1. David Hitlin ICHEP 2014 July 5, 2014 1 The Straw Tube Tracker and Crystal Calorimeter of the Mu2e Experiment David Hitlin Caltech ICHEP 2014 July 5, 2014

2. David Hitlin ICHEP 2014 July 5, 2014 2 A search for muon to electron conversion in the field of an Al nucleus – Initial state: muonic Al atom – Final state: a single mono-energetic electron The Standard Model rate is 10 -54 There is an observable rate in many new physics scenarios – Best current limit is from SINDRUM-II: CR(   e on Au) < 6  10 -13 @ 90% CL – Mu2e will have a single event sensitivity of 2.5  10 -17 The Mu2e experiment at Fermilab e-e- Michel spectrum resolution effects

3. David Hitlin ICHEP 2014 July 5, 2014 3 One cycle of the muon beamline μ are accompanied by e -, e +, π, anti-protons … these create prompt backgrounds strategy: wait for them to decay. extinction = (# protons between bunches)/(protons per bunch) requirement: extinction < 10 -10 selection window, defined at center plane of the tracker Proton pulse arrival at production target shapes are schematic, for clarity

4. David Hitlin ICHEP 2014 July 5, 2014 4 Stopping target and detectors Jan 19, 2014 straw tube tracker 17 Al foil stopping target BaF 2 calorimeter incoming muon beam = 7.6 MeV field gradient

5. David Hitlin ICHEP 2014 July 5, 2014 5 Requirements Tracker provide a resolution with core σ < 180 keV/c for a 105 MeV/c electron in the nominal 1 Tesla solenoidal field. Non-Gaussian tails, particularly any high-side tail, must be controlled such that the DIO background results in much less than one event at design sensitivity. have an acceptance of at least 20% for conversion electrons (105 MeV/c) Be capable of operating in an ambient vacuum. have a low enough leak rate to not drive the pressure in the detector solenoid above 10 −4 Torr. The estimated allowed leak rate, inclusive of virtual leaks and slow out-gassing, is 7 cm 3 /minute. not require the experiment to go down for repairs more than once/year. be repairable in two days. have electrical power distribution systems which can cope with vacuum failures that would put the device in the Townsend regime. withstand rates of 5 MHz/straw (time averaged, highest rate straw) in the baseline tracker, or 500 kHz/cm 2. operate at reduced and reversed magnetic field Calorimeter an energy resolution  E  5% (FWHM/2.35) at 100 MeV to confirm the more precise electron momentum measurement from the tracker control or measure temperature and gain variations such that the combined response of a calorimeter crystal and its readout does not vary by more than 0.5%, i.e., is small compared to the energy resolution a timing resolution better than  t ~ 0.5 ns to ensure that energy deposits in the calorimeter are matched in time with events reconstructed in the tracker a position resolution better than  x,y  1 cm to allow comparison of the position of a calorimeter energy cluster to the extrapolated trajectory of a reconstructed track provide rejection of cosmic ray muons of ~200 while retaining high signal efficiency (~90%) for conversion electrons) provide a trigger, using hardware, software or firmware, that can be used to identify events with significant energy deposits in order to control the required bandwidth of the DAQ system operate in the unique, high-rate Mu2e environment and maintain its functionality with gamma radiation exposures up to 50 Gy/crystal/year and for a neutron flux equivalent to 10 11 n _1 MeVequivalent /cm 2 have adequate monitoring of temperature, pressure and radiation dose rate to allow extraction of optimum performance for the calorimeter, as well as safe of operation of the system. 5

6. David Hitlin ICHEP 2014 July 5, 2014 6 Tracker

7. David Hitlin ICHEP 2014 July 5, 2014 7 Tracker design principle beam’s-eye view of the tracker m  /2 mm no hits in tracker some hits in tracker, tracks not reconstructable reconstructable tracks By construction, most DIOs miss the tracker

8. David Hitlin ICHEP 2014 July 5, 2014 8 Tracker: strawtubes operating in vacuum Panel: 2 layers, 48 straws each Plane: 6 self supporting panels 5mm metalized Mylar straw

