1. NLC - The Next Linear Collider Project NLC IR Layout and Background Estimates Tom Markiewicz/SLAC Snowmass 2001, 05 July 2001 LCD Meeting, 25 September 2001

2. NLC - The Next Linear Collider Project The Experts Takashi Maruyama (SLAC) Pairs and Neutron Backgrounds Jeff Gronberg (LLNL) Gamma-Gamma to Hadrons Stan Hertzbach (U. Mass) Synchrotron Radiation Lew Keller (SLAC) Muons Collimator Efficiency

3. NLC - The Next Linear Collider Project Introduction At LCWS2000 background ESTIMATES were based on: –New (i.e. short) final focus –L* = 4.3 m –Large (ver.1) Detector –NLC 500 GeV and 1 TeV “B” IP beam parameter sets –Extraction line beginning at 6 m with 1 cm radius aperture This talk has –Latest IP beam parameters ~4x the luminosity with 190 bunches each with 0.75E10 e- –L* = 3.8m with LumMon @ 3.5m –March 30, 2001 LD and SD detectors –Same extraction line Neutrons from the dump –Same Final Focus but newest shortest collimation scheme more muon backgrounds given similar halo assumptions relative z location of calorimeters and L* is what matters

4. NLC - The Next Linear Collider Project “Large” and “Silicon” Detectors (same scale) 3 Tesla5 Tesla

5. NLC - The Next Linear Collider Project LD and SD Detector Masking 32 mrad 30 mrad

6. NLC - The Next Linear Collider Project LCD-L2 (3T) with 4.3m L* Optics QD0 SD0 M1 Calorimeter Pair LumMon M2 Beampipe Low Z shield 30 mrad Cal acceptance Support Tube

7. NLC - The Next Linear Collider Project IP Backgrounds: Beam-Beam Interaction Disrupted primary beam Extraction Line Losses Beamstrahlung photons e+,e- pairs from beams.  interactions Hadrons from beams.  interactions Radiative Bhabhas Background Sources Machine Backgrounds: Synchrotron Radiation Muons Production at collimators Direct Beam Loss Beam-Gas Collimator edge scattering Neutron back-shine from Dump “Bad”, get nothing in exchange 1) Don’t make them 2) Keep them from IP if you do “Good”, scale with luminosity 1) Transport them away from IP 2) Shield sensitive detectors 3) Detector Timing

8. NLC - The Next Linear Collider Project Beams attracted to each other reduce effective spot size and increase luminosity H D ~ 1.4-2.1 Pinch makes beamstrahlung photons: 0.9-1.6  /e- with E~3-9% E_beam Photons themselves go straight to dump Not a background problem, but angular dist. (1 mrad) limits extraction line length Particles that lose a photon are off-energy Physics problem: luminosity spectrum Extraction line problem: NLC 1 TeV design has 77 kW of beam with E< 50% E_nom, 4kW lost (0.25% loss) Photons interact with opposing e,  to produce e+,e- pairs and hadrons Beam-Beam Interaction SR photons from individual particles in one bunch when in the electric field of the opposing bunch   e+e- (Breit-Wheeler) e   ee+e- (Bethe-Heitler) ee  eee+e- (Landau-Lifshitz)   hadrons

9. NLC - The Next Linear Collider Project Energy Distributions NLC-1 TeV Tesla 500 GeV

10. NLC - The Next Linear Collider Project NLC Extraction Line 150 m long with chicane and common  and e- dump Problem: Handling the large low E tail on the disrupted beam cleanly enough to allow extraction line diagnostics Working plan: Ignore for now- not a problem @ 500 GeV; @ 1 TeV either measure Pol, E upstream, steal undisrupted pulses for diagnostics, calibrate other 4kW lost in EXT @ 1 TeV

11. NLC - The Next Linear Collider Project e+,e- pairs from beams.  interactions At NLC-1000: 44K per bunch @ =10.5 GeV (0.85 W)

12. NLC - The Next Linear Collider Project Direct Pairs P T of e+e- from given bunch = Sum of –Pt from individual pair creation process small – Pt from collective field of opposing bunch large limited by finite size of the bunch

13. NLC - The Next Linear Collider Project Dead-Cone Formalism  max from D x,  x,  z Tauchi, LC95

14. NLC - The Next Linear Collider Project e+e- Pair p T vs. theta Distribution 50 mrad Hard edge from finite beam size “High” pT inside cone Low pt/high angle curl in field e+,e- with high intrinsic pt can hit small radius VXD

