Motivation

• There is a consensus that it is not possible to obtain a software (π0) calibration with few days delay (this is to be verified, this is the major starting point)

• Then, the only way to control e.g. trigger rates is to use the LED system

• The existing LED system:– fibers to be replaced to more rad hard ones (quartz). Total of ~ 40

km to be purchased.– LEDs to be replaced to green or blue ones (also, they should be

more stable than existing red ones)– the LED drivers and power supplies can be kept (with maybe little

modifications)

Quartz Fibers

• DRAKA– Rad Hard, Super Rad Hard, multimode 50/125 µm

• < 1 CHF/m• small diameter, a bright LED will be needed to inject enough light.

– Hard Polymer Silica cladding, 200 µm core• no info on radiation hardness; however at least factor of 10

compared to plastic; is it enough?

• Fryazino (Russia) (also used in the CMS FCAL)– special production is possible, with any desired core

diameter, material and length (the list of lengths in ECAL is available)• negotiations started

Light injection: first test• a 300 µm core 7 m long fiber is available (from CMS ECAL

laser calibration system)– we have performed a test with a ECAL PMT using an existing

xCAL LED driver with various LEDs. Good results obtained with a UV LED.

– we will continue work on LED selection, aiming in finding a green LED which is bright enough.

optical connectors• 6k optical connectors (black plastic pieces) can be produced in

Vladimir (Russia)

Cherenkov light

• in quartz, capture of the Cherenkov light is in principle possible

• LED flashes not affected: out of bunch crossings• number of Cherenkov photons in 350-500 nm range produced

by MIP in 1 mm quartz is 15 (!). Hence 4 for 300 µm fiber• losses:

– capture fraction in fiber (reduction factor > 2)– attenuation in 40 cm piece of plastic fiber within a module (factor 2?)– quantum efficiency of PMT (0.25, attenuation factor 4)

• to produce 100 MeV signal, ~1200 MIPs have to cross one fiber in one event unrealistic CAN BE NEGLECTED

manpower, etc

• from the experience of the existing system construction, our (conservative) estimate is ~ 4 persons x 4 months

• optical fiber cleavers of various types are available in ITEP