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

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?

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 mm2; 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).

2) New MC production up to 1 MeV

Fundamental in order to:1) Compare emulsion

exposure withoutshielding and with5 cm of iron;

2) Check the former MCproduction performed withhigher thresholds;

Lack of statistics...

Nice agreement betweenthe resulting spectra withthe one found in literature

Spallation neutronsare the most abundantcomponent

3) Emulsion cuts implemented into MC

impact ≤ 20 mslope ≤ (0.010 + 0.1 slope) rad

Effective for low energy particle.

An additional cut on the energyloss 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

10 cm of Lead

4) All scintillator data analysed

Test 1 Test 2

neutron

Pro

ton r

eco

il

muon

Scintillator counting statistics:

Test #

Iron(cm)

Livetime(sec)

Count/secDatax102

Count/secMCx102

Ratio(Data/MC)

2 25 157594 14.40±0.09 13.95±0.08 1.03±0.01

2 50 952514 3.77±0.02 3.75±0.02 1.00±0.01

1 65 79280 1.71±0.05 1.67±0.01 1.02±0.03

2 75 1109808 1.05±0.01 1.09±0.01 0.96±0.01

1 90 79280 0.61±0.03 0.64±0.01 0.95±0.06

Good agreement at the level of 5% (taken as systematic error) due to atmosphere, season ...

Emulsion – MC comparison:zenith angle distributions

(0 cm – 5 cm – 25 cm – 40 cm)

Emulsion data(corrected forefficiency)

MC data(with cuts)Errors only

statistical

Emulsion – MC comparison:zenith angle distributions

(50 cm – 70 cm – 75 cm – 100 cm)

Emulsion data(corrected forefficiency)

MC data(with cuts)

Emulsion – MC comparison:integral distribution in zenith

MC simulation:5% systematics

on absoluteflux knowledge

Emulsion data:10% systematics

on efficiencycorrections

Details on the integral distribution

40 cm of iron: minimum e40 cm of iron: minimum e++ee-- flux flux

RigenerationRigenerationphenomenaphenomenafrom muonfrom muonactivity in ironactivity in iron

Original CROriginal CRe.m. showerse.m. showers

Residