Calorimetry Content Introduction Interaction of particles with matter EM and hadronic showers Calorimeter designs Example from CMS Electromagnetic Calorimeter Hadron Calorimeter Experience with Collision Data Experimental Technique in High Energy and Particle Physics T. Ferbel Calorimetry, Energy Measurement in Particle Physics R. Wigmans 2 nd CERN School (03/05/12) Nachon Ratchasiama, Thailand Sunanda Banerjee
in Particle Physics The word is derived from the Latin word Calor, meaning heat. Generally it is the measurement of the quantity of heat exchanged. A Calorimeter is a device used for making such measurements. are blocks of instrumented material in which particles to be measured are fully absorbed and their energy is transformed into a measurable quantity. They were originally developed as crude cheap instruments for some specialized applications in particle physics experiments However in modern colliders, calorimeters form a crucial component of the experiment measuring energies of electrons, photons and jets. The interaction of the incident particle with the detector material (through electromagnetic, weak or strong processes) produces a shower of secondary particles with progressively degraded energy. Higher the energy of the incident particle, larger is the number of secondary particles produced. Counting the number of produced particles may make an estimate of the incident energy. Counting of secondary particles can be done in a number of waysgiving rise to various types of calorimeters S. Banerjee2
What to Measure? Generally a calorimeter is related to the heat energy exchanged between two bodies. Here during showering eventually (when there is not enough energy left any more for further particle production), the particles get absorbed in the material. The amount of absorbed energy will be converted into heat, which explains the name calorimeter. The energetic yield is very small: for instance, the total absorption of a 100 GeV proton in a 10 kg block of iron causes the latter to raise its temperature by only 4x10 12 C. Since the amount of heat produced by the energy depositions is too small to be measured, one has to determine the energy with a different method. The deposited energy in detector material is eventually converted into an electric signal. Showers initiated by hadrons are distinctly different from the ones initiated by electrons and photons. This gave rise to two distinct type of calorimeters: Electromagnetic calorimeters Hadron calorimeters S. Banerjee3
Interaction of particles with matter Particles passing through matter interact with nuclei as well as with atomic electrons. The physical processes are broadly classified into two categories: Discrete processes (bremsstrahlung, annihilation, elastic, ) Continuous processes (energy loss, multiple scattering, ) Continuous energy loss (charged particles in matter) At small β, -de/dx decreases with momentum A minimum is reached at βγ 4 At large β, γ 2 term dominates relativistic rise At very large βγ, saturation due to screening density effect S. Banerjee4
Energy Loss Individual collisions are classified as Distant collision: atoms react as a whole excitation, ionization Close collision: with atomic electrons knock-on Very close: with nuclei radiation If no discrete process happens, particles eventually stops after losing all energies S. Banerjee5
Discrete processes Discrete processes: Bremsstrahlung Annihilation (positrons) Elastic scatterings Pair production Z 1 q γ * e + e - γ Z 1 q γ γ γ e + Compton scattering Photo-electric effect Decays of unstable particles (em/weak) Strong interaction for hadrons Unchanged Breaks target coherent incoherent projectile elastic inelastic k 0 γ * θ e - k p S. Banerjee6
Electromagnetic Shower e ± γ At energies above 100 MeV, e ± loses energy mainly through bremsstrahlung emitting photons At similar energies, γ s interact with mainly through pair production generating e ± At high energies, σ(e) ~ constant S. Banerjee7
EM Showers e + /e - /γ cascade (degrading energy in each stage) mainly through successive bremsstrahlung and pair production Number of particles in the shower increases till the energies of the particles reach E ε c, critical energy Beyond this energy, ionization/excitation takes over and the shower decays out S. Banerjee8
