1. Hall D Photon Beam Simulation and Rates Part 1: photon beam line Part 2: tagger Richard Jones, University of Connecticut Hall D Beam Line and Tagger Review Jan. 23-24, 2006, Newport News

2. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 2 I. Photon Beam Line Simulation estimate background rates estimate background rates evaluate options for shielding evaluate options for shielding 1.has a detailed model of coherent bremsstrahlung 2.describes the detailed beam line geometry, fields 3.simulates electromagnetic processes accurately 4.includes photonuclear interactions at some level To accomplish these goals, we need a Monte Carlo simulation that:

3. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 3 Photon Beam Line Simulation Detailed photon beam line simulation: HDGeant  has built-in coherent bremsstrahlung generator to simulate beam line with a realistic intensity spectrum  beam photons tracked from exit of radiator  assumes beam line vacuum down to a few cm from entry to primary collimator, followed by air  beam enters vacuum again following secondary collimator and continues down to a few cm from the liquid hydrogen target  includes all shielding and sweep magnets in collimator cave  monitors background levels at several positions in cave and hall The same simulation also includes the complete GlueX target and spectrometer, detector systems, dump etc.

4. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 4 Geant3plus: HDGeant: all of the std Geant3 physics models, plus:  muon pair production  modified Geant to turn a fraction of the e - e + pairs into μ - μ +  cross section formulas translate simply m e m   rates are down by factor (m e /m  ) 2 -- but not insignificant  photonuclear reactions  large mass of data on these cross sections, not all relevant  final results will depend on hadronic interactionsin any case.  final results will depend on hadronic interactions in any case.  GELHAD package from BaBAR was adopted   N quasi-elastic scattering, single  + /  0 production,  +  - production (vector dominance model), p+n emission (quasi-deuteron model) Photon Beam Line Simulation

5. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 5 Photon Beam Line Simulation Hall D collimator cave tagger building vacuum pipe Fcal Cerenkov spectrometer cut view of simulation geometry through horizontal plane at beam height

6. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 6 Photon Beam Line Simulation overhead view of collimator cave cut through horizontal plane at beam height collimators sweep magnets iron blocks concrete lead 12 m air vac

7. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 7 Photon Beam Line Simulation Hall D collimator cave tagger building vacuum pipe Fcal Cerenkov spectrometer cut view of simulation geometry through horizontal plane at beam height virtual detector plane x z

8. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 8 Photon Beam Line Simulation Development : Progress so far :  Simulation has been used to optimize the amount and placement of shielding in the collimator cave.  Study of background rates in the GlueX start counter and trackers are being used to constrain the design of those detectors. Ongoing development:  The Hall D team is working with the Jlab RadCon group to cross- check our rate results for the Hall D beam line.  Elements from HDGeant (geometry, coherent bremsstrahlung generator, fields) have been shared, and many things checked.  Latest results (P. Degtiarenko) are consistent with conclusions based on previous Hall D studies. results follow  Some errors have been corrected: results follow

9. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 9 Beam Energy Spectrum: photon energy (GeV) counts

10. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 10 Background Rates: z = -1 m particle flux (/cm 2 /s)

11. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 11 Bethe-Heitler muons radial position (cm) flux (muons/cm 2 /s)  + /  – flux vs. position pair production in the collimator. At these energies, the primary source of muons is pair production in the collimator. within an order of magnitude of cosmic rays. With appropriate shielding (included in the simulation) the rates at the detector are within an order of magnitude of cosmic rays.

12. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 12 II. Photon Tagger Simulation estimate background rates in focal plane counters estimate background rates in focal plane counters evaluate options for shielding evaluate options for shielding 1.detailed field map of the tagger 2.design for the vacuum box downstream exit region 3.focal plane hodoscope model Elements needed for tagger simulation (in addition to beam line)

13. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 13 Photon Tagger Simulation cut view of simulation geometry through horizontal plane at beam height goniometer quadrupole magnet tagger dipoles vacuum chamber to electron beam dump Hall D Tagger Building fixed array hodoscope microscope photon beam line detailed magnetic field map (from TOSCA) 350 x 30 x 1600 = 17 M points

14. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 14 Photon Tagger Simulation CB events begin with a CB ,e - pair inside the diamond radiator beam emittances realistic for the 12 GeV machine electron tracked in the magnetic field of the quadrupole and dipoles focal plane scintillators are “sensitive volumes” photon beam exits from tagger inside vacuum, continues 70 m down to collimator cave without leaving vacuum Runge-Kutta method 1 mm Kaptonhodoscope exit window is 1 mm Kapton 1 cm Alother walls of vacuum chamber are 1 cm Al exposed side of electron exit channel is 5 mm Al

15. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 15 Photon Tagger Simulation GlueX Detector Review report One issue highlighted in the GlueX Detector Review report, October 2004: energies close to the endpoint the vacuum chamberor the dump pipe A potential concern is the high flux of electrons with energies close to the endpoint interacting with the mechanical structure of the vacuum chamber or the dump pipe. Because of the shallow bend angle of the spectrometer, downstream spray could cause background in the tagging detectors. Recommendation: Recommendation: Perform a Monte Carlo simulation of the tagging system with particular attention to background in the tagging counters caused by high-energy electrons.

16. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 16 Photon Tagger Simulated Events concrete wall

17. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 17 Photon Tagger Simulation Resolution in focal plane microscope in energy and emission angle

18. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 18 Photon Tagger Simulation monitor all particles reaching one of the central fibers of the FP microscope gammaspositrons electrons gammas only all hits, single fiber all hits, combine neighboring hits

19. Richard Jones, Hall D Beam Line Tagger Review, Newport News, Jan 23-24, 2006 19 Summary A complete set of tools for detailed physics simulation has been developed covering the Hall D Photon Beam and Tagger systems. Backgrounds at the entrance to the detector and also at the tagger focal plane have been examined. The shielding for the collimator region has been optimized based on the simulation, leading to acceptable background rates in the GlueX detector. Backgrounds coming from the exit region of the tagger vacuum will be minimized using the simulation by refining the mechanical design and optimizing the shielding in that area.