PhD students meeting 01/27/2010 Philippe Doublet 1

Designing a detector for a future e-e+ linear collider

Precision measurements based on Particle Flow & high granularity calorimeters.

PhD students meeting 01/27/2010 Philippe Doublet 2

News of particle physics

From the report of the High Energy Physics Advisory Panel (2004)

1 Are there undiscovered principles of nature : new symmetries, new physical laws?2 How can we solve the mystery of dark energy?3 Are there extra dimensions of space?4 Do all the forces become one?5 Why are there so many kinds of particles?6 What is dark matter? How can we make it in the laboratory?7 What are neutrinos telling us?8 How did the universe come to be?9 What happened to the antimatter?

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An e-e+ collider at the Terascale

• New discoveries are expected at the Terascale i.e. energies O(1 TeV) :– WW scattering

• Historically, combining results of proton colliders with electron colliders has led to great progresses and discoveries.– An e-e+ collider will precisely measure what will be discovered at LHC

12 August 1999

Scientific panels charged with studying future directions for particle physics in Europe, Japan, and the United States have concluded that there would be compelling and unique scientific opportunities at a linear electron-positron collider in the TeV energy range. Such a facility is a necessary complement to the LHC hadron collider now under construction at CERN. Experimental results over the last decade from the electron-positron colliders LEP and SLC combined with those from the Tevatron, a hadron collider, have led to this worldwide consensus.

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Why an e-e+ collider ?

Excellent knowledge of the initial state

Direct probe of the couplings and/or new particles (via loops, Z’, …)

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Why linear ?

• Energy losses per orbit via synchrotron radiation :

E α γ4/R

• For a given energy and radius, Eloss,e- / Eloss,proton = (mproton/me-)4 ~ 1013

• To compensate, need R~1013R !

• If E 2 E, then E 16 E !

• LEP : Emax,e- ~ 104 GeV, R = 4.3 km : maximum radius considering energy losses go to linear

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Properties of the International Linear Collider

• √s up to 500 GeV (possible upgrade at 1TeV )– Range of energy : 90 GeV 500 GeV– Use of superconductive technology

• Must be able to tune energy :– top threshold scan– Higgs– SUSY particles

• Luminosity L = 1034 cm-2s-1

– Expected after 4 years : L = 500fb-1 at 500 GeV

• 80% polarised electrons :– Left – right production asymmetries– Suppress backgrounds

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Physics goal of an e-e+ collider• Higgs

– Mass, width, couplings (branching ratios), spin– Also study of ZHH

• Top quark– Mass, cross-section, AFB

t , ALRt

• WW scattering at 1 TeV

• SUSY mass spectrum

• Other BSM scenarios :– Z’– 4th generation– …

Higgs-Strahlung process to study the Higgs

Top quark production

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Example for the Higgs

• Study of Higgs-Strahlung– L = 250fb-1, √s = 250 GeV, mH = 120 GeV

Higgs recoil mass with Zµ+µ-

Hengne Li, LAL

• ~600 MeV expected mass resolution (µ + e channels, model independant, 30 MeV precision)

• ~2% precision on the cross-section

S/N ~ 2.3

S/√(S+N) ~ 48

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My next study : top production

• Top mass : combining semileptonic decays and hadronic decays of the W give mt ~ 30 MeV (stat.)

• Top cross section : 0.4% uncertainty (stat.)

Wlv (leptonic decay of the W)

Wqq’ (hadronic decay of the W)Reconstructed top mass (semileptonic events)

ILD LOI

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Structure of the ILD detector

3D view of the proposed ILD detector

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Requirements for subdetectors

• Tracking (vertex detector + main tracker)– Excellent measure of p of charged tracks, do b(c)-tagging– Momentum : δp/p² < 5x10-5 GeV-1

• Calorimetry (ECAL + HCAL )– Measure energy of the particles via their energy deposition

(especially photons and neutral hadrons)

– Energy : σE/E < 3 to 4% (combining tracker + calorimeters)

• Magnetic field (coil + return yoke)– 3.5 Tesla magnetic field ( ~ CMS coil)

• What drives the requirements ? Particle flow

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Using the Particle Flow approach

• Final states at ILC :– mainly multi-boson (ZH, WW, ZZ, ZHH, ZWW, ZZZ)– or fermions + bosons (eeH, eeZ, tt, ttH, ννWW,

ννZZ)

• MW~80GeV, MZ~91GeV, MH>115GeV– Performance depends

on mass resolution of the jets– Need to reconstruct ALL

the particles

~68% ~70% JETS

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How to reconstruct all final state particles ?