9. David Hitlin ICHEP 2014 July 5, 2014 9 Arrangement of 48 straws in a panel 9 days

10. David Hitlin ICHEP 2014 July 5, 2014 10 Straw tube performance simulagtion with Garfield/G4 10

11. David Hitlin ICHEP 2014 July 5, 2014 11 Tracker: strawtubes in vacuum relative rotation: Tracker = 20 stations 2 planes = 1 station6 panels = 1 plane Total straws 23,040

12. David Hitlin ICHEP 2014 July 5, 2014 12 Signal sensitivity for a 3 Year Run Reconstructed e - momentum Stopped μ: 5. 8 × 10 17 For R = 10 -16 N μe = 3.94 ± 0.03 N DIO = 0.19 ± 0.01 N Other = 0.19 SES = (2.5 ± 0.1) × 10 -17 Errors are statistical only

13. David Hitlin ICHEP 2014 July 5, 2014 13 Calorimeter

14. David Hitlin ICHEP 2014 July 5, 2014 14 The energy resolution of the calorimeter (~5% at 105 MeV) cannot compete with the momentum resolution of the tracker in discriminating against DIOs – However, E/p resolution allows e/  discrimination Excellent time resolution (<0.5 ns) is extremely useful – In combination with E/p, allows excellent rejection of cosmic rays that evade the veto system that surrounds the detector solenoid – Provides a means of seeding track finding starting at the calorimeter rather than at the very busy target region, thereby improving track- finding efficiency by ~10% – Can provide an orthogonal trigger Calorimeter functionality

15. David Hitlin ICHEP 2014 July 5, 2014 15 BaF 2 scintillating crystal calorimeter Two disk geometry – 930 crystals/disk Hexagonal BaF 2 crystals; APD or SiPM readout Provides precise timing, PID, background rejection, alternate track seed and possible calibration trigger. 33 mm across flats 200 mm long

16. David Hitlin ICHEP 2014 July 5, 2014 16 Geometric optimization 16 Radii of disks Separation of disks

17. David Hitlin ICHEP 2014 July 5, 2014 17   = 0.9 ns @ 220 nm (15%)    650 ns @ 300 nm (85%) Photosensor requirements Work in a magnetic field Have good quantum efficiency in the UV To fully take advantage of the rate capability implies by the fast component, must discriminate between 220 & 300 nm, i.e., “be “solar-blind” Have good timing characteristics Page 17 BaF 2 presents opportunities and challenges Scintillation properties

18. David Hitlin ICHEP 2014 July 5, 2014 18 Scintillation pulse shapes BaF 2 Ren-yuan Zhu LaBr 3 LSO LYSO LaCl 3

19. David Hitlin ICHEP 2014 July 5, 2014 19 There is an existing Hamamatsu MPPC, developed for the MEG LXe calorimeter, that has extended UV response (QE~17%), but it does not have fast timing characteristics and is not solar-blind A Caltech/JPL/RMDinc consortium has undertaken the development of a sensor with these characteristics – A standard APD is thinned, “delta-doped” with a monolayer of boron and coated with an antireflection filter This technique has previously been used at JPL to produce UV-sensitive imaging CCDs for astronomy Page 19 Needed: a fast, solar blind APD with high quantum efficiency S. Nikzad, “Ultrastable and uniform EUV and UV detectors,” SPIE Proc., Vol. 4139, pp. 250-258 (2000).

