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CALOR2002. The Future of Calorimetry In High Energy Physics Dan Green Fermilab. Outline. Introduction Status Improvements in Detectors Non-compensation “constant term” Mixed Media Energy Flow Missing E T Intrinsic Limitations Transverse Position Leakage and Depth Signal Speed

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The Future of Calorimetry

In High Energy Physics

Dan Green


  • Introduction
  • Status
  • Improvements in Detectors
    • Non-compensation “constant term”
    • Mixed Media
    • Energy Flow
    • Missing ET
  • Intrinsic Limitations
    • Transverse Position
    • Leakage and Depth
    • Signal Speed
    • Energy/Mass Error
  • Future Developments and New Physics
  • As the energy frontier advances, calorimetry will become increasingly important since dE/E is, at worst, constant with energy, while tracking has dP/P ~ P.
sm particles
SM Particles
  • Whatever happens, New Physics will decay into SM particles.
calorimetry and sm particles
Calorimetry and SM Particles
  • Calorimetry will be used for jets of quarks and gluons as well as showers of electrons and photons. Neutrinos will be inferred from missing ET measured in calorimeters. Muon particle id will use calorimetry for isolated muons (but Ecrit~ 300 GeV). Tau id will come from “narrow” jets, ->W, W->,,A.
hcal ecal and particle id
HCAL + ECAL and Particle ID

e, , 

in “ECAL” + HCAL. Particle ID uses differences in Xo and  (e,) and in radiation cross section (e, ).

critical energy for muons
Critical Energy for Muons

At some point the muon becomes much harder to identify as an object that “only ionizes”.

calorimetric resolution
Calorimetric Resolution
  • Single Particle -> Jet -> Dijet -> Event Total Energy

Jet energy error is ~ single particle error, if the only error is energy measurement.

Dijet mass error is determined by jet error

Missing energy error is also determined by single particle error.

  • Belle/Babar are running very successfully. However, major luminosity increases will not be possible with the existing calorimetry.
  • CDF and D0 are data taking and aim for high L.
  • LHC detectors are being built and have some “headroom”. However, an increase of 10x in the LHC luminosity cannot be simply accommodated.
  • LC detectors are being designed for high precision measurements.
ecal sampling and de
ECAL - Sampling and dE

With fine sampling, W << 1, and small source capacity (accordion) precision , high speed, EM calorimetry is possible.

energy resolution crystals
Energy Resolution - Crystals

e.g. PbWO4 – CMS

Fully active devices have no sampling

fluctuations. However, there is

noise and photon statistics, and light

collection non-uniformity.

dE/E ~ 0.7 % at 100 GeV

even though stochastic

coefficient is only ~ 2.3 %

state of the art at lep cdf d0
State of the Art at LEP, CDF/D0
  • LEP – Use beam constraints. dM/M ~ 3.6%
  • CDF – No FSR cuts made, no pileup, dM/M ~ 14 %. Big differences need critical examination.
detector improvements i
Detector Improvements - I

Non-compensation leads to dE/E which decreases as ln(E).

non compensation and de e
Non-Compensation and dE/E

As energy increases fo -> 1 and effect of e/h is reduced. At very high energy non-compensation is not an issue.

evading mixed media
Evading “Mixed Media”
  • If you identify energy as hadronic, you can correct for non-linearity due to different ECAL and HCAL materials but not non-compensation.
  • Works over a large energy range. Still dfo and e/h > 1 cause dE.



particle id transverse
Particle ID - Transverse
  • Need particle id. Particle id in CMS uses transverse size in ECAL ( ~ Xo) and the ECAL/HCAL energy partition.
  • Test beam data in ECAL on e and pion transverse rms size, R.

Limited at the LHC by pileup causing id errors due to the intrinsic size of a hadron shower ~ .



detector improvements ii
Detector Improvements - II
  • Tracking from CMS, ECAL 5% stochastic, 1% constant, and HCAL 50% stochastic and 3% constant.
  • Note that a jet has <zmax> ~ 0.22. For charged particles < 100 GeV (jets < 0.5 TeV) use tracks to measure E.

For present energy scales at the LHC and LC use tracker energy measurement if possible. At a VLHC this will not help.

tracking and energy flow
Tracking and Energy Flow
  • A jet cone of

radius 0.9 has

~ 400 towers

of HCAL and

~ 10,000 towers

of ECAL in CMS.

Tower occupation

is sparse -> can

identify tracks with

“isolated” towers.

HCAL lego shown.

optimal jet cone size
Optimal Jet Cone Size
  • Of the ~ 400 towers in the cone, only ~ 24 clusters are occupied – i.e. sparse. At low luminosity a shallow minimum exists at R ~ 1.0.




track matching
Track Matching
  • For a Monte Carlo sample of 120 GeV Z’ match tracks in  and  to “hadronic” clusters within the jet – cone size ~ 0.9. Units are HCAL tower sizes.




improved dijet mass
Improved Dijet Mass
  • There is a ~ 22 % improvement in the dijet mass resolution. This is welcome but clearly implies that calorimeter resolution is not the whole story.

