Calibration of a Digital Hadron Calorimeter with Resistive

Calibration of a Digital Hadron Calorimeter with Resistive Plate Chambers José Repond Argonne National Laboratory Internal Si. D Meeting, by phone, May 8 th, 2009

Reconstruction of the energy of a shower Assumption an algorithm (e. g. a PFA) assigned certain hits in the calorimeter to a hadron shower The energy of this shower can be reconstructed (to first order) as where Hi …. Hits assigned to the shower (measurement) αsampl …. Sampling term (could depend on ΣH) Might be different for charged and neutral hadrons Bi …. Average contribution from background hits ε 0 …. Average MIP detection efficiency of all RPCs εi …. MIP detection efficiency of the RPC with hit I μ 0 …. Average pad multiplicity of all RPCs μi …. Pad multiplicity of RPC with hit i

Calibration constants Time independent constants αsampl – To be determined in test beam and with Monte Carlo simulation ε 0, μ 0 – To be determined with Cosmic rays and/or testbeam. Used in the simulation of the RPC response. Time dependent variables Bi – To be determined with noise runs (expected to be negligible) εi, μi – To be determined with track segments in collision data

Determination of ε 0, μ 0 Choose a sensible ε 0, μ 0 e. g. ε 0= 90% , μ 0=1. 5 Assumptions (not really needed) There are only minor fluctuations in ε, μ within a layer Establish operating conditions for ε 0, μ 0 in each layer of each module Most likely will only adjust HV setting, and leave threshold identical Options: Cosmic rays (~ 1 day per module) Broadband muons at test beam Momentum selected muons at test beam

Determination of the sampling constant αsampl Expose modules to test beam pions of energy Ebeam Measure Hi Determine Repeat at different energies to establish possible dependence on Σhi Simulate response of calorimeter to pions using ε 0, μ 0 → Validation of simulation (cross check) Simulate response of calorimeter to neutral hadrons using ε 0, μ 0 Determine sampling term as

Determination of the background rate Bi Measurement of Bi Utilize self-triggered option of front-end ASIC Current experience Rate ~ 0. 1 - 0. 2 Hz/cm 2 Assumptions Gate width 300 ns 5 x 107 readout channels Expected noise rate in entire DHCAL Default value Btotal = Rate x Number of channels x Gate width ~2 hits/event (Calibration ~ 12 hits/Ge. V) → Noise corresponds ~ 200 Me. V Can be ignored

Determination of εi, μi as function of time Assumption Fluctuations in ε, μ in a given layer uniform over surface of layer Two methods a) Track segments in ILC collisions b) Cosmic rays

a) Track segments Reconstruct a track segments within a hadron shower or from muons e+e- → μ+μUtilize preceding and following chambers for track reconstruction Technique already applied to the analysis of testbeam muon and pion data (see JINST 3 P 05001 (2008)) Number of measurements needed Assume ε 0 = 90% and an error of 1% is acceptable N = 104 x p x q ~ 103/module Expected rates Assume operation at 500 Ge. V → σ ~ 4, 700 fb-1 (mostly qqbar) Assume 1 fb-1/day → 4, 700 events/day Assume 1 measurement/event/hemisphere → 9, 400 measurements/day/HCAL Assume (8 x 3 + 2 x 4) = 32 modules → 300 measurements/day/module Need ≤ 5 days for a 1% precision

b) Cosmic rays Flux At sea level flux ~ 1 cm-2 min-1 through horizontal surface Require p > 10 Ge. V → Flux ~ 0. 1 cm-2 min-1 Detector underground, reduce flux by x 2 → 0. 05 cm-2 min-1 Horizontal planes Assume area of 2 m 2 → 1000 events in 1 min Vertical planes Will take longer → Need <1 hour for a 1% precision (everywhere) Power pulsing? → additional factor of 200 → Need a week for a 1% precision

Expected fluctuations of εi , μi Dependence on ambient temperature and atmospheric pressure being studied Changes in general small Δε = -0. 06% · Δp (100 Pa) + 0. 3% · ΔT(0 C) + 0% ·ΔH(%) Δμ = -0. 25% · Δp (100 Pa) + 2% · ΔT(0 C) + 0% ·ΔH(%) Proposed monitoring scheme is expected to be adequate (environmental corrections possible, but probably not necessary)

Neutral hadrons in ECAL + DHCAL Need to be studied with charged pions in testbeam → Data available in 2010 Need to be studied with charged pions at the ILC Again relies on a viable simulation of hadronic showers Leakage of em showers into the DHCAL Needs to be studied at the testbeam → Data available in 2010

Cross checks at the ILC Overall energy scale can be cross checked with 2 – jet events (using jets with differing γ, h 0 fractions) At 500 Ge. V ~ 2800 events/day Reconstructed W± and Z 0 boson masses At 500 Ge. V ~ 1900 W+W- events/day