Calorimeters for Precision Timing Measurements in High Energy Physics

Calor 2014

Gieβen 10.04.2014

Adi Bornheim, Cristian Pena, Artur Apresyan, Maria Spiropulu, Javier Duarte, Si Xie, Anatoly Ronzhin

Caltech, FNAL

Outline

Introduction Timing measurements of high energy particles

with scintillating crystals. Cosmic Test and Test Beam Setup Results Summary

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Timing in high energy experiment

10.04.2014

High energy physics collider experiments (eg at LHC) : Size of the detector few meters, timing for final state particles of few GeV up to few 100 GeV.

Goal : Associate calorimeter measurements with primary vertex location. From MC simulations : Need single channel resolution of a few 10 ps. See also presentation «Timing Performance of the CMS Electromagnetic

Calorimeter and Prospects for the Future»

∆tvertex (0.2 – 1.0 ns)

∆tflight (4 – 12 ns, calo front face, > 1 ns for low pT charge particles)

∆tdetection (1.0 ns, photons in dense detector)

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Electromagnetic Type Detection in Crystals

Photo Detector Crystal

γ

tTOF tC Conversion

Depth (Photons)

tS Scintillation

process

tT Transit time

jitter

tP Photo

detector jitter

x

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tD DAQ

The contribution of the DAQ system – for our tests DRS4 based - to the

overall timing resolution will be discussed by A. Apresyan in the following talk.

Photon Traces in LYSO Crystal

t0 t1 t2

t3 t4 t6

For high energy showers in high light yield crystals, number of scintillation light yield is very large (>105 / GeV).

Photon detection at one location in the crystal will be an averaged transit time spectrum

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Shower Shape and Size Size of the shower given by radiation length X0. We use 1.7 cm, 10 cm and

20 cm LYSO crystals as well as 1.5 mm thick LYSO plates. In dense scintillators X0 is of the order 1 cm. LYSO crystals : 1.2 cm. From simulation studies : Shower fluctuations in 100 GeV photon showers

cause fluctuation of the mean shower time of the order of few 10 ps, dominated by the conversion depth.

Mean shower depth varies by several X0 as a function of energy. ⇒ Shower propagation takes 100s of ps.

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Scintillation Light Time Spectrum Scintillating crystals get often classified in fast and slow by their light

output decay constants. This is often 10s of ns – PWO, LYSO : ~40 ns. Timing information is extracted from the leading edge of the signal – the

rise time of the light output is important. LYSO :

Scintillation light output rise time tR = 75 ps. 35000 photons/MeV, tD = 33 ns. See : S Seifert, J H L Steenbergen, H T van Dam and D R Schaart, 2012

JINST 7 P09004. doi:10.1088/1748-0221/7/09/P09004

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Photo Detector Timing Performance Typical timing performance parameters of photo detectors are the rise

time, single photon timing jitter, n-photon timing jitter. As we measure signals with many photons there may be additional

factors typically not quoted by manufactures – like the 100000-photon timing jitter.

Part of our program is to characterize the timing performance of various photo detectors.

We are considering PMTs, SiPMs, MCPs, HAPDs. Rise times of faster devices may be smaller than transit time spread.

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Hamamatsu MCP-PMT

Optical Transit Time Spread The effect of the scintillation photon arrival at the photo detector we refer

to as Optical Transit Time Spread.

From previous slides follows : For a large crystals (eg. 20 cm) and showers from high energy particles (we consider 1 to 1000 GeV), the optical transit time spread may be the dominating factor in the timing resolution.

Experimental program to explore ultimate timing resolution, in particular the impact of the optical transit time spread.

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γ x

γ x

t1

t2

EM shower propagation

snapshot

Scintillation light propagation

cS < c

Precision Timing Test Setup

We used two setups so far : • Cosmic Test Stand at Lauritsen Laboratory in

Caltech. • Beam Test Setup in Fermilab Test Beam

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Cosmic Timing Test Stand

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Cosmic Timing Test Stand @ Caltech

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Light Propagation in Crystals The effective propagation speed of an large ensemble of photons from

scintillation depends on the geometry, surface structure, transparency ( … ) of the crystal.

