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Detector Design Issues: gg Interaction Region

Detector Design Issues: gg Interaction Region. David Asner/LLNL Linear Collider Retreat, Santa Cruz, June 27-29, 2002.

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Detector Design Issues: gg Interaction Region

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  1. Detector Design Issues:gg Interaction Region David Asner/LLNL Linear Collider Retreat, Santa Cruz, June 27-29, 2002 This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

  2. Overview Historically gg physics studies assumed an ideal detector Recently, comparable performance to e+e- is assumed Is this assumption valid? Is the required detector design for gg the same as e+e-? What is different about the gg IR? What is different about gg interactions?

  3. s-channel higgs production Mass measurement Cross section x BR bb, WW*, ZZ*, Zg, gg MSSM deviation from SM CP properties Heavy MSSM H0,A0 Discovery Tanb, H0,A0 mass splitting H+H- production Charged higgs mass Width, BR to extract tanb ggh*  hh Higgs self coupling gg tnH+, csH+ Use polarization to measure L,R chiral couplings gg squarks,sleptons gg c+c- Measure c1,c2 mass Mixing angles BR to sleptons,sneutrinos gg W+W- 10x e+e- cross section gg tt Somegg Analyses in Progress gg and e+e- Physics: Similar detector performance • QCD • Extra-dimensions • b tagging is at least as important at gg • Reflected in the number of studies of h bb

  4. Integrating Laser Optics in gg IR • Essentially identical to e+e- IR • 30 mRad x-angle • Extraction line ± 10 mRadian • Large final mirror 6cm (0.2X0) thick Lucite, with central hole 7 cm radius. • Remove all material from the flight path of the backgrounds Mirror placement for LCD-Large

  5. 2D Interaction Region: Snowmass 2001 • Cylindrical carbon fiber outer tube • Vacuum boundary with transition from thick cylinder to thin beampipe. • Sections of “strongback” for optical support • Thermal Management

  6. Off-energy e+/e- pairs hit the Pair-LumMon, beam-pipe and Ext.-line magnets Radiative Bhabhas & Lost beam <x10 Solutions: Move L* away from IP Open extraction line aperture Low Z (Carbon, etc.) absorber where space permits Neutrons from Beam Dump(s) Solutions: Geometry & Shielding Shield dump, move it as far away as possible, and use smallest window Constrained by angular distribution of beamstrahlung photons Minimize extraction line aperture Keep sensitive stuff beyond limiting aperture If VXD Rmin down x2 Fluence UP x40 Neutron Backgrounds (e+e- IR)The closer to the IP a particle is lost, the worse • gg Interaction Region • Extraction line aperture is 10mRad • L1 and L2 of Silicon have direct line of site to the beam dump • Greatly increased neutron flux

  7. Neutrons from the Beam Dump Limiting aperture for gg is 10mRad # Neutrons per Year for e+e- Limiting Aperture Integral Geometric fall off of neutron flux passing 1 mrad aperture 0.5 1.0 Radius (cm) z(m)

  8. Neutron BackgroundsSummary Neutron hit density in VXD NLC-LD-500 GeV e+e- NLC-LD-500 GeV gg Beam-Beam pairs 1.8 x 109 hits/cm2/yr expect similar Radiative Bhabhas 1.5 x 107 hits/cm2/yr expect similar Beam loss in extraction line 0.1 x 108 hits/cm2/year expect similar Backshine from dump 1.0 x 108 hits/cm2/yr 1.0 x 1011 hits/cm2/yr TOTAL 1.9 x 109 hits/cm2/yr 1.0 x 1011 hits/cm2/yr Figure of merit is 3 x 109 for CCD VXD Takashi Maruyama & Jeff Gronberg L1 & L2 cannot use CCD – Active Pixels?

  9. Summary: LD @ 500 GeV (e+e- IR)

  10. LD Detector Occupancies (e+e- IR) from e+e- Pairs @ 500 GeV TESLA NLC gg requires single bunch resolution – relies on few ns TPC timing

  11. Time Resolution and Bunch Structure 3 Tesla TPC time res 1.4 ns =  2 gg bunches gg 95x120 Hz with 1.5x1010 e/bunch

  12. Photons have Structure • Three types of gg collisions • Direct • Once resolved • Twice resolved “g”=0.99 g + .01 r Electroweak Electroweak (DIS) Strong (rr collider)

  13. Resolved Photon Backgrounds:#1 Concern gg collisions are NOT like e+e- 1.5x1010 e- and 1x1010g • About 98% of interactions are gg • About 80% g*g* and 18% gg* • Cross section to hadronic final states is about 400nb (pt>2 MeV) • Total gg luminosity ~100 nb-1 s-1 • Expect 3 - 4 underlying hadronic events per “interesting” event • |cos Q|<0.9 about 50 GeV, |cos Q|<0.8 about 25 GeV

  14. Resolved Photon Background Cos Q vs Energy (GeV) 85 tracks/crossing (|cos Q| < 0.9) pavg = 0.6 GeV (p > 0.2 GeV)

  15. Conclusion • gg IR design requires larger aperture extraction line 10mRad • VXD L1 & L2 have direct line of site to beam dump • CCD’s cannot handle neutron flux 1011n/cm/y • Need to study the impact on detector performance (b-tagging) if • Only have a 3 layer CCD-VXD, L3, L4 & L5 • Replace L1 & L2 with active pixels • All layers active pixels • Need detector design for these scenarios • Radiation Summary Table for LD–500 GeV: Redo for gg IR • Detector Occupancy Table: Include resolved photons • Simulation to assess if occupancy is low enough for pattern recognition + TPC time stamp to resolve single crossing

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