1 N. Davidson E/p single hadron energy scale check with minimum bias events Jet Note 8 Meeting 15 th May 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)

4 1 GeV vs 3GeV pions Found 50k single 1GeV pions - csc singlepart_singlepi_et1.recon.AOD.v Not flat in et, but in e (?) Not clear if 99% of energy in cone of R=0.4 for 1GeV pions Chance of cluster within R<0.05 reduced For 50k events

5 Results 1 GeV bias approx 10% 3 GeV bias approx 3% (within error) 900GeV minimum bias results similar. Work to improve bias continuing 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.

6 Track-Cluster Matching Would it be useful to measure low momentum pion energy for all tracks regardless of track- cluster matching? To understand: Efficiency of cluster reconstruction Pion energy loss Mean E/p depends on how good the matching is. Is this due to: No ‘true’ pion cluster but a match to backgound? The nature of the shower or clustering algorithm? Will is be possible to measure this with minimum bias? What is this? Region examined so far

7 Plan to use Athena 12 data (from today) For Pile-up samples (from mark) Look at EtSum range for pile-up. Could low EtSum events be used? Can the background be measured and subtracted? For single minbias events A lot more data is available (x10 stats?). Looking now at 1mm data while others are still running. Examine how and 12 compare. Examine how 1mm vs 30 μ data compare. Undertake plans outlined in previous talks.