MAP 2014 Spring Workshop Fermilab 27-31 May, 2014 Accelerator Physics Center Computational Issues Sergei Striganov Fermilab MAP 2014 Spring Workshop Fermilab 27-31 May, 2014

Outline MARS-EGS Occupancy estimates Conclusion

MARS vs MARS-EGS5 Background energy spectra Background entrance into detector

Gamma flux: entrance to detector vs entrance to nozzle Gamma flux: entrance to detector vs entrance to nozzle. Beam pipe – 5 cm radius, nozzle minimal radius – 2 cm vertical coordinate horizontal coordinate Maximum at positive (negative) entrance to nozzle and negative (positive) entrance to detector – backscattering from nozzle jaws!

Electron flux: entrance to detector vs entrance to nozzle Electron flux: entrance to detector vs entrance to nozzle. Beam pipe – 5 cm radius, nozzle minimal radius – 2 cm vertical coordinate horizontal coordinate Maximum at positive (negative) entrance to nozzle and negative (positive) entrance to detector – backscattering from nozzle jaws!

Nozzle geometry – 2 vertex setups Maximum at entrance to nozzle = 2 cm, entrance to detector = -5cm Maximum at positive (negative) entrance to nozzle and negative (positive) entrance to detector – backscattering from nozzle jaws! Simulation of backscattering very sensitive to details!

Hit calculations Hit definition: charged track left sensitive volume + charged track is stopped in sensitive volume. To estimate occupancy we need to perform simulation for chosen pixel size. Appropriate electron transport threshold should be determined as function of pixel size. Electron/positron from background files produced only 3% of background in vertex and tracker detectors. Above difference between MARS-EGS5 and MARS electron/positron simulation does not important for Higgs factory backgrounds calculation. In MARS minimal energy of produced δ-electron Ed= electron transport threshold. Number of produced δ-electron ~ 1/Ed .

Simple estimate of occupancy Simulations were performed with MARS background files in EGS5 mode with 3, 10, 20, 30 keV thresholds. Number of charged tracks leaving detector weakly depends on Ed , number of stopped tracks is proportional ~ 1/Ed . Low energy δ-electron are produced with large angle to δ-electron direction. Part of them is stopped in same pixel as track going from this pixel. To avoid double counting we need to choose adequate electron transport threshold. Electron ranges in silicon: 3 keV – 0.14 μm, 10 keV – 1.5 μm, 20 keV – 5 μm, 30 keV – 10 μm. Probability to stop in neighbor pixel: energy < 10 keV energy < 3 keV 5 μm 30% 2.8% 10 μm 15% 1.4% 20 μm 8% 0.7% 10 keV is close to estimated from above 20 kev is minimal estimate for 5 μm 30 kev is minimal estimate for 10 μm 10 keV estimate is only 30% large than 30 keV estimate in simulation. .

Occupancy in vertex detector (3 keV threshold) name hit/cm2 5x5 μm, % 10x10 μm,% 20x20 μm,% Barrel 1 2.3 104 1.2 4.8 19.2 Barrel 2 2.2 103 0.11 0.44 1.8 Barrel 3 542 0.43 Barrel 4 559 0.45 Endcup 1 8.9 103 0.2 0.8 3.6 Endcup 2 5.7 103 0.57 2.26 Endcup 3 3.6 103 0.36 1.45 Endcup 4 1.2 103 0.5

Occupancy in vertex detector (10 keV threshold) name hit/cm2 5x5 μm, % 10x10 μm,% 20x20 μm,% Barrel 1 1.3 104 0.66 2.64 11 Barrel 2 1.3 103 0.06 0.24 9.6 Barrel 3 300 Barrel 4 142 0.1 Endcup 1 4.9 103 0.49 1.96 Endcup 2 3.1 103 0.31 1.64 Endcup 3 1.9 103 0.20 0.80 Endcup 4 662 0.26

Occupancy in vertex detector (30 keV threshold) name hit/cm2 5x5 μm, % 10x10 μm,% 20x20 μm,% Barrel 1 1.1 104 0.53 2.12 8.48 Barrel 2 1.1 103 0.05 0.2 0.8 Barrel 3 234 0.19 Barrel 4 111 0.09 Endcup 1 3.9 103 0.39 1.56 Endcup 2 2.3 103 0.24 0.94 Endcup 3 1.5 103 0.15 0.60 Endcup 4 581 0.23

Summary There are significant differences in energy spectra and entrance point distribution of background electrons/positrons calculated using MARS-EGS and MARS. Most of electrons coming to detector through beryllium beam pipe are produced by backscattering of high energy electron on nozzle jaws. Simulation of backscattering is very delicate procedure and should be checked. MARS-EGS and MARS results for gammas are in satisfactory agreement. About 97% of hits in vertex&tracker are produced by neutrals (gamma and neutrons), so problem with electron simulation does not important for this application. Precise calculation of occupancy calculation impossible without detail simulation of detector. But it is possible to make estimate with about 30-50% accuracy.

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