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An Active TARget for MEG-II, a status report

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Presentation on theme: "An Active TARget for MEG-II, a status report"— Presentation transcript:

1 An Active TARget for MEG-II, a status report
G.Cavoto INFN Roma Riunione referee INFN Pisa, 14 gennaio 2014

2 MEG target geometry Emerging positrons into MEG DCH t volume z
Muon depth Muon beam ~20 deg Current MEG target total thickness (t) is 205 microm polyethilene photon XEC Muon are stopped along z [effective thickness t/sin(20deg)] Some spill-out in downstream region Positron affected by multiple scattering and energy loss (proportional to t) Positron can annihilate and produce background photons (proportional to t) Spill-out [endplate] 14/1/2014

3 Active TARget concept Light collection y
Only one end of the fiber instrumented! 14/1/2014

4 Performance comparison
MEG Upgrade ATAR made of 250 mm thick square scintillating fibers. Fully efficient ATAR is considered Use cylindrical all stereo DCH with full efficiency and best R resolution (100 mm) WITH A PERFECT SPECTROMETER ATAR gives slightly better performances 14/1/2014

5 Use both positron (28 MeV) and muon beams
PSI PiE5 test beam May 13 Housing for target and ext. trigger Alignment Ext trigger BTS Beam Collimator Beam Ext. trigger with small scint +SiPM (BC400 2x2x2 mm3 coupled to 3x3 mm2 SiPM) Use both positron (28 MeV) and muon beams for prototype v2 14/1/2014

6 Results with positrons
28 MeV positron beam (change Separator HV) Use downstream external trigger (in synch with RF) Fiber Ext trigger Prot. V2: Electron (Sr90) and positrons seen with reduced efficiency (~35%) 14/1/2014

7 Results with muons Surface muon stopped in target
Trigger on emerging Michel positron Signal on fiber from emerging positron (muon is microsec away) Ext trigger Fiber Very little time, 10 days forseen in 2014. Start a new prototype (V3) to recover missing efficiency 14/1/2014

8 Update since last september
New full-scale prototype (V3) tested in lab (PSI) Double readout fiber (with/without Al coating): estimate maximal total collected light and detection efficiency Single readout fiber with reflector at the end (sputtered Al and painted Al) Array with coated Al around fiber and sputtered Al on the free end of the fiber (to measure the optical cross-talk) Study of the induced background coming from support (passive/active) into the experiment. First design of the mechanical integration of an active (or passive) target within the new DCH. A collaboration PSI (P.R.Kettle, A.Papa,G.Rutar) and INFN Roma (G.Cavoto, E.Ripiccini) Support from PSI technical services. 14/1/2014

9 90Sr lab test 14/1/2014

10 The double-readout prototype
Measure the total detected light 14/1/2014

11 Signal charge spectrum
Doubly readout fibers, one SiPM at each end Calibrated spectrum One SIPM only Sum of two SiPM signal Expected 5 p.e. Measured 4.3 14/1/2014

12 Efficiency estimate At least one p.e. in presence of external trigger
Collimator size known with relatively large error. A conservative error of 10% relative on efficiency must be used. A lesson learned: use of optical cement worsens efficiency There is still about 20% efficiency missing (SiPM/fiber mechanical coupling? ) 14/1/2014

13 Single readout fiber results
ATAR MEG-II configuration Test of different Al mirror on not-instrumented end 14/1/2014

14 Results for single readout fiber
Al mirror on one end gives on the other instrumented end 1.5 more light than no mirror (as expected) 14/1/2014

15 Optical cross-talk Array of 4 fibers:
new prototype (V3): fibers with 30 nm sputtered Al coating Prot V2 Prot V3 14/1/2014

16 XEC background More material (thicker target, service fibers, support) might induced a larger background in XEC (positron Bremsstrahlung, annihilation in flight) AIF + Br. (dotted) AIF background from target itself scales with target thickness Radiative (dashed) What about the other material ? 14/1/2014

17 MEG-II Geant4 material simulation
CDCH with 2pi coverage + passive target 140 mum thickness, 15 deg angle, no holes R[cm] All the photons emitted from Michel positron (no cut on their energy) XEC COBRA endcap CDCH endplate Support Passive target z [cm] 14/1/2014

18 Different support and service fibers
Baseline passive target ATAR with service fibers 14/1/2014

19 Energy deposited in XEC
Number of events with detected photon in XEC per positron Baseline-2pi Baseline (CDCH with missing sector) ATAR-2pi Ee>51MeV only Full EXEC [MeV] EXEC: energy deposited in XEC by photons and converted in scintillation No striking difference between different layouts 14/1/2014

20 Mechanical integration of an ATAR
Discussion started Incoming Muon beam SiPM located on the first endplate All inside DCH inner radius (168 mm) Upstream sector (DCH extension, within COBRA volume) Service fibers (A)TAR need be moved (CEX and CW calibration targets) 14/1/2014

21 Multiple uses of ATAR Continuous beam monitoring (detecting light from muons) MEG “normalization”: counting muons Y- beam spot measurement If ATAR can be 90deg rotated: X- and Y-beam spot available Muon beam centering (done now with auxiliary device and time consuming) 14/1/2014

22 Conclusion and plans We have a fiber+SiPM assembly with a 75% efficiency to detector electrons ATAR services not expected to worsen XEC background (besides target material itself does) Discussions of possible solution to integrate ATAR in MEG-II going-on Aim to experimentally detect positrons from stopped muons in the target. Produce a new (V4) version of ATAR prototype Test it in lab (Sr90 setup) (beginning 2014) INFN LNF BTF single tagged electrons and positron in Mar/Apr and later in 2014 PSI PiE5 (positron and MUON): 10days in Fall 2014 Hopefully this device will be considered for the MEG-II detector 14/1/2014

23 Back up 14/1/2014

24 Constraint at the target
A point on ATAR can help in reducing such effect k is proportional to the momentum resolution (this effect tends to vanish if momentum resolution improves) 14/1/2014

25 Beam and target Thin Passive Target need REDUCED Range Straggling
Use of SUBSURFACE MUONS PROBLEM is RATE REDUCTION from P3.5 ➪ Longer Measuring Times 14/1/2014

26 SiPM specs 14/1/2014

27 mip signal (0.5mm) Prot V1 14/1/2014

28 mip signals on single 0.25mm fiber
SiPM Hamamatsu S C Prot V1 Prot V1 With Al x1.8 more light! No Al Detection efficiency ~80% (ext. scint trigger) Similar results with sputtering 14/1/2014

29 Measurements of collimator
14/1/2014

30 Distribution of Max E emitted photons
ATAR-2pi-service EXEC>40 MeV Ee > 51 MeV generated only Target + CDCH XEC ATAR DCH DCH Outer cylinder 14/1/2014


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