Precision Timing Detectors for

for High Luminosity Hadron Colliders

DESY

03.02.2017

Adi Bornheim Caltech

Physics at HL-LHC

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Fast Timing Fundamentals

∆U

∆t

For good time resolution, need: 1. fast rise time (trise) ⇒ primary signal rise time (scintillation : LYSO ~30

ps, Si sensors ~1ns) 2. low Signal-to-Noise (∆U/U) ⇒ primary signal amplitude : LYSO ~30k

photons/MeV (1.07 MeV/mm MIP) , Si sensors ~30k e/h pairs in 300 µ for a MIP

3. more time samples (nsamples)

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H→γγ Vertex ID at HL-LHC

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• Vertex ID uses ΣpT to find hard vertex.

• At HL-LHC to many PU vertices with high ΣpT.

• With a timing measurement for two photons, can calculate the z and t location of the vertex.

• H→γγ important mode for precision higgs physics. • Clean signal with large visible cross section makes it a key

driver for measurements of Higgs production and decays dynamics.

• Standard candle for di-Higgs to bbγγ. • Analysis utilizes full detector capabilities – tracking and

calorimetry : Holistic event reconstruction.

4D Triangulation with Photon Timing

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t⋅cγ1

t⋅cγ2

• With two time and position measurements eg. from two photons and with the constraint from the beam axis x and y location, the vertex x and t can be calculated.

• Equivalent to GPS with two satellites.

Physics impact of Photon Vertexing

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For more details see ECFA workshop 2016 in Aix-les-Bains.

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Construction & Installation: Barrel

Timing Performance of CMS ECAL

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Large PbWO crystal calorimeter. Results from pp collision data at LHC : Electron showers from Z→ee decay ∆tTOF :

~270 ps, single channel : ~190 ps, without path length correction : ~380 ps

Constant term of resolution : ~20 ps in test beam, ~70 ps in situ (same clock).

Studies on jet timing vertex resolution suggest very promising performance.

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 properties :

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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Optical Transit Time Spread Effect of the scintillation photon arrival at the photo detector we

refer to as Optical Transit Time Spread.

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

γ x

γ x

t1

t2

EM shower propagation snapshot

Scintillation light propagation cS < c

100 GeV γ

23 cm

Time evolution of a shower from photon in CMS ECAL PbWO crystal (25 cm long).

1.5 [ns] 0.0 0.5 1.0 10

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PbWO Light Timing Structure

CMS ECAL MC studies for Phase II upgrade.

Light extraction at one end of the crystal.

Precise understanding of the pulse shape needed to optimize readout electronics.

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Shower and light propagation, c = 1

Shower, light propagation + refractive index PbWO

Shower, light propagation, refractive index + tSCINT PbWO

200 ps/bin

200 ps/bin

amp.

[au]

am

p. [a

u]

PbWO with MCP

LYSO with MCP

CMS PbWO xtal

MCP as photo sensor reflective tube coupling

MCP as photo sensor clear cookie coupling

2x2x2 cm LYSO xtal

Rise time (19%-90%) ~1 ns for both, limited by digitizer MCP-PMT rise time ~150 ps.

PbWO vs LYSO pulse shapes.

Full Size Crystal Timing

• Measurements on large (10 cm & 20 cm) LYSO crystals. • Light & shower propagation effects in large crystals. • Time resolution of ~50 ps achieved with 32 GeV.4 • CALOR2014 , CALOR2014 talk

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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

∆t re

f -∆

t N

∆t re

f -∆

t F

∆tN -∆tF

CMS ECAL Timing Studies

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CMS ECAL, CALOR 2016

Front side readout of CMS PbWO crystal with 2 SiPMs.

Limited to ~70 ps.

NINO chip readout with DRS sampling of the digital output.

Shower depth fluctuations limit precision.

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LYSO Shashlik Calorimeter • Stacked tiles of LYSO & tungsten • WLS fiber light readout • LYSO : radiation resistant, very high yield • Large light yield implies:

more stable pulse shape, better S/N better time measurement

• Measured 10%/sqrt(E) and ~1% constant term.

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Shashlik Test Beam

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• Proof of concept demo of calorimetric precision timing with shashlik fiber prototype.

