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The CMS Experiment at LHC

The CMS Experiment at LHC. The CMS Experiment at LHC. A che serve LHC? Macchina di “scoperta” A che serve CMS? Esperimento di “scoperta” Come si fa a scoprire “qualcosa” ? Tre modi fondamentalmente: A) Si cerca “qualcosa” dove ci si aspetta di trovarlo;

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The CMS Experiment at LHC

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  1. Leonello Servoli – Esperimento CMS a LHC The CMS Experiment at LHC

  2. Leonello Servoli – Esperimento CMS a LHC The CMS Experiment at LHC • A che serve LHC? Macchina di “scoperta” • A che serve CMS? Esperimento di “scoperta” • Come si fa a scoprire “qualcosa”? Tre modi fondamentalmente: A) Si cerca “qualcosa” dove ci si aspetta di trovarlo; (es. quark Top, bosone di Higgs) B) Si cercano eventuali “qualcosa” alla “cieca” (es. supersimmetrie, ricerce di esclusione, etc.) C) Si cerca un “segnale” di tipo noto anche se non ci sono indicazioni che ci debba essere.

  3. Leonello Servoli – Esperimento CMS a LHC The CMS Experiment at LHC

  4. Leonello Servoli – Esperimento CMS a LHC The CMS Experiment at LHC

  5. Leonello Servoli – Esperimento CMS a LHC Modalità A) di scoperta → La teoria prevede un fenomeno che dovrebbe essere visto effettuando una misura sperimentale. → Esistono misure più o meno indirette che limitano l'intervallo di esistenza del fenomeno (es. massa quark top). Misure indirette Misure dirette (CDF) Mtop = 172 GeV

  6. Leonello Servoli – Esperimento CMS a LHC Modalità B) di scoperta → La teoria prevede un fenomeno che dovrebbe essere visto effettuando una misura sperimentale. → Non esistono limiti stringenti sull'intervallo di esistenza del fenomeno (es. ricerca supersimmetrie). Zona permessa

  7. Leonello Servoli – Esperimento CMS a LHC Modalità C) di scoperta → Si cerca un fenomeno che non é previsto dalla teoria. → Es. Ricerca di risonanze nella distribuzione della massa invariante di due jet. La motivazione è che se un pogetto sconosciuto viene prodotto, deve decadere in oggetti noti, prima o poi, che possono quindi essere rivelati.

  8. Leonello Servoli – Esperimento CMS a LHC Cosa guardare? Evento H → ZZ → 4m Che cosa si misura? Z decade rapidissimamente...... Nessun sensore può vederlo direttamente. Ogni Z decade in altre particelle. Alcune sono sufficientemente stabili perché possano raggiungere dei rivelatori. Es. m.

  9. Leonello Servoli – Esperimento CMS a LHC Cosa guardare? Evento H → ZZ → 4m Che cosa si misura? Z decade rapidissimamente...... Nessun sensore può vederlo direttamente. Ogni Z decade in altre particelle. Alcune sono sufficientemente stabili perché possano raggiungere dei rivelatori. Es. m.

  10. Leonello Servoli – Esperimento CMS a LHC Evento H → ZZ → 4m “Golden Channel” Occorre trovare 4m soddisfacenti alla condizione pt > 25 GeV

  11. Leonello Servoli – Esperimento CMS a LHC Ricerca di “oggetti fisici” Quindi occorre essere in grado di rivelare una serie di “oggetti fisici” che sono i prodotti finali dei decadimenti che si vogliono studiare. → muoni → elettroni → tau → fotoni → jet → energia mancante (un caso diverso → neutrini e altro)

  12. Leonello Servoli – Esperimento CMS a LHC Ricerca di “oggetti fisici”

  13. Leonello Servoli – Esperimento CMS a LHC

  14. Leonello Servoli – Esperimento CMS a LHC Chi fa cosa.....

  15. Leonello Servoli – Esperimento CMS a LHC Rivelazione di particelle cariche Serve un magnete che pieghi la traiettoria delle particelle nel piano perpendicolare alla direzione del campo magnetico (piano r-f)

  16. Leonello Servoli – Esperimento CMS a LHC

  17. Leonello Servoli – Esperimento CMS a LHC Radius ~ 110cm, Length ~ 270cm ~1.7 R-phi (Z-phi) only measurement layers 6 layers TOB R-phi (Z-phi) & Stereo measurement layers ~2.4 4 layers TIB Pixel Vertex 3 disks TID 9 disks TEC The Tracker System Concept: Rely on “few” measurement layers, each able to provide robust (clean) and precise coordinate determination 2 to 3 Silicon Pixel, and 10 to 14 Silicon Strip Measurement Layers Goal:spT~ 1-2% * pT

