1. Muon Collider Machine-Detector Interface and Detector Backgrounds International Workshop on Future Linear Colliders LCWS11 Granada, Spain September 26-30, 2011 Nikolai Mokhov Fermilab Accelerator Physics Center

2. LCWS11, Granada, September 26-30, 2011 OUTLINE 2Muon Collider MDI & Backgrounds - N.V. Mokhov Introduction Backgrounds and Heat Loads MARS15 Modeling Radiation Loads on IR Magnets and Detector Main Characteristics of Backgrounds Summary and Plans

3. Introduction Physics goals of a Muon Collider (MC) can only be reached with appropriate design of the ring, interaction region (IR), high-field superconducting (SC) magnets, machine-detector interface (MDI) and detector. All - under demanding requirements, arising from the short muon lifetime, relatively large values of the transverse emittance and momentum spread, unprecedented dynamic heat loads (0.5-1 kW/m) and background particle rates in collider detector. LCWS11, Granada, September 26-30, 20113Muon Collider MDI & Backgrounds - N.V. Mokhov

4. MDI-Detector Team Lattice, SC magnets, MDI; MARS15 N. Mokhov, Y. Alexahin, V.Y. Alexakhin, E. Gianfelice-Wendt, V.V. Kashikhin, S. Striganov, A. Zlobin Detector; ILCroot V. Di Benedetto, C. Gatto, A. Mazzacane, N. Terentiev LCWS11, Granada, September 26-30, 20114Muon Collider MDI & Backgrounds - N.V. Mokhov

5. Detector Backgrounds Muon Collider detector performance is strongly dependent on the background particle rates in various sub-detectors. Deleterious effects of the background and radiation environment produced by muon decays are one of the fundamental issues in the feasibility study of MC ring, IR, MDI and detector. First studies in mid-90’s; last two years: impressive progress on lattice, SC magnets, MDI and detector modeling. This study: √S=1.5 TeV, one bunch of 2×10 12  + and  - LCWS11, Granada, September 26-30, 20115Muon Collider MDI & Backgrounds - N.V. Mokhov

6. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 6 Muon Beam Decays: Major Source of Backgrounds (1) Contrary to hadron colliders, almost 100% of background and radiation problems at MC arise in the lattice. Although incoherent e + e - pair production at IP and beam loss on limiting apertures can result in noticeable background levels, muon decays have been identified as the major source of detector backgrounds at MC. The decay length for 0.75-TeV muons is D = 4.7×10 6 m. With 2e12 muons in a bunch, one has 4.28×10 5 decays per meter of the lattice in a single pass, and 1.28×10 10 decays per meter per second for two beams.

7. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 7 Muon Beam Decays: Major Source of Backgrounds (2) Magnet local coordinate system

8. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 8 Muon Beam Decays: Major Source of Backgrounds (3) Electrons from muon decays have mean energy of approximately 1/3 of that of the muons. At 0.75 TeV, these ~250-GeV electrons, generated at the above rate, travel to the inside of the ring magnets, and radiate a lot of energetic synchrotron photons tangent to the electron trajectory. Electromagnetic showers induced by these electrons and photons in the collider components generate intense fluxes of muons, hadrons and daughter electrons and photons, which create high background and radiation levels both in a detector and in the storage ring at the rate of 0.5-1 kW/m (to be compared to a good practice number of a few W/m in hadron colliders).

9. LCWS11, Granada, September 26-30, 2011 Muon Collider MDI & Backgrounds - N.V. Mokhov9 Background Effects on Detector Performance Detector component radiation aging and damage. Reconstruction of objects (e.g., tracks) not related to products of  +  - collisions. Deterioration of detector resolution (e.g., jets energy resolution due to extra energy from background hits).

10. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov10 Radiation Issues in MC SC Magnets Quench stability: peak power density and heat transfer Dynamic heat loads: cryo plant capacity and operational cost Radiation damage: Component lifetime Residual dose rates: Hands-on maintenance

11. 1.5-TeV IR & Chromatic Correction Section 8-T dipoles in IR to generate large D at sextupoles to compensate chromaticity and sweep decay products; momentum acceptance 1.2%; dynamic aperture sufficient for transverse emittance of 50  m; under engineering constraints. Iterative studies on lattice and MDI with magnet experts. LCWS11, Granada, September 26-30, 201111Muon Collider MDI & Backgrounds - N.V. Mokhov

12. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 12 IR Nb 3 Sn Magnets: A = 10  max + 2cm Quadrupoles: on limits of current state-of-the-art Nb 3 Sn technology; G~200 T/m, A=80 to 160mm; L~2m, with tungsten liners in some of them Dipoles: open midplane – field quality and stresses are the issue. 160-mm coil aperture, 55-mm gap with spacers, L=6m, B=8 T. Tungsten rods cooled at room temp Magnet interconnects: up to 50 cm for end parts, multipole correctors and tight ~20-cm 5  tungsten masks (don’t forget neutrino hazard for TeV beams).

