1. LCSW - Beijing, March 2010 ATF2 backgrounds1 What can we learn at ATF2 concerning ILC Backgrounds Hayg GULER LLR-Ecole Polytechnique Palaiseau, France

2. LCSW - Beijing, March 2010 ATF2 backgrounds2 Outline Background sources : ATF2 vs ILC Background measurements program at ATF2 Background measurement apparatus Plans for measurements in 2010

3. LCSW - Beijing, March 2010 ATF2 backgrounds3 Background Sources : ATF2 vs ILC

4. LCSW - Beijing, March 2010 ATF2 backgrounds4 Why ATF2 for background studies ? Good opportunity to test in accelerator environment some simulations tools which are used for LC to predict background (BDSIM, G4,...) Even if the energy is much lower, some effects can be studied like the machine related background (DUMP, Halo, Beam-Gas, … ) Also interesting to “test” some simulation methods, like event biasing Build background measurement detectors and methodology which can be used in other machines

5. LCSW - Beijing, March 2010 ATF2 backgrounds5 ILC background sources Machine produced background before IP o Beam tails (halo) from linac o Synchrotron radiation o Muons o Beam-gas scattering Beam Beam background @ IP o Bremsstrahlung o Coherent/incoherent pair production o Hadron production Spent beam background o Backscattering of particles (specially neutrons) D. Schulte, CERN, 2007

6. LCSW - Beijing, March 2010 ATF2 backgrounds6 ILC vs ATF2 background sources Machine produced background before IP o Beam tails (halo) from linac o Synchrotron radiation o Muons o Beam-gas scattering Beam Beam background @ IP o Bremsstrahlung o Coherent/incoherent pair production o Hadron production Spent beam background o Backscattering of particles (specially neutrons) D. Schulte, CERN, 2007

7. LCSW - Beijing, March 2010 ATF2 backgrounds7 Background sources @ ATF2 Synchrotron radiation : This is major background at FFTB experiment, but at ATF2, critical energy at bending magnet (assuming 1 Tesla) is about 1 keV. As a result, synchrotron photons can be easily stopped by beam pipe. Scattering with residual gas Because ATF2 beam line is relatively short (~50m), number of photons of this background is negligibly small. Beam halo scattering with beam pipe by Bremsstrahlung This is the major background in ATF2. It has large energy up to beam energy (1.3GeV), and large number of photons created without halo-cut components Particles from beam dump This may also be large background, but it can be eliminated by geometry, if we put the detector behind the beam dump.

8. LCSW - Beijing, March 2010 ATF2 backgrounds8 Measurement Program Forward background – Bremsstrahlung Beam Halo study Beam size  Background = f (β) Backscattered Background – Neutrons and Low energy E.M

9. LCSW - Beijing, March 2010 ATF2 backgrounds9 Simulation tools : BDSIM, GEANT4 BDSIM tool is a C++, Geant4 based (all physics processes from Geant4) Designed flexibly : adopting OO each beam-line element is constructed as separate object Accelerator tracking code : Inside beam-pipe new approach (CPU time consuming) otherwise “normal” G4 tracking inside materials Code used to predict background levels for ILC/CLIC

10. LCSW - Beijing, March 2010 ATF2 backgrounds10 Beam HALO Measurement From where the HALO has been generated ? From which ”parameters” does it depends ? o Beam tube gas pressure o Synchrotron radiation o Touschek scattering o Optics related effects (non scattering process) Possibilities @ ATF2 in HALO measurement o Measure the beam Halo @different positions (WS) o Study the Beam Halo transport o Measure the beam Halo @different beam conditions o Possibilities to extrapolate from Halo generated low energy background (photons, e+/e-) to high energy background for ILC (muons)

11. LCSW - Beijing, March 2010 ATF2 backgrounds11 Example losses vs Z (BDSIM) Possibilities from HALO distribution to deduce the Background using BDSIM Can be cross checked by dedicated measurement, very complicated multi-parameter system depending on : Beam conditions (accelerator parameters), Halo Simulation : geometry description, detectors, simulations methods HALO Measurement @ATF BDSIM Simulation : Input = 10σ Gaussian Halo

