Study of the MPPC for the GLD Calorimeter Readout

1. Study of the MPPC for the GLD Calorimeter Readout Satoru Uozumi (Shinshu University) for the GLD Calorimeter Group (KNU, Kobe, Niigata, Shinshu, ICEPP Tokyo, Tsukuba) • Introduction • Performance of 1600-pixel MPPC • GLD calorimeter prototype • Summary & Plans

2. International Linear Collider • Center-of-mass energy at 500 ~ 1000 GeV. • Four detector concepts are currently proposed. • Various precision measurements with clean e+e- collision. • e+e- -> Higgs, SUSY, W, Z, tt … -> Multi-jet final states • Precise jet energy measurement is crucial ! GLD LDC SiD 4th

3. Particle Flow Algorithm (PFA)- A powerful method for precise jet energy measurement - Key : Momentum resolution > Energy resolution (central tracker) (calorimeter) • Charged particles (~60% in a jet) are measured by central tracker. • Photons (mainly from p0 decays, ~30%) are measured by electromagnetic calorimeter. • Neutral hadrons (mainly KL0, ~10%) are measured by hadron calorimeter. ETOT = pe+ p+ pcharged hadron+ E+ Eneutral hadron [ tracks only] [calorimeter only] For the PFA, separation of jet particles in the calorimeter is indispensable.

4. The GLD Calorimeter • Sampling calorimeter with W/Pb - scintillator sandwich structure with WLSF readout • Particle Flow Algorithm (PFA) requires fine granularity for the calorimeter • Employ well-established plastic scintillator. • Scintillator stirp structure to achieve fine granularity. • Huge number of readout channels. • ~10M (ECAL) + 4M (HCAL) • Used inside 3 Tesla solenoid,. The MPPC is feasible for the GLD calorimeter readout !

5. What are required for the photon sensor? • Gain, Photon Detection Efficiency (P.D.E.) comparable to PMTs. • Gain at least 105. • P.D.E. ~ 20% (capable to distinguish MIP signal). • Dynamic range enough to measure ~100 GeV photons. • corresponds to ~5000 photoelectrons. • MPPC is non-linear device. -> necessary to know right response curve for correction. • Stability & Robustness. Tolerance to temperature variation, long-term use, magnetic field, neutron radiation. • Uniform performance among many pieces. • Acceptable dark noise rate, inter-pixel cross-talk probability. • Noise rate < 1 MHz, Cross-talk probability ~ a few per cent. • Low cost, compactness. • Price order of $1~5, package fitting to 2 mm thick scintillator strip.

6. Small package 1600 pixel MPPC 4 mm 1.3 mm • 1600 pixel MPPC with compact plastic package • (S10362-11-025MK) • Sensor size = 1 x 1 mm2. • suitable for attaching to scintillator strips. 3 mm Front Side Scintillator strip (1 x 4 x 0.3 cm) 1 x 1 mm WLS fiber MPPC Side view

7. Gain, Dark Noise Rate, Cross-talk • 30 oC • 25 oC • 20 oC • 15 oC • 10 oC • 0 oC • -20 oC Noise > 0.5 p.e. • 30oC • 25oC • 20oC • 15oC • 10oC • 0oC • -20oC DV0/DT = (56.0±0.1)mV/oC • 30 oC • 25 oC • 20 oC • 15 oC • 10 oC • 0 oC • -20 oC DV (over-voltage) • C … Pixel capacity • V0 … Breakdown voltage • These basic properties are almost OK. • Still need to improve temperature • dependence of breakdown voltage

8. Variation of the Gain over 700 MPPCs Variation = 0.45 V Variation < 3.3 % • Device-by-device variation is less than a few %. • g No need for further selection or categorization on massive use ! • Just need small tuning of operation voltages.

9. Variation of the Dark Noise (400 pieces) Noise > 0.5 p.e. Noise Rate (kHz) DV = Vbias – V0 (V) • Noise rate is far less than 1 MHz with all the samples. • Device-by-device variation is order of ~10 %.

