Forward Region and Beam-Beam-Background

1. Forward Region and Beam-Beam-Background André Sailer (CERN) CLIC Physics and Detector Meeting 21st July, 2009

2. Outline • Backscatters from Beam-Beam-Background • Detector Model • Forward Detectors • Magnetic Field Options • AntiDID, DID, Only Solenoid • Distribution of Incoherent Pairs on Forward Region • Backscattering and Background in the Vertex Detector André Sailer, LC Physics/Detector Meeting

3. Background Studies • Studying the Amount of the Beam-Beam-Backgrounds in the Detector at CLIC • Special Focus on • the impact of the Magnetic Field on the Background • Only Solenoid, AntiDID, DID • Background in the Vertex Detector (VXD) • How to reduce the Background? André Sailer, LC Physics/Detector Meeting

4. Detector Model • CLIC01_ILD • Vertex Detector • 3 double Layers at R=31/45/60mm • All layers 25cm long • 50 µm Active Silicon • Threshold: 3.4 keV • 4 Tesla Magnetic Field • Hadronic Calorimeter • 8.5λ • Absorber: Tungsten, 1cm thick, 77 layers Vertex Detector André Sailer, LC Physics/Detector Meeting

5. X Z Changes in the Forward Region • Crossing Angle • From 14 to 20 mrad • Final Quadrupole • L* = 3.5 m • Iron around both Beam pipes • Later in this talk: Changed to current QD0 Design • Removed LHCal • BeamCal • Start Z=3.2m • Inner Radius: 20mm ILD00_fw LHCal Quad LumiCal BeamCal CLIC01_ILDfwp02 André Sailer, LC Physics/Detector Meeting

6. LumiCal • Centered on Outgoing Beam axis • Sandwich Calorimeter • 30-40 Layers • 3.5 mm Tungsten Absorber • ~0.3 mm Silicon • At ILC used to • Measure Bhabha Events to determine Luminosity • Covered by Iftach's Talk • http://indico.cern.ch/conferenceDisplay.py?confId=47144 André Sailer, LC Physics/Detector Meeting

7. IP BeamCal Side • Centered on Outgoing Beam axis • Sandwich Calorimeter • 30/40 Layers • 3.5 mm Tungsten Absorber • ~0.5 mm Radiation Hard Sensor • ~10 MGy/Year • Diamond, GaAs…? • Silicon in Detector Simulation • At ILC used for • Beam Parameter Measurements through Beam-Beam-Pairs • Electron Veto of SM Events • Masking for Inner Detectors • Smallest Aperture • 20/25 mm along outgoing Axis Calorimeter 10cm Graphite Front face Incoming Outgoing André Sailer, LC Physics/Detector Meeting

8. Magnetic Field Options • Solenoid: 4 Tesla • R-Z-Field map used for ILD since mokka-06-08 (~2 months old) • Additional Detector Integrated Dipole (DID) • 20 mrad Field map used for LDC • Used for DID and AntiDID (Just flip the Sign) • AntiDID is used at the ILC to guide Beam-Beam-Background to the outgoing Beam pipe • Preferred Field for Luminosity Measurement • But as we just saw, large Reduction in Luminosity André Sailer, LC Physics/Detector Meeting

9. Detector Simulation Mokka-06-08 Three different magnetic Field Options Detector: p02 Recording Planes in front of LCal, BCal and Quad to register passing particles Incoherent Pairs Generated with GP Beam Particle Distributions provided by Daniel (Only one Set, are there more?) 10 BX Generated Statistical fluctuations small Simulation of Beam-Beam-Background André Sailer, LC Physics/Detector Meeting

10. LumiCal Plane AntiDID w/o DID DID Impact Energy [GeV/mm²] Backscatter André Sailer, LC Physics/Detector Meeting

11. BeamCal Plane AntiDID w/o DID DID Impact Energy [GeV/mm²] Backscatter André Sailer, LC Physics/Detector Meeting

12. Quadrupole Plane AntiDID w/o DID DID Impact Energy [GeV/mm²] Backscatter André Sailer, LC Physics/Detector Meeting

13. Numbers André Sailer, LC Physics/Detector Meeting

14. Backscatters into VXD • Without DID: Rate in the VXD frighteningly high • Distribution not Uniform (or rather only ~1/R) • Concentration highest  Downstream Beam pipe Hits in the Vertex Detector for 10 BX [1/mm²] André Sailer, LC Physics/Detector Meeting

