CALOR2002

1. CALOR2002 The Future of Calorimetry In High Energy Physics Dan Green Fermilab

2. Outline • 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

3. Introduction • 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.

4. SM Particles • Whatever happens, New Physics will decay into SM particles.

5. 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.

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

7. Critical Energy for Muons At some point the muon becomes much harder to identify as an object that “only ionizes”.

8. 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.

9. Status • 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.

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

11. 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 %

12. CMS and PbWO4 – R&D

13. Hadron Cascades - EM Clusters dE Layer #

14. 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.

15. Detector Improvements - I Non-compensation leads to dE/E which decreases as ln(E).

16. 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.

17. 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. EH EE

18. 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 ~ .  e R

19. 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.

20. 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.

21. 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. MJJ/Mo dE/E R

22. 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. d d ET

23. 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%)

24. 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.

25. 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.

26. 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.

27. 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.

28. 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.

29. Angular/Position Resolution Tesla ECAL study – fine grained. dx ~ Xo * a /E d ~ dx/R. EM shower angle limited by stochastic shower fluctuations.

30. Transverse Size - HCAL • Shower size then limits the number of resolvable “particles” in a jet, especially the dense “core” of a jet. Limits set to “energy flow”

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

32. CMS - Leakage and “Catcher” There is a finite probability of a single hadron to “leak” a large fraction of its’ energy.

33. Hadron Showers “Leak” With g splitting and with pion decays, depths > 10  are not useful.

34. 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

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

36. Speed - LA Pulse Shaping LHC calorimetry is fast enough to minimize pileup effects.

37. HPD Pulse Formation - Bias Calorimeter signals at LHC is ~ contained in 1-2 bunching crossings. Photocathode Si Diode E field 10 kV h

38. 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.

39. 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.

40. 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. dM/M M/Mo

41. 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. ].

42. 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.

43. 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?

44. Scintillator - Dose/Damage This technology will not survive in the endcap HCAL if the LHC L increases (independent of C.M. energy).

45. 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?

46. 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.

47. 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 luminosity.

48. 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.

49. 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.

50. Summary • 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.