Evaluation of MPPC photon sensors for the PHOS upgrade in ALICE at CERN ATHIC 2014 7.Aug.2014 K.Tarunaga D.Sato, T.Sugitate Hiroshima University, Japan Outline • • • • PHOS (PHOton Spectrometer) Time of Flight MPPC (Multi-Pixel Photon Counter) Basic study using a laser pulser - Signal distribution, Gain and Linearity • Timing study using cosmic-ray - Event selection, Time-walk correction and Timing resolution • Summary ATHIC 2014 Kazuya Tarunaga 2 PHOS (PHOton Spectrometer) • PHOS characteristic - Lead-tungstate crystals(PWO) read out with APD - High granularity - High energy resolution σ/E = 3.5% (at 1 GeV) • Physics goal - Measurement of direct photons -> Precise measurement at low energy is critical. • Upgrade purpose PWO Crystal APD & Preamplifer - Neutral hadron rejection (e.g. anti-neutron) -> Good timing resolution is required. (～ sub-nano seconds) ATHIC 2014 Kazuya Tarunaga 3 𝑇𝑂𝐹𝛾 − 𝑇𝑂𝐹 𝑛 > 3𝜎 Time of Flight 𝛾 and 𝑛 are distinguishable Counts n 3𝜎 γ n γ PHOS TOF β =p/E required resolution σ [ns] 1 0.71 2.12 2 0.89 0.61 3 0.95 0.28 4 0.97 0.16 5 0.98 0.10 Required Resolution (anti-neutron mass: 1 GeV) p [GeV/c] ATHIC 2014 Kazuya Tarunaga 4 MPPC (Multi-Pixel Photon Counter) • Single photon sensor consisting of multiple APD pixels • High gain (105～106) • Good timing resolution • Operable in a magnetic field MPPC S12572-025C (http://hamamatsu.com) Hamamatsu Photonics Type No. S12572-010C S12572-025C ATHIC 2014 MPPC & Preamplifer(Current amp) Sensitive Number of Pixel Size Area Pixels 3×3 mm2 10×10μ m2 90,000 3×3 mm2 25×25μ m2 14,400 Kazuya Tarunaga 5 Basic study using a laser pulser Wavelength:403nm Power:174mW Width:80ps MPPC Laser Head 1kHz Optical Fiber Cable Filter HV 63~72V Pulser Gate Generator • • • • Measurement of Gain Bias voltage dependence Temperature dependence Linearity ATHIC 2014 In a Temperature Control Unit Temperature Control Unit -25~25℃ 1ch CS-ADC (RPC-022) Gate 8cm Optical Fiber Cable Filter MPPC Gate MPPC Kazuya Tarunaga 6 A distribution of the photon peaks, compared with a Poisson distribution of n = 2.6 Signal distribution 2p.e. 1p.e. 0p.e. 3p.e. 4p.e. 5p.e. 6p.e. 7p.e. 8p.e. 9p.e. The data seems deformed from the pure poisson because of cross-talks and after-pulses. • Single photon detection and good separation of photon peaks when the number of incident photon is small. ATHIC 2014 Kazuya Tarunaga 7 Low temp. (-25℃) Gain 14.4k-type High temp. (25℃) d 90k-type d: the average distance between the peaks 𝑑×𝑟 𝐺𝑎𝑖𝑛 = 𝑒 r: ADC resolution 0.25 [pc/ch] e: elementary charge 1.602×10-19 [C] • Gain becomes higher as temperature goes down. • Gain is proportional to the bias voltage. • 2 types of MPPC have different gain properties. ATHIC 2014 Kazuya Tarunaga 8 ADC Mean [ch] Linearity 𝑓 𝑥 = 𝑝0 × 1 − exp − 𝑝1 𝑝0 ×𝑥 Linear Plot 𝑝0: number of pixels 𝑝1: photon detection efficiency • The 90k-type has around 10 times wider dynamic range than that of 14.4k-type. • The data for very intense lights are not reproduced by this function due to a possible short recovery time. ATHIC 2014 ADC Mean [ch] Expected Number of Photons Kazuya Tarunaga Log-Log Plot Expected Number of Photons 9 Timing study using cosmic-ray ADC Gate Generator Gate TDC Coincidence Start Temperature Control Unit: −25℃ • A coincidence of two finger counters with PMT’s produces a trigger for a punch-through event. • MPPC, APD and all PMT’s are read out by CAMAC ADC and TDC. ATHIC 2014 Kazuya Tarunaga 10 Event selection Cosmic-Ray event Noise event • Applying pedestal