15. Origin of Background Hits Background hits in the VXD and FTD and their assumed Origin (p02, w/o DID) • Concentrated Hits on VXD and FTD • Coming back from Beam pipe after BeamCal • Other Backscatters more uniformly distributed Origin of the particles causing Hits in the Tracking Detectors André Sailer, LC Physics/Detector Meeting

16. How to reduce the Background? • AntiDID • Coming from the inner Edge of BeamCal or Beam pipe behind BeamCal • Increase inner Radius of BeamCal and Beam pipe? • Has to be done anyway for LumiCal • Due to Coherent Pairs also needed for BeamCal: Greater than 6 mrad Aperture • Downstream Quadrupole André Sailer, LC Physics/Detector Meeting

17. Further Developments of the Forward Region • Step by Step • Separate Effects • P03 • Only Incoming Quad • 35 mm Radius • Beam pipes changed for Quadrupole • Incoming 3.7 mm • Outgoing 25 mm • P04 • Calo Layers: 30  40 • Larger inner Radii • LCal: 8.5  10 cm • BCal: 2  2.5 cm CLIC01_ILDfwp03 Quad LumiCal BeamCal CLIC01_ILDfwp04 André Sailer, LC Physics/Detector Meeting

18. Smaller Quadrupole w/o DID • Some Incoherent Pairs still hit QD0 • ~7TeV/BX • More Shielding necessary ? • Filling the empty Volume in BeamCal • Causes Problems for the Detector • Move BeamCal closer to IP, Place Shielding between QD0 and BeamCal • Backscatters not a Problem Energy [GeV/mm²] André Sailer, LC Physics/Detector Meeting

19. Effects on Hits in the VXD • From P02  P03 • Smaller QD0, less Backscatters • From P03  P04 • Larger inner Radii • Less Backscatters from BeamCal, none from LumiCal • More Backscatters from the Beam pipe hit VXD P04 P02 André Sailer, LC Physics/Detector Meeting

20. Backscatters from Beam pipe Origin of the Particles causing a Hit in one of the Tracking Detectors, with the Origin behind one BeamCal (Z>3.34m) Centered on the Outgoing Beam axis. • Origin of the Backscattered Particle not uniformly distributed around Beam pipe • Somewhat Higher Concentration for larger |Y| • Radial Beam pipe size limited by QD0 • Use a Beam pipe with an Elliptical/Racetrack cross section behind BeamCal • Backscatters should be blocked by BeamCal André Sailer, LC Physics/Detector Meeting

21. Conclusions and Outlook • Simulations for the 3 Magnetic Field Options and different Forward Region Layouts have been done • Without AntiDID Number of Backscatters hitting VXD increases dramatically • Number of Backscatters to the VXD is still too high • LumiCal with 10 cm inner Radius • Incoherent Pairs do not hit LumiCal • Negligible Backscattering, no Graphite needed • BeamCal • Larger inner Radius does not decrease background • Reduced masking, because of the limited beam pipe Radius • (Smaller) Quadrupole • Without AntiDID: Is still hit with some of the incoherent Pairs • Not an issue from Backscatters for VXD • Beam pipes • Largest source of Backscattering, mainly behind BeamCal • Using a different cross section will probably reduce the backscattering due to better masking by BeamCal André Sailer, LC Physics/Detector Meeting

22. Thank you for you Attention!

23. Back-up Slides

24. Where do the hits come from? • Added Recording Planes • A thin sheet of sensitive air before LumiCal, BeamCal and Quadrupole (QD0) • Also made parts of the beam tube sensitive • No thresholds • Records everything that passes • Does not change simulation • Output in LCIO format André Sailer, LC Physics/Detector Meeting

25. Identification Algorithm • Recording Planes are used to identify the source of backscatters • Using MC information • Did the particle causing a hit in the (e.g.) VXD hit a recording plane? • If not, check parent particle(s) • If hit was recorded, hits are attributed to this Backscatter source • LumiCal, BeamCal, QD0, Tube • If nothing was found: IP André Sailer, LC Physics/Detector Meeting

26. IP BeamCal BeamCal Front face Incoming Outgoing SiW Calorimeter Recording Plane 10cm Graphite André Sailer, LC Physics/Detector Meeting

27. AntiDID Impact Energy [GeV/mm²] Backscatter André Sailer, LC Physics/Detector Meeting

28. Only Solenoid Impact Energy [GeV/mm²] Backscatter André Sailer, LC Physics/Detector Meeting

29. DID Impact Energy [GeV/mm²] Backscatter André Sailer, LC Physics/Detector Meeting