physics requirements for calorimetry at a linear collider andré s. turcot
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Physics Requirements for Calorimetry at a Linear Collider André S. Turcot Brookhaven National Lab Santa Cruz Linear Collider Retreat June 27-30 2002. Overview. There are key physics processes that set the performance requirements for the Linear Collider Calorimetry - PowerPoint PPT PresentationTRANSCRIPT
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