1 N. Davidson, E. Barberio E/p single hadron energy scale check with minimum bias event Hadronic Calibration Workshop 26 th -27 th April 2007

2 Introduction The hadronic energy scale can be checked in situ by looking at the ratio between pion momentum (p) from the inner detector (should be close to actual) and the calorimeter energy (E). Goal is to know energy scale to 1% Coverage of |eta|<2.5 Current work on single pions from tau decay does not cover the low E range (below 20GeV). Minimum bias events can cover this range. Used 50k minimum bias monte carlo events (equivalent amount collected with approx. luminosity of pb -1 ) csc pythia_minbias.recon.AOD.v Used 100k minimum bias monte carlo events at 900GeV. csc pythia_minbias_900.recon.AOD.v Comparison of minimum bias to single pion monte carlo. Used: 50k single 1GeV pions - csc singlepart_singlepi_et1.recon.AOD.v k single 3GeV pions - csc singlepart_singlepi2.recon.AOD.v

3 Approach E taken as the sum of caloTopoCluster energies (calibrated to EM scale only) in cone. Cone size of ΔR cone =0.4 found to be optimal Track extrapolated to 2 nd layer of EM Calorimeter must match at least one cluster within ΔR match <0.05 Require clusters and tracks in |eta|<2.4 Bias to E/p in minimum bias due to: Correlated background contaminating clusters from: Neutral particles Charged particles with no track in ID. Tracks not belonging to pions Cuts made to remove bias: Based on tracks: Number of tracks in event < 15 ΔR track isolation >0.8 >1 B Layer Hit Based on clusters Cluster Multiplicity < 4 Energy difference in cones ΔR=1.0 and Δ R=0.4 < 200MeV Energy fraction in cone ΔR=0.2 > 0.7xEnergy in cone ΔR=0.4 Approx. 1 track in 200 survive. (or 1 per 10 events) For 50k events

4 Results and Plan Results: 1 GeV bias approx 10% 3 GeV bias approx 3% (within error) 900GeV minimum bias results similar. Work to improve bias continuing Also need to study: Additional calibration schemes Trigger Tracks from high momentum tail requires higher statistics (Atlfast?) Pile-up some samples becoming available now Sample E/p mean RMS -minimum bias -single pion (after cuts) -single pion (before cuts) Error: ±0.011 Sample E/p mean RMS -minimum bias -single pion (after cuts) -single pion (before cuts) Error: ±0.011 For 50k minimum bias events. Single pions weighted to have the eta distribution of minimum bias tracks passing cuts.