12. LCSW - Beijing, March 2010 ATF2 backgrounds12 Backscattered production Electromagnetic background o Low energetic photons o Backscattered electrons Hadronic background (neutrons) o Produced (mainly) by photo-productions o Slower component : nucleon-nucleon effects o Delayed from EM background o Use TOF to separate from EM background

13. LCSW - Beijing, March 2010 ATF2 backgrounds13 Hadronic background (neutrons) E.M backscattered background (γ,e-,e+) What's coming from the DUMP ? 1.3 GeV Electron Beam BDSIM Simulation electrons Photons Neutrons

14. LCSW - Beijing, March 2010 ATF2 backgrounds14 Neutron production for 3 ”models” QGSP Quark-Gluon string with precompound Precompound call nuclear desexitation routine 12 GeV → 50 TeV BERT BERTini cascade Unique evaporation model to de- excite the remnant nucleus Up to 10 GeV HP High precision neutron Allow precise transportation of neutrons LHEP Low and high energy parametrized Fast parametrized model based on GHEISHA Average energy and momentum are well described BDSIM user defined Hadronic Physics list

15. LCSW - Beijing, March 2010 ATF2 backgrounds15 Standard vs Biased simulations Stand alone G4 simulation Not yet implemented in BDSIM 50 e- simulated Simulation “standard” : ~1 Hit in detector / 10K e-

16. LCSW - Beijing, March 2010 ATF2 backgrounds16 Standard vs Biased simulations Simulation “standard” : ~1 Hit in detector / 10K e- 50 e- simulated Biased simulation : artificial multiplication of particles going in the left part of the DUMP

17. LCSW - Beijing, March 2010 ATF2 backgrounds17 Standard vs Biased simulations Simulation “standard” : ~1 Hit in detector / 10K e- 50 e- simulated Biased Simulation : ~500 Hit in detector / 10K e-

18. LCSW - Beijing, March 2010 ATF2 backgrounds18 Neutrons background predictions Event biasing is indispensable to predict Hits in a detector in case of rare event simulation

19. LCSW - Beijing, March 2010 ATF2 backgrounds19 Measurement apparatus

20. LCSW - Beijing, March 2010 ATF2 backgrounds20 What do we need ? ATF2 EM background is always made of a burst of particles. Measuring the energy deposit longitudinal profile may help to get information on photon spectrum. We also need to measure the neutrons and having detectors with different sensitivity to them would help. Separate neutrons from E.M. by using T.O.F Small and light detectors to be flexible in finding background sources in very crowded area

21. LCSW - Beijing, March 2010 ATF2 backgrounds21 Experimental setup Crowded FF area Modules can be assembled as longitudinally segmented calorimeter Tungsten slabs CsI Plastic Modules can be used individually Each module = {1 crystal + 1 PMT} Fast detectors :Pure CsI,Plastic,fast PMTs. CsI vs Plastic for sensitivity to neutrons CsI more sensitive to slow neutrons Plastic more sensitive to more energetic neutrons

22. LCSW - Beijing, March 2010 ATF2 backgrounds22 Cosmic test bench Detector box Record (x,y) position of muons Light collection as function of muon impact point on scintillator is extracted, and then, will be passed to the simulation of the detector response. Cosmic test bench @ LLR Cosmic bench test used at lab which records impact points and direction of incident muons. Allows to measure unbiased mips for PM intercalibration, and absolute calibration wrt simulation.

23. LCSW - Beijing, March 2010 ATF2 backgrounds23 Examples of observed signals (trigger = kicker) plastic CsI Direct EM peak from line Demonstrated by changing detector position. Fast neutrons from dump Slow neutrons from dump

24. LCSW - Beijing, March 2010 ATF2 backgrounds24 Forward background measurement Data taken during Shintake monitor shift during wire scans Charge = f(Time)

25. LCSW - Beijing, March 2010 ATF2 backgrounds25 Future plans Software & simulations : – Implement in BDSIM : FF geometry, realistic beamline (Magnet shapes), measurement modules – Event biasing methods in BDSIM (geometry biasing) – Realistic description of magnetic fields in optical element (Background off axis) Detector side : – New 2*4 channel oscilloscope to save data in EPICS to make correlations with beam & accelerator conditions Measurement side : – Background at different optics (as a function of β) during dedicated shifts – Systematic Halo measurements – Neutron production measurement (DUMP, Forward) – Beam-Gas, Backscattered E.M, S.R.,...