• Optical signal integration and transport.

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Pulse Shapes from WLS fibers

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• Pulse shape (rise-time) has significant dependence on type of WLS fiber

• DSB1 fibers have significantly faster rise-time than Y11 • ~2ns (DSB1) compared to ~7ns (Y11) • Direct contact with LYSO crystal gives ~1ns

Zoom-in version

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Shashlik Timing Performance

• Performance of solid LYSO cube and LYSO/W scales with the rise time difference due to the WLS.

• Few 10 ps resolution achievable with LYSO based calorimeter, reaching ~32 ps at 32 GeV equivalent signal.

• SH cell timing extracted from same light signal which allows excellent energy resolution.

• http://dx.doi.org/10.1016/j.nima.2015.04.013

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SiPM & Capillary Readout

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Quartz capillary with liquid WLS (DSB) B. W. Baumbaugh, R. Ruchti, et al, IEEE2015

Clear plastic light guide to couple WLS CAP

DSB WLS Plastic fiber

SH Cell Timing with SiPM

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Capillary and plastic fiber timing the same at fixed amplitude. Time resolution per fiber similar for fixed particle energy. SH cell timing around 60 ps per fiber (48 ps four fibers combined). SiPM timing with ps laser around 10 ps. Reference timing detector not unfolded, around 10 ps resolution.

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Shashlik Time Resolution • Observe 1/√E scaling vs energy (number of photons) • Achieve ~50ps resolution at the highest energy • Time resolution limited by S/N (no amplifier on the SiPM output).

DSB

Calorimetric Timing in CMS

Boundary conditions from CMS Phase II Calorimeter Upgrade : • PbWO ECAL Barrel : Replacement of Very Front End and :

– Cope higher L1 rates (750 kHz) – Mitigate “nuclear counter” induced noise in APDs (spikes) – Reduce impact of increased noise from APD dark current

• Endcap Calorimeter replacement with Silicon/Tungsten & Silicon/Steel calorimeter (EE & FH HGCAL) + Scintillator/Steel Backing HCAL : – Current CMS Endcap will not withstand HL-LHC radiation doses. – Cope higher L1 rates (750 kHz) – Higher transverse granularity in the hadronic section. – Longitudinal granularity

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CMS ECAL Barrel HL-LHC Upgrade

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• ECAL timing from LHC Run I : 150 ps global (70 ps local). • New Very Front End (VFE) with Trans-Impedance Amplifier (TIA)

& Oversampling (optimal with 160 MS/s). • Full detector readout, L1 accept rate 750 kHz @ 12.5 µs latency. • Timing performance limited by the APD/cable to VFE. • Timing resolution expected at 30 ps down to about 20 GeV. • More details see eg. TWEPP 2016.

CMS ECAL Laser Timing

Micro Channel Plates • MCPs achieve <10 ps resolution for MIPs. • Crucial tool to study timing detectors. • Operation in secondary emission mode

avoids the need for a photo cathode. • Significant R&D for large area MCPs (LAPPD). • For LHC, would need large area, radiation

hard, segmented and high rate capable. • NIM-A 795 (2015) 288-292.

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σT : 7 ps (single device : 9.6/√2)

Pixelated MCP, multiple measurements on a shower

EM shower temporal coherence

Single Si Pad Timing

• Si pad : Hamamatsu, 6x6 mm, 325 µm, no gain. • 0.2 mm steel box, 1.5 cm “thick” • ORTEC VT120C pre-amplifier • Hamamatsu C5594 amplifier

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Experimental Setup

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Trigger counter 2x2 mm

x-y stager

Energy and Timing Measurements

• Correlation between beam energy and signal amplitude (recall, only one 6x6 mm pad).

• Timing resolution improves with signal amplitude.

• More details see http://dx.doi.org/10.1016/j.nima.2015.11.129 NIM-A

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At 6 X0

Amplitude Dependence

• Signal amplitude spread varies due to limited containment on single Si sensor. Use to look at timing resolution vs amplitude.

• Timing resolution strictly scales with the signal amplitude.

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Timing with Si/W Calorimeter

• CMS plans to replace endcap calorimeter with a Si/W – Si/Fe (HGCAL) + Scint/Brass (BH) calorimeter for HL-LHC upgrade.

