June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Physics Requirements

for Calorimetry at a Linear Collider

André S. Turcot

Brookhaven National Lab

Santa Cruz Linear Collider Retreat

June 27-30 2002

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Overview

• There are key physics processes that set the performance requirements for the Linear Collider Calorimetry– In many cases, measurements will be statistics limited – To fully exploit the physics potential of the machine we

will have to consider fully hadronic final states

• In the following, I will try to give an overview of those processes where calorimetry will play a key role

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Physics Benchmarks

• Higgs: – Precision Higgs physics will be statistics limited– Use of hadronic Z decays will be necessary

• ElectroWeak: – Separation of Hadronic Gauge Boson Decays– Why? We must adopt the paradigm that the W/Z is a

fundamental particle equivalent to the photon • Top Quark:

– Reconstruction of 6 jet final states– Jet Energy Resolution/Reconstruction

• SUSY Searches: Hermiticity, Missing ET Resolution

• Precision EW: Luminosity Profile

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Energy Resolution?

• Energy Resolution is not the true figure of merit

• Physics is driven by jet resolution

• e.g. D0 U/AR e/h = 1 (EM) = 15%/E (pion) 50%/E

• Yet (jet) 80%-100%/E

Calorimeter design should be guided by Jet Energy Resolution Current State of the Art is Energy Flow Analysis Requires highly segmented tracking calorimetry

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Hermeticity

• Hermeticity enters in two key roles– Determination of the event missing energy– Tagging of scattered beam particles

• SUSY drives the hermeticity issue• Two photon, ee -> eeff backgrounds will be problematic

– Scattered e(s) in ee -> ee X can easily produce missing ET

– ET(max) = EBEAM x sin where defines calorimeter fiducial

• For 500 GeV and 40 mrad coverage, ETMISS can be up to 10 GeV

Hermeticity in forward region will be crucial

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Higgs Physics

ZH WW

• Measurement of the hWW coupling requires separation vvh and Zh production channels – Missing mass is

discriminating variable • e.g. BR(h->WW*)

– Degrading the jet resolution from 30% to 60% corresponds to a factor 2 in luminosity

• hZ production with hadronic Z final states have a large impact

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Higgs Physics Self Coupling

• Flagship measurement for a Linear Collider

• Verify shape of potential• Does the Higgs generate its

own mass?• Critically depends on the

calorimeter performance– 6j final state with 4 b

jets

• For 1 ab-1 and 60%/E jet resolution -> 3 sigma signal,

• For 30%/E -> 6 sigma signal• Evidence vs. a measurement

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

SUSY and Calorimetry

• Consider two possible SUSY scenarios

• “High” tan scenarios – multiple soft tau leptons – Tau ID could be a driving

issue– Hermeticity will be critical

as the ee xsec is enormous

– Measurement of the tau polarization in cascade decays will provide a key insight

• “Small” Gaugino mass differences: O(5) GeV– Small visible mass in final

states!– Hermeticity in forward

region again will be the critical issue

– Irreducible eeqq bckgnds will require excellent visible mass resolution to isolate signal

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Further SUSY Considerations

• Given that the SUSY breaking mechanism is a black box, we must be prepared for surprises

• GMSB scenarios can produce non-pointing photons– Rely on calorimeter to determine Impact Parameter – Measure Gaugino lifetime (key input to any theory)

• Quasi-degenerate Gauginos– Small visible mass, hermeticity will be essential

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Tau Physics

• The Tau lepton will be a sensitive polarimeter for LC physics– However, most processes will be statistics limited– LEP expts. had 200K tau pairs, we will not be so blessed– Need ability to cleanly separate v and v final states

• Could be critical depending on physics scenario that is realized

• Tests of CP violation in Higgs decays • Stau NLSP scenarios• High tan solutions • Z’ effects for 3rd generation• More mundane level, tau ID and controlling jet fake rates

– What is acceptable fake rate? 10-3 ?

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Gauge Boson Scattering

• Measurement of the WL WL

scattering amplitudes • Must cleanly distinguish

between evWZ, vvZZ and vvWW using purely hadronic final states– relying on leptonic final

states is not possible– Uninteresting evWZ 4x

larger• Going from 30%/E to 60%/E

corresponds to loosing 45% of the integrated L (Brient)

vvWW

vvZZ

evWZ

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Gauge Boson Identification

Videau, Calor2002

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Top Quark Physics

• Precise measurement of the Top Quark mass – There are two complementary techniques

• Direct measurement above threshold (pole mass)– Requires good jet reconstruction efficiency– “Bootstrap” reconstruction

• find jet pairs -> W, W+b -> top – Hadronic W mass resolution is important

• Suppress 6-f final states and combinatorics • Recall LEP W mass measurement (4 jets -> 3

pairings)• Threshold scan requires precise dL/dE spectrum

– Places premium on small angle bhabha scattering

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Timing Considerations

• Depending on choice of machine technology timing information from the calorimeter may be necessary

• Consider beam bunch structure– Tesla: 300 ns spacing in 1 ms trains @ 5 Hz– NLC/JLC: 2ns spacing in 300 ns trains @ 180 Hz

• May need to suppress contribution from 2-photon events in different bunches

• Topologies such at () ETmiss require ability to veto cosmics– Depends details of signal integration times

• Time-of-flight may be useful for quasi-stable massive charged particles

June 28, 2002 UCSC Linear Collider Retreat

André S. Turcot

Conclusions

• To fully realize the physics potential of a linear collider we will have to rely reconstructing fully hadronic final states

• Given the fundamental nature of the W and Z bosons we must accept a new paradigm that they must be fully reconstructable and distinguishable in complex events

• In many key physics processes, the figure of merit is the jet energy resolution

• Our current understanding of jet energy resolution points to a solution relying upon an Energy Flow Algorithm– Any proposed calorimeter must be amenable to the

implementation of an Energy Flow analysis