Mean 81.7 GeV, (21%) Mean 105.5 GeV, (17%)

cdf study photon jet
CDF Study – Photon+Jet
  • CDF studied energy flow in photon + J events using shower max (particle id) and tracking information. A similar ~ 24% improvement was seen.
detector improvements iii
Detector Improvements - III
  • Study done for CMS. Three major sources of missing ET – incomplete angular coverage, B field “sweeping” to small angles and calorimetric energy resolution. Pileup scales as ~ sqrt(<n>) .
  • Clearly need radiation hard calorimetry to go to smaller angles – as C.M. energy increases particularly. Presently dose < 1 Grad at || = 5.
energy flow and missing e t
Energy Flow and Missing ET?
  • Use tracker at LHC to remove calorimetric deposits due to charged hadrons in pileup events. Within the desired event, use tracker in “energy flow” mode to reduce B field and dE effects.
  • The plan is to reduce the effect of pileup at high luminosity (not with neutrals) and to reduce the effects of B field sweeping and calorimetric energy error just as in the dijet case (energy flow), but now for all energy deposits.
  • If these effects can be reduced, the angular coverage should be extended down to smaller angles. At higher s, with a longer “plateau” smaller angle coverage will be needed in any case.
improved missing et
Improved Missing ET

Missing ET is a global variable. There is a 16% improvement in the missing ET significance using energy flow (no pileup). Data set is badly mismeasured high Et dijets.

intrinsic limitations
Intrinsic Limitations
  • Transverse size set by shower extent, either Xo or -> limit to tower size.
  • Longitudinal depth set by containment to ~ 20 Xo and ~ 10 . Limit on depth set by jet leakage.
  • Speed limited by 25 nsec bunch crossings at LHC. No reduction in pileup if signals are faster.
  • Jet resolution limited by FSR at LHC not calorimeter energy resolution.
angular position resolution
Angular/Position Resolution

Tesla ECAL study – fine grained.

dx ~ Xo * a /E

d ~ dx/R.

EM shower angle limited by stochastic shower fluctuations.

transverse size hcal
Transverse Size - HCAL
  • Shower size then


the number of


“particles” in a

jet, especially the

dense “core” of

a jet. Limits set

to “energy flow”

energy leakage
Energy Leakage

Good hadron energy measurements will require a depth > 10  due to late developing shower leakage and fluctuations .

cms leakage and catcher
CMS - Leakage and “Catcher”

There is a finite probability of a single hadron to “leak” a large fraction of its’ energy.

hadron showers leak
Hadron Showers “Leak”

With g splitting and with pion decays, depths > 10  are not useful.

intrinsic limitations1
Intrinsic Limitations
  • Jet “splitting”, g -> QQ and Q -> qlv, puts intrinsic limit on required depth. Jets themselves “leak”.

Jets “leak” too – 0.1 % will lose > ½ of the energy due to splitting.

# Jets with energy > Missing ET

splitting and susy
Splitting and SUSY

The jet splitting creates a SUSY background. Cutting on angle is not very incisive.

speed la pulse shaping
Speed - LA Pulse Shaping

LHC calorimetry is fast enough to minimize pileup effects.

hpd pulse formation bias
HPD Pulse Formation - Bias

Calorimeter signals at LHC is ~ contained in 1-2 bunching crossings.


Si Diode E field

10 kV h

hadron collider dijet dm m
Hadron Collider- Dijet dM/M
  • A series of Monte Carlo studies were done in order to identify the elements contributing to the mass error. Quote low PT, Z -> JJ. dM/M ~ 13% without FSR.

FSR is the biggest effect. The underlying event is the second largest error (if cone R ~ 0.7). Calorimeter resolution is a minor effect.

high l pileup
High L Pileup
  • At high luminosity (LHC) there is a minimum dM/M at R ~ 0.6 balancing fragments falling out of cone with inclusion of underlying event energy. Pileup is small for boosted Z -> JJ if R ~ 0.6 cone is used.

n.b. no FSR here, so dM/M ~ 9% for “boosted” Z. Pileup is not the dominant effect.

lhc cms study of fsr
LHC – CMS Study of FSR
  • MJJ/Mo plots for

dijets in CMS with and

without FSR. The

dominant effect of FSR

is clear.