13. MARS15 Modeling Segment of the lattice |z| < z max, where z max = 250 m, implemented in MARS15 model with Nb 3 Sn quads and dipoles with masks in interconnect regions and liners inside. Detailed magnet geometry, materials, magnetic fields maps, tunnel, soil outside and a simplified experimental hall plugged with a concrete wall. Detector model with B z = 3.5 T and tungsten nozzle in a BCH 2 shell, starting at ±6 cm from IP with R = 1 cm at this z. 750GeV bunches of 2×10 12  - and  + approaching IP are forced to decay at |z| < z max, where z max = 75 to 250 m at 4.28×10 5 / m rate. All physics processes included. Cutoff energies optimized for materials & particle types, varying from 2 GeV at z ≥ 100 m to 0.001 eV in the detector. LCWS11, Granada, September 26-30, 201113Muon Collider MDI & Backgrounds - N.V. Mokhov

14. MARS15 IR Model LCWS11, Granada, September 26-30, 201114Muon Collider MDI & Backgrounds - N.V. Mokhov

15. Details at -6 to +20 m (plan view) LCWS11, Granada, September 26-30, 201115Muon Collider MDI & Backgrounds - N.V. Mokhov Quads: G~200 T/m, dipoles: B=8T Tungsten masks with 5  x,y elliptic openings: QF 80mm QF 110mm QD 160mm QD 160mm QD 160mm OMD B=8T 15cm 25cm20cm thick

16. LCWS11, Granada, September 26-30, 2011 Energy Deposition in IR Dipoles 16Muon Collider MDI & Backgrounds - N.V. Mokhov The open midplane design for the dipoles provides for their safe operation. The peak power density in the IR dipoles is about 2.5mW/g, safely below the quench limit for the Nb 3 Sn superconductor based coils at the 1.9-K operation. 7-mm wide Albemet spacers in the gap (with a minimal impact on the coil heating). Dynamic heat load W-rods: 200 W/m 1.9-K LHe: 245 W/m

17. LCWS11, Granada, September 26-30, 2011 Energy Deposition in IR Quadrupoles 17Muon Collider MDI & Backgrounds - N.V. Mokhov First 4 quadrupoles are operationally stable, while the level in next three IR quadrupoles is 5 to 10 times above the limit. This can be reduced with thicker masks and tungsten liner in the quad aperture a (cm) 5x5x Q1 5y5y s (m) Q2 Q4 B1 Q5Q6Q3 Q2 Q5

18. Machine-Detector Interface W  = 10 o 6 < z < 600 cm x:z = 1:17 BCH 2 cladding Q1  = 5 o LCWS11, Granada, September 26-30, 201118Muon Collider MDI & Backgrounds - N.V. Mokhov Sophisticated shielding: W, iron, concrete & BCH 2

19. Nozzle at IP It is with a limiting aperture of R~3mm at ~1 m from the IP, with an interior conical surface which opens outward as it approaches the IP. These collimators have the aspect of two nozzles spraying electromagnetic fire at each other, with charged component of the showers being confined radially by solenoid magnetic field and photons from one nozzle being trapped (to whatever degree possible) by the conical opening in the opposing nozzle. Tungsten with borated polyethylene cladding. LCWS11, Granada, September 26-30, 201119Muon Collider MDI & Backgrounds - N.V. Mokhov

20. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 20 Nozzle Optimization Optimum: z~120 cm with r=3.6mm at this z Aspect ratio x:z = 1:35

21. How Nozzle & Masks Work: Ten  - Decays at -6 to +20 m LCWS11, Granada, September 26-30, 201121Muon Collider MDI & Backgrounds - N.V. Mokhov

22. Load to Detector: Nozzle Effect ParticleMinimal 0.6-deg10-deg Photon1.5 x 10 11 1.77 x 10 8 Electron1.4 x 10 9 1.03 x 10 6 Muon1.2 x 10 4 8.00 x 10 3 Neutron5.8 x 10 8 4.00 x 10 7 Charged hadron 1.1 x 10 6 4.67 x 10 4 Number of particles per bunch crossing entering detector 0.6-deg 10-deg X:Z=1:20 A factor of 1000 for , e ± LCWS11, Granada, September 26-30, 201122Muon Collider MDI & Backgrounds - N.V. Mokhov

23. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov23 Bethe-Heitler Muons for 2 Beams

24. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov24 Muon Flux in Orbit Plane at |z| < 100 m 

25. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov25 Neutron and Photon Fluence n  Maximum neutron fluence in the innermost layer of the silicon tracker for a one-year operation are at a 10% level of that in CMS at the luminosity of 10 34 cm -2 s -1

26. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov26 Charged Hadron and Muon Fluence  ch.h

27. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov27 Absorbed and Residual Dose Gy/yr mSv/hr ~10% of that in CMS in the innermost layer of the silicon tracker Peak is less than 1% of that in CMS

28. Source Term to Feed Detector Simulations MARS15 calculated source term at IS (entrance to black hole shown) to feed detector simulation groups LCWS11, Granada, September 26-30, 201128Muon Collider MDI & Backgrounds - N.V. Mokhov Interface surface (IS): around IP (r=2.2 cm z=±13 cm), nozzle outside up to z=±600 cm, r=655 cm cylinder and z=±750 cm planes High-statistics files of particles entering detector through IS have been calculated and released: Two 0.75-TeV beams Minimal variation of weights E th = 0.1 MeV TOF and full origin info Two groups (with external weight w 0 ):  ±25m, 0.5 M decays, w 0 =23  ±(25-190)m, 24 M decays, w 0 <<1

29. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov29 See Corrado Gatto’s talk

30. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov30 Main Characteristics of Backgrounds at IS 1.Origin in lattice 2.Spatial distributions at interface surface 3.Particle and energy flows into detector 4.Momentum spectra 5.Time distributions

31. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 31 Origin in Lattice The origin of all particles (except muons) entering the detector is the straight section of about ±2 to ±25 m near the IP with a broad maximum from 6 m (back of nozzle) to 17 m (IP side of the first dipole). This is the combined effect of Angular divergence of secondary particles Strong magnetic field of dipoles in IR Tight tungsten masks Good performance of optimized nozzles Confinement of decay electrons in the aperture (inside detector), forcing them to hit the nozzle on the opposite side of IP

32. Source Tagging LCWS11, Granada, September 26-30, 201132Muon Collider MDI & Backgrounds - N.V. Mokhov

33. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 33 Origin in Lattice: Muons On the contrary, Bethe-Heitler muons hitting the detector are created in the lattice as far as 200 m from IP, with 90% of them produced at ±100 m near IP. The fine structure of these distributions is related to the lattice details.

34. Source Tagging: Muons LCWS11, Granada, September 26-30, 201134Muon Collider MDI & Backgrounds - N.V. Mokhov

35. Longitudinal Distributions of Entry Points LCWS11, Granada, September 26-30, 201135Muon Collider MDI & Backgrounds - N.V. Mokhov  + beam Maxima at abs(z)<1.5m: thinnest shielding

36. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 36 Lateral Distributions of Entry Points The fact that most particles (except muons) are produced close to the IP and not affected by the strong dipole magnetic field results in the azimuthal symmetry of the source term with the corresponding distributions at MDI being flat within r < 3 m. Angular distributions of these particles on the interface surface also have the azimuthal symmetry.

37. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 37 Lateral Distributions of Entry Points: Muons On the contrary, Bethe-Heitler muons are strongly affected by the magnetic fields of the dipoles on their long way to IP. As a result, azimuthal distributions of these muons have a strong asymmetry. E.g., for  + beam, secondary  + are deflected by the IR element magnetic fields to the same side as a  + bunch. Secondary  - are deflected to the opposite side. Many secondary muons and associated n,  and e ± hit the detector at large lateral distances horizontally!

38. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov38 Muons Entering Interface for  + Beam Ring outside ++ -- Azimuthal distributions are practically flat (at r < 3 m) for all particles but muons

39. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov 39 Particle Fluence in Horizontal Plane at z=0 Ring outside

40. LCWS11, Granada, September 26-30, 201140Muon Collider MDI & Backgrounds - N.V. Mokhov Particle and Energy Flow into Detector ParticleE th (MeV), MeV/c, TeV  0.21.8×10 8 0.91164 n0.14.1×10 7 45172 e + /e - 0.21.0×10 6 6.05.8 Ch. Hadr.14.8×10 4 51312 Muon18.0×10 3 23030184 Mean numbers, momenta and total kinetic energy flow of background particles (with cutoff indicated) per bunch crossing Total: 540 TeV

41. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov41 Momentum Spectra at MDI

42. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov42 Time Distributions at MDI wrt Bunch x-ing

43. Time Gate for Background Rejection in CLICCT LCWS11, Granada, September 26-30, 201143Muon Collider MDI & Backgrounds - N.V. Mokhov With aggressive 3-ns time gate, one gets rejection ~1000 for neutrons and ~260 for all other background particles (assuming fast < 0.5 ns vertex and tracker silicon detectors) CLICCT = VXD + SiT + FTDTOF – T0 time gate Timing wrt expected arrival time at CLICCT for IP photons

44. LCWS11, Granada, September 26-30, 2011Muon Collider MDI & Backgrounds - N.V. Mokhov44 Double-Layer Criterion First MARS15-ILCroot results by N. Terentiev on combination of modest 10-ns timing gate and double-layer approach for n+  backgrounds in vertex barrel: o Rejection of ~30 and remaining occupancy 1-2% in inner two layers o Rejection of ~2400 and negligible remaining occupancy in outer two layers

45. LCWS11, Granada, September 26-30, 2011 Summary 45Muon Collider MDI & Backgrounds - N.V. Mokhov Design solutions have been found and tested in simulations for a 1.5-TeV lattice at L=10 34 cm -2 s -1 for its beam dynamics performance, IR magnet quench and mechanical stability and reasonable dynamic heat loads to 1.9-K cryogenics. Detector background simulations are advancing well, MDI optimization is underway, main features of background are well understood, files are available to the community (to be updated soon). Detector response modeling in presence of machine backgrounds has been started and progressing very well, focusing on combination of timing and double-layer criteria. Near-term plans: repeat this for √S =3 TeV muon collider.