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Test with cosmic rays at LNGS - final results - S. Bastianelli, L. Degli Esposti, R.Diotallevi, G. Mandrioli, P. Righini, G. Rosa, M. Sioli OPERA meeting, LNGS, May 19-22, 2003

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What’s new: Emulsion data completely analysed (Test 1 and Test 2); An additional MC production without shielding (hard job: from TeV primaries down to 1 MeV secondaries!); “Emulsion cuts” reproduced into MC; Scintillator data recovery of Test 1; Mutual comparison Scint-Emul-MC; The inheritance of this test: must we fear exposures to CRs?

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1) Analysis of emulsion data Eight 3-plate stacks scanned: 25-50-75 cm of iron (Test 1=48 days exposure) 0-5-40-70-100 cm of iron (Test 2=74 days exp.) Scanned area in each plated=150-200 mm 2 ; Base-tracks/plate of the order of 10-20k; Plate-to-plate connections and efficiency corrections only in “effective scanning areas”, i.e. in common zones of adjacent plates with large enough statistics; Angular distributions and integral fluxes in the range 20- 300 mrad; Systematic error is taken to be as the relative difference between plate12 and plate23 countings (ranging from 10% at small coverage up to 1% at large coverages).

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2) New MC production up to 1 MeV Fundamental in order to: 1)Compare emulsion exposure without shielding and with 5 cm of iron; 2)Check the former MC production performed with higher thresholds; Lack of statistics... Nice agreement between the resulting spectra with the one found in literature Spallation neutrons are the most abundant component

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3) Emulsion cuts implemented into MC impact ≤ 20 m slope ≤ (0.010 + 0.1 slope) rad Effective for low energy particle. An additional cut on the energy loss has been applied dE/dX ≤ 2(dE/dX) mip Effective for non-relativistic protons. Scintillator cuts are unchanged: Released Energy > 20% of the muon signal (to reproduce discriminator thresholds) Emulsion stack

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10 cm of Lead 4) All scintillator data analysed Test 1Test 2 neutron Proton recoil muon

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Scintillator counting statistics: Test # Iron (cm) Livetime (sec) Count/sec Datax10 2 Count/sec MCx10 2 Ratio (Data/MC) 22515759414.40±0.0913.95±0.081.03±0.01 2509525143.77±0.023.75±0.021.00±0.01 165792801.71±0.051.67±0.011.02±0.03 27511098081.05±0.011.09±0.010.96±0.01 190792800.61±0.030.64±0.010.95±0.06 Good agreement at the level of 5% (taken as systematic error) due to atmosphere, season...

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Emulsion – MC comparison: zenith angle distributions (0 cm – 5 cm – 25 cm – 40 cm) Emulsion data (corrected for efficiency) MC data (with cuts) Errors only statistical

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Emulsion – MC comparison: zenith angle distributions (50 cm – 70 cm – 75 cm – 100 cm) Emulsion data (corrected for efficiency) MC data (with cuts)

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Emulsion – MC comparison: integral distribution in zenith MC simulation: 5% systematics on absolute flux knowledge Emulsion data: 10% systematics on efficiency corrections

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Details on the integral distribution 40 cm of iron: minimum e + e - flux Rigenerationphenomena from muon activity in iron Original CR e.m. showers

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Residual energy spectra after 40 cm of iron coverage After 40 cm: Muon flux: 1.78 mm -2 day -1 Median muon energy: 2 GeV e + e - flux: 0.2 mm -2 day -1 Median e + e - energy: 8 MeV e + e - flux with cuts: 0.02 mm -2 day -1 Median e+e- energy: 40 MeV

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An interesting by-product of emulsion data analysis: Azimuthal distributions of emulsion tracks are strongly asimmetric... Possible interpretations (to be confirmed by MC): very low energy CR components splitted in charge by the Geomagnetic Field (it carries information on charge ratio at very low energies) =0 is the Geomagnetic North

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Conclusions and future An native-coarse test allowed us to perform “precision” measurements! Emulsion-Scintillator-MC data fairly agree at 5-10% level; We have a reliable and experimentally tested MC code, ready to use for further checks in the future; We can safely conclude about the best choice for the iron coverage; Further fine-tuning studies are required, in order to explore a mixed solution for the coverage; Next obliged step: a whole brick exposure...

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