15. NLC - The Next Linear Collider Project Controlling e+,e- Pair Background Direct Hits Increase detector solenoid field to wrap up pairs (3 Tesla adequate, 4 T better) Increase minimum beam pipe radius at VXD and stay out of pair “dead cone” Secondaries (e+,e-, ,n) Remove point of first contact as far from IP/VXD as possible Increase L* if possible Largest exit aperture possible to accept off-energy particles Keep extraneous instrumentation out of pair region Masks Instrumented conical “dead cone” protruding at least ~60cm from face of luminosity monitor and 8-10cm thick to protect against backscattered photons Low Z (Graphite, Be) 10-50cm wide disks covering area where pairs hit the low angle W/Si Pair Luminosity monitor

16. NLC - The Next Linear Collider Project LCD-L2 (3T) with 3.8m L* Optics QD0 SD0 M1 Calorimeter Pair LumMon M2 Beampipe Low Z shield 32 mrad M1 acceptance Support Tube 6.3 mrad Lum-Mon acceptance 1 mrad exit aperture QF1 SF1 52 mrad Cal acceptance Feedback BPM & Kicker

17. NLC - The Next Linear Collider Project Pair Stay-Clear from Guinea-Pig Generator and Geant

18. NLC - The Next Linear Collider Project Pair hits at z = 4 m  4cm  2cm High momentum pairs mostly in exit beampipe Low momentum pairs trapped by detector solenoid field

19. NLC - The Next Linear Collider Project Photons in the LD TPC @ 1 TeV Scoring plane @ r=30 cm Source:Either direct or secondary hits on the beampipe Photon Distribution in Barrel Cal similar Positron annihilation peak

20. NLC - The Next Linear Collider Project Photons in the Endcap CAL @ 1 TeV R=18cm scoring plane LDSD

21. NLC - The Next Linear Collider Project LCD Hit Density/Train vs. Radius Before conversion

22. NLC - The Next Linear Collider Project 10/17/2000 LCD-L2 Hit Densities vs. Radius

23. NLC - The Next Linear Collider Project e+/e- pairs and radiative Bhabhas hitting the Pair Lum-Mon, beam-pipe and magnets in the extraction line. Disrupted beam lost in the extraction line. 0.25 % beam loss in recent redesign Disrupted beam and beamstrahlung photons in the dump Neutron hit density in VXD NLC-LD-500 GeV NLC-SD-500 GeV Beam-Beam pairs1.8 x 10 9 hits/cm 2 /yr 0.5 x 10 9 hits/cm 2 /yr Radiative Bhabhas1.5 x 10 7 hits/cm 2 /yrno hits Beam loss in extraction line0.1 x 10 8 hits/cm 2 /year 0.1 x 10 8 hits/cm 2 /year Backshine from dump1.0 x 10 8 hits/cm 2 /yr 1.0 x 10 8 hits/cm 2 /yr TOTAL1.9 x 10 9 hits/cm 2 /yr 0.6 x 10 9 hits/cm 2 /yr Neutron Backgrounds The closer to the IP a particle is lost, the worse Figure of merit is 3 x 10 9 for CCD VXD

24. NLC - The Next Linear Collider Project 10/17/2000 VXD Neutron Dose Rate OLD PAIR & RB Estimate OLD but still VALID DUMP & Dumpline Estimate NEW PAIR & RB Estimate

25. NLC - The Next Linear Collider Project Neutrons from Lost Pairs and Rad. Bhabhas Neutrons which reach the IP are produced close to the IP, mainly in the luminosity monitor

26. NLC - The Next Linear Collider Project Neutrons from the Beam Dump Controlled by Shielding and Geometry Geometric fall off of neutron flux passing 1 mrad aperture [parent distribution for next slide]

27. NLC - The Next Linear Collider Project Dump-produced Neutron flux at z=0 as a function of radius 1.2E10 neutrons hit the beampipe within +/-5cm at r>1.0 cm 30% scatter into VXD Divide by area of VXD L1 to get quoted hit density = 0.25E9/cm^2/y Fall off for r>1.0 cm due to limiting aperture of EXTRACTION LINE QUAD DOUBLET (currently 10-11 mm from L=6-10.8 m from the IP; SR concerns MAY require larger aperture) Fall off as r -> 0cm comes from reduced solid angle view of the dump As r is reduced need to integrate more of this curve. Limiting Aperture

