Speaker
Description
To operate at Run-5 luminosities $(\,1.5 × 10^{34}\,\,\mathrm{cm}^{−2} \,\mathrm{s}^{−1}\,)$, the LHCb electromagnetic calorimeter is being upgraded to PicoCal, which requires radiation-tolerant materials and fast timing to mitigate pile-up and spillover. The inner regions of the PicoCal will adopt a Spaghetti Calorimeter (SpaCal) design, based on scintillating fibres (polystyrene or garnet crystals) embedded in dense absorbers (lead or tungsten). Current R\&D focuses on the joint selection of suitable fibres and fast photomultiplier tubes (PMTs). Organic fibres must combine fast scintillation kinetics (decay time $\tau_d \lesssim 8$ ns, rise time $\tau_r \lesssim 1$ ns), light yields exceeding 6000 photons/MeV, and radiation tolerance up to at least 200 kGy. PMTs' integrity and characteristics, especially window transparency, must not be degraded under radiation up to 1 MGy.
We report on a coordinated R&D programme that encompasses photomultiplier-tube (PMT) performance studies and the characterisation of plastic-scintillator samples produced by the Institute for Scintillation Materials (ISMA, Ukraine) within the Eurizon Fellowship Programme.
On the photodetector side, we conducted extended ageing studies of fast PMTs for the tungsten SpaCal readout, focusing on the Hamamatsu R9880U-20 and R14744U-100, and carried out an irradiation campaign at CERN IRRAD that also included the R7600. These campaigns quantify the evolution of PMT gain and photocathode quantum efficiency under high integrated anode charge (up to ≈1000 C). Complementary test-beam measurements with SpaCal prototypes at the CERN SPS and at DESY confirm that the considered PMTs are suitable to meet the design timing requirements.
In parallel, we screened and characterised plastic-scintillator samples from ISMA for fast rise/decay kinetics, high light yield, transmission, emission and absorption spectra, and spectral compatibility with PMT photocathodes. Following high-dose proton irradiation at CERN IRRAD, the samples exhibited promising optical and timing performance, supporting fibre production for further characterisation.
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