Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb Beam Test of LGADs Hartmut F.W. Sadrozinski with Astrid Aster, Vitaliy Fadeyev, Patrick Freeman, Zachary Galloway, Herve Grabas, Edmond Lee, Zhijun Liang, Abe Seiden, Andriy Zatserklyaniy SCIPP, Univ. of California Santa Cruz, USA Marta Baselga, Pablo Fernández-Martínez, David Flores, Virginia Greco, Salvador Hidalgo, Giulio Pellegrini, David Quirion, IMB-CNM, Barcelona, Spain Nicolo Cartiglia, Francesca Cenna, Marco Ferrero INFN Torino, Torino, Italy Beam Test set-up Amplitude spectra Time resolution Thin sensors Low-energy protons

Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb Low-Gain Avalanche Detector (LGAD) Marta Baselga, Trento Workshop Feb High-Field: Gain

Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb November nights in the H6 Beam Line… FZ LGAD (run 6474 G = 10-15) with Civitek Broad Band (BB) amp & CSA amp 50um epi LGAD (run 6827 G = 2-3) with Civitek BB. And Trigger: fast SiPM Data taken with digital scope at 10 ps sample speed. 300 FZ BB 300 FZ CSA 50um epi SiPM Trigger Trigger: (OR of 300um FZ sensors). AND.SiPM ( SiPM resolution ~50 ps?). Thanks to the AFP beam test group (Joern Lange and Michael Rijssenbeek) for help and use of the trigger

300um FZ: 1 MIP = 55mV 50um epi: 4 MIPs = 13mV A(300um, G=15) = 17* A(50um, G=3) The 300um FZ data are well explained as a sum of 3 Landau distributions: 1, 2 and 3 MIPS Multiple Landau fit to Amplitude Spectrum Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

5 Multiple Landau fit to 1000V, 800V, 600V Bias Spectra were taken at 3 bias voltages. The fits to 1, 2 and 3 MIPS peaks can be used to determine the beam composition and the linearity and voltage dependence of the gain, (clearly seen by the straight red line). Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

BUT: Define the ratio of MPV at bias V relative to 600V bias. The observed bias dependence of the MPV ratio is larger than the one of the total charge measured with back-side  -TCT! Is this predicted by simulations? The max amplitude (MPV) of 1-3 MIPS scales with the bias. The ratio of the max amplitude (MPV) of 2 and 3 MIPs relative to 1 MIP is constant vs. bias. Bias Dependence of the Amplitude of MIPs Hartmut F.-W. Sadrozinski, Beam Test of LGADs, 10th Trento, Feb. 2015

Properties of the Landau distributions The ratio sigma/MPV is constant as a function of multiplication, indicating that the excess noise factor is not playing a role yet Pulse Height Dispersion  A/A = d According to our fits, the Landau have a smaller width than what is proposed by the parametrization of Meroli et al. Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Time Resolution and Slew Rate The time resolution depends on rise time τ r, and τ r depends on the collection time (i.e. the detector thickness). 3 terms: time walk due to amplitude variation, time jitter due to noise, binning. Introducing the slew-rate S/ τ r = dV/dt (binning error is negligible at 10 ps sample rate) we find that for constant noise N, to minimize the time resolution, we need to maximize the slew-rate dV/dt of the signal. Need both large and fast signals. Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

(300um FZ, BB) (50um epi, BB) The expected dependence of the time resolution on the amplitude is observed both for FZ and epi sensors. The time resolution varies from about 200 ps at low amplitude to about 100 ps at high amplitude. Fixed low threshold and low CFD analysis are comparable, The time jitter is a large fraction of the time resolution. Amplitude Dependence of Time Resolution Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Surprise: Essentially σ nj is independent of the amplitude, for FZ and epi, which means that the time-walk corrections are not working (yet!). For FZ beyond an amplitude of ~45 mV, there will be more than one MIP in an event. For epi: all events are multi-MIP. Time Walk Contribution to the Time Resolution Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb As a measure of the time walk, define a jitter-less time resolution σ 2 nj as the time resolution with the jitter subtracted σ 2 nj = σ 2 t - σ 2 j

1000V Ch 2, 300um, G = 15, C = 11 pF 500V Ch 1, 50um, G = 3, C = 34 pF Slew-Rate for MIPs: dV/dt(300um,10pF) = 4*dV/dt(50um, 34pF) dV/dt distribution Time-walk resolution is ~ independent of slew-rate: NO 1/(dV/dt) Slew-Rate dependence of the Time Resolution Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Large Amplitude events: > 1 MIP Amplitude distribution varies with slew-rate dV/dt. 50% of large dV/dt events are Multi-MIP events! About 50% of the large amplitude events show irregular rising edge due to overlap of several MIPs.

