1 N. Davidson E/p minimum bias update with Athena Analysis Meeting 12 th June 2007

Looked at mc (with 1mm problem) 400k minbias events: trig1_misal1_csc pythia_minbias.recon.AOD.v k single pions with et=1GeV trig1_misal1_mc singlepart_singlepi_et1.recon.AOD.v k single pions with et=10GeV trig1_misal1_mc singlepart_singlepi_et10.recon.AOD.v Will repeat with 30 micron samples and compare. Recall: P – taken from track momentum (precise) E – taken as the sum of caloTopoClusters energies within a cone of ΔR=0.4 centered on the track position when extrapolated to the 2nd layer of the EM calorimeter. Only tracks with matching cluster within ΔR<0.05 are considered Only clusters with are used.

3 Tracks: 11 vs 12 Number of tracks Track Resolution

4 Clusters: 11 vs 12 For 3GeV pions: CaloTopoClusters calibrated to local hadronic scale Cluster Multiplicity E/p

5 Selection of isolated pions (et=1GeV) Cuts made to remove bias in 11: 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 version 12: Can make harder cuts since there are more statistics Changes: Removed cut on number of tracks as this was ineffectual ΔR track isolation >1.0 magnitude of energy difference in cones ΔR=1.0 and Δ R=0.4 < 100MeV Approx. same number of tracks surviving

6 Results An improvement to the E/p bias can be made using a smaller cone size of 0.2 By requiring an isolated 0.2 cone get E/p comparable to 0.4 cone for the single sample For Cone 0.2: Sample E/p mean RMS -minimum bias (0.2) -single pion cone 0.4 -single pion cone 0.2 Error: ±0.007 Sample E/p mean RMS -minimum bias -single pion (after cuts) -single pion (before cuts) Error: ±0.007

7 Pions with et=10GeV approx 1/100 events have a track with 8GeV<pt<12GeV ¾ with matching cluster within R < 0.05 ¾ with matching 0.4 Cone Jet within R < 0.2 Cluster based E/p before cuts mean = (cf single pion) RMS = (cf single pion) Jet based E/p before cuts mean = 2.78 (cf 1.11 single pion) RMS = (cf single pion) However higher Pt tracks correlated with large contamination out of 400k events: 450 tracks remain with track isolation within tracks with no truth neutral or track within 0.4 More stats & work needed on this

8 Pile-up First look at pile-up sample 5.6 events Bias to E/p scales with the sum of energy in the event. Difficult to find events with energy sum similar to single event Method of cuts to find isolated pion probably not possible Will need to use some kind of background subtraction