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Beam-Beam Background and the Forward Region at a CLIC Detector

Beam-Beam Background and the Forward Region at a CLIC Detector. André Sailer (CERN PH-LCD) LC Physics School, Ambleside 22st August, 2009. Outline. Detector for CLIC and my work on it Forward Region Design Backscatters Conclusions & Outlook. Linear Collider Detector for CLIC.

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Beam-Beam Background and the Forward Region at a CLIC Detector

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  1. Beam-Beam Background and the Forward Region at a CLIC Detector André Sailer (CERN PH-LCD) LC Physics School, Ambleside 22st August, 2009

  2. Outline • Detector for CLIC and my work on it • Forward Region Design • Backscatters • Conclusions & Outlook

  3. Linear Collider Detector for CLIC • As discussed on Thursday morning (and today) • Some Changes are necessary for the Current ILC Detectors to work properly at 3 TeV CLIC • My work is concerned with the Beam-Beam Background, i.e. Incoherent and Coherent Pairs going towards the Forward Region • Looking at Backscatters into the Main Detector, focused mostly on the Vertex Detector and reducing backscatters

  4. Software • Beam-Beam Background simulated using Guinea-Pig • Perfectly aligned Beams • Full Detector Simulation using Mokka (Geant4) • Analysis with Marlin

  5. LHCal Quad LumiCal BeamCal (including 10cm graphite) Forward Region • ILD Forward Region • CLIC Forward Region • Incoherent Pairs out to ~80 mm (at 2.5m) • Don’t destroy LumiCal • Larger Inner Radius (From 80(85?) to 100mm) • Let out the Coherent Pairs ~10^8 Particles • Coherent Pairs Out to ~6mrad • Larger Inner Radius for BeamCal (From 15 to 25mm) • Make LumiCal and BeamCal Longer (40 radiation lengths) to contain 1.5 TeV electron showers • FF Quad at L*=3.5m • Remove LHCal • Beam pipe as large as possible • ~1 cm distance to QD0

  6. Backscatters • Main source of Backscatters (that hit the VXD) is the inner wall of the beam pipe (Cyan colored hits in the picture) • Can get rid of 50% them by using racetrack formed beam pipe (in horizontal (y) direction) • Rate is still 9 Hits per mm² per Bunch Train • Supposedly OK for B-Tagging, study is ongoing • Predicted Rate from simpler simulation factor ~5 less

  7. Conclusions & Outlook • Backscattering is more of a Challenge at CLIC • No AntiDID field, larger number of particles, higher bunch repetition rate • Full Detector Simulation needed to get a realistic picture of backscattering • Still trying to reduce Backscatters into the VXD • Check how much useful BeamCal is for SM Veto of Electrons • Change Geometry for better masking • Make Sure Coherent Pairs really leave through BeamCal • Look at background in other sub detectors • Forward Tracking, TPC, Calorimeters • Fluctuations from non perfect bunch collisions • …

  8. Back-up Slides

  9. Hits in the VXD depending on Forward Region Geometry • From Step 1  Step 2 • Smaller QD0, less Backscatters (larger one was not shown before) • From Step 2  Step 3 • Larger inner Radii for LCal and BCal • Less Backscatters from BeamCal, none from LumiCal • More Backscatters from the Beam pipe hit VXD Step 3 Step 1

  10. 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 are blocked by BeamCal • Reduce Background from Backscatters by ~40% • Still 9 Hits per mm² per Bunch Train

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