momentum distribution of background particles on interface surface. We can simulate this distribution using “inclusive” approach much faster and with better statistical accuracy.

27. “No-correlation” model Simulation algorithm: 1) Sample number of gammas using Gaussian distribution with known mean and rms 2) Calculate number of electron using relation 3) Sample number of neutrons, muons, charged and other neutral hadrons using Gaussian distribution with known mean and rms. 4) For each particle type generate coordinates on interface surface, momentum component and arrivinig time from precalculated distributions, which do not depend on number generated particles.

28. Conclusions Current sample of background particles does not contradict simple “no-correlation” model. Is it possible to simulate bunch-to-bunch fluctuation using this model and current background files. To perform same study in “exclusive” approach we need enlarge background files about 2000 times. We can calculate space-momentum-time distributions for different particle type using “inclusive” approach. This approach provide possibility to obtain same statistical accuracy with smaller CPU consumption.