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Optimizing Forward Geometry Design for ILC: Beam Parameters and Neutron Fluence Acceptance Constraints

This document outlines the forward geometry design requirements from IP to LumiCal and BeamCal for the International Linear Collider (ILC). It discusses acceptance criteria, clearance constraints, beam parameters, and solenoid field strengths. The current beam pipe design is evaluated for different scenarios, such as the ILC at 500 GeV with various magnetic field strengths. Pair distribution and neutron fluence considerations are addressed, highlighting the impact on different beam parameters and options. Suggestions for beam pipe modifications and materials to absorb low-energy particles and neutrons are also provided.

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Optimizing Forward Geometry Design for ILC: Beam Parameters and Neutron Fluence Acceptance Constraints

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  1. Background and Forward Geometry Takashi Maruyama

  2. Introduction • Forward region design requires a coherent design from IP to LumiCal and to BeamCal • Acceptance • Clearance from pairs • Beam parameters • Solenoid field strength 5 Tesla vs. 4 Tesla • No-DID or Anti-DID • Beampipe • Talk about forward geometry and background constraints

  3. SiD Forward Region Cooper SiD Workshop • Very useful discussions at SLAC during IRENG07 • The general layout of forward calorimetry follows parameters provided by Bill Morse and concepts suggested by Tom Markiewicz.

  4. Current Beam pipe is designed for ILC 500 GeV Nominal + 5 Tesla 4 Tesla 5 Tesla R (cm) Z (cm) For 4 Tesla, R=1.2 cm is tight and 43 mrad is too small. R=1.4 cm and 110 mrad beam-pipe would work.

  5. Current Beam pipe is not compatibe with the Low P or High Lumi options. 500 GeV Low P + 5 Tesla 500 GeV High Lum + 5 Tesla R (cm) Z (cm) 110 mrad beam-pipe would work as long as R= 1.2 cm  1.5 cm (Low P), and R= 1.2 cm  1.8 cm (High Lumi).

  6. Neutrons from the dump x (cm) C 2.4 cm quadrupole 2.4 cm 7 mrad n 2.11010 n’s/cm2/y 3.0 cm C’ Be Si VXD W BeamCal VXD Layer 1 fluence (one beam): 1.01010 n’s/cm2/y w/o BeamCal 2.4108 n’s/cm2/y w BeamCal z (cm)

  7. IP Beampipe radius and VXD layer 1 • Rbp = 1.2 cm and Rvxd1= 1.4 cm • OK for ILC 500 GeV Nominal + 5 Tesla • Intolerable neutron fluence if the Beamcal aperture is 1.5 cm • Increase to Rbp = 1.4 cm and Rvxd1= 1.6 cm? • Will work for • ILC 500 GeV Nominal + 4 Tesla • ILC 500 GeV Low P + 5 Tesla • Neutron fluence is acceptable • Keep Rbp = 1.2 cm and Rvxd1= 1.4 cm for LOI?

  8. Pair distribution at Z = 168 cm • Beam parameters – Nominal, Low Q, High Y, Low P, High Lumi • Solenoid field strength – 5 Tesla vs. 4 Tesla • Crossing angle (14 mrad) + DID/ANTI-DID ILC 500 GeV Nominal beam parameters + 5 Tesla ANTI DID No DID Y (cm) X (cm)

  9. Pair Radius in cm at Z=168 cm Radius in black is measured from solenoid axis (x,y) = (0., 0.). Radius in red is measured from extraction line (x,y) = (-1.176 cm, 0.)

  10. Bhabha and Pairs at Z=168 cm • Anti-DID • Nominal OK • Low P OK • No DID • Nominal OK • Low P Not OK 36 mrad Y (cm) -7.22 cm 4.87 cm X (cm)

  11. SiD Beam Pipe Cooper/Krempetz

  12. Beampipe

  13. Pairs at Z = 295 cm No DID Anti-DID ILC 500 GeV Nominal R < 5 cm R < 6 cm Y (cm) ILC 500 GeV Low P R < 6 cm R < 8 cm X (cm) X (cm)

  14. Preliminary BeamCal Sensor Layout Cooper • Assumes 6” silicon sensor technology. • Wedges rotated in alternate planes for overlap. # of pads would likely be increased Beam pipes through Beam Cal may be merged to improve vacuum conductance Outgoing beam pipe Incoming beam pipe Segmentation and readout can be different for r< 7cm and r>7cm Pairs are confined within r < 6 cm.

  15. Low Z material ILC 500 GeV Nominal + DID • Low Z layer in front of BeamCal to absorb low energy e+/e- coming out of BeamCal • 10 cm thick Be (0.28X0) • Other material to absorb neutrons as well Borated Poly is more effective in absorbing neutrons but X0 is longer.

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