1. Update on SBS Simulations Andrew Puckett and Freddy Obrecht University of Connecticut SBS Weekly Meeting 3/3/2015

2. Outline Progress in geometry description: GRINCH ECAL Beamline RICH Others Other code developments: More detailed ROOT output More robust data structures, consistent “look and feel” of ROOT Tree “Self-explanatory” and “Self-documenting” root trees Recent simulation results: ECAL energy and coordinate resolution under GEP 12 GeV 2 conditions RICH and GRINCH backgrounds under SIDIS conditions GEM backgrounds for SIDIS conditions Ongoing projects 3/4/15SBS Weekly Meeting2

3. GRINCH Implementation 3/4/15SBS Weekly Meeting3 GEANT4 model developed by H. Yao (W&M) imported to g4sbs framework To-do: update PMT quantum efficiency (currently based on RICH PMTs) Detailed description of containment volume Understand and mitigate sources of background

4. RICH update 3/4/15SBS Weekly Meeting4 Virtually complete description of RICH aluminum box and steel shielding for PMTs from CAD drawings New acceptance, PID performance and background studies under way

5. Full Experiment Monte Carlos—SIDIS 3/4/15SBS Weekly Meeting5 SIDIS event generator based on DSS2007 fragmentation functions and CTEQ6 PDFs, built into g4sbs C++ without external dependencies Investigation of beamline shielding for SIDIS starting: Challenging background environment: more forward angles than G En high-Q 2, similar luminosity, more challenging magnetic field DIS e- in BigBite at 30 deg. SIDIS hadrons in SBS at 14 deg. Toy model of beamline lead shielding “Bare bones” He-3 target in air, 60 cm thick, glass windows—magnetic shielding and collimation of backgrounds needed

6. GEp geometry updates 3/4/15SBS Weekly Meeting6 ECAL shaped for acceptance matching with SBS (F. Obrecht), ~1,940 channels required assuming (4.2x4.2x45) cm 3 lead- glass blocks Final clamp geometry from drawings Beamline correction magnet geometry included (V. Nelyubin)

7. ECAL details 3/4/15SBS Weekly Meeting7 Module dimensions: Lead-glass 4.2x4.2x45 cm 3 Air gap 0.45 mm Mylar wrapping 0.15 mm Optical properties: Index of refraction, PMT quantum efficiency, mylar reflectivity, TF1 chemical composition, etc. taken from old GEANT3 code Equilibrium transparency under thermal annealing and GEP conditions from S. Abrahamyan model Active channels surrounded by steel “ filler ” blocks to fill out rectangular structure Side view of the same event showing C’kov radiation and propagation (bars optically isolated from each other) Horizontal staggering of blocks  improve coordinate resolution

8. FPP Studies 3/4/15SBS Weekly Meeting8 New, more detailed ROOT output will allow complete analysis of FPP particle multiplicity, energy and angular distributions—analyze systematics of polarimetry, test charge-exchange polarimetry feasibility Neutrons Pions Protons

9. 3/4/15SBS Weekly Meeting9 Single scattering in FPP2

10. 3/4/15SBS Weekly Meeting10 Single scattering in FPP1

11. 3/4/15SBS Weekly Meeting11 Double scattering event

12. Other new code developments for g4sbs Ability to define geometry, material, or other calibration parameters from text file “databases” at run time First use case: complicated ECAL geometry “Detector Maps”—Track correspondence between channel/copy numbers and physical locations in the ROOT output so the end user doesn’t have to “Dynamic” ROOT Trees: Create experiment-specific ROOT tree branches—only write data for sensitive detectors active during the run based on (unique) sensitive detector names “Self-explanatory” and “self-documenting” ROOT trees More detailed and meaningful post-event processing of hits in detectors: extensive use of STL containers to avoid double-counting of “hits” when particles have multiple tracking steps in a sensitive volume—built into ROOT output rather than requiring subsequent analysis Fully dynamically sized “hit” arrays in ROOT output using STL vectors No fixed-size arrays uniform “look and feel” of ROOT trees 3/4/15SBS Weekly Meeting12

13. Efficient Recording of Complete Particle Histories 3/4/15SBS Weekly Meeting13 For each sensitive detector, record PID, momentum and vertex info for all unique particles involved in producing any hits in a sensitive detector Each particle is only recorded once per detector in which it was involved in making hits Trace particle history all the way back to primary particles Expensive for heavy, showering detectors (calorimeters) Can be enabled/disabled for individual detectors in user scripts

14. “Self-explanatory” layout of information in ROOT Tree

15. ECAL resolution studies (Obrecht) Implemented clustering algorithm from GEP-III in ROOT macro Used threshold of 3 photoelectrons to define “good” hits Average number of photoelectrons ~ 450/GeV Elastic ep events under GEP 12 GeV 2 conditions Select events with good proton track in SBS Assume highest-energy cluster is the elastically scattered electron (in elastic ep simulation, this assumption almost always works, other “clusters” are low-energy, delta-rays etc.) 3/4/15SBS Weekly Meeting15

16. ECAL energy resolution from GEANT4 3/4/15SBS Weekly Meeting16 ECAL energy resolution under GEP high-Q 2 conditions: σ E /E ~ 6% (averaged over full Q 2 acceptance of ECAL) (little to no energy dependence of resolution) Somewhat worse than what would be expected from photoelectron statistics—more shower fluctuations due to Eloss in front materials?

17. ECAL position resolution from GEANT4 3/4/15SBS Weekly Meeting17

18. SIDIS Cherenkov Background Rates 3/4/15SBS Weekly Meeting18 PRELIMINARY RICH (left) and GRINCH (right) counting rates for SIDIS configuration Caveats: results obtained with “bare-bones” He-3 target in air—target is only ~1/3 of material along beamline More effective shielding and collimation of target can reduce rates Investigation of background sources for Cherenkov counters ongoing using (new) detailed particle histories RICH: 700 kHz/PMT average (0.7% occupancy for 10 ns window) GRINCH: 3.8 MHz/PMT average (3.8% occupancy for 10 ns window)

19. SIDIS GEM Backgrounds 3/4/15SBS Weekly Meeting19 SBS GEM tracker for SIDIS average hit rate at first plane ~ 35 kHz/cm 2 (10X below GEP case)

20. Ongoing projects—To-Do list Describe HCAL and BigBite calorimeter geometries Define beamline shielding and target collimation for SIDIS Understand and suppress Cherenkov backgrounds Get realistic field maps for all configurations GEP polarimetry studies: energy, angular distributions and particle multiplicities Charge exchange Add spin tracking Interface MC data to Hall A analyzer Improve event generators—address “minimum bias” concern from DOE review More detailed trigger simulations Documentation and user support 3/4/15SBS Weekly Meeting20

21. Summary and conclusions Major developments of g4sbs facilitate deeper analysis Significant progress toward complete experiment description Code in JLab-managed repository on github: https://github.com/JeffersonLab/g4sbs/ Latest developments available in “uconn_dev” branch Mostly tested and debugged Work in progress Documentation and user “how-to’s” forthcoming Acknowledgements: SBS Simulation and DAQ group 3/4/15SBS Weekly Meeting21