1. Min-DHCAL: Measurements with Pions Benjamin Freund and José Repond Argonne National Laboratory CALICE Collaboration Meeting Max-Planck-Institute, Munich September 9 – 11, 2015

2. 2 The Min-DHCAL Layer structure No absorber interleaved Each layer (2mm Cu + glass + readout board + 2 mm Fe) → 0.4 X 0 or 0.04 λ I Stack 50 layers, one every 2.54 cm Corresponds to → 20 X 0 or 2 λ I Measurements Fermilab test beam in November 2011

3. 3 Data collected Beam line Fermilab FTBF secondary beam (was supposed to be the tertiary beam) Momenta 1 – 10 GeV/c

4. 4 Simulation GEANT4 Version 10.0.p02 4 different physics lists RPC_sim_5 Emulates RPC Charge spread with 2 Gaussians Tuned with muons and positrons

5. 5 Equalization of the RPC Response Procedure Same as for muons and positrons Uses through going muon tracks Equalization on run-by-run basis μ+μ+ e+e+

6. 6 Hit and Event Selection Hits eliminated Hits in area of 2 x 5 cm 2 around ground of each chamber (<<1% loss) Hits with same geometrical address, but different time stamps (<<1%) Hits outside the standard 200 ns window (1 – 2% loss) Simulated hits corresponding to dead ASICs in data (~0.4%) Event cleaning cuts One cluster with at most 4 hits in first layer Maximum number of hits in time bins 2&3 (eliminates multi-particle events) At least 6 layers with hits (eliminates spurious triggers)

7. 7 Particle Identification Identification of an interaction layer I.L. First layer of two consecutive layers with at least four hits Pion selection No Cerenkov hits Identified interaction layer I.L. > 4 (eliminates remaining positrons) I.L. < 11 (reduces longitudinal leakage) Comments 4 < I.L. < 11 eliminates lots of statistics Cerenkov not simulated Cerenkov needed to cut positrons Muons efficiently cut

8. 8 Systematic Errors Data Calibration uncertainty → 50% of difference between raw and equalized result Limited rate capability → Use of first 0.5 second of spill → 1 – 2% effect (most distributions not affected) Contribution from accidental noise hits → Negligible Contamination from muons/positrons → Negligible (no visible enhancements) Definition of the I.L. → Variation of cut on number of hits by ± 5% in data All errors assumed independent (also from energy to energy point) Dominant error from equalization Simulation For each variable, the average % difference between e + data and simulation taken as error Different physics lists shown individually and not treated as error

9. 9 Number of Hits Comments Data looks good No evidence of contamination from μ +, e + Fit with Novosibirsk function (rather good) Simulation shows 2 nd bump at higher hit number ← not understood μ e+e+

10. 10 Mean of hit distributions Comments Mean obtained from Novosibirsk fit Fit to power law aE m → Response very linear (m~1) 1 GeV data point not reliable (low statistics and contamination from μ + ) Good agreement between data and MC

11. 11 Mean of hit distributions Comment Ratio MC/data mostly within systematic errors Some discontinuity in the simulation

12. 12 Reconstructed Energies E rec = (N hit /a) 1/m Comments Data looks good Novosibirsk fit ~ OK 3,4 GeV: all simulations agree, but different from data 6,8,10 GeV: QGSP_BERT differs from other simulations. None describe the data

13. 13 Energy Resolution σ E /E [%] Beam energy [GeV] Comments Leakage → Resolution not improving with energy (remember: depth only 2 λ I ) Data and MC agree within systematic uncertainties

14. 14 Radial Shower Shapes Comments Quite good at 3 GeV Too narrow simulated showers at 6 and 10 GeV Discrepancy increases with energy

15. 15 Longitudinal Shower Shapes Comments Pretty good agreement at 3 GeV Longer simulated showers at higher energies Discrepancy increases with energy Fit to sum of 2 Gamma distributions

16. 16 Shower Maximum Comments Determined from fit to sum of 2 Gamma distributions No maximum below 4 GeV Simulated showers consistently longer (Remember: longitudinal shapes of e + well simulated)

17. 17 Hit Density Distribution Comments Agreement with simulations within systematic errors at 3 GeV Discrepancies at higher energies outside errors at higher energies Note: data does not change much with increasing energy, simulation does

18. 18 Summary Analysis of Min-DHCAL pions well advanced Comparison with simulation Usually better agreement at lower energies Unusual features at higher energies 2 nd bump in hit distribution Narrower simulated showers Longer simulated showers Hit distribution off beyond errors → Paper draft in preparation