Update on SBS Simulations

Andrew Puckett and Freddy Obrecht

University of Connecticut

SBS Weekly Meeting

3/3/2015

SBS Weekly Meeting 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 GeV2 conditions• RICH and GRINCH backgrounds under SIDIS conditions• GEM backgrounds for SIDIS conditions

• Ongoing projects

3/4/15

SBS Weekly Meeting 3

GRINCH Implementation

3/4/15

• 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

SBS Weekly Meeting 4

RICH update

3/4/15

• Virtually complete description of RICH aluminum box and steel shielding for PMTs from CAD drawings• New acceptance, PID performance and background studies under way

SBS Weekly Meeting 5

Full Experiment Monte Carlos—SIDIS

3/4/15

• 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 GEn high-Q2, 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

SBS Weekly Meeting 6

GEp geometry updates

3/4/15

ECAL shaped for acceptance matching with SBS (F. Obrecht), ~1,940 channels required assuming (4.2x4.2x45) cm3 lead-glass blocks

Final clamp geometry from drawings

Beamline correction magnet geometry included (V. Nelyubin)

SBS Weekly Meeting 7

ECAL details

3/4/15

Module dimensions:• Lead-glass 4.2x4.2x45

cm3

• 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

SBS Weekly Meeting 8

FPP Studies

3/4/15

• 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

SBS Weekly Meeting 93/4/15

Single scattering in FPP2

SBS Weekly Meeting 103/4/15

Single scattering in FPP1

SBS Weekly Meeting 113/4/15

Double scattering event

SBS Weekly Meeting 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

3/4/15

SBS Weekly Meeting 13

Efficient Recording of Complete Particle Histories

3/4/15

• 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

“Self-explanatory” layout of information in ROOT Tree

SBS Weekly Meeting 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 GeV2 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.)

3/4/15

SBS Weekly Meeting 16

ECAL energy resolution from GEANT4

3/4/15

• ECAL energy resolution under GEP high-Q2 conditions:• σE/E ~ 6% (averaged over full Q2 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?

SBS Weekly Meeting 17

ECAL position resolution from GEANT4

3/4/15

SBS Weekly Meeting 18

SIDIS Cherenkov Background Rates

3/4/15

• 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)

SBS Weekly Meeting 19

SIDIS GEM Backgrounds

3/4/15

SBS GEM tracker for SIDIS average hit rate at first plane ~

35 kHz/cm2 (10X below GEP case)

SBS Weekly Meeting 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

3/4/15

SBS Weekly Meeting 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

3/4/15