1. The new MEG tracker Marco Grassi MEG Italia

2. CSN1 25/09/20122 Present system  16 chambers composed as follow 4 x12  m of kapton (cathodes) 50  m BeCu cathode wires 25  m NiCr anode wires 2 x 7 +3 mm He:C 2 H 6 (50/50)  Single chamber x ~ 0.23 10 -3 X 0  Full e+ turn : x ~ 1.7 10 -3 X 0  Weak points  Mechanical complexity & positioning  Individual chambers  Electrical layouts  Cathode production  Noise on vernier strips

3. CSN1 25/09/2012 3 Performance summary Single hit resolution  R (mm) 250 (core) 300 (RMS)  Z (mm) 700 (core)1000 (RMS) Track resolution  (p) 350 KeV (core)  (  ) 7. mrad(at  = 0, 11 mrad aver.)  (  ) 10. mrad  (Y) 1.1 mm  (Z) 1.8 mm TC – DC reconstruction DC-TC matching eff. 41 %

4. CSN1 25/09/20124 Selected technology We are finalizing the following detector single volume gaseous detector U – V wire stringing for hit positioning along the wire low mass gas (He : iC 4 H 10 - 90% : 10%) thin wires and small cell size Tentative goals Single hit resolution ~100  m in r Momentum resolution ~150KeV Angular resolution ~5 mrad DC-TC matching eff. ~90 %

5. Signal events with TC CSN1 25/09/20125 TC Hits Empty space after removing PMTs

6. Key item #1: Single hit resolution Resolution on the impact parameter: 130 ÷ 350  m  He/iC 2 H 4 gas mixture  25  m wires Limiting factors  Primary ion. Density  Time measurements 6 Garfield simulation KLOE Prototype MEG aims at better performances  Faster electronic chain HF preamplifiers + DRS  Better use of all clusters in the signal Cluster timing Role of an active target (G. Cavoto) CSN1 25/09/2012

7. Key item #2: chamber ageing CSN1 25/09/20127 Z [cm] Positron hit rate density by MC simulation: Michel e+ generated over 4  rate 1x10 8 mustop/s max rate 45 kHz/cm 2 For 300 dd and 2x10 5 gain this corresponds to 0.5 C/cm R[cm]

8. Schedule and Milestones CSN1 25/09/20128 Prototypes  Small prototype for hit resolution  Si telescope for high precision tracking  Short prototype for ageing  Long prototype for validation of construction procedure

9. Key elements Benefit from past experience and know how (Lecce) Work in parallel (Rome, Lecce, Pisa) Use or reuse of existing infrastructures (Pisa, Lecce) CSN1 25/09/20129

10. Small prototype to measure achievable resolution - 8x8 small squares cell (0.7x0.7cm 2 ) - 50 cm long - He/Isobutane 90/10 - No stereo angle - Lecce FE board to test cluster timing - Test with Pisa telescope - wire stringing in progress Mylar windows to reduce MS of incoming muons Hit resolution Roma CSN1 25/09/201210

11. Hit resolution 11 Pisa CSN1 25/09/2012  Reuse spare BaBar tracker elements  Resolutions at the DUT location 20 – 40  m  Trigger with external scintillator telescope  Operative by middle of October Si strip telescope for precise cosmic muon tracking

12. tracks T3 T2 T1 Δ  Arrange 3 cells with the central one displaced by   Measure t i drift times, compute d i drift distances  For straight tracks it results independently of drift distance and angle (almost)  Measure single hit resolution averaged on all impact parameters and angles if Hit resolution estimate Lecce 2Δ

13. Setup close to working point  8 mm drift tube  20  m wire, He/isobutane  200  m wall thickness  100  m nominal stagger   2x10 5 gain  <1 muon /min  Measured for b>1mm using first cluster only Hit resolution estimate Lecce Remarks  Goal resolution obtained for large impact parameter using the first cluster only  More than 40 hits (out of 60) have adequate resolution

14. CSN1 25/09/2012 14 FE decoupling/ protection/ matching 2° stage/ Output driver 1° stage  Use of commercial IC AD8009 OpAmp and THS4509 Diff OpAmp  Fulfill BW, gain and linearity requirements  Design in the 7 mm spacing  Mitigated power consumption: now at 40 mW  Different prototypes available Lecce

15. Ageing prototype and gas system CSN1 25/09/201215  Gas volume at ultra vacuum grade cleanness  Thin windows on both short sides  Dedicated small prototypes  25 / 50 or 25/ 80  m wires  He/iC 4 H 10 (CO 2 or H 2 O doping)  7x7 mm 2 cells  2x10 5 gain  Gas system with premixed bottle  Supply Rome and Lecce prototypes  Operational within first half of Oct. Pisa

16. Next year commitments CSN1 25/09/201216

17. Preliminary sj division CSN1 25/09/201217 Total~350 kEu

18. Work Packages CSN1 25/09/201218 Lecce Design Wiring machine FE electronics Mounting PCB Mechanics Material proc. Pisa Design Mechanics Assembly Material proc. Test DAQ & trigger Roma HV Material proc. Preliminary subdivision constraints from resources and costs Discussion in progress PSI Gas system