For our 20 cm LYSO crystal we measure a mean propagation speed for light from a cosmic muon of about 11 cm/ns (~1/3 x c). Refractive index of LYSO is ~1.8.

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Geometric Timing Spread Location of the muon trespassing the crystal is given by the size of the trigger

counters. Plots below are from a test setup with PMTs. Observed signal signal rise time

of this setup : 2 ns. Reducing size from 3 cm to 1 cm reduced the differential timing distribution

from 300 ps to 160 ps. Clear evidence that the mean time tracks the geometry of the light produced in

the crystal.

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Narrow Trigger Counter Wide Trigger Counter

∆tmax= ∆t1 -∆t2

∆t [ns] ∆t [ns]

Test Setup – Beam Test @ FNAL

LYSO crystal, 20x2.5x2.5 cm3

Photo detectors (here : PMTs)

Light tight box

Mounting base plate

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Test Setup – Beam Test @ FNAL

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Fermilab Test Beam March 2014 All results are preliminary

Test Beam – Perpendicular Setup Wire chamber used to define 16x16 mm area of the beam and

as trigger. Beam size ~2 cm. Reference Photek MCP 40 mm diameter active area, crystal

readout with Hamamatsu MCP, 8 mm diameter active are . Time resolution will be discussed in A. Apresyan presentation.

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Beam

MCP Reference

Lead 2.6 cm

MCP Crystal Readout

MCP Crystal Readout

LYSO Crystal (10 cm)

Wire Chamber

2 cm

Time Of Flight Resolution – Perpendicular Setup

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Measurement with and without lead absorber, 8 GeV electron beam. Beam located 2 cm away from one end of the crystal. Time resolution (difference between one crystal readout MCP and

reference MCP) : typically better than 60 ps. Geometric spread of the impact position (1.6 cm) should contribute

significantly to this. Reference MCP and readout resolution not unfolded.

With lead Without lead

Test Beam – Longitudinal Setup

Wire chamber used to define 16x16 mm area of the beam and as trigger. Beam size ~2 cm.

Reference MCP : Photek, 40 mm active area. Crystal readout MCP : Hamamatsu, 8mm active area.

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Beam

MCP Reference

MCP Crystal Readout

farside

MCP Crystal Readout

nearside

LYSO Crystal (20 cm) Wire Chamber

Longitudinal Setup Electron beam, 8 GeV. Differential time (near side – far side crystal readout) resolution :

53 ps, core width 30 ps. To be compared with the 160 ps from the cosmic muon test.

In the longitudinal setup, transverse geometric spread negligible. Longitudinal shower fluctuation may impact timing measurement.

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σt = 30 ps

Time Of Flight Resolution - Longitudinal Setup

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Time of flight resolution with respect to reference MCP : ~50 ps. Near side MCP readout shows non-gaussian distribution.

Near Side MCP Far Side MCP σt = 47 ps σt = 49 ps

Simulation : Conversion Depth vs Time GEANT simulation of 100 GeV photon : Correlation between conversion

depth and scintillation photon arrival at crystal near and far side face. Stronger correlation at the near side face.

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Z γ

16 cm

Conversion depth pos Z [cm]

phot

on a

rriv

al ti

me

[ps]

Near side crystal face Far side crystal face

Shower Depth Effects in Data Near side correlation is visible in data. On this data set, using correlation to correct shower depth effects

improves resolution significantly.

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∆tN -∆tF ∆tN -∆tF

∆t re

f -∆

t N

∆t re

f -∆

t F

∆tN -∆tF

LYSO Crystal Plates Small LYSO plates (1.4x1.4x0.15 cm) as foreseen for LYSO

Shashlik prototype. Measure time resolution around 50 ps for 8 GeV electrons. Geometry and alignment of the setup more difficult to control.

Further data analysis ongoing.

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Summary

We study the timing measurement performance with LYSO crystals for particles in the GeV energy range.

We achieve timing resolutions of around 50 ps without unfolding reference measurement resolution.

We find evidence that : The timing measurement is driven by the mean time of the

shower evolution. Geometric effects of the shower evolution and light

propagation are dominating factors in the residual time resolution.

Single channel time resolution of a few 10 ps seems achievable.

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