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TRID(ENT) studies. TRID “Twin Ring Imaging Detector” proposed for upgrade of RICH system instead of maintaining existing RICH-1 and RICH-2 vessels (see presentation at last LHCb week, and note LHCb-PUB-2012-012)

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Trid ent studies
TRID(ENT) studies

  • TRID “Twin Ring Imaging Detector” proposed for upgrade of RICH systeminstead of maintaining existing RICH-1 and RICH-2 vessels(see presentation at last LHCb week, and note LHCb-PUB-2012-012)

  • Fits into available space in RICH-2 region, gives improved performance with fewerphotodetectors, and frees up space in RICH-1 region

  • Two major issues identified for further study before a decision is taken: 1. Window separating the gases 2. Occupancy of the photodetectors

Roger Forty (CERN)

RICH meeting, 15 January 2013

Detector concept old slide
Detector concept (old slide)

  • RICH-2 only covers < 120 mrad a new device needed, like a somewhat larger RICH-2: 950 < z < 1240 cmMakes use of space liberated by M1 (and perhaps also SPD/PS)

  • Twin gas radiators separated by windowAssumed transmission of 95%(C4F10 photons traverse twice)

  • Space is reserved for TORCH(time-of-flight for low-momentumPID) TRID + Torch = TRIDENT(Triple Radiator IDENTification)


Plan view (half)

TRID(ENT) studies

1 window old slide
1. Window (old slide)

  • Only new item requiring R&D

  • Difference in density of radiator gases → pressure difference across window ~ 1 mbar per m of height

  • Assume gas pressures balanced at beam level→ maximum pressure difference close to frame

  • Some window distortion is acceptable at few-cm level

  • Material: Mylar, Plexiglass, Glass?Transmission only needs to match that of borosilicate MaPMT window

TRID(ENT) studies

Engineering study
Engineering study

  • FEA studied by Matthew Brock (Oxford)for two large plates of glass in frame (as well as other configurations)

  • For 10-mm thick glass plates, maximum displacement = 2 mm, maximum stress = 3 N/mm2(i.e. a safety factor of ~ 10)

  • Remaining issue is radiation tolerance:expect O(MRad) near beam pipe, O(kRad) at outer edge

  • Borosilicate glass should be OK in outer region (after all, the MaPMT windows will be made of it…) but probably not near beam pipeQuartz would certainly be OK near beam pipe, but more expensive

  • However, a 10 mm quartz plate is exactly what is needed for TORCHSo (at least in longer term) the window could act as the TORCH radiator

TRID(ENT) studies

2 occupancy
2. Occupancy

  • Detailed answer should come from the full simulation (in progress)

  • To get a quick estimate, have interfaced fully-simulated LHCb Monte Carlo events to my ray-tracing code

  • Chris Jones set up Brunel v44r1 to dump information for tracks in RICH-2File then read in to the ray tracing, used to generate Cherenkov light for each track and trace it to the TRID detector plane

  • Results should be interpreted with care:

    • Track information only available for tracks that would give light in the existing RICH-2, i.e. region < ~ ±1 m around the beam(However, this is exactly region where highest occupancy expected)

    • There will be MC particles which do not have an associated track,which are ignored in this approach

  • First some considerations about reflection loss

TRID(ENT) studies

Reflection loss
Reflection loss

  • Checked angles of incidence of photonspassing through window: mostly small,but tail up to ~ 60º

  • To be more realistic, should considerFresnel coefficients – depend onphoton polarisation:

    Rscorresponds to polarisation in plane of interface, Rp in orthogonal plane

  • Cherenkov light is polarised in plane containing photon and track

  • Eventually should be implemented photon-by-photon for each transitFor now just determine mean loss, if assume Rp(min)or Rs (max) Result: 5–12 % per transit through window

  • Increased assumption on loss from 5% to 10% for each transit


TRID(ENT) studies

D etector plane old slide
Detector plane (old slide)

  • For chosen optical layout, plot image on photodetector plane:

  • C4F10 photons (red), only plotted when outside instrumented area (dashed line)

  • CF4 photons (green, over full acceptance)(black, for tracks in RICH-2 acceptance)

  • Instrumented area is tiled with 4×4 MaPMT modules:

    • 32 fully instrumented (orange squares)

    • 84 half-instrumented (yellow squares, placed in region where photon yield is not the limiting factor)

  • Striking twin-ring imagesillustrated for two randomly-chosen tracks

Region shown in occupancyhistosbelow

TRID(ENT) studies

Standard monte carlo
Standard Monte Carlo

  • MC11a, B inclusive, luminosity = 2 ×1032cm-2s-1, Ecm = 7 TeV, 1000 events

Plot impact pointof all photons ondetector plane (on one side)Separately for thetwo radiator gases


Each bin corresponds to number of photons hitting a 64-channel MaPMT with lens(for 1000 events)


TRID(ENT) studies


  • Sum the distributions from C4F10 and CF4:

  • On average there are 14 tracks/event in RICH-2 Average occupancy over histogram = 1% (but missing wide-angle tracks)Peak TRID occupancy = 5.4 photons/event/MaPMT = 8.4%

TRID(ENT) studies

High luminosity
High luminosity

  • High lumi samples provided by Sajan Easo: Ecm = 14 TeV, 1000 events B signal MC, luminosity = 1 ×1033 (Lumi-10) and 2 ×1033(Lumi-20)

  • Make same plots (summed over both gases):

  • Tracks/event in RICH-2 = 34 48Max occupancy = 17% 21%



TRID(ENT) studies


  • Outstanding issues for TRID addressed: window and occupancy

  • Engineering of the window has been successfully studied Radiation tolerance is remaining issue (avoiding scintillation)Search for suitable glass, or quartz, or combination Required solution closely matches requirements for TORCH radiator→ possibility for an elegant integrated TRIDENT design

  • Occupancy studied with hybrid approach, based on tracks from full MCRoughly equal contribution from the two radiators (by design)but they peak in different places on detector planeOverall occupancy looks reasonable (with caveat concerning method):Maximum = 17% for nominal upgrade lumi of 1 ×1033 cm-2s-1If necessary, could remove lenses from worst MaPMTs→ reduce by ×2

  • Further study planned starting from MC particles rather than tracksAnd eventually with full simulation

TRID(ENT) studies

Extra old slide
Extra (old) slide

  • TRID performance parameters compared to current RICH-1 & 2(measured using same procedure)

  • Similar resolution for CF4: larger pixel error compensated by chromatic Dramatically improved resolution for C4F10 (by a factor of two): due to longer focal length + borosilicate window of MaPMT

  • Momentum limit for 3s K–p separation used as a figure of meritSignificant improvement for C4F10 radiator

  • Occupancy should not be a problem (but needs full simulation to check)If needed, C4F10 photon yield can be reduced by adjusting window positionGiven the improved resolution, fewer photons provide same performance

TRID(ENT) studies