Min-DHCAL: Measurements with Pions

Benjamin Freund and José RepondArgonne National Laboratory

CALICE Collaboration MeetingMax-Planck-Institute, Munich

September 9 – 11, 2015

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The Min-DHCAL

Layer structure

No absorber interleaved Each layer (2mm Cu + glass + readout board + 2 mm Fe)

→ 0.4 X0 or 0.04 λI

Stack

50 layers, one every 2.54 cm Corresponds to

→ 20 X0 or 2 λI

Measurements

Fermilab test beam in November 2011

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Data collected

Beam line

Fermilab FTBF secondary beam (was supposed to be the tertiary beam)

Momenta

1 – 10 GeV/c

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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

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Equalization of the RPC Response

Procedure

Same as for muons and positrons Uses through going muon tracks Equalization on run-by-run basis

μ+

e+

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Hit and Event SelectionHits eliminated

Hits in area of 2 x 5 cm2 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)

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Particle IdentificationIdentification 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

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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

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Number of Hits

Comments

Data looks good No evidence of contamination from μ+, e+

Fit with Novosibirsk function (rather good) Simulation shows 2nd bump at higher hit number ← not understood

μe+

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Mean of hit distributions

Comments

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

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Mean of hit distributions

Comment

Ratio MC/data mostly within systematic errors Some discontinuity in the simulation

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Reconstructed Energies Erec = (Nhit/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

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Energy Resolution

σ E/E [%

]

Beam energy [GeV]Comments

Leakage → Resolution not improving with energy (remember: depth only 2λI) Data and MC agree within systematic uncertainties

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Radial Shower Shapes

Comments

Quite good at 3 GeV Too narrow simulated showers at 6 and 10 GeV Discrepancy increases with energy

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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

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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)

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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

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Summary

Analysis of Min-DHCAL pions well advanced

Comparison with simulation

Usually better agreement at lower energies Unusual features at higher energies

2nd bump in hit distribution Narrower simulated showers Longer simulated showers Hit distribution off beyond errors → Paper draft in preparation