10. Photon Detection Efficiency (P.D.E.) • P.D.E. = Q.E. x egeometry x eGeiger • Measured by injecting same light pulse into both MPPC and PMT, • and comparing light yield. LED WLSF MPPC 0.5 mm f holes ~ 16 % PMT MPPC PMT The 1600-pixel MPPC has comparable P.D.E. with conventional photomultipliers (15~20%).

11. Dynamic range • The MPPC is a non-linear device, because one pixel can detect one photon at once. • For a short light pulse input, response to input light can be theoretically • calculated as • However for the 1600-pixel MPPC, it is not the case ! • Since recovery time is order of a few ns, one pixel can detect a photon • several times. ? Recovery time << light input width Recovery time >> light input width

12. Recovery Time Measurement • Inject blight laser pulse • (width=52 ps) into the MPPC • After delay of Dt, inject blight LED • light pulse, and measure MPPC • outpu for the LED pulse. • Compare the MPPC output for the • LED pulse with and without the • first laser pulse. MPPC delay LED Oscilloscope view Black … MPPC output for Laser pulse Green … MPPC output for LED pulse Red … Laser + LED Blue … (Laser+LED)-Laser Dt Ratio of Blue / Green shows recovery fraction. t (msec)

13. Recovery fraction (%) Delay Recovery Time Result The curve is fitted by a function at 25 oC tD : dead time t : recovery time • Vbias = • 71.0 V • 71.5 V • 72.0 V • Recovery time of the 1600-pixel MPPC ~ 4 ns. • The shape does not depend on bias voltage.

14. w Response Curve Response curves taken with various width of LED light pulses. (gate width = 100 ns) LED PMT w = 50 ns 24 ns w = 50 ns 16 ns 8 ns 24 ns 1600 8 ns 16 ns • Dynamic range is enhanced with longer light pulse, • Time structure of the light pulse gives large effects in non-linear region. • No significant influence with changing bias voltage. • Knowing time structure of scintillator light signal is crucial • -> study is ongoing.

15. The GLD ECAL prototype Beam test has been performed at DESY using 1-6 GeV e+ beams. MPPCs (1600 pixels) Tungsten (3.5 mm thick) Scintillator layer (3 mm thick) e+ Frame Scintillator strip (1 x 4.5 x 0.3 cm) WLS fibre

16. MIP events (data without absorber) WLS Fibre readout strip Direct readout strip MPPC MPPC WLS fibre Scintillator strip MPPC Signal (ADC counts) Beam position (mm)

17. Results with tungsten absorber The calorimeter with the MPPC is working! Dynamic range seems to be enhanced (expect more study with higher beam energy in 2008). 1 23456 GeV 6 GeV e+ center injection No MPPC saturation correction Deviation from Linearity < 4 %

18. Summary • We are developing the 1600-pixel MPPC for the GLD calorimeter collaborating with Hamamatsu Photonics. • Basic properties are almost sufficient for the requirement. • Comparable gain / P.D.E. with photomultipliers. • Acceptable noise rate (~100kHz) and cross-talk probability (~10 %) • Variation of the gain among 800 pieces is small enough (<4%). • Dynamic range is enhanced thanks to the short recovery time! • However need more study for time structure of light signal from scintillator. • Result of the beam test demonstrates that the MPPC is feasible for the GLD calorimeter readout. • Further improvements of the MPPC performance is still underway with Hamamatsu (package, temp. dependence, dynamic range, etc…).

19. Backups

20. Jet Reconstruction @ ILC The tracks are used instead of making a calorimetric measurement of the energies of the charged hadrons (with large errors). Z → qq @ 91.2GeV Particle Flow Algorithm (PFA)

21. 4 mm Excellent photon counting ability 1.3 mm 3 mm 0,1,2,3,4,5,6,7, . . . Photoelectrons ! Front Side 1 photoelectron 2 photoelectrons

22. The MPPC has lots of advantages The MPPC is a promising photon sensor, and feasible for the GLD Calorimeter readout !