cuts of PMT’s ADC distribution to extract punchthrough muon events ATHIC 2014 Kazuya Tarunaga 11 Time-walk correction threshold The trigger timing of a leading discriminator depends on its pulse height. This time-walk effect is corrected with a standard technique. discriminator signal time ATHIC 2014 𝑇𝐷𝐶 = Kazuya Tarunaga 𝑝0 𝐴𝐷𝐶 + 𝑝1 𝑝0, 𝑝1: 𝑐𝑜𝑛𝑠𝑡 12 MPPC and APD timing resolution 𝑇𝑂𝐹𝑀𝑃𝑃𝐶 𝑇𝐷𝐶𝑃𝑀𝑇1 + 𝑇𝐷𝐶𝑃𝑀𝑇2 = 𝑇𝐷𝐶𝑀𝑃𝑃𝐶 − 2 𝑇𝑂𝐹𝐴𝑃𝐷 MPPC 𝑇𝐷𝐶𝑃𝑀𝑇1 + 𝑇𝐷𝐶𝑃𝑀𝑇2 = 𝑇𝐷𝐶𝐴𝑃𝐷 − 2 APD 𝜎𝑀𝑃𝑃𝐶 = 0.50 ± 0.02 ns 𝜎𝐴𝑃𝐷 = 13.4 ± 0.4 ns • σMPPC = 0.5 ns for MPPC and σAPD = 13.4 ns for APD are found for the same events. ATHIC 2014 Kazuya Tarunaga 13 Summary • Basic study using the laser pulser - MPPC is tested in the range from -25 to 25 degrees. - The gain of MPPC is proportional to the bias voltage. - The 90k-type has around 10 times wider dynamic range than that of 14.4k-type. • Timing study using cosmic-ray - σMPPC = 0.5 ns for MPPC and σAPD = 13.4 ns for APD for the energy deposit of about 300 MeV equally distributed along the crystal length. • The anti-neutron energy deposit is larger and concentrated in a small space than this event, therefore a better timing resolution can be expected. • Simulation study is needed to evaluate the realistic PHOS performance with MPPC. ATHIC 2014 Kazuya Tarunaga 14 Backup ATHIC 2014 Kazuya Tarunaga 15 MPPC Spectrum 2p.e. 1p.e. 0p.e. Laser On 3p.e. 0p.e. Laser Off 4p.e. 5p.e. 6p.e. 7p.e. 8p.e. 1p.e. • Single photon detection and good separation of photon peaks when the number of incident photon is small • When the laser off, the 0p.e. peak exists and the 1p.e. peak corresponds to dark count ATHIC 2014 Kazuya Tarunaga 16 Crosstalk and Afterpulse In a MPPC pixel, secondary photons different from the incident photon might be generated in the avalanche process. an incident photon Crosstalk is a phenomenon that these secondary photons leak out into adjacent pixels and detected. In a MPPC pixels, the generated carriers are sometimes trapped by crystal defects in the avalanche process. Afterpulse is a phenomenon that the pulse different from the true pulse is generated by the carriers are released. γ’ a secondary photon an incident photon trapped by crystal defects released at a certain time delay ATHIC 2014 Kazuya Tarunaga 17 Before Event Selection ATHIC 2014 Kazuya Tarunaga 18 Before Event Selection ATHIC 2014 Kazuya Tarunaga 19 After Event Selection ATHIC 2014 Kazuya Tarunaga 20 After Event Selection ATHIC 2014 Kazuya Tarunaga 21 Result PMT1+PMT2 PMT3 MPPC APD ATHIC 2014 Timing Resolution σ [ns] 0.0765 ± 0.002 0.109 ± 0.003 0.504 ± 0.016 13.4 ± 0.4 Kazuya Tarunaga 22 100+8+1ns PMT1 100+8+1ns 100+4+1ns 100+8+1ns PMT2 APD 26ns MPPC 2ns PMT3 Width:60ns G.G.2 2ns Cool Box 8ns FAN IN/OUT D I S 8ns SHAPER 1ns 1ns C R 8ns I 8ns 8ns ATHIC 2014 ATT A C D S C G.G.4-8 Width:20ns Delay:1200ns 1ns G.G.5 2ns 2ns 2ns G.G.6 G.G.3 8ns Width:7μs G.G.4 2ns 1ns 1ns G.G.7 2ns 2ns 2ns 2ns 2ns 2ns G.G.8 2ns 1ns 8ns 1ns COIN1 COIN2 1ns 1ns G.G.1 1ns Width:15ns Threshold:25mV Width:20ns Kazuya Tarunaga A P D H C Width:7μs 53ns 53ns 58ns 4ns 53ns 4ns T D C 2 T D C 1 Width:20ns TDC1 Full Scale:118ns TDC2 Full Scale:2μs 23 The circuit diagram of MPPC preamplifier ATHIC 2014 Kazuya Tarunaga 24 The circuit diagram of APD preamplifier ALICE collaboration, ALICE high-momentum particle identification: Technical Design Report, CERN-LHCC-98-019, http://cdsweb.cern.ch/record/381431 ATHIC 2014 Kazuya Tarunaga 25
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