1) Associate charged tracks and clusters (tracker + E/HCAL)

2) Reconstruct the photons (ECAL)

3) Reconstruct neutral hadrons (E/HCAL)

• Why ?– Ejet = 65% charged

+ 26% photons + 9% neutral h.

• Need excellent tracker and very good E/HCAL

Example of particle separation

ECAL

HCAL

γ π+

KL

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Concept driven by the particle flow

Di-jet masses for separation of WW and ZZ di-boson events

ALEPH-like detector ILD-like detector

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Challenges for an ILC detector

• Measure bosons very well (ttbWbW, ZH, ZHH, ννWW, ννZZ, ttH, …)

• Particle Flow concept– Reconstruct every particle– Associate the particles to jets

• Need an excellent W/Z separation – Momentum : δp/p² < 5x10-5 GeV-1

– Energy : σE/E < 3 to 4%

• factor 2 times better than LEP

• ~50% less luminosity needed

– Impact parameter (b&c-tagging)

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What about prototypes ?

• Principle :– high granularity to separate showers on a topological

basis (see neutrals’ contributions inside the shower)

• Goal : – build prototypes to validate high granularity concept

• Huge energy fluctuations in showers• e/h ratio not well known : don’t fully rely on energy but geometry• Validate models of hadronic showers

• Prototypes exist and have been intensively used under testbeams

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Calorimeters under testbeams• Testbeam periods at DESY,

CERN (2006-07) and FNAL (2008)

• Goals : energy, position and angular resolution, validation of hadronic shower models

The calorimeters tested at Fermilab in May 2008.

Si-W ECAL, Analog HCAL : fibers and scintillating tiles, Tail Catcher : fibers and scintillating strips.

A 120 GeV proton event

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The Si-W ECAL prototype

• Sandwich structure of W (absorber) and Si (detector)

• 30 layers• 1 cm x 1 cm Si pixels

– 9720 channels

• 3 W depths 3 stacks– Molière radius, RM = 0.9 cm

• Total depth = 24X0 ~ 1λI

– Full containment of EM showers

– ~ 2/3 of the hadrons may interact in the ECAL

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Results for the ECAL

• Resolution studies done with electrons

• Linearity within 1%• Data & MC agree

%1.01.1)(

1.06.16

GeVEEMeas

MeasE

Energy resolution studies

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Why study hadronic showers in the ECAL ?

• Bad knowledge of hadronic showers, very complex environment

• 1 x 1 cm² pixels– Tracking possibilities– Look inside showers

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Using the granularity of the ECAL

• Applied to hadrons– Identify MIPs i.e.

particles passing through the ECAL with a minimum deposited energy (easy)

– Find hadronic interactions (medium)

– Disentangle several kinds of hadronic interactions (hard)

• My work : pions,1 GeV < E < 10 GeV

2D views of a pion interacting in the ECAL.

Structure : MIP – interaction - cluster

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Procedure developped

1. Identify a MIP

2. Delimit the interaction region

3. Define the structure of the shower

Work done so far :• Development of an algorithm : « MipFinder »• Getting the interaction layer• Describe the shower (ongoing)• Learning : C++, SM, extra dimensions, …

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Benchmark for the MipFinder

• Count the number of entering particles

• Done with muon and pion runs, data & MC

Figures :

1. (top) Efficiency of the MipFinder with 10 GeV simulated muons

2. (bottom) Fraction of events of 0, 1, 2 and 3+ particles entering the ECAL at FNAL

Algorithm validated

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Finding the interaction region

First step : find the interaction layer– 3 physics lists used (~30,000 events each for every energy)– Data selected among TB done at FNAL (>100,000 events per

energy) *not shown here*– Discrepancies seen at 2 GeV (bad hadronic models at low

energies)

Simulation of 2 GeV pions

Interaction layer found by the algorithm for 3 different physics list of Geant4

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My future work & one step beyond

• Describe the interaction region and further• Work on simulated events for ILD : e-e+ tt

for the search of extra dimensions• Get PhD !

• About the ECAL, ILD, ILC :– New technological prototype of the ECAL

being developed « the EUDET module »– ILD concept validated, now moving towards

detailed design with more realistic simulations

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For you to remember

• Future e-e+ linear collider for precision measurements and discoveries

• Studies of WW scattering, top quark, Higgs, new physics

• Detector based on the particle flow approach (reconstruct every particle to form jets)

• Successful runs of particle flow Si-W ECAL with potential for hadronic shower studies