As expected from the pulse pictures, the constant fraction discriminator (CFD) analysis with large fractions does not work for large amplitudes (multiple MIPs): the timing error rises with amplitude instead of falling! Time resolution vs. Amplitude (300umFZ, BB) Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb Better when limiting the pulse amplitude to 1 MIP?

In the CERN Beam Test, the Capacitance was 10 pF Weightfield WF2 simulation shows that changing to 2 pF (smaller sensors) improves slew rate by factor 2 Time resolution depends on slew-rate dV/dt (≈Signal/rise time) Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb Effect of Detector Capacitance (300um FZ) N. Cartiglia, F. Cenna et al. “Weightfield”, 2014 IEEE NSS-MIC

The beam test had large LGAD diodes with 34 pF capacitance. We now have LGAD diodes with C = 6 pF which will improve the slew rate by factor 3.7 Future sensors with C = 2pF will improve the slew-rate by a factor 5.2 Risetime 34pF7.1E-10 2 pF3.9E-10 Effect of Detector Capacitance (50um epi) Lower capacitance will improve dV/dt Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Large dE/dx increases the slew-rate dV/dt Predictions from WF2 simulations: For MIPs in 50 um sensors time resolution: 30 ps with gain = 10 time resolution: 84 ps without gain Predicted time resolution for protons in Ultra-fast Silicon Detectors without gain: With USFD with gain = 10, the time resolution is improved by another factor3 ! Low-energy protons afford very good time resolution, allowing the measurement of the proton energy by time-of-flight TOF. Time Resolution for low-energy Protons Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Direction and energy of (low-energy!) secondaries are measured in telescopes of Ultra-Fast Silicon Detectors (UFSD) and projected back to identify the beam location. D = 30 cm UFSD: 50 um thin, pixels 300um x 300 um, Time resolution of 30 ps, i.e. “100ps & Gain = 10” allows energy measurement by TOF Energy resolution on secondaries: 100 MeV pions: 16% 100 MeV protons : 4% UFSD will operate at 10 MHz rate and provide real-time beam diagnostics. Protons Head phantom Hadron beam Longitudinal distribution of energy deposition (Bragg peak) and number of secondaries Interaction Vertex Imaging IVI with UFSD Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Protons of 200 MeV have a range of ~ 30 cm in plastic scintillator. The straggling limits the WEPL resolution. Replace calorimeter/range counter by TOF: Light-weight, combine tracking with WEPL determination Future: 4-D UFSD as WEPL Detector in pCT? Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015

Beam Tests = “Lessons learned”. Multi-MIPs events need to be eliminated so that the slew-rate dependence of the time resolution can be studied. Time resolution of about 200 ps has been found for single MIP, in agreement with simulations for the capacitances present. Improvements can be expected with lower capacitances (smaller detectors), especially for the 50 um epi sensors. Predictions for the time resolution of therapeutic low-energy protons in thin sensors show very good energy resolution using Time-of-Flight TOF over a 30 cm distance. Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb Conclusions: Beam Test

o Ultra-fast silicon detectors (UFSD) afford very good time resolution for low-energy proton (or ions) since they have very high slew-rare. o The large slew rate due to the high specific energy loss of low- energy protons is enhanced by a factor 3 when a UFSD with gain = 10 is used. Timing resolution of < 10 ps for protons with E < 150 MeV are predicted. o The fact that UFSDs have their best timing capability when the sensor is thin (< 50 um) goes hand-in-hand with the fact that tracking of low-energy protons need thin sensors to reduce MCS (Multiple coulomb scattering). Use of UFSD in ToF for low-energy Protons Hartmut F.-W. Sadrozinski,Beam Test of LGADs, 10th Trento, Feb. 2015