CMS Hadronic Forward Calorimeter Restoration of Functionality Iowa, BU, FNAL severe descoping of HF in 2002 $$ for HB, tracker tail catcher for late developing hadronic showers - eliminated ½ of quartz fiber gone, quartz cladding replaced with plastic fiber diameter doubled…2x coarser sampling insufficient to see muons, the natural calibration…5 GeV/pe (no other detector in front or behind to cross-correlate) air light guides from beam region to PM’s outside calorimeter - cut PMs directly in the path of π’s from penetrating showers & from μ’s fasting timing (1 ns) interpolator removed, cannot kill out of time background metal envelope, thin-windowed PMs eliminated instead thick, all glass PMs on HF Task Force to ameliorate much of this, some asap, others at Upgrade I

2006 – 2009 HF CERN Summer Test Beam Studies BU team TB 06 &07 serious problem revealed in CMS mockup in CERN HF Test Beam Cherenkov light from π’s and μ’s traversing PM glass cause large false high energy depositions…up to 4 TeV equivalent w/ Freeman critical to physics missions of Hadronic very Forward 1) missing energy trigger…may swamp the L1 trigger menu 2) tagging jets for high mass Higgs searches for the invisible Higgs e.g. proposed BU thesis Lawson TB 08 inserted scintillating crystal tags w/Freeman long time constant light separable from fast Cherenkov signal? did not work…scintillation light from thinnest crystals overwhelms Cherenkov confirmed feasibility of quartz plate tail catcher behind PM box BU air light guides developed at BUOsborne prototyped perfected at BU cosmic tower TB 09 evaluated 4-anode mesh dynode PMs w/Iowa, Fairfield (and SiPM evaluations also perfected in these Test Beam runs)

1” square, mesh dynode PM…a 1 to 1 replacement for current tube 43% quantum efficiency, makes up for x2 loss of quartz, can calibrate muons thin front window (~0.5mm), no glass on sides…cuts Cherenkov background tails 4 anodes…tags thru muons, and corrects energy measurement

HF mockup & SiPMs in CMS test beam line at CERN, summer ’09

with µ beam parallel to PM window… raw PM rate ~20 x bigger with current PM that with mesh PMpulse height 2-5 x bigger than with beam perpendicular

tag Cherenkov window events…and correct energy measurement corrected energy = 4/3 energy in non-tagged anodes works beautifully...1 box of 8 PMs to be installed in February

RESERVE

Normalization/calibration: Single PMT and 4 tower readout on calorimeter: HF PMT: R7525 Mini: R9880U-110 4Anode: R7600U-200-M4 1Anode: R7600U-200

150 GeV Muons into PMT at 90°