1 Muon Collider Backgrounds Steve Geer Fermilab Steve Geer MC Detector & Physics DOE June 24, 2009

2 INTRODUCTION  Muon Collider detector backgrounds were studied actively 10 years ago ( ). The most detailed work was done for a 2  2 TeV Collider →  s=4 TeV.  Since muons decay (  2TeV =42ms), there is a large background from the decay electrons which must be shielded.  The electron decay angles are O(10) microradians – they typically stay inside the beampipe for about 6m. Hence decay electrons born within a few meters of the IP are benign.  Shielding strategy: sweep the electrons born further than ~6m from the IP into ~6m of shielding. Steve Geer MC Detector & Physics DOE June 24, 2009

3  2 x muons/bunch  2 x 10 5 decays/m  Electron decay angles are O(10)  rad  Mean electron energy = 700 GeV Mean energy = 700 GeV 2  2 TeV Collider As the decay electrons respond to the fields of the final focus system they lose 20% of their energy by radiating on average 500 synchrotron photons with a mean energy of ~500 MeV … & are then swept out of the beampipe. DECAY BACKGROUNDS Steve Geer MC Detector & Physics DOE June 24, 2009

4 Shielding Simulations Shielding design group & final focus design group worked closely together & iterated Used two simulation codes (MARS & GEANT), which gave consistent results Shielding design & simulation work done by two experts (Mokhov & Stumer) in great detail, & involved several person-years of effort. Steve Geer MC Detector & Physics DOE June 24, 2009

5 Final Focus/Shielding Geometry Steve Geer MC Detector & Physics DOE June 24, 2009 Beam-Beam region (  * = 3mm): length = 3 mm, radius = 3  m (rms),  T bunch = 10  s  Fate of electrons born in the 130m long straight section: 62% interact upstream of shielding, 30% interact in early part of shielding, 2% interact in last part, 10% pass through IP without interacting.

6 Shielding Details Steve Geer MC Detector & Physics DOE June 24, 2009

7 More Shielding Details Steve Geer MC Detector & Physics DOE June 24, 2009 r=4cm Z=4m Designed so that, viewed from the IP, the inner shielding surfaces are not directly visible.

8 Background calculations & shielding optimization was performed using (independently) MARS & GEANT codes … the two calculations were in broad agreement with each other (although the designs were different in detail). Results from Summer 1996 GEANT MARS I. Stumer N. Mokhov Steve Geer MC Detector & Physics DOE June 24, TeV Collider Backgrounds

9 Particles/cm 2 from one bunch with 2  muons (2 TeV) r (cm)  np  e  calo0.003 muon GEANT (I. Stumer) Results from LBL Workshop, Spring 1997 Steve Geer MC Detector & Physics DOE June 24, 2009

10  Consider a layer of Silicon at a radius of 10 cm.  GEANT Results (I. Stumer) for radial particle fuxes per crossing: 750 photons/cm 2  2.3 hits/cm neutrons/cm 2  0.1 hits/cm charged tracks/cm 2  1.3 hits/cm 2 TOTAL 3.7 hits/cm 2   0.4% occupancy in 300x300  m 2 pixels  MARS predictions for radiation dose at 10 cm for a 2x2 TeV Collider comparable to at LHC with L=10 34 cm -2 s -1  At 5cm radius: 13.2 hits/cm 2  1.3% occupancy Steve Geer MC Detector & Physics DOE June 24, 2009 VERTEX DETECTOR HIT DENSITY

11 Occupancies Steve Geer MC Detector & Physics DOE June 24, 2009 TOTAL CHARGED PARTICLES

12 S. Geer, J. Chapman: FERMILAB-Conf Photon & neutron fluxes in inner tracker large but mean energies O(MeV) & radial fluxes ~ longitudinal fluxes (  isotropic) Clock 2 layers out at variable clock speed (to maintain pointing) & take coincidence. Blind to soft photon hits & tracks that don’t come from IP Steve Geer MC Detector & Physics DOE June 24, 2009 PIXEL MICROTELESCOPE IDEA

13 PIXEL MICROTELESCOPE SIMULATION - 1 Steve Geer MC Detector & Physics DOE June 24, 2009

14 PIXEL MICROTELESCOPE SIMULATION - 2 Steve Geer MC Detector & Physics DOE June 24, 2009

15 Electromagnetic: Consider calorimeter at r=120 cm, 25 r.l. deep, 4m long, 2  2 cm 2 cells:  GEANT  400 photons/crossing with ~1 MeV  ~400 MeV   E ~  (2 ) = 30 MeV  For a shower occupying 4 towers: = 1.6 GeV and  E = 60 MeV Hadronic: Consider calorimeter at r=150 cm, 2.5m deep (~10 ), covering degrees, 5  5 cm 2 cells:  ~ 400 MeV   E ~  (2 ) = O(100 MeV) These estimates were made summer 1996, before further improvements to final focus + shielding reduced backgrounds by an order of magnitude … so guess background fluctuations reduced by  3 compared with above. Steve Geer MC Detector & Physics DOE June 24, 2009 Calorimeters

16 Bethe-Heitler Muons (  Z  Z  +  - ) Special concern: hard interactions (catastrophic brem.) of energetic muons travelling ~parallel to the beam, produced by BH pair production. Believe that this back- ground can be mitigated using arrival-times, pushing calorimeter to larger radius, & spike removal by pattern recognition … but this needs to be simulated Steve Geer MC Detector & Physics DOE June 24, 2009

17  Muon collider physics, backgrounds & detectors have not been intensely studied for 10 years. Since then a few things have happened: -A decade of detector development driven by LHC & ILC requirements - Physics landscape has evolved -Community expectations for detector performance have evolved -Muon Collider baseline design details have evolved  New design studies for the final focus require, in the near future, a new shielding design study (final focus magnet configuration is changing) - started to rebuild the needed physics/detector/ background/final focus team.  Later this year we are planning to hold a workshop at FNAL on Muon Collider physics, detectors, and backgrounds: -Revisit theoretical motivation -Explore detector R&D synergies with ILC/CLIC -Prepare the way for an eventual apples-to-apples comparison with CLIC Steve Geer MC Detector & Physics DOE June 24, 2009 New Work

18 Comparison with CLIC We are not yet in a position to make an apples-to- apples comparison with CLIC, but ….. Steve Geer MC Detector & Physics DOE June 24, 2009 hits/mm 2 /bunch train 30mm  O(1) hit/mm 2 /bunch train  FROM CLIC Machine- Detector interface studies: CLIC NOT AN APPLES-to- APPLES COMPARISON … BUT … Background hit densities appear to be similar to MC … so there may be many detector design issues in common between the 2 machines

19 Summary Background levels at a 4 TeV Muon Collider are expected to be similar to those at the LHC with L=10 34 cm -2 s -1 Detailed studies were done 10 years ago, and things have evolved. New studies to update the picture are beginning. We believe there is much synergy with CLIC physics, detector, & backrgound studies. Steve Geer MC Detector & Physics DOE June 24, 2009