  • The d(M/Mo)/(M/Mo)

rms rises from

~ 11% to ~ 19%, the

distribution shifts to

smaller M/Mo, and a

radiative low mass tail

becomes evident.



exploring new physics
Exploring New Physics
  • Higher Mass -> higher luminosity -> radiation damage and occupation increase.
  • Fundamental 2 body goes as square of mass as does needed L in best case [ xf(x) ~ const. ].
new physics in s l
New Physics in (s,L)
  • In colliders L and/or C.M. energy increases are both possible.
  • For masses ~ C.M. Energy, required L rises rapidly -> energy is most important, .
  • For masses << C.M. energy, L goes as the square of the mass.
increased lhc l
Increased LHC L?
  • Higher Mass states or higher L in hadron colliders will require calorimetry which can withstand > 10 Mrad (ECAL) and > 2 Mrad (HCAL) for ||<3.
  • Hermiticity will require coverage to smaller angles as the C.M. energy increases and the “plateau” extends. Already the angular truncation is important at LHC.
  • Forward calorimetry will need to endure > 1 Grad. Dose ~ . Use gas and Cerenkov light?
scintillator dose damage
Scintillator - Dose/Damage

This technology will not survive in the endcap HCAL if the LHC L increases (independent of C.M. energy).

two photon physics at p p
Two Photon Physics at p-p

At high s, the proton can radiate photons. With 2 very small angle recoil tags, 2 photon physics can be studied in a p-p machine. New detectors needed?

babar l upgrade
Babar – L Upgrade
  • ECAL CsI crystals – light loss and increased occupation. A 10x increase in L could not be tolerated by the present detector choices.
the lc program
The LC Program
  • At the LC, cross

sections w.r.t

LEP are down

by large factors.

Therefore, high

L is needed – e.g.

HH production

(HHH coupling)

requires a very

large integrated


alc study snowmass
ALC Study - Snowmass
  • Boosted Z have

dM/M ~ 3%

dE/E ~ 18%/E for jets. This is to be compared to ~ 60% at the LHC.

tesla detector studies
Tesla Detector Studies
  • Energy flow calorimetry achieves ~ 3% mass resolution (fine grained – size ~ Xo, , many depth segments ~ 3-d shower development information)
  • Large cones and ~ no underlying event in simple topologies help reduce the effects of FSR and fragmentation and leave the calorimeter resolution as now much more important.
  • Calorimetry will be increasingly important to HEP in the future (energy frontier).
  • Detectors now being built or designed have made and will make improvements to the state of the art of calorimetry.
  • Intrinsic limits due to fluctuations in transverse position, longitudinal position, energy deposits, signal formation and jet leakage will remain.
  • Studies of higher mass states will require operation at yet higher luminosity which will put in premium on radiation resistance.
gluon splitting
Gluon Splitting
  • Gluon Splitting is a major source of real missing transverse energy
  • Require missing ET to not point at a jet? OK but not very efficient.
ann rev areas of interest
Ann. ReV & Areas of Interest
  • ’91 – Wigmans - Calorimetry
  • ’94 – Moe & Vogel - Double Beta Decay Gratta, Newman, Zhu – Crystal ECAL
  • ’95 – Lutz & Schwarz – Si Detectors
  • ’96 – Ruchti – Scintillating Fibers Booth, Cabrera, Fiorini – Cryodetectors
  • ’97 – Ricci, Brillet – Gravity Wave Detectors, Aharonian & Akerlof – Gamma Ray Astronomy with Cerenkov Telescopes
  • ’99 – Sauli & Sharma – Micropattern Gas Detect
missing et and fsr
Missing ET and FSR

Only minor EF improvements in missing ET. FSR is soft at wide angles

missing et and jet axis
Missing ET and Jet Axis
  • Missing ET azimuthal angle is not well correlated to jet axis
  • Implies SUSY cuts on QCD background is not very efficient.
searches for dark matter
Searches for Dark Matter
  • Bolometry sessions for Calor2000
  • If SUSY look for

elastic recoils, scale

~ 10 keV and 10-8 pb

next generation cryo detectors
Next Generation - Cryo Detectors
  • Elastic scatter of neutralino off nuclei. Present sensitivity 10-6 pb. Next generation, 10 kg, > 10 keV, (0.01-1.0) counts /(kg*day).
  • With  = 4 x 10-6 pb, M = 100 GeV, with 10 keV threshold (Ge) -> 1.0 /(kg*day)

If next generation is successful, many SUSY points will be covered. Complements HEP searches.

cdf study fsr
CDF Study - FSR
  • CDF studied the effect of FSR. One can achieve good resolution if extra jets are rejected – but reco efficiency is low. Typical 1/M radiative tail.
simple shower monte carlo
Simple Shower Monte Carlo
  • Write a simple M.C. where all effects can be controlled. Note the 1/E tail – let a quark jet radiate gluons.
  • If you want R = 0.9 to contain > 80% of the jet energy, the efficiency will only be ~ 50%.
susy and dm
  • SUSY will be

searched for at

LHC and LC.

n.b. – SUSY is a dark matter candidate giving correct relic abundance since annihilation is weak. Favors light SUSY.