1. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 1 Calorimetry at LHC  Why should I want a calorimeter ?  Interaction relevant for Electromagnetic Calorimeters  Calorimeter characteristics: linearity and resolution  The ATLAS and CMS em calorimeters: different choices  Hadronic interactions and issues relevant to hadron calorimeters  ATLAS and CMS hadronic calorimeters C.Roda INFN & Universita` di Pisa

2. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 2 References R. Wigmans, “Calorimetry, Energy Measurements in Particle Physics” all figures without other cited source are from this book Priscilla B.Cushman, “Electromagnetic and Hadronic Calorimeters” D.Prieur, “Etalonnage du calorimetre electromagnetique du detector ATLAS”, PhD Thesis M.Diemoz, “Calorimetri elettromagnetici a cristalli per la fisica delle alte energie” Lezioni Villa Gualino 3.2.2005 U.Amaldi, “Fluctuations in Calorimetry measurements” 1981 Phys.Scr.23 409 C.W.Fabjan and F.Gianotti, “Calorimetry for particle physics”, Reviews of Modern Physics, Vol.75, October 2003 R.Wigmans et al., “On the energy measurement of hadron jets” ATLAS & CMS TDRs

3. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 3 What is a Calorimeter ? The Calorimeter concepts originates from thermodynamics: thermally isolated box containing a substance under study of which we want to measure the temperature. “Our” calorimeters also measure temperature as an energy measurement. The very basic concept is thus taken from thermodynamics but the sensitivity we need is much higher, the effect of 1 TeV (1 eV = 10 -19 J) in 1 liter of water (c water = 4.19 J g -1 K -1 ) at 20 o is:  T = E / c water M = 1.6 10 -7 / 10 3 4.19 = 3.9 10 -7 K the sensitivity that we need is much higher. …also calorimeter in particle and nuclear physics are invasive devices: Calorimeters are detectors able to measure the particle energy through total absorption. The first idea to use calorimeter was originated by the need to measure not only charged particles (bending magnetic field) but also neutral particles:  0  …there were born around the 1970 …

4. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 4 Wigmans - Calorimetry

5. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 5 Key role in the past UA2 measurement of W → jj invariant mass before and after background subtraction, the wider is the peak the more difficult it is to see the signal on the QCD background. The sigma of the signal peak is 8 GeV of which 5 GeV are attributed to calorimeter resolution. Here the resolution is not enough to separate the W and Z peaks.

6. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 6 General charcteristics Sensitivity both to neutral and charged particles; Energy measurement precision (more or less)  with  E spectrometer measurement precision  with  p; Do not need magnetic field (infact it is easier without); Shower length  ln(E) thus dimension are compact; Particle identification; Not only E but also spatial measurement through segmentation; They can have a fast response, useable at high rate and for trigger signals. CALO E

7. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 7 Key role in LHC Higgs discovery: H →  H → ZZ → 4 e (particle identification against jets) SUSY discovery: easiest event signature is given by excess of events high E T miss e high p T jets; top mass measurement tt → WWbb → l  jjbb, W → jj; precise E T miss measurement requires precise and hermitic calorimetries. forward jet tagging … I hope I have convinced you that there are numerous reasons why we need a calorimeter… Also we will see how some of the mentioned physics channels will be used to define the design requirements of the LHC calorimeters.

8. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 8 A few concepts on Electromagnetic interactions

9. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 9 How does a EM shower forms ? e  interaction with matter First issure is to understand the mean energy deposit/interaction PhotonElectrons and Positrons PDG 2004

10. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 10 What do we need to understand … Since the cross section of these processes depends on the particle energy the relevance of each process changes as the shower develops. The cross section depends on Z of the material thus the characteristics of the signal depends strongly on the type of material we use to build the calorimeter. Now we try to better understand the relevant points of this processes for what concerns shower formation.

11. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 11 Electron and positron Bremsstralung Radiation of real photons in Coloumb field nuclei. QED mean energy loss per unit length (per gr -1 cm 2 ) proportional to energy of the particle; Scaling factor for high energy ele in one X 0 the particle reduces its energy by 63%. X 0 can be multiplied by the density to measure in cm E > 100 MeV it is the most important process for energy loss for e+e-

12. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 12 Ionization loss Interactions of electrons with the atoms characterized by many interactions with a small release of energy. Material ZX 0 /cmEc/MeV Liquid Ar181437 Fe261.822 Lead820.567.4 Sol Liq Two regimes of energy loss → the border is set by the critical energy E C :

13. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 13 Electrons vs photons There is a main difference between the interactions of electrons (and positrons) and photons with matter at high energy. Electrons loose energy but they do not disappear, photons as they interact they are destroyed. electronsphotons

14. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 14 Pair production Interaction of photons with the field of the nucleus (or of the electrons):  nucleus → nucleus + e + e - Threshold: E  ≥ 2 m e High energy approssimation, E independent Reduction of photon beam intensity. Photons scaling factor is of the same order of electrons:  pair = 9/7 X 0  1.3 X 0

15. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 15 Photoelectric and Compton interaction  A → A + e -  e →  ’ e ’ In both interactions secondaries do not follow the direction of the incident electron, almost no reminder of initial particle direction.  shows strong dependence on E shell

16. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 16 Direction of particles that release energy ?

17. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 17 Photon cross sections Carbon Z = 6 Lead Z = 82 Particle Data Book 2004

18. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 18

19. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 19 In summary how the shower is formed  The shower is formed through a process of particle multiplication that degrades the particle energy;  Interplay between different interaction processes depends on Z of material;  As the energy of the particles reaches very low energies  eV,KeV, electrons and positrons are absorbed by the material which is “heated” by the released energy.

20. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 20 Scaling of shower profile with E and X 0 The position of the shower maximum X Maximum is approximatly described as a function of X 0 – since both gamma pair and brem scale with it - and the particle initial energy by the simple formula: t o = - 0.5 for electrons 0.5 for photons

21. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 21 Electron longitudinal shower profile Electron longitudinal shower profile in copper Shower maximum moves with energy as log(E) [Wigmans – Text Book]

22. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 22 Photon/electron difference Few photons do not interact at all Almost no electrons do not release [Wigmans – Text Book]

23. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 23 X 0 scaling is approximate Shower Mx is deeper in Lead than in Aluminium: multiplication continues for longer since critical energy is lower in Lead than in Aluminum (7.4 MeV vs 43 MeV). [Wigmans – Text Book] 10 GeV e-

24. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 24 X 0 scaling is approximate Shower “decade” slowlier in lead than in aluminum since the total number of particle created is 3 times higher than in Aluminium. [Wigmans – Text Book] 10 GeV e- EGS4

25. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 25 Consequence on longitidunal Shower containment Percentual shower containment More radiation lengths of U than of Al needed to absorb 95% of em showers.

26. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 26 Calorimeter dimension Calorimeters of 25X 0 allows to contain electron showers at 1% up to 300 GeV. 25X 0  25-50 cm Material needed for 95% shower containment:

27. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 27 Transverse profile The lateral shower development is dominated by two effects: multiple scattering at the early phase of the shower; long free path for low energy photons in Compton energy range. The measurement of the transverse size, integrated over the full longitudinal range, is given by the Molière radius (same units as X 0 ): On average 90% of the shower is contained in 1 R M.

28. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 28 Transverse profile 10 GeV e- in copper Transverse profile at various depths. Two regimes: multiples scattering and Compton photons travelling away from the axis. MaterialZX 0 /cmEc/MeVR M /cm LAr1814378 Fe261.8221.7 Lead820.567.41.6

29. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 29 What are the particle that deposit energy Fraction of energy deposited to the material by a 10 GeV electron: The low energy particles are responsible for most of the energy deposition.

30. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 30 What is the range of the particle that release energy

31. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 31 From energy deposit to signal From the energy deposit we have to generate the signal. Two calorimeter design possibilities: Homogeneous: the calorimeter consists of a single material which acts both as absorber and active device that transform all e+ e- energy deposit in signal. Sampling: absorber and active device are made of different materials and signal is generated from a sample of the total e+ e- energy deposit.

32. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 32 Signal generation The most used techniques to generate the signal in calorimeters are: Cerenkov radiation from e+ e- Scintillation signals Ionization of the detection medium All these tecniques are characterized by a threshold energy which is the minimum detectable energy E s. Light collection Charge collection

33. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 33 What I need from the calorimeter Linearity in a given energy range: Signal = a E The larger the range the more difficult it is for example range @ LHC [MIP → TeV] Signal/Energy: pC/GeV, ADC count/MeV … The request might seem easy but many different source might spoil the calorimeter response (a). a = Signal/Energy

34. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 34 Factors that affect the linearity Spoiling the linearity: Saturation effects: of electronics, of energy deposition … Leakage (transverse or lateral) noise, this at low side Example: PMT saturation. Injected charge (a.u.) PMT signal (a.u.) PMT signal/injected charge Linearity within 2% 1 1.02 0.98

35. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 35 What else I need from a calorimeter Response to monochromatic source of energy E Calorimeter signal background H   good resolution Signal = constant integrated B    → S/  B  1/   … but   = f(  calo)  (calo) defines the energy resolution for energy E. m  H   bad resolution Perfect good bad

36. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 36 What affects the resolution Up to this moment we have described the behaviour of the calorimeter, fluctuations around this value are the sources of the calorimeter resolution. The sources of fluctuations are various: Signal quantum fluctuations (i.e.: photoelectric statistics …) Sampling fluctuations Shower leakage Instrumental effects (i.e.: structural non-uniformity, electronic noise, light attenuation, …) Usually in each calorimeter, and in each energy range, one of these sources dominates.

37. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 37 Simple model: a particle of energy E will produce N signal quanta: N  E/E c N is the number of e+ e- that realese energy by ionization and excitation. The signal S is proportional to the total track length (T) : T  X 0 E/Ec The measured energy E M is proportional to the particle energy E: E M = k T Resolution and signal quanta fluctuation

38. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 38 Resolution and signal quanta fluctuation Stochastic term Assuming (for the moment) that  k = 0 E M = k T Fluctuation of number of track segments is poissonian → gaussian for large number of track segment

39. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 39 Resolution and signal quanta fluctuations The intrisic limit to the energy resolution is given by the maximum detectable track length which depends on the signal threshold energy: T detectable = f s T  f s X 0 E/Ec f s fraction of N particles over energy threshold E s. Thus: E M = k T detectable  k f s X 0 E/Ec Low energy threshold for detecting → high f s

40. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 40 Crystal calorimeters have best intrinsic limit on energy resolution Compare processes with different energy threshold Scintillating crystalsCherenkov radiators Real Resolution with all contributions:

41. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 41 Resolution in sampling calorimeters In sampling calorimeters there is a further contribution to fluctuations which is due to the sampling procedure and usually dominates other stochastic fluctuations: Absorber plates Active mean Electron shower in a cloud chamber with lead absorber Rossi gave a semi-emipirical expression for the sampling fluctuations considering the fluctuation of the number of particles crossing “a set of active layers equally spaced at distance x”:  Emip = energy lost by a mip on a sampling layer (Active + absorber)

42. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 42 Resolution in sampling calorimeters The higher the number of planes the smaller the  Emip → the better the energy resolution However this is clearly only part of the story …

43. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 43 Sampling fluctuations The previous formula however fails to describe the correct dependence of the resolution with the active layer thickness … it goes in the opposite direction.

44. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 44 Sampling fluctuations We have seen that the calorimeter signal is given by many low energetic (  MeV) e+ and e-: e+ e- created in active layers e+e- created in absorber that reach the active layers the pathlength of particles with E  1MeV is fraction of the distance between active layers thus increasing the number of boundary surfaces between layers increases the contribution to the signal The fluctuations depend on: Sampling fraction Sampling frequency d d/2d/2

45. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 45 Sampling fluctuations  f samp ↓ resolution ↓d ↓ resolution

46. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 46 Other contribution to energy resolution Many other sources affect the energy resolution which can be parametrized as the sum of three terms added in quadrature assuming independent sources: a = stochastic term, fluctuations in signal quanta b = noise term (Stot = Sparticle + Snoise): electronic noise but also contribution from pile-up c = smearing of the calorimeter response due any structure non uniformity that cause variation in the signal generation, non hermetic coverage (cracks)

47. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 47 Resolution constant term It is the leading term at high energies. It is affected by non uniform response of the detector as a function of the impact point position (equalization), temperature… It is mainly related to the precision and stability of setting working conditions … E M = kT detectable where now we are considering the variation of k: Very hard work to have a low constant term in order not to spoil resolution at high energy expecially if the stochastic term is low….

48. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 48 Resolution and shower leakage These fluctuations are non poissonian since are due to fluctuations in numbers of interactions in first calo layer …and increase with ln(E) lateral shower leakage much less fluctuating the longitudinal one Usefull parametrization for longitudinal fraction energy lost f < 10%: i.e. for f = 5% → 13% degradation in energy resolution

49. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 49 Resolution and shower leakage CHARM Collaboration NIM 1980 178,27 Percentual energy loss Longitudinal dominated by first interaction, lateral by fluctuations of many low energy particles  pair = 9/7X 0

50. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 50 Which is the source I should take care of … Es.: ATLAS EM barrel Calorimeter 0.7%

51. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 51 A Calorimeter for the Large Hadron Collider 10 34 10 33 <10 32 Lumi cm -2 s -1 100 10 0.3 Int. Lumi/y fb -1 14LHC (high lumi) 14LHC (low lumi) 1.8TeVatron Run I E CM TeV

52. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 52 Good and Bad at LHC

53. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 53 Minimum bias e pileup per bunch  tot (pp)  100 mb 10 10 2 10 3 10 4 Centre-of-mass energy (GeV)  tot (pp) and  inel =  tot -  el -  diff @ LHC  inel  70 mb Pileup: =  inel x L x  t = 70 mb x 10 34 cm -2 s -1 x 25 ns  20 interactions/BC Big change with respect to previous machines: LEP:  t = 22  s << 1 SppS:  t = 3.3  s  3 HERA:  t = 96 ns << 1 Tevatron :  t = 3.5  s << 1 Tev RunII:  t = 0.4  s  2

54. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 54 Minimum bias characteristics ~ 500 MeV pp inelastic events at  s = 14 TeV Roughly speaking at high luminosity: dn charged /d   dn neutral /d   7.5 in  = 1  +-  0.6 GeV  da  0  0.3 GeV pseudo rapidity Calorimeter acceptance –5 <  < 5 (  = 0.8 o ): most energy is lost down the beam pipe ~ 1100 GeV transverse energy (~ 3000 particles) in the calorimeters every 25 ns Nch /  = 1 E(TeV)\  = 1

55. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 55 A calorimeter for this environment ATLAS and CMS have been designed to: Minimize the pile-up in:  time: fast detector with a time response compatible with the bunch crossing distance 25/50 ns  space: high granularity thus high number of channels  Radiation resistance:  Radiation resistance: appropriate tecnique for each rapidity range.  Measurement of neutrinos:  Measurement of neutrinos: high ermeticity  Use of performance on important channels  Use of performance on important channels to define the reuirement on calorimeter performance. For EM calorimeters H→  …

56. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 56 Performance for Em calorimeters: H→  Natural width: for M H  100 GeV →  H /M H ≤ 10 -3 Experimental width of m  = 2 E 1 E 2 (1 - cos   ) : Same for ATLAS and CMS …

57. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 57 ATLAS and CMS calorimeter systems are completely different Solenoidal inner section + Toroidal outer section Solenoidal field up to muon spectrometer Pictures approximately to scale …CMS requires a compact detector

58. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 58 Very similar requirements but … ATLAS and CMS makes different choices: ATLAS require segmented calorimeter to have redudant mesurement of  angle CMS relies on vertex reconstruction from tracking and point to homogenous calorimeter with very low stochastic term aiming for excellent energy resolution.

59. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 59 ATLAS and CMS electromagnetic calorimeters Compact Excellent energy resolution Fast High granularity Radiation resistance E range MIP → TeV Homogeneous calorimeter made of 75000 PbW0 4 scintillating crystals good energy resolution Fast High granularity Longitudinally segmented Radiation resistance E range MIP → TeV Sampling LAr-Pb, 3 Longitudinal layers + PS

60. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 60 CMS choice: crystal calorimeter Compact Transverse segmentation MaterialX 0 /cmEc/MeVR M /cm Fe1.8221.7 Lead0.567.41.6 PbWO 4 0.892.2 Crystal dimensions: longitudinal 25 X 0 = 22.2 cm Transverse 1 R M = 2.2 cm 95% of the shower contained in 2 R M Module type 2 - Rome

61. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 61 CMS electromagnetic calorimeter: fast Conduction band valence band band gap  E,  T Slow component is induced by defects and impurities. In high quality crystals 80% is emitted in 25 ns.

62. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 62 Photon detectors for CMS Example of problematics due to the readout device and to the experimental environment. NIM A378 (1996) 410-426 Very sensitive to magnetic field (4T) … not impossible but very much care should be taken to correct for all the effects and loss of amplification. One of the drawback with PbWO 4 is the low light yield 100  /MeV thus photon detector should amplify the light: first choice PMTs.

63. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 63 Photon detectors for CMS Si-PhotoDiode OK for B field, however … no moltiplication → very large tails from electrons going through the silicon. Si-Avalanche PhotoDiode OK for B field, however … x25 moltiplication and good resolution. NIM A378 (1996) 410-426

64. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 64 The constant term in the resolution Many sources to be kept under control: Longitudinal uniformity of light collection Strong light yield variation with temperature (- 2.3%/ 0 C) APD gain variation with applied tension (- 3%/Volt) and termperature (-2.3%/ 0 C) Light collection uniformity light transmission due to radiation damage Other terms: Leakage front and rear

65. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 65 CMS EM Resolution Resolution as a function of energy from test on beam: final prototype matrix

66. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 66 A slice of ATLAS electromagnetic calorimeter Sampling: accordion lead structure filled with LAr 47 cm Longitudinal dimension :  25 X 0 = 47 cm (CMS 22 cm) 3 longitudinal layers 4 X 0  0 rejections separation of 2 photons very fine grain in  16 X 0 for shower core 2 X 0 evaluation of late started showers Total channels  170000 Particles from collisions

67. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 67 Signal formation in LAr Gerbe EM e-e- e-e- e+e+ Plomb E ~ 1kV/mm Argon liquide Electrode  ions e-e- HT I phys Signal is given from collection of released electrons Drift velocity depends on electron mobility and applied field. In ATLAS : Lar gap 2 mm  V = 2kV HV 400 ns  16 LHC BC LAr

68. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 68 Good and bad with LAr High number of electron-ion pair produced No amplification neeeded of signal, low fluctuations Liquid → Very uniform response (purification) Stability with time Main fluctuations are due to sampling fluctuations Intrinsically radiation hard cheap slow time response 400 ns boling temperature 87K → criogeny needed Temperature sensitivity 2% signal drop for  T=1

69. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 69 LAr Calorimeter in the LHC environment … In order to cope with pileup background the time response is shaped with a short resolving time pulse with 0 time integral:  Each “  ” is a bunch crossing  Signal used is only a fraction thus I need good S/N  but shaping time has 0 time integral → mean value of pileup is cancelled.

70. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 70 LAr Calorimeter at LHC rates … The “perpendicular” geometry allows to have low detector capacitance (series of electrodes) and signal close to preamplifier (low inductance) this give high S/N. The accordion geometry allows to have this feature without very large variation of sampling fraction for perpendicular crossing particles. Series Parallel

71. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 71 Signal in ATLAS electromagnetic calorimeter The accordion geometry makes also the calorimeter particularly hermetic, much easier to get the signal out but also “solve” the time response problem Signals on copper electrodes due to current induced by electrons: 2 mm gap in 500 ns

72. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 72 LAr barrel EM calorimeter after insertion into the cryostat The cryostate for the ATLAS electromagnetic calorimeter

73. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 73 ATLAS EM calorimeter The constant term in the resolution is dominated by:  the equalization of the electronic readout. The equalization procedure requires to know the shaping function of each cell at few percent level → equalization with an electronic control signal  the non uniformity in the electric field and in the sampling fraction introduced by the accordion structure.

74. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 74 Contribution to constan term in resolution ATLAS em 90 GeV e- Some contribution also come from variation of sampling fraction due to the accordion structure

75. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 75 Which uniformity do I get ? Scan on a complete module with monoenergetic electrons Scan in  Const. term  0.57% over ~ 500 spots

76. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 76 Comparing the design resolution E (GeV)  (E)/E Many of us are working to make this resolutions become reality for the whole calorimeter CMS vs ATLAS

77. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 77 Comparing the resolution on prototypes modules E (GeV)  (E)/E E (GeV)  (E)/E

78. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 78 Comparison of performances on H→  Resolution on   invariant mass: CMS 0.7 GeV ATLAS 1.2 GeV CMS better resolution requires a very precise control of constant term ATLAS has better power to measure the  direction → potentially a higher efficiency … is a question of point of views …

79. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 79 Two calorimeters two points of view CMS goes for excellent energy resolution thus points on a technique which has a very small stochastic term, also requires a very compact calorimeter for B field choice ATLAS points to a moderate energy resolution but to a tecnique where the intrinsic uniformity is almost for free and requires also angle reconstruction and more powerful capabilities for particle id.

80. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 80 Hadronic interactions

81. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 81 An extra complication… The extra complication of strong and nuclear interation makes hadron calorimeters more difficult to optimize. The performance that one can expect from an hadron calorimeter at the moment are resolution of the order of 50% - 100%/  E and linearity with a few percent  5% (recall 3%-10 %/  E and <1% for EM calorimeters. The first hadron interaction is governed by: X 0, I [cm] Material Z I /cm X 0 /cm Fe2616.81.8 Cu2915.11.4

82. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 82 Hadron interactions When a hadron interact the are two components: Electromagnetic fraction: ,  0 →  s and develop and electromagnetic shower same as the one we already discussed. Hadron fraction: neutrons, protons, pions. As an example in lead this energy deposit is divided in: 56% ionizing particles (2/3 spallation protons) 10% neutrons (very low energy neutrons) 34% invisible (mainly nuclear binding energy, few pion decays …) Average deposit from simple model (Wigman).

83. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 83 The electromagnetic fraction The average electromagnetic energy f em depends on the energy of the incident particle E 0 : k  0.8 and E 0 = average energy needed for  0 production  1 – 2 GeV. This is obtained assuming that 30% of energy goes to  0 at each interaction, the value of k is related to the track multiplicity. Gabriel et al. E (GeV) Fe E 0 = 0.7 GeV k = 0.8 Pb E 0 = 1.3 GeV k = 0.8

84. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 84 Global view of mean energy deposit Lead f0f0 MIP Rev.Mod.Physics Vol.75 Oct.2003 Invisible

85. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 85 What are the implication of this type of shower We have seen that there are two types of shower components: electromagnetic E e ( ) and hadronic E h (  ). The calorimeter reponse to the two components is different:  e,  h in general  e >  h. Calorimeter response to hadrons: R h =  e E e +  h E h E e >> E h E e <<E h R h =  e E e +  h E h  e >  h

86. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 86 What are the implication of this type of shower We have seen that there are two types of shower components: electromagnetic E e ( ) and hadronic E h (  ). The calorimeter reponse to the two components is different:  e,  h in general  e >  h. Calorimeter response: R =  e E e +  h E h E e >> E h E e <<E h R h =  e E e +  h E h  e =  h R

87. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 87 What are the implication of this type of shower Calorimeter response to hadrons and electrons: Often indicated as e/h

88. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 88 Non linearity due to e/h

89. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 89 Longitudinal Hadronic shower shape 95% containment 300 GeV   8 i.e.: 85 cm U. For electron containment of same energy 10 cm U.

90. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 90 Longitudinal leakage Position of shower maximum: tmax  ln(E) For 98% containment of 10 GeV = 2, for 100 GeV 7

91. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 91 Mean is a rough concept for hadrons … four different longitudianl profiles

92. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 92 Transverse shower shape Two components: em core + non-em halo mainly non relativistic particles 95% containment 80 GeV   1.5 / 32 cm For electrons 95% containment of same energy 3.5 cm A factor  9 for in both directions.

93. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 93 Lateral leakage The em components increases and the shower gets sharper. 150 GeV 10 GeV

94. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 94 Energy resolution The energy resolution is dominated by fluctuations in: visible energy - ultimate limit for hadronic fluctuations em component – this is the dominant factor in calorimeter with e/h  1 as is the case for non compensated calorimeter em component 150 GeV  - As we have seen this fluctuation induces a worse resolution as e/h is different from 1.

95. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 95 Effect of e/h on hadron lineshape

96. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 96 Dealing with e/h The calorimeters with e/h  1 are said to be non- compensated. In order to recover linearity and to improve the hadronic resolution two possible strategies: Hardware compensation: tuning the sampling fraction, sampling frequency and the type of materials used in sampling calorimeters it is possible to enhance the response to the hadronic part of the shower thus reaching e/h = 1 Software compensation exploting the longitudinal and transverse segmentation of the calorimeter it is possible to correct event by event the reconstructed energy by weighting differently em-like deposits and hadron-like deposits. ATLAS and CMS have chosen the software compensation.

97. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 97 An hadronic calorimeter for LHC The same consideration made for EM requirements in LHC environment (radiation hardness, rates …) are true for Hadronic calorimeters. Calorimeters will have the main impact on performances for: Jets : collimated particles with different energies produced by parton hadronization ET miss: Jets are the worst reconstructed objects thus have impact on Et miss resolution Single hadrons i.e. from tau or W decays Request on resolution and linearity set with benchmark channels: W → jj, top mass, sensitivity to compositness

98. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 98 Response to jets Jets are composed by many low energetic particles. Very semplified model for jet composition. 100 GeV jet R.Wigmans et al. “On the energy measurement of hadron jets” It is very important to understand the behaviour of the calorimeter up to 1 GeV hadron to understand the performances to jets.

99. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 99 The Hadronic calorimeter The hadronic calorimeter is composed by: - EM calorimeter section (about 1, 25X 0 ) - Hadronic calorimeter section We will see that the performances on hadrons are due to both these sections.

100. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 100 LAr/Cu 1.7 < |  | < 3.2 4 longitudinal sections ATLAS Hadronic section Both hadronic and em LAr/Cu or W 3.2 < |  | < 4.9 3 longitudinal sections Tile Calorimeter |  | < 1.7 Fe / Scintillator 3 longitudinal sections Longitudinal depth about 8 -10 Different technologies to cope with higher radiation at higher eta.

101. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 101 Atlas central hadronic section Barrel Ext. Barrel Principle of operation of TILE

102. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 102 TileCal - Sezione centrale Tile Preassembly TileCal modules

103. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 103 CMS Hadronic section Central Hadronic |  | < 1.7 : Brass/Scintillator + WLS 2 + 1 (HO) Longitudinal section 5.9 + 3.9 (|  | =0) Endcap Hadronic 1.3< |  | < 3 : Brass/Scintillator + WLS 2/3 Longitudinal sections Forward calorimeter 2.85 <  < 5.19: Ferro/fibre di quarzo Brass has been chosen since it is a non magnetic material COIL

104. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 104 CMS Hadron Calorimeter

105. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 105 CMS and ATLAS The choices made for the hadronic central section by ATLAS and CMS are similar: sampling calorimeters with scintillator as active material. In both case the dominant factor on resolution and linearity is the e/h  1 ATLAS: e/h had  1.4 e/h em  1.5 CMS: e/h had  1.4 e/h em  1.6 ATLAS higher segmentation and better stochastic term gives better total resolution

106. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 106 e/h at work… 15% E  /p e/  Ebeam (GeV)

107. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 107 CMS Energy resolution on pion   interacting in HCAL In HCAL or ECAL  no weigthing o passive weighting  dynamic weighting Effect of different e/h + no longitudinal sampling in EM

108. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 108 ATLAS energy resolution on pions Linearita < 2% Shown for ATLAS but similar for CMS NIM A449(2000) 461-477   EM scale  Corrected with longitudinal samples

109. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 109 CMS and ATLAS Calorimeter ATLAS has much higher longitudinal segmentation thus correct the hadron signal with sw compensation. CMS has chosen a non segmented em calorimeter and a less segmented hadron calorimeter thus is more difficult to obtain sw compensation Also the presence of the coil and calorimeter design of CMS starts with a much higher stochastic term It should be noticed that when considering jets there are many effects related to jet reconstruction (out of cone correction, parton to jet calibration…) that affect the resolution. Again we see a different point of view … a different bet

110. Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 110 Conclusions I hope I have given you an idea of what are the reasons behind the design and the choices of the calorimeters. I have skipped many items that are important for calorimeters: Calorimeter calibration, how do I set the E scale … Calorimeter monitoring, how do I keep the E scale Effect of detector integration on calo performances Particle ID with calorimeters position measurement with calorimeters Jet reconstruction and calibration ….. you can find much more than I said in the references that I listed at the beginning of the presentation. Good luck and I wish to all of us a great discovery times …