19. Spare

20. X-rays sources CSN1 25/09/2012 20 Two generators available in Pisa  Both with X-rays of 5-10 keV  X-rays attenuation length in iC 4 H 10 at 10% ~ 1 m  Low power generator 1 W corresponding to 10 7 X-ray/cm 2 /s on the detector standard simple stable generator  High power generator Tunable from 100 W up to a 1.2 kW Up to 10 10 X-ray/cm 2 /s on the detector Could rise X-rays energy Requires water cooling Desired acceleration factor 30-50: total charge in less than 2 weeks

21. Accumulated charge CSN1 25/09/201221 Order of magnitude  tests in KLOE for cumulated charges of 3 mC/cm reported tiny, barely detectable effects  For 300 dd at 1x10 8 mustop/s and 2x10 5 gain this corresponds to 0.5 C/cm Experimental test needed  X-ray source  Dedicated small prototype with baseline parameters  20 and 50  m wires  He/iC 4 H 10 (or He/iC 4 H 10 /CO 2 - He/iC 4 H 10 /H 2 O)  7x7 mm 2 cells  2x10 5 gain

22. CSN1 25/09/201222 Long prototype Full length prototype is planned to test details of construction procedure This prototype is not requested for making decision on the proposed system Test of wire stringing procedure in our case Test of wire tensioning Test of reproducibility Possible test ion COBRA magnetic field

23. CSN1 25/09/201223 Mechanical structure A prototype of a tracking chamber for Mu2e is under construction in Lecce by non MEG members optimized for Mu2e constraints MEG has different and relaxed requirements:  End plates could be infinitely rigid  Inner and outer dimension are fixed  Design PCB with wire pads, electronics and connectors for both chamber ends  Mount electronics and connectors  Solder wires with correct tension  Glue together the PCBs and spacers  Sustain tension with external rigid end-plates

24. CSN1 25/09/201224 Material Hand made estimate  Less material than in the present system (1.7x10 -3 X 0 )  Gases and wires equally share the chamber thickness  Non negligible contribution from target  Combined  0 = 7.4x10 -3 rad Geometry Number of planesn10 Cell dimensionmm7 Field wire spacingmm4 Guard wire spacingmm5 Signal Wire diam.mm0.025 Field wire diam.mm0.050 Protective foil radiuscm17.0 Signal positroncm14.0 ItemDescriptionThickness 00 10 -3 X 0 mrad MEG target (115  m Polietilene) 0.23 0.0029 Sense wires (25  m Ni/Cr) 0.16 0.810.0057 Field wires (50  m Al) 0.60 guard ring wires (50  m Al) 0.01 protective foil (20  m Kapton) 0.14 0.0022 Inner gas(pure He)0.06 0.430.0041 Tracker gas(He/iBut. 90/10)0.36 Total1 full turn w/o target1.37 0.0077 Second order optimization 1.Different field wire spacing 2.Larger outer cell size

25. CSN1 25/09/201225 Reconstruction Completely new code Controlled on a dedicated sample Reconstruction code: Kalman filter Track model: state vector and covariance matrix propagation in B field complete material simulation (GEANE) MC data: GEANT hits without Z information Detector response not yet implemented in MC: detector emulated by smearing MC hits in the transverse direction 100  m to simulate expected response 10  m to study material effects Reconstruction: only the first e+ turn is used

26. CSN1 25/09/201226 Reconstruction: real case Assign a reasonable hit smearing : 100  m in the transverse direction  (p) ≈ 140 KeV  (  ) ≈ 8.1 mradall  angles  (  ) ≈ 6.2 mrad  (  ) ≈ 5.2 mrad at 

27. CSN1 25/09/201227 Reconstruction: material limit Explore the material effect in case of no contribution from hit resolution: 10  m hit smearing in the transverse direction  (p) ≈ 100 KeV  (  ) ≈ 6.1 mradall  angles  (  ) ≈ 5.1 mrad Momentum resolution is already adequate Check of material budget

28. CSN1 25/09/201228 Reconstruction: thinner target 1.material effect no contribution from hit resolution: 10  m MC hit smearing 205 mm :  (p) ≈ 100 KeV  (  ) ≈ 6.1 mrad all  angles  (  ) ≈ 5.1 mrad 105 mm :  (  ) ≈ 5.5 mrad all  angles  (  ) ≈ 4.4 mrad Modifying the target contribution in quadrature 2.Reasonable detector effect: 100  m MC hit smearing 205 mm :  (p) ≈ 140 KeV  (  ) ≈ 8.1 mrad all  angles  (  ) ≈ 6.2 mrad 105 mm :  (p) ≈ 130 KeV  (  ) ≈ 7.1 mrad all  angles  (  ) ≈ 5.1 mrad  (  ) ≈ 4.9 mrad at  =0

29. Example of track identification CSN1 25/09/201229 1 signal event + 13 Michel tracks conservative side (x,y) Plane (z,y) Plane Usual number of Michel tracks is  (7 ÷ 8) for 10 8 mustop/s

30. CSN1 25/09/201230 Wires and Cells Starting dimensioning Chamber with stereo wires with U and V views Square projective cells of 0.7 cm Stereo planes U e V rotated by ~ 8 deg with respect to Z Z resolution ~ 7 time the transverse resolution 25 and 60  m anode and field wires He / iC 4 H 10 mixture at 90/10 ratio Total length 180 cm Outer radius 29.2 cm ~1380 anode wires ~7500 field wires