26. LCSW - Beijing, March 2010 ATF2 backgrounds26 Thank you !

27. LCSW - Beijing, March 2010 ATF2 backgrounds27 Items MESSAGE : On a besion de connaitre leur besoins !!! Background sources : ATF2 vs LC Measurements @ ATF2 – Tableau differents effets ATF2 vs ILC – ATF2 | ILC | commentaires How : experimental apparatus – Montrer signaux de PM plastic/CsI –

28. LCSW - Beijing, March 2010 ATF2 backgrounds28 Elastic scattering o Mott scattering : deflexion by the Coulomb potential of the particles in the residual gas o Elastic scattering changes the direction of the beam particles while the energy is not affected o Create Halo → Losses Inelastic scattering o Dominant process at high energy o Bremsstrahlung with the residual nucleon gas Beam gas scattering

29. LCSW - Beijing, March 2010 ATF2 backgrounds29 Wire Scanner generated background From (All) different Wire scanners  Study angular distributions  measurements in LW and Shintake area  measurement around area 1 and 2  PLIC group ?  TOF useful ? Wire Scanner generated background measurement 2 1

30. LCSW - Beijing, March 2010 ATF2 backgrounds30 Wire Scanner generated background measurement Independent G4 simulation Simplified simulation : WS + tube o need complete BDSIM simulation (Dipoles, Quadrupoles,...) Measure @ different-Z from WS the photon background Useful LW detector to cross check Useful Shintake detector ?

31. LCSW - Beijing, March 2010 ATF2 backgrounds31 Backscattered γ/X and neutrons: Use TOF to separate from Bremsstrahlung photons Possibility to measure neutrons, and be sensitive (?) to rebounds in the beam pipe Enough space to measure ? Backscattered γ/X and neutrons inside beampipe

32. LCSW - Beijing, March 2010 ATF2 backgrounds32 Backscattered neutrons from DUMP Measurements in 2007 at ATF using pure CSI detector E.M background Neutrons background ? Neutrons detection : Angular distribution around the DUMP Time of Flight (TOF) based measurements

33. LCSW - Beijing, March 2010 ATF2 backgrounds33 Backscattered neutrons from DUMP Neutrons detection : Angular distribution around the DUMP Time of Flight (TOF) based measurements

34. LCSW - Beijing, March 2010 ATF2 backgrounds34 TOF Neutrons @ different distances from DUMP: Fast/thermal neutrons discrimination Fast neutrons/EM background discrimination Backscattered neutrons from DUMP

35. LCSW - Beijing, March 2010 ATF2 backgrounds35 Can use Paraffin to moderate fast neutron to separate fast neutrons from thermal neutrons Backscattered neutrons from DUMP

36. LCSW - Beijing, March 2010 ATF2 backgrounds36 Background @ IP → 2 Origins Forward Background o E.M Bremsstrahlung : Halo hitting beampipe o Beam hitting wire scanner o Laser hitting beam Backward background o Backscattered neutrons background o Backscattered E.M background  (X rays, low Energy e-) BDSIM simulation @ IP → ATF2 beam line Gammas e- Neutrons Shielding necessary to measure only one component

37. LCSW - Beijing, March 2010 ATF2 backgrounds37 Backscattered Background @ different distances from beam DUMP Gammas e- Fast neutrons (E>5 MeV) Neutrons 1.3 GeV Electron Beam 2m3m4m5m BDSIM Simulation

38. LCSW - Beijing, March 2010 ATF2 backgrounds38 How ?

39. LCSW - Beijing, March 2010 ATF2 backgrounds39 Detector Concept Considering all constraints : o Money to build the detector o Places @ ATF2 to measure background o our measurement list/program Need a flexible (evolutive) detector Need a mobile detector Need an hybrid detector o To detect e.m background  X rays, gammas, electrons o Neutrons  Fast and slow component

40. LCSW - Beijing, March 2010 ATF2 backgrounds40 Our detectors – so far 3 pure CsI detectors o 60mm*60mm*20mm o UV filter (keep UV) 5 Plastic scintillators (BC-408) o 60mm*60mm*38mm Readout : o Photomultiplier o Oscilloscope Shielding ? o Needed for PMTs ? o Inside a detector box