• It has been demonstrated that a <20 ps resolution can be achieved with a single Si pad sensor w/o gain if placed in an EM shower.

• An EM shower will have a few 10 pads contributing to the measurement.

• Precise timing readout in the design specs of the HCGAL readout chip. See eg. presentation at C. TWEPP2016. 03.02.2017 Adi Bornheim, Precision Timing 31

HGCAL

BH

JetMET with Precision Timing

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• High pile-up has major impact on JetMET reconstruction.

• At low pT (40 GeV) PU energy in the jet cone exceeds the jet energy by a factor 2 or more.

• Each PU event adds 3 GeV in quadrature to the MET resolution, resulting in about 40 GeV for 200 GeV.

Track Time Tagging • At 200 PU, increasingly difficult to separate nearby vertices. • Vertex merging causes degradation in isolation and MET variables. • ΣpT of merged vertices promotes PU events to be ranked higher

than hard interaction in vertex ID. • Further studies ongoing on rate of PU track merging to vertices. • For more details see 2016 ACES workshop

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2

Further track timing applications

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As vertices start to overlap within effective tracking resolution, rate of pileup tracks associated to hard interaction vertex increases.

Corresponding degradation of charged isolation, b-tagging, Jet/MET performance.

MIP Timing Detector

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For HL-LHC upgrades – with ~todays technology: • Assuming a timing layer between tracker and calorimeter, choose

granularity such that each track can be time tagged and occupancy below 10% to avoid double hits.

• Use CMS HGCAL simulation (1 cm2 Si pads) to estimate occupancy. • 1 cm2 granularity sufficient up to eta ~2.4. • Impact point taken from tracker to associate time tag to track. • CMS Timing Layer : Barrel area ~40 m2 , Endcap ~9 m2 • ATLAS HGPT coverage : 2.5 < eta < 5.

CMS ECAL Barrel Timing Layer

• LYSO/SiPM layer. 15 ps for MIP demonstrated in TB. • Granularity ~1 cm2 (4 per PbWO crystal), ~300000

channels, LYSO 3 mm, entire detector few (~2 ?) cm thick, attached to the tracker support tube.

• CMS decision by April 2017. • SiPMs not rad hard enough for CMS endcap.

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M. Lucchini et al, CALOR2016, CALOR2016

Low Gain Avalanche Diodes • Recent results from arxiv 1608.08681 • Low-Gain Avalanche Detectors (LGAD) design, employing n-on-p

silicon sensors with internal charge multiplication in a thin, low-resistivity diffusion layer below the junction.

• UFSD used in this test belongs to the first production of thin (50 μm) sensors, with an pad area of 1.4 mm2.

• With three sensors aligned on a track, 15 ps are achieved.

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Deep Depleted APD • Deep Depleted APD with mesh readout • Large MiP signal (3600 eh pairs × 3 internal APD gain of few 100) • Weighting field controlled with sintered Au (bottom) and mesh

(top) layer, Landau contribution limited, may offer additional benefit due to its electrical properties.

• Eg. S. White, Elba, Fast Timing Detector R&D for the HL-LHC era

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Timing Calorimeter with CdTe

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EM Showers are photon rich CdTe has high sensitivity for low energy photons

10x10x1 mm3 CdTe, Acrorad Ltd.

• CdTe sensors can be thick (few mm). • 50k electrons / 300 µm • Density ~2.5x larger than Si • Larger Z results in larger cross

section for soft x-ray photons.

CdTe Pulse Shapes

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• Charge carrier mobility in CdTe is very different than in Si.

• Holes move slower, electrons vary with local field.

• Pulse rise times of ~1.3 ns observed.

Signal Dynamics in CdTe

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• Excellent timing resolution down to 20 ps achieved.

• Resolution varies across sensor. 25 ps average across sensor.

• Further studies ongoing for different sensor sizes, thickness, etc.

• Submitted to NIM.

Summary

• Precision timing detectors with a few 10 ps resolution can have a major impact on HL-LHC event reconstruction.

• A range of detector technologies available to achieve this performance.

• System integration aspects a challenge. • Many groups involved in R&D, exciting work,

ready for a large scale application.

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Backup

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