28. NLC - The Next Linear Collider Project Integrated Dump Neutron Flux vs. Radius Detector Group Constantly Asking why inner VXD radius can’t be x2 SMALLER As Beampipe radius is reduced by x2 Flux from dump up x10 Hit density up by x40 dump becomes equal to pairs as source of neutron hits SR issues (S. Hertzbach talk)

29. NLC - The Next Linear Collider Project Control of Pair-Induced Neutrons Neutron Hit Density vs. Extraction Line Aperture VXD Neutrons from Pairs with 10 cm Be Shield 50 cm Be Shield is 3-4x better

30. NLC - The Next Linear Collider Project Neutrons in the LD Barrel Cal @ from e+e- pairs at 1 TeV In plot see contribution from +z side only Similar for SD

31. NLC - The Next Linear Collider Project Summary: LD @ 500 GeV

32. NLC - The Next Linear Collider Project Summary: SD @ 500 GeV

33. NLC - The Next Linear Collider Project Summary: LD @ 1 TeV

34. NLC - The Next Linear Collider Project Summary: SD @ 1 TeV

35. NLC - The Next Linear Collider Project e + e -  e + e -   e + e - Hadrons NLC: Analysis began Spring 2001 (Gronberg & Hill / LLNL) CAIN simulation plus JETSET Need to integrate 190 bunches Doesn’t appear to be a problem but one detector element with good time resolution will help if it is Analysis still “young” If we scale TESLA’s event rate/BX by n  2 (50%) and x 190 bunches get much larger numbers TypeEvts/ BX Evts/ Train Photons / Event Chg. Trks/ Event Etot/Event (Barrel, Endcap, Mask) All0.00230.4610 35 GeV ( 3, 3, 29 GeV)

36. NLC - The Next Linear Collider Project e + e -  e + e -   e + e - Hadrons Energy Distribution BarrelEndcapMask

37. NLC - The Next Linear Collider Project Synchrotron Radiation At SLD/SLC SR WAS a PROBLEM SR from triplet WOULD have directly hit beam-pipe and VXD Conical masks were installed to shadow the beam pipe inner radius and geometry set so that photons needed a minimum of TWO bounces to hit a detector Quantitative measurements of background rates could be fit by a “flat halo” model where it was assumed that between 0.1% and 1% (in the early days) of the beam filled the phase space allowed by the collimator setting. At NLC/TESLA Allow NO direct SR hits ANYWHERE near IP SR due to BEAM HALO in the final doublet, not the core of the beam Collimate halo before the linac AND after the linac Halo estimates are ~10 -6 of beam; designing system to handle 10 -3 Optical solutions to handle halo under development

38. NLC - The Next Linear Collider Project HALO Synchrotron Radiation Fans with Nominal 240  rad x 1000  rad Collimation (Similar plots for TESLA)

39. NLC - The Next Linear Collider Project Halo Collimators= Potential Muon Source Locations No Big Bend, Latest Collimation & Short FF Betatron Betatron Cleanup Energy FF

40. NLC - The Next Linear Collider Project Muon Backgrounds 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

41. NLC - The Next Linear Collider Project Muons Reaching z=0: 500 GeV/beam Shows what happens without spoiler

42. NLC - The Next Linear Collider Project LD Muon Endcap Background #e- Scraped to Make 1Muon Calculated Halo is 10 -6 Efficiency of Collimator System is 10 5 Bunch Train =10 12 Engineer for 10 -3 Halo No Spoilers

43. NLC - The Next Linear Collider Project Muon Rates in LD per lost e-

44. NLC - The Next Linear Collider Project 10/17/2000 250 GeV/beam Muon Endcap Background Engineer for 10 -3 Halo Bunch Train =10 12 Calculated Halo is 10 -6 Efficiency of Collimator System is 10 5

45. NLC - The Next Linear Collider Project Conclusions As we have pushed up luminosity x4, shrunken L* from 4.3 to 3.5m, and reduced length of beam delivery system from 5km to 1km, backgrounds have risen in absolute terms to a level per train meriting attention –Backgrounds/Unit of Luminosity constant before geometry mods –Geometry adjustment always possible –Nanosecond level detector timing would make everything except neutron-dominated VXD lifetime a non-issue –Large detector Neutron damage lifetime needs more investigation Conclusion to all previous background talks was “not a problem” but now I am beginning to feel we need to start investigating detector response and optimizing detector design and performance with respect to these processes.