EM Shower Parameters Energy loss due to radiation is governed by L R, radiation length of the material traversed. L R in g.cm -2 Both bremsstrahlung and pair production are highly forward peaked. Lateral growth of the shower comes dominantly from multiple scattering at these energies Low energy end of a shower is generated through collision process Beyond shower maximum, there is an exponential decay of the shower [exp(-t/λ Att )] Angular distribution for Compton scattering, photo-electric effect is isotropic causing further increase in the lateral size of the shower Shower profile is determined by Moliere radius ρ M. 95% of energy deposited is contained in a cylinder of radius 2ρ M. S. Banerjee9
EM Showers 98% of the shower is contained in (t max +4λ att ) where the position of shower maximum t max increases only logarithmically with incident energy E. Lateral size of the shower changes with shower depths broader at or beyond shower maximum. While radiation length (hence shower length) depends strongly on material, lateral size is roughly material independent. Showers initiated by electrons and photons are different in the first few radiation lengths. For a fully absorbed shower the difference is reduced. S. Banerjee10
Hadronic Shower They are similar to electromagnetic shower, but with greater variety and complexity due to hadronic processes Strong interaction is responsible for Production of hadronic shower particles, ~90% of these are pions. Neutral pions decay to 2 γ s which develop em showers Interaction with nucleus neutrons/protons are released from nucleus and the binding energy is lost from producing more shower particles EM showers produced by π s develop in the same way as those due to e ± /γ s. Fraction of π increases with energy. Typically EM energy fraction is ~30% at 10 GeV increasing to ~50% at 100 GeV. The remaining energy is carried by ionizing particles, neutrons and invisible component (lost in binding energies or carried by ν s from decays). In lead they are roughly in the ratio 56:10:34 and two-third of ionizing energy is due to protons. S. Banerjee11
Fluctuations in Hadronic Showers There is a large variety of profiles in hadronic showers This depends on π multiplicity in each step of interactions Leakage plays an important role even though the average containment is high S. Banerjee12
Hadronic Shower Typical scale is collision length Shower maximum occurs at t max (λ) ~ 0.2 lne +0.7 Decay of shower is slower: power law (λe 0.13 ) rather than logarithmic in E Transverse dimension is controlled by λ laterally it takes less material to contain the shower at higher energies (larger fraction of EM energy) S. Banerjee13
Signals in Calorimeter The energy deposit in the calorimeter material needs to be transformed into some signals which can be measured through detector electronics. Use ionization process example is liquid argon calorimeters the ionized electrons/ions are drifted by electric field, amplified and collected as electrical pulse Use excitation process example are scintillation light emission in organic and inorganic material the light is transmitted to photo-detectors and converted photo-electrons are amplified and collected as electrical pulse Use Cerenkov radiation charged particles in the shower traversing with speed higher than speed of light in the medium (mostly electrons) will emit this radiation and they can be converted into signal as in the case of scintillation light example is lead glass calorimeter S. Banerjee14
Signal in Calorimeter Signal generation and particle absorption are two separate process and can be combined in two ways giving rise to 2 types of calorimeters Homogeneous calorimeters the absorber and the active medium are one and the same mostly done in electromagnetic calorimeters (more for cost and performance considerations) Sampling calorimeters the two roles are played by different media S. Banerjee15
Other considerations Also consider Cascading and shower creation is quite fast. However timing for the signal generation process depends on the choice of technique may worth considering technique to be used Radiation environment signal generation and collection are often dependent on the level of radiation for example light transmission in crystals are affected by integrated radiation level (dosage and neutron fluence). Total volume of the detector the larger the volume, more is the chance of unstable particles to decay and having missing energies Ease of usage use materials which do not need special care to control humidity, temperature, Cost of the materials used S. Banerjee16
Considerations Most of the energy deposited in calorimeter comes from very soft shower paticles. In EM showers the end of the shower is dominated by Compton scattering and photo-electric effect (and not pair production/bremsstrahlung). The angular distribution of shower particles are not so strongly forward peaked. So geometries with fibre structure are as good as sandwich geometries. Sampling thickness depends on type of calorimeter Typical shower particle in EM showers are 1 MeV electron which have range smaller than 1 mm in typical absorber material Typical shower particle in hadron shower are 50-100 MeV protons and 3 MeV neutrons with range around 1 cm Lead based detectors S. Banerjee17
Linearity Electromagnetic shower results in the entire incident energy getting deposited in the material. This will result in a linear response with the exception of saturation effects When shower particles are sampled using ionization technique in avalanche mode, response does not increase linearly at high particle density Scintillation process also shows saturation effect when de/dx is large (Birk s law) for both organic and inorganic materials S. Banerjee18
Linearity (Hadron Calorimeter) Hadron shower has the complication of having two components in shower generation process and the ratio of the EM part and the pure hadronic part (e/h) is usually larger than 1. For hadronic showers as a function of energy the two components add with different proportions giving a non-linearity for all values of e/h away from 1. The value of e/h can be controlled by trying to make use of the low energy neutrons by use of elastic scattering (low Z materials) S. Banerjee19
Resolution Energy resolution (σ/e) of calorimeter is driven by several factors: Electronic noise which gives (1/E) dependence Shower leakage or calibration effect which gives a constant term Fluctuations that are ruled by Poisson statistics which gives (1/ E) dependence Shower fluctuations (# of shower particles) Signal quantum fluctuations (photo-statistics) Sampling fluctuations Resolution of ATLAS EM Calorimeter S. Banerjee20
CMS as an example CMS uses one technology for the EM calorimeter and 2 technologies for hadron calorimeter Homogeneous crystal for the EM calorimeter Sampling devices for the hadron calorimeter Scintillation Cerenkov radiation S. Banerjee21
Choice for ECAL Choice of crystal is driven by Has to be fast (bunch crossing time 25 ns) Has to be radiation hard Has to be compact Choose PbWO 4 for its high density (8.28 g/cm 3 ), short radiation length (0.89 cm) and small Moliere radius (2.2 cm) with more than 80% of produced light emitted in 25 ns Light output is low need amplification in environment with high B- field. Use Avalanche Photo Diode (APD) or Vacuum Photo Triode (VPT) S. Banerjee22
Property of PbWO 4 Light yield in PbWO 4 is typically ~10 PE/MeV (depends on T, read out) For lead glass (which uses only Cerenkov), light yield is 500-1000 PE/GeV Expect substantial Cerenkov component in PbWO 4 Measure the Cerenkov component using directional property and timing structure of the Cerenkov component Use a specific setup with single crystal read out on either side using PMT S. Banerjee23
Crystal Property Anisotropy as well as timing measurements yield measurable Cerenkov component in PbWO 4. It amounts to 10-15% at room temperature Variation of light output is 2.1% per C at 18 C. Longitudinal light transmission is ~70% and crystals emit blue-green light with a broad maximum at 420-430 nm. Try to utilize uniform light collection efficiency along crystal length. This is achieved by depolishing one lateral face. S. Banerjee24
Calorimeter Layout CMS ECAL is divided into a barrel and two endcap parts at η = ±1.479. The barrel modularity is 360-fold in φ and (2x85)-fold in η with a total of 61200 crystals. It is located at a radial distance of 1.29 m from the centre of CMS and a non-pointing geometry is chosen (crystal axis is not along the line joining centre but with 3 tilt). Each crystal corresponds to 22x22 mm 2 at front face and 26x26 mm 2 at the rear face and 230 mm long corresponding to 25.8 L R. S. Banerjee25
Barrel ECAL The crystals are contained in thin-walled (0.1 mm) alveolar (aluminium + glass fibre-epoxy) structure (sub-module). Nominal gap between crystals is 0.35 (0.5) mm in a sub-module (module). There are 17 pair of shapes each sub-module having one pair of shapes only. Sub-modules assembled into modules containing 400 to 500 crystals and finally to a super-module containing 1700 crystals covering η = 0-1.479, φ = ±10. S. Banerjee26
Endcap ECAL The endcaps cover the rapidity range 1.479 < η < 3.0. They are located 3154 mm from the centre of CMS. All crystals are identical with front/rear faces of cross section 26.82x26.82/30.0x30.0 mm 2 and length of 220 mm (24.7 L R ). They are grouped into super-crystals each containing 5x5 crystals in C-fibre alveola structure. They are grouped in 4 Dee s for the 2 endcaps with each Dee holding 3662 crystals Crystals and Super-crystals are arranged in a rectangular x-y grid with crystals focusing 1300 mm beyond interaction point. S. Banerjee27
Photo Detectors Criteria for photo-detectors Need to be fast Have to operate at high B-field (4 Tesla solenoidal field) Have to be radiation hard (more for endcap) Have high enough gain (compensate low light from PbWO4) Need to be insensitive to nuclear counter effect Choice for Barrel Detector: Avalanche Photodiodes Two APD s per crystal Each with active area of 5x5 mm 2 High quantum efficiency ~75% Low noise dark current ~ 3nA Typical gain ~50 at operating voltage 340-430 V Small effective thickness ~ 6µm equivalent to 100 MeV energy deposit for a MIP traversing APD High temperature sensitivity of the gain (~ 2.4%/ C) S. Banerjee28
Endcap PD + Thermal Stability Choice for Endcap Detector: Vacuum Photo Triode (photo multiplier with a single stage gain) Anode of very fine Cu mesh (10 µm) to operate at 4T B-field Large active area (280 mm 2 ) Moderate quantum efficiency (~22%) Moderate gain (~10) Better tolerance against radiation and temperature changes Thermal stability needs to be maintained within ±0.05 C at 18 C (the overall temperature gradient of crystal + APD system ~ 3.8%/ C) Thermal screen in front of the crystal Insulating foam to decouple crystals from front end electronics Circulating water to take away heat from the screen and the back aluminium grid S. Banerjee29
Choice for HCAL ECAL of CMS provides ~1.1 λ int ~70% of the hadrons will have their first interaction in ECAL and showers will start there. HCAL for CMS need to provide sufficient interaction length to contain the entire shower of HCAL. One need the following characteristics Has to be a fast device Get the best possible flat response (linear in energy) Moderate resolution Radiation hard particularly in the very forward region Non-magnetic being operated in a magnetic field Choose a mixed technology: Brass/plastic scintillator sandwich in the central part of the detector Iron/quartz fibre in the very forward region (use Cerenkov radiation) S. Banerjee30
HCAL Layout The design of the HCAL leads to good hermiticity, good transverse granularity as well as the criteria initially demanded The dashed lines are at fixed η values The HCAL barrel and endcaps sit behind the tracker and the electromagnetic calorimeter as seen from the interaction point S. Banerjee31
HCAL Barrel (HB) HB is a sampling calorimeter covering η < 1.3 HB is divided into two half-barrel sections (HB+ and HB ) It is restricted between the outer extent of the barrel ECAL (R = 1.77 m) and the inner extent of the magnet coil (R = 2.95 m) HB consists of 36 identical wedges (each half barrel has 18 wedges: each wedge is 20 wide in φ) Each wedge is segmented into four azimuthal angle (φ) sectors. The innermost and outermost plates are made of stainless steel for structural strength. S. Banerjee32
HB The absorber consists of a 40 mm thick front steel plate, followed by eight 50.5 mm thick brass plates, six 56.5 mm thick brass plates, and a 75 mm thick steel back plate. The active material is plastic scintillator: front and back plates are 9 mm thick while the rest are 3.7 mm thick. The front layer of scintillator is a special Bicron plate which produces ~20% more light σ-shaped wave length shifting fibres (0.94 mm diameter) collect the light and is transmitted via clear fibres to optical decoding device S. Banerjee33
HCAL Endcap (HE) HE is also a sampling device covering 1.3 η 3.0 The calorimeter is supported on the pole-piece of the magnet and is between 3919.5 and 5541 mm from interaction point The plates are bolted together in a staggered geometry that contains no dead material. The absorber consists of 79 mm thick brass plates with 9 mm gaps for the scintillators. There are up to 18 scintillator layers with the front layer having 9 mm thick scintillator plate and the rest are all 3.7 mm thick Light is collected by WLS fibre & transmitted to photo detector using clear fibres S. Banerjee34
Hadron Outer (HO) To contain hadron shower sufficiently within HCAL for η < 1.15, it is extended outside the solenoid as HO. The magnetic field is returned through an iron yoke designed in the form of five 2.536 m wide (along z-axis) rings. HO is placed as the first sensitive layer in each of these five rings. Solenoid coil acts as an additional absorber. For Ring 0, there is a second layer behind 195 mm thick tail catcher iron plate. Ring 0 has two scintillator layers at radial distances of 3.82 and 4.07m while other rings have a single layer at R = 4.07 m. There are 12 φ sectors each having 6 scintillator trays (10 mm thick) and read out using 0.94 mm WLS fibres with 4 σ-grooves per tile. S. Banerjee35
Hadron Forward (HF) η = 3:5 experiences very large particle fluxes (on average, 760 GeV energy is deposited per p-p interaction into the two HF s, compared to only 100 GeV for the rest of the detector) Use 18 steel wedges on either side of interaction point at a distance of 11.15 m with a radial coverage from 125 mm to 1570 mm Quartz fibre of 0.9 mm diameter (0.6 mm diameter fused-silica core and polymer hard cladding) is used to take out the signal to PMT s sitting behind a shielding. Signal is generated when charged particles emit Cerenkov radiation. Only light that hits the core-cladding interface at an angle larger than the critical angle (71 ) contributes to the calorimeter signal. Half of the fibres (Long) run the entire (1650 mm) of the absorber while the other half (Short) starts 220 mm from the front face. S. Banerjee36
HCAL ReadOut System HB/HE/HO use the same technique: signal is generated in plastic scintillators, captured in WLS fibres (captures blue light and re-emits green light which undergoes total internal reflection), transmitted using clear fibres and generated to electric pulse using a photo transducer with sufficient gain Hybrid Photo Diode (HPD) Fibres bring signals from individual layers while the final readout sums up signals from many layers belonging to a given (η,φ). This is done by routing fibers from all tiles in a tower to the same HPD pixel through the Optical Decoding Unit (ODU). The analogue signal from the HPD or PMT is converted to a digital signal by QIE (Charge-Integrator and Encoder). The CMS QIE has two independent input amplifiers (Inverting and Non inverting) so that it can accept and amplify the negative HPD pulses of HB/HO/HE as well as positive pulses from the PMTs used in HF. S. Banerjee37
Response in Calorimeter Ideally the signal measured in a calorimeter should have linear dependence on incident energy This is satisfied in electromagnetic calorimeter the entire energy of electrons/photons gets absorbed through atomic excitation and ionization. Non-linearity can happen only through signal saturation or shower leakage. This is not true for hadron showers the non-em part of the shower has an invisible energy component and the fraction of the non-em part depends on the incident energy. One way to bring back linearity is to have the response ratio for e and π to be the same. CMS uses two calorimeters with totally different e/π for crystal calorimeter it is ~4 while for brass/scintillator sandwich it is ~1.4. This is verified in a number of test beam activities. S. Banerjee38
Response of CMS Calorimeter Calo Response (MCideal calib.: ele50) Simulated mean/beam energy 0.9 0.8 0.7 0.6 0.5 0.4 All Events H2 QGSP-BERT-EML 9.3.cand02 pro H2 QGSP-BERT-EML 9.3.cand02 pim H2 QGSP-BERT-EML 9.3.cand05 pro 0.3 H2 QGSP-BERT-EML 9.3.cand05 pim TB06 data (v6d1) noho CMS uses prototypes of their hadron calorimeter modules (brass-scintillator sampling calorimeter) and one super module of electromagnetic calorimeter (PbWO 4 crystals) in the H2 test beam Uses negative and positive beams between 2-350 GeV/c with good particle identification for low energy beams TB06 data (v6d1) noho 0.2 2 1 10 10 Calo Response (MCidealMIP calib.: Beam ele50) Energy [GeV] Simulated mean/beam energy 0.9 0.8 0.7 0.6 0.5 MIPS in ECAL 0.4 0.3 0.2 1 10 H2 QGSP-BERT-EML 9.3.cand02 pro H2 QGSP-BERT-EML 9.3.cand02 pim H2 QGSP-BERT-EML 9.3.cand05 pro H2 QGSP-BERT-EML 9.3.cand05 pim TB06 data (v6d1) noho TB06 data (v6d1) noho S. Banerjee39 10 Beam Energy [GeV] 2
Measurement with Collision Data Electrons/photons are identified using shower shapes in ECAL and its performance is well understood. Energies of isolated charged particles as well as jets are also well understood. S. Banerjee40
But as data accumulates.., Rare high energy deposits are observed in the calorimeters These give rise to isolated high energy clusters and tails in missing transverse energy which are signals for new physics But they are a bit unusual anomalous hits in calorimeters S. Banerjee41
Story for ECAL Anomalously large signals are observed in the ECAL with the appearance of very large energy deposits in a single crystal. S. Banerjee42
ECAL Spikes The events are characterized by: They are uniformly distributed only in the barrel part of the calorimeter where the readout is by APD; they are not seen in the endcap crystals which are read out by VPTs. The rise time of the electronic pulse is consistent with an instantaneous signal from the APD, not the typical decay spectrum of the crystal. The rate of spike events is approximately one per 10 3 minimum-bias events. Typical signal. Spike signal. The average pulse shape for typical and spike events. The blue dots are the actual signal sampling of an anomalous signal. S. Banerjee43
Steps to Understand Spikes Understand the origin of these hits: Spikes happen during collision data taking. Not noticed during the Cosmic Ray runs spanning previous years The rate is roughly proportional to the minimum bias rate But they were also observed in test beam with hadrons: S. Banerjee44
Data driven approach Look at the closeness of tracks in the data to the spike hits Fairly large number of tracks match to the basic clusters with large E/p Dumb-spike model adds one random spike to each data event APD Hits are caused by particles from interaction S. Banerjee45
Try Simulation Most likely the spikes are produced by showers of particles like other energy depositions in the calorimeter So they can be simulated in detector simulation which follows showering due to passage of particles APD volumes Crystals First level of changes: o Treat crystals and APD volumes as independent sensitive detector o Energy deposits in each of them will get different gain factors S. Banerjee46
Energy Deposits Energy deposits in single APD volumes are summed up Match the rates observed in the data by considering hits of energy above 75 kev Simulated rate roughly matches with the data Clearly there are also many hits with smaller energy Fall off is slower than exponential S. Banerjee47
EM Physics in Simulation Verify the energy deposits in simulation by using muons and look at MIP energy in the APD MIP peak is observed with Mean energy of 1,7 kev Peak around 1 kev Simulation matches with expectation EM Physics is well described in the simulation S. Banerjee48
Timing of the Hits: Features of the Hits Time distribution of SimHits is similar to that observed in the data Main feature is a sharp turn-on at time consistent with ultra-relativistic particles from IP More late time event is seen in data Source of the hit: More often the energy is due to de/dx loss of hadrons in the APD Small but substantial energy loss is due to electrons Time distributions of the two components are similar but not identical S. Banerjee49
Source of the Hits Generator level particles as source Dominantly π s Also K L and antineutrons But neutrons are down in the list Particles entering the calorimeter Lots of neutrons More pions will interact within calorimeter & make more neutrons S. Banerjee50
Association in η and φ APD hits and generator level particles are well correlated in η Some of the particles headed toward endcap also cause hit in APD Correlation in φ for pions are affected by bending in the magnetic field Correlation in φ is sharp for neutrals S. Banerjee51
Do we know enough about APD? Get a more realistic description of APD in term of material, dimension and relative amplification factors S. Banerjee52
Improved Simulation An alternative description of ECAL barrel is made with detailed structure of APD capsules Two sensitive layers with high (5µm) and low (45µm) gain exist S. Banerjee53
