1. Backgrounds in the NLC BDS ISG9 December 10 – 13 2002 Takashi Maruyama SLAC

2. Background and collimation Major source of detector background: Halo particles hitting beamline components generate muons and low energy particles. Halo particles generate sync. radiations that hit VXD. Beam-gas scattering generates low energy particles. Collimate Halo particles: Spoilers and Absorbers Collimation depth – (n x  x, n y  y ) Reduce halo size using Octupoles What is Halo, and How much: Drozhdin’s 1/x-1/y model Flat distribution with 50  x,50  x ’,200  y,200  y ’,3%  E/E Pencil beam hitting SP1 Calculated halo ~10 -6, but design collimation for 10 -3.

3. 2001 Collimation System & FF integrated design New scheme of the Collimation Section and Final Focus with ODs Energy collimation Betatron collimation Final Focus IP FD IP FD IP FD S SA SA SA A A FD A Final Focus collimation A IP Octupole Doublets

4. NLC Beam Delivery Section in Geant 3 1480 m 295 cm sp1 sp2 a2 sp3 a3 sp4 a4 sp5 a5 E-slit FF Collimators TRANSPORT lattice Magnets (bands,quads, sexts, octs) location, orientation, length, field strength, aperture Geant 3 Spoilers and Absorbers IP

5. Muon Backgrounds from Halo Collimators No Big Bend, Latest Collimation & Short FF If Halo = 10 -6, no need to do anything If Halo = 10 -3 and experiment requires <1 muon per 10 12 e- add magnetized tunnel filling shielding Reality probably in between 18m & 9m Magnetized steel spoilers Betatron Betatron Cleanup Energy FF

6. 250 GeV/beam Muon Endcap Background Engineer for 10 -3 Halo Bunch Train =10 12 Calculated Halo is 10 -6 Collimation Efficiency 10 5

7. LCD Detector in GEANT3/FLUKA GEANT3: e+/e- and  backgrounds FLUKA: Neutrons

8. NLC Detector Masking Plan View w 20mrad X-angle LD – 3 Tesla SD – 5 Tesla 32 mrad 30 mrad R=1 cm Apertures: 1 cm beampipe at the IP 1 cm at Z = -350 cm

9. VXD Hits from 250 GeV e- hitting QD0 250 GeV e- e-, e+ QD0 z

10. Synchrotron radiations FF doublet aperture 1 cm bends quads Photons from quads Photons from bends

11. Sync. Radiation vs.  IP nyny nxnx cm x IP y IP  Track particle with n  backward from IP to AB10.  Track particle to IP and generate sync. radiations.  Find sync. radiation edge as a function of (nx, ny). nx = 18.5  x +, 17.2  x - ny = 50.9  y  Find AB10 and AB9 apertures as a function of (nx, ny)

12. Sync. radiation at z = -350 cm nxnx nyny x y Apertures at AB10 & AB9 AB10 AB9 AB10 AB9 x y nxnx nyny n x = 16.2  x+ nx = 16.8  x- ny = 41.6  y

13. Spoiler/Absorber Scattering Spoilers/Absorbers Settings for NO OCT Half apertures X Y (um)  x  y Sp1 ~ SP4 settings with OCT x2.5 ESP 0.5 X0 ~x5 beamloss * * * * TRC 6500 3900 8000

14. Synchrotron Radiation and Collimation Depth 1) x’ < 570  rad = 19 x 30.3  rad y’ < 1420  rad = 52 x 27.3  rad 2) x’ < 520  rad = 17 x 30.3  rad Y’ < 1120  rad = 41 x 27.3  rad Criteria: No photons hit R > 1 cm at 1) z = 0 cm or 2) z = 350 cm x y

15. Halo Model X’ X (cm) Y (cm) Y’ 10 -5 y (cm) x (cm)  1/x and 1/y density over A x = (6 – 16)  x and Ay = (24 – 73)  y  E/E = 1% (Gaussian)  Halo rate 10 -3

16. Particle loss distribution Z (m) OCT-OFF OCT-ON 42% to IP 82% to IP ESP EAB AB10 AB7 DP2

17. Particle distributions at FF absorbers. AB10 AB9 AB7 DP1DP2 y is OK, but x is tight.

18. Integral Particle Loss Distribution

19. Sync. Radiations at IP X (cm) Y Log10(E) (GeV) Quad Bend .3 Ne- =4.8 MeV Hit 1 cm

20. 42% to IP 50  x,50  x ’,200  y,200  y ’,3%  E/E OCT-OFF 1/x – 1/y FLAT Z (m) ESP EAB AB10 AB7 FLAT Halo 42% to IP 0.6% to IP

21. Integral Particle Loss Distribution ESP EAB

22. Transmission rate through E-slit and beam-loss in FF OCT-OFF OCT-ON Pencil beam hitting SP1

23. Summary NLC BDS and collimation system are studied using Geant 3. FF absorbers are set so that no sync. radiations hit the detector apertures. Assuming 10 -3 halo, the particle loss is < 10 -8 in FF and the muon background is tolerable. Octuples allow x2.5 looser spoiler settings. OCT-OFF settings are well optimized, but OCT- ON settings need further optimization.