20. David Hitlin ICHEP 2014 July 5, 2014 20 Thinned drift region and  -doped potential produce high QE at 220 nm and improved time response Solar-blind response with good efficiency produced by atomic layer deposition (ALD) filter Page 20 Expected performance of the  -doped APD BulkSurface Blocking ratios (220 vs 310 nm) 3 layer = 12:1 5 layer = 400:1 7 layer = 15,000:1 calculated measured

21. David Hitlin ICHEP 2014 July 5, 2014 21 The proverbial bottom line A large area delta-doped, ALD-coated APD, currently being developed, Can fulfill the Mu2e requirements for a BaF2 calorimeter with excellent time resolution and high rate capability

22. David Hitlin ICHEP 2014 July 5, 2014 22 Time resolution <0.5 ns Calculated energy resolution of the Mu2e calorimeter Performance depends on backgrounds photoelectron yield and electronics noise Position resolution of calorimeter clusters 10.3 mm in x and y

23. David Hitlin ICHEP 2014 July 5, 2014 23 Time resolution cut on calorimeter clusters improves track- finding efficiency Page 23 Seeding track with a calorimeter cluster Figure 6. Distribution of the hits in the tracker before (left) and after (right) the application of a cut on the  t HITS variable described in the text. The situation for the pattern recognition is dramatically improved.

24. David Hitlin ICHEP 2014 July 5, 2014 24 Calorimeter provides excellent rejection of cosmic ray muons e/  discrimination using E/p and timing

25. David Hitlin ICHEP 2014 July 5, 2014 25 Provides a switchable 6 MeV line Based on the B A B AR calibration system 19 F(n,  ) 16 N calibration system

26. David Hitlin ICHEP 2014 July 5, 2014 26 FEA analysis of crystal supports on the inner and outer radii Outer disk radius = 660 mm Inner disk radius = 351 mm N. of crystals = 930 Crystal size = 33 mm

27. David Hitlin ICHEP 2014 July 5, 2014 27 The Mu2e tracker and calorimeter systems design fully meet the experiment’s design requirements Both systems are in an advanced stage of design and prototyping, with beam tests planned or underway Mu2e commissioning to start at the beginning of 2020 Page 27 Conclusions

28. David Hitlin ICHEP 2014 July 5, 2014 28 Mu2e schedule Calendar Year Solenoid design, construction and commissioning are the critical path Today assemble and commission the detector:

29. David Hitlin ICHEP 2014 July 5, 2014 29 Page 29

30. David Hitlin ICHEP 2014 July 5, 2014 30 The Mu2e Collaboration Boston University Brookhaven National Laboratory University of California, Berkeley and Lawrence Berkeley National Laboratory University of California, Irvine California Institute of Technology City University of New York Duke University Fermilab University of Houston University of Illinois, Urbana-Champaign Lewis University University of Massachusetts, Amherst Muons, Inc. Northern Illinois University Northwestern University Pacific Northwest National Laboratory Purdue University Rice University University of Virginia University of Washington, Seattle Laboratori Nazionale di Frascati INFN Genova INFN Lecce and Università del Salento Istituto G. Marconi Roma INFN,, Pisa Universita di Udine and INFN Trieste/Udine JINR, Dubna Institute for Nuclear Research, Moscow 135 members from 28 institutions About half of us: Nov 2013 http://mu2e.fnal.gov

31. David Hitlin ICHEP 2014 July 5, 2014 31 Detector solenoid is surrounded by a cosmic ray veto (CRV) Mu2e CRV Status: 11/8/2013 CRV-T CRV-L CRV-D CRV-R CRV-U Four layers of extruded plastic scintillator Fiber/SiPM readout (neutron damage is an issue) Al and concrete shielding Correlated hits are a concern

32. David Hitlin ICHEP 2014 July 5, 2014 32 The “Ralf event” In massive MC runs to optimize the CRV, an event was found that evaded the CRV, passed through the target and the tracker, and stopped in the calorimeter The calorimeter, however, provides substantial additional background rejection, through  /e PID, with a combination of timing information and E/p

33. David Hitlin ICHEP 2014 July 5, 2014 33 Ren-yuan Zhu A fast crystal “figure of merit” Motivates R&D on fast crystals and appropriate solid state readout

34. David Hitlin ICHEP 2014 July 5, 2014 34 Geometry and Readout

35. David Hitlin ICHEP 2014 July 5, 2014 35 clearance 20+4.5 5 15 5 15 5 70 cm digi HV-LV