1. Study of response uniformity of LHCb ECAL Mikhail Prokudin, ITEP

2. Outline ► Motivation ► Geometry of modules ► Experimental setup ► Procedure ► MC modeling ► Results  light yield ► Conclusion

3. Motivation ► “Shashlik” technology  cheap  fast enough ► trigger  radiation hard  easy to segment ► Resolution  a – stochastic term ~8%/sqrt(E)  b – constant term ► stochastic term  decrease thickness of absorber ► increased volume ratio  increased Morier radius ► more shower overlaps ► keep volume ratio constant  photostatistics ► constant term  increase the volume ratio  technology ► die-mold price ~10k $ ► MC model of light propagation in scintillator tile 7% RD36 data

4. Modules geometry ► LHCb ► inner: 4x4cm 2 cells ► middle: 6x6cm 2 cells ► outer: 12x12cm 2 cells  67x4mm layers of scintillator  66x2mm layers of lead ► Prototype  4x4cm 2 cells  280x0.5mm layers of scintillator  280x0.5mm layers of lead

5. Experimental setup Beam e, μ Beam plug Calorimeter 25.111m10.97m2.935 new chamber old chambers Calorimeter assembly 8 modules (12x12cm 2 x1) for leakage control testing module LED1 LED2 PIN LED monitoring system scheme

6. Coordinate determination ► Beam size: 3x3cm 2 ► Energy cut: 60-65% MPV position ► Details of calorimeter construction are visible Shifts corrected for each position Same procedure for electrons Muons

7. Muons. Procedure ► energy only in central cell ► 1x1 mm 2 regions ► fit with Landau distribution  first fit to estimate ranges  second fit with ► f(x start )=0.4*Max ► f(x end )=0.05*Max  no Landau Gauss convolution ► much more statistics

8. Electrons. procedure ► Collect energy in 3x3+4 cells  wider signals with if other 4 cells included ► 1x1 mm 2 regions ► Iterative fit procedure  [-1.2 δ, +2 δ ] region

9. MC modeling ► Signal nonuniformity  Light collection nonuniformity ► Special ray tracer program  Scintillator tile thickness variations ► Measured directly  Convolution with particle energy deposition  “natural” smearing  energy deposition nonuniformity  dead material ► GEANT

10. Ray tracer program ► Optics  refraction ► Fresnel formulas  reflection ► mirror ► diffuse  attenuation ► in medium ► on surface  all processes could depend on wavelength ► Geometry  geometrical primitives ► cylinder ► box  Boolean operations  voxelization ► Main optical parameters  quality of scintillator surface  whiteness of paint  size of “edging”

11. Example of ray tracer test ► Edge effect in light collection  compensate dead material between tiles  not trivial  LHCb innovation

12. LHCb inner module ElectronsMuons Scale!

13. LHCb inner module. Between fibers Near fibers Between fibers ElectronsMuons Gray – MC. Black – data. Scale!

14. Prototype module Prototype. 0.5мм LHCb. 4мм Scale!

15. Prototype module and inner LHCb module Gray – MC. Black – data. Scale! Between fibers Near fibers Between fibers Near fibers LHCb inner Prototype

16. LHCb outer module ► 12x12cm 2 ► Distance between fibers 15mm  10mm in inner module ► Only 2 delay wire chambers  worse position resolution ► One set of optical parameters to describe all data! Between fibers Near fibers Gray – MC. Black – data.

17. Light yield Experiment ► Use monitoring system MC ► Generate photons uniformly inside tile volume ► Inner module for normalization Testbeam Cosmic setup MC inner300031003000 middle360035003600 outer250026002570 prototype700-600

18. Conclusions ► Measurements of uniformity of LHCb calorimeter response presented  different probes ► electrons ► muons  different modules ► inner ► outer ► prototype  absorber and scintillator thickness 0.5mm ► Calorimeter response uniformity modeled  thickness measurements  light collection ► ray tracer code developed ► tile model created  Geant ► dead material simulation ► Model parameters extracted  and checked for various geometries

20. Coordinate determination ► Modify coefficients  residuals ► keep mean at 0 ► narrow ► Cut χ 2 <4  denominator from “Delay wire chambers...” by J.Spanggaard.

21. Lacing

22. Ray tracer testing ► Visualize trajectories  individual photons  using ROOT for drawing

23. Geant model ► Geant3 ► Gorynych framework  for ITEP FLINT experiment ► Tile model with holes and fibers  same as for ray- tracing ► 67x4mm scintillator layers  66x2mm layers of lead ► Dead material  steel tape, 0.2mm thick  white paint, 0.15mm at edge of tile Steel tape, 0.2 mm White paint, 0.15 mm Fiber in each hole