Energy Loss of Muons in the EMC

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1 Energy Loss of Muons in the EMC Johannes Albrecht University of Heidelberg EMC workshop, Dec. 5,

2 Outline Study single crystal muon response: Compare de/dx of muons in EMC with Bethe Bloch calculation Determine calibration corrections using de/dx of muons Compare barrel / endcap calibration for data and MC EMC workshop, Dec. 5,

3 Samples and cuts used Data samples: Use 94*10 6 events from run 4 data and 64*10 6 events from MC (SP5 μμ gamma) Use Analysis 21: Select e + e - μ + μ - (gamma) BGF2Prong Event selection code written by S. Schenk and U. Langenegger Additional cuts to select muons: Lower momentum cut: 2 GeV Number of Crystals involved = 1 Use raw energy over crystal length as de/dx Fit with Landau twice, 1 st as input for 2 nd, 2 nd over 1.5 σ range EMC workshop, Dec. 5,

4 Bethe Bloch prediction versus MC We had difficulties to describe the muon energy loss in MC by a simple Bethe Bloch calculation (as presented in EMC meeting on Nov. 10) Bethe Bloch as described by PDG including density correction Bethe Bloch and MC differ O(15%) Reason for discrepancy: Single crystal cut Explanation: by restricting to single crystal events, we cut the high energy tail of muon energy loss due to δ-electrons Big fraction (~80%) of muon events deposit energy in many crystals Energy loss with single crystal cut is not well described by Bethe Bloch de/dx in GeV/cm 1) de/dx and Bethe Bloch BB 15% Eraw / l 2) Number of crystals for μ-signal Number of crystals EMC workshop, Dec. 5,

5 Bethe Bloch prediction versus MC Analyse de/dx without single crystal cut: Take full range of energy deposition δ-electrons deposit energy in many crystals Now: good agreement between BB prediction and MC Conclusion: In order to determine an absolute energy scale we cannot use the single crystal cut More sophisticated analysis necessary rerunning of ntuple in progres ==> in the following: keep single crystal cut de/dx in GeV/cm de/dx and Bethe Bloch EMC workshop, Dec. 5,

6 Muon momentum dependence of de/dx Extract energy dependence of de/dx: Analyse barrel and endcap separately this analysis concentrates on barrel Procedure: Divide momentum range (2-10 GeV) in 20 equal sized bins Create a histogram for each bin and fill it with raw energy / length Fit Landau function to histogram Plot peak value as function of momentum n events 1) sample fits de/dx in MeV/cm EMC workshop, Dec. 5,

7 Muon momentum dependence of de/dx Fit Bethe Bloch formula with two parameters: scale and delta (density effect) With this we are able to correct energy dependence of de/dx Note a different increase in MC and data needs more study! Eraw/l in MeV/cm Eraw/l in MeV/cm 1) data: de/dx and fitted BB parameters not very physical data, barrel 2) MC: de/dx and fitted BB parameters not very physical MC, barrel EMC workshop, Dec. 5,

8 de/dx versus theta index Calculate event-by-event the ratio of de/dx and BB prediction Plot ratio for all 56 θ-bins MC: distribution is flat in central barrel, small theta dependence left at the edges Data: ring dependent structures at the 2% level confirms earlier analyses energy dependence is unfolded: structures due to mis-calibration of rings or to different response for muons? use deviations to obtain a set of calibration constants MC data 1) MC: de/dx over BB 2) data: de/dx over BB 1% θ-index 1% θ-index Previous talks in EMC meetings about muon dedx: F. Gruell, Oct. 6 and J. Ritchie, Nov. 10 EMC workshop, Dec. 5,

9 Effect of muon corrections on π 0 's If rings are mis-calibrated, new constants should improve π 0 width Joerg Marks included the obtained calibration constants in his π 0 procedures Only marginal improvement observed before pi0 correction after pi0 correction with muon corrections ANALYSIS NOT YET FINISHED EMC workshop, Dec. 5,

10 Muon response in barrel and endcap de/dx in MeV/cm data, endcap 1) MC ratio: (de/dx) barrel / (de/dx) endcap MC MC: endcap and barrel on same scale Data:dE/dx in endcap systematically ~2-3% higher data, barrel Observation in good agreement with π 0 calibration 2) data ratio: (de/dx) barrel / (de/dx) endcap data EMC workshop, Dec. 5,

11 Conclusion We understand the previously observed differences between deposited energy and calculated de/dx Relative calibration constants for θ-rings determined Comparison between barrel and endcap: MC: same scale for barrel and endcap Data: energy scale is significantly different What's next? study π 0 width with new correction constants study energy loss without 1 crystal cut rerunning of ntuples in progress EMC workshop, Dec. 5,