41. LCSW - Beijing, March 2010 ATF2 backgrounds41 Detection devices 38mm 60mm 20mm 60mm Measured Background Plastic Scintillator Pure-CsI x 5x 3

42. LCSW - Beijing, March 2010 ATF2 backgrounds42 CsI crystals Pure CsI used @ATF/KEK: Fast (16ns decay time) but low light signal (2 γ/keV) Sensitive to full E.M + Nuclear background ☺ Can use PMT to ”collect” signal photons Don't need pre-Shower system Use TOF to separate neutrons from E.M background☺

43. LCSW - Beijing, March 2010 ATF2 backgrounds43 BC-408 plastic scintillators Useful to have a second detector which reacts in different way than pure-CsI o Different response to neutron detection o Can separate e- from gamma (use lead pre-shower or not) Very large light output ☺ Rise time : 0.9 ns Decay time : 2.1 ns Capability to separate neutrons from E.M background ? o Use TOF to discriminate neutrons from E.M background

44. LCSW - Beijing, March 2010 ATF2 backgrounds44 Possible detector design Lead Brick

45. LCSW - Beijing, March 2010 ATF2 backgrounds45 Detector Mobility The aim of the box detector is to measure background along the ATF/ATF2 beamline no definite place has been define one need to keep the flexibility the change the detector position as often as needed.

46. LCSW - Beijing, March 2010 ATF2 backgrounds46 Detector calibration November-December 2008 : o Recieve all crystals from Saint-Gobain o Build the detectors December-January : o E.M calibration :  Use radioactive sources @ LLR  Use DESY e- beam (1 to 6 GeV) o Calibration to neutron signal :  Need to calibrate neutron response :  Neutron beam @ saclay (France) ?  @KEK ? Others ?

47. LCSW - Beijing, March 2010 ATF2 backgrounds47 Time Schedule Detectors Mount and tests @LLR Detectors Mount and tests @LLR Detectors @ KEK First Measurements

48. LCSW - Beijing, March 2010 ATF2 backgrounds48 To measure list What

49. LCSW - Beijing, March 2010 ATF2 backgrounds49 Event Biasing in BDSIM → How ? Backround (Bremstrahlung) Backround (Bremstrahlung) Biasing

50. LCSW - Beijing, March 2010 ATF2 backgrounds50 Jane Tinslay - Geant4

51. LCSW - Beijing, March 2010 ATF2 backgrounds51 Movie BDSIM

52. LCSW - Beijing, March 2010 ATF2 backgrounds52 CsI vs Plastic scintillator (1 MeV)

53. LCSW - Beijing, March 2010 ATF2 backgrounds53 CsI vs Plastic scintillator (10 MeV)

54. LCSW - Beijing, March 2010 ATF2 backgrounds54 CsI vs Plastic scintillator (100 MeV)

55. LCSW - Beijing, March 2010 ATF2 backgrounds55 CsI vs Plastic scintillator (1 GeV)

56. LCSW - Beijing, March 2010 ATF2 backgrounds56 Hybrid The background @ ATF/ATF2 has an electromagnetic component generated by the electron beam HALO hitting the beampipe (and other accelerator components). In addition the electron beam hitting the beam dump generate backscattered electromagnetic background. The Hadronic component is mainly coming from the beam dump, mainly composed by backscattered thermal neutrons. The calorimeter “ final aim ” is to measure and characterize the background. One possible solution is to use different crystals sensitive to each background component (photons, electrons, thermal neutrons, fast neutrons,...).

57. LCSW - Beijing, March 2010 ATF2 backgrounds57 Use additionnal information Use WS information → Know beam Size Use LW information → Measure background = f(time) Use Shintake photon detector information o Measure background = f(time) Use PLIC information : measure beam losses = f(time) Goal : Have a detailled time dependent picture of the losses and background @ any place around the ATF2 area beamline

58. LCSW - Beijing, March 2010 ATF2 backgrounds58 Our plans in background measurement Forward background o Measure the beam HALO and transport o Measure the beam losses and compare to simulation (BDSIM) o Evaluate the beam-gaz scattering o Measure the backscattered electromagnetic background Characterize the hadronic background o Measure the backscattered neutron background from the beam DUMP (separate it from the E.M background) o Measure neutrons background @ any place o Test the neutron transport in BDSIM