  18. Leonello Servoli – Esperimento CMS a LHC The concept in reality:

  19. Leonello Servoli – Esperimento CMS a LHC Quali sensori? Silicon detectors Come funzionano i rivelatori a silicio? Microstrips Rivelatore polarizzato inversamente per avere un volume completamente svuotato da portatori maggioritari. 300 – 500 mm

  20. Leonello Servoli – Esperimento CMS a LHC Module components production & assemblyThe numbers 6,136 Thin + 18,192 Thick sensors 440 m2 of silicon wafers 210 m2 of silicon sensors Large scale industrial sensor production 9,648,128 strips  channels 75,376 APV chips Reliable, High Yield Industrial IC process Hybrids Pitch adapters Frames 6,136 Thin sensor modules (1 sensor / module) 9,096 Thick sensor modules (2 sensors / module) Automated module assembly 25,000,000 wire bonds State of the art bonding machines

  21. Leonello Servoli – Esperimento CMS a LHC Shells, Rods and Petals

  22. Leonello Servoli – Esperimento CMS a LHC The ConceptSilicon Pixel vertex detector

  23. Leonello Servoli – Esperimento CMS a LHC Distributed Patch Panel Receiver Module Opto-hybrid Inline Patch Panel 12 96 FED  Detector Hybrid 1  TOB TEC CMS Cavern Counting Room TIB TID Putting it in perspectiveTracker read-out dominates CMS data volume CMS Silicon Strip Tracker has no 0 suppression: CMM noise subtraction (Pixels have local 0 suppression => intrinsic noise immunity crucial) Analogue information from all 107 strips/event read-out at 100KHz event rate Use analogue optical link: developed for Tracker now used throughout CMS After digitization and 0 suppression in the FED, Tracker data volume ~ / event => Drives requirements of DAQ

  24. Leonello Servoli – Esperimento CMS a LHC Quali sensori? Silicon detectors

  25. Leonello Servoli – Esperimento CMS a LHC 30 cm 93 cm The ConceptSilicon Pixel vertex detector The region below 20cm is instrumented with Silicon Pixel Vertex systems (First layer at R ~ 4cm) The Pixel area is driven by FE chip The shape is optimized for resolution CMS pixel ~ 100m * 150m 4 107 pixels Shaping time ~ 25ns With this cell size, and exploiting the large Lorentz angle We obtain IPtrans. resolution ~ 20 m for tracks with Pt ~ 10GeV With this cell size occupancy is ~ 10-4 This makes Pixel seeding the fastest Starting point for track reconstruction Despite the extremely high track density

  26. Leonello Servoli – Esperimento CMS a LHC The Silicon Tracker Concept:expected performance The CMS Tracker provides ~ 1% Pt resolution over ~ 0.9 units of , and 2% Pt resolution up to  ~ 1.75, beyond which the lever arm is reduced With material Without material Without / with material Even at 100 GeV muons are significantly affected by multiple scattering: a finer pitch, and higher channel count Would therefore yield only diminishing returns in improving the Pt resolution

  27. Leonello Servoli – Esperimento CMS a LHC The Silicon Tracker Conceptexpected performance: For 10 GeV Pt tracks,(d0) < 30for< 1.5; degrading to ~40for= 2.4 10GeV  10GeV  For 10 GeV Pt tracks,(Z0)< 50for< 1.5; degrading to ~ 150for= 2.4 Dominated by Pixel geometry and multiple scattering

  28. Leonello Servoli – Esperimento CMS a LHC Resistance to Radiation Damage

  29. Leonello Servoli – Esperimento CMS a LHC - - - - - - - - - - The Silicon SensorsThe reverse biased p-on-n diode Bulk depletes from P+ implants, “front-side“ to N+ implant, “back-side” Electron-hole pairs generated in the depleted region drift to the N+ and P+ electrodes respectively and generate a signal ~ to the depleted sensor thickness Electron-hole pairs generated in the (conductive) un-depleted region recombine locally, and generate no signal Even in a partially depleted sensor, the signal on the “front-side” is localized Oxide Al Strips OV + P+ implants + + + + + + N Bulk + + + - +HV N+ Implants