Hits in High Gain Part The simulation has a 15 kev threshold to save an APD hit. (about 1 GeV measured energy) We see an increase in APD hit energy produced by protons, in the 5 micron layer, due to protons produced in the epoxy layer S. Banerjee54
Energy in APD by PID and Mother Fraction of minbias events Depth 1 Depth 2 15 kev APD energy lower cutoff 15 kev APD energy lower cutoff EM particles drop quickly with energy. Protons and ions fall slowly with energy. Similar in 45 micron layer but protons drop faster in 5 micron layer. Neutrons are enhanced in high-gain region due to epoxy. S. Banerjee55
Origin of Particle hitting APD 75 kev APD energy lower cutoff Heavy ions come from APD high gain region. Protons come from epoxy exponentially close to APD. S. Banerjee56
Origin of Mother ρ neutrons 75 kev APD energy lower cutoff ρ ρ z photons z pions Mother Neutrons are produced in crystals. Mother photons are produced near APD. Pions come from IP and crystals. z S. Banerjee57
The Local APD Coordinates Origin of particle hitting APD ρ' Z Geant4 coordinate system for APD volume S. Banerjee58
Time Distribution of APD Hits While high energy APD fall of with time, lower energy hits have a nearly flat time distribution. The particle living the longest (t>200 ns hits) is almost always a neutron (few % μ + ). These are neutrons with several MeV of kinetic energy. S. Banerjee59
Do we understand Data? CMS Preliminary After Before After Time CMS Preliminary Much improved understanding of the data S. Banerjee60
Issue in Hadron Calorimeter Missing transverse energy is a key measurement from the calorimeter system. As statistics grow, one starts seeing long tails which are due to hits in the hadron calorimeter Some of the energetic hits have some peculiar characteristics PMT Hits S. Banerjee61
HF Noise Forward Hadron Calorimeter observed even larger energy deposits. Even muons in test beams gave rise to large pulse It was identified that when beam points to a PMT, this can happen Cerenkov radiation from the glass window could be source S. Banerjee62
Characteristic of the Noise HF has two set of fibres Long fibers: extends for the full length of HF Short fibers: start at a depth of 22cm from the front of HF Anomalous high energy deposit is observed only in one type of fibres in a given tower S. Banerjee63
Understand through Simulation Describe PMT s behind HF in the Forward Shield area Declare photo cathode to be sensitive and record SimHit for energy deposits in photo cathode Abandon Shower library approach in HF and use a different parameterization S. Banerjee64
HF Geometry Description The absorber part is described With the description of all the fibres Average material (mixture of Steel/Quartz/Air) Shielding structure around HF is described in detail Gaps between wedges & supporting platform are not Default Simulation New Parameterizaiton Moderators HF BSC1 S. Banerjee65
HF Components The shielding behind HF were described by solid blocks of lead/steel/ polyethylene now air core light guides are introduced aligning with the PMT positions in the Readout Box Fibre bundles are of different cross sections depending on iη index also the last two iη-towers have different φ granularity Aircore LG Fibre bundles S. Banerjee66
Hits in Forward Hadron Calorimeter Transport all hadrons entering HF using Geant4. The electromagnetic component of the shower in HF is replaced using parameterization. Energy spectrum as well as anomalous hit rate are well reproduced Dominant sources are muons from decays in flight and hadron shower punch through CMS Preliminary CMS Preliminary S. Banerjee67
Summary are essential in a high energy physics experiment of today Lots of R & D activities take place to design an acceptable calorimeter for a given application Physics priorities in a given experiment drives the final choice of technology Even after all preliminary works, real application gives surprises in real life application Journey with calorimeters is not yet over for CMS high luminosity future of LHC demands more activities in improving or replacing the existing CMS calorimeters S. Banerjee68
Back Up S. Banerjee69
Kinetic Energy Spectra Fraction of minbias events Depth 1 Depth 2 75 kev APD energy lower cutoff EM hits give lower energy spikes. The epoxy seems to increase protons mothered by neutrons at lower APD hit energy. The kinetic energy of the mother is NOT low. S. Banerjee70
Kinetic Energy of Mother Fraction of minbias events 75 kev APD energy lower cutoff S. Banerjee71