  30. Leonello Servoli – Esperimento CMS a LHC Al Strips OV - + - + P+ implants - - - + - + - + - - - + - + - P bulk + - - - + - + +HV N+ Implants The Silicon SensorsRadiation damaged reverse biased p-on-n diode Radiation damage eventually results in “type inversion” The initially N bulk undergoes “type inversion” and becomes P The depletion voltage decreases and then increases again with higher fluence The effectively P bulk depletes from N+ implants, “back-side”, to P+ implant, “front-side” Electron-hole pairs generated in the depleted region drift to the N+ and P+ electrodes respectively and generate a signal ~ to the depleted sensor thickness Radiation induced defects trap charge, leading to a loss of signal unless high fields In the partially depleted sensor, the signal on the “front-side”is no longer localized Sensor leakage current increases linearly with fluence (by ~ 3 orders of magnitude)

  31. Leonello Servoli – Esperimento CMS a LHC The Silicon SensorsThe radiation hard P-on-N strip detector Radiation hardness “recipe” P-on-N sensors work after bulk type inversion, Provided they are biased well above depletion At room temperature and above, radiation induced defects diffuse and some eventually form clusters which further increase the sensor depletion voltage “reverse annealing” Defect mobility below ~ 0C is sufficient low that reverse annealing is effectively frozen out Maintain radiation damaged silicon below ~0C (constantly) Sensor leakage current depends ~ exponentially on temperature: it doubles for every ~7C temperature increase Insufficient cooling efficiency will result in an exponential “thermal run-away” of the irradiated sensor Operate sensors below ~ -10C, to reduce required cooling efficiency & material

  32. Leonello Servoli – Esperimento CMS a LHC Surface damage +++++ +++++ ----- ----- P+ implants +++++ - - - - - “P” Bulk N+ Implants The Silicon SensorsThe radiation hard P-on-N strip detector Radiation hardness “recipe” P-on-N sensors work after bulk type inversion, Provided they are biased well above depletion Optimize design for high voltage stability, as well as low capacitance Use Al layer as field plate to remove high field at strip edges from Si bulk to Oxide (much higher Vbreak) Strip width/pitch ~ 0.25: reduce Ctot while maintaining stable high bias voltage operation (avoid strip pitch > 200m to ensure stable high voltage operation) Surface radiation damage can increase strip capacitance & noise, and degrade high voltage stability Use <100> crystal instead of <111> Take care with process: implants, oxides…

  33. Leonello Servoli – Esperimento CMS a LHC The Silicon SensorsThe radiation hard P-on-N strip detector Radiation hardness “recipe” P-on-N sensors work after bulk type inversion, Provided they are biased well above depletion Match sensor thickness (& resistivity) to fluence (Vdep) to optimize S/N over the full life-time: Use 320m thickness for R < 60cm, Strip ~ 10cm => S/N ~ 18 (14) Use 500m thickness for R > 60cm, Strip ~ 20cm => S/N ~ 21 (16)

  34. Leonello Servoli – Esperimento CMS a LHC

  35. Leonello Servoli – Esperimento CMS a LHC Calorimetria elettromagnetica

  36. Leonello Servoli – Esperimento CMS a LHC Calorimetria elettromagnetica

  37. Leonello Servoli – Esperimento CMS a LHC

  38. Leonello Servoli – Esperimento CMS a LHC

  39. Leonello Servoli – Esperimento CMS a LHC Calorimetria adronica Calorimetria adronica

  40. Leonello Servoli – Esperimento CMS a LHC Calorimetria adronica Sciame adronico

  41. Leonello Servoli – Esperimento CMS a LHC Calorimetria adronica

  42. Leonello Servoli – Esperimento CMS a LHC Calorimetria adronica

  43. Leonello Servoli – Esperimento CMS a LHC Muon Detectors

  44. Leonello Servoli – Esperimento CMS a LHC Muon Detectors

  45. Leonello Servoli – Esperimento CMS a LHC

  46. Leonello Servoli – Esperimento CMS a LHC Muon Detectors

  47. Leonello Servoli – Esperimento CMS a LHC Muon Detectors

  48. Leonello Servoli – Esperimento CMS a LHC Muon Detectors

  49. Leonello Servoli – Esperimento CMS a LHC Muon Detectors

  50. Leonello Servoli – Esperimento CMS a LHC Lettura dei segnali Il problema della rivelazione di segnali comprende la parte della loro lettura , trattamento e trasmissione al sistema di Acquisizione Dati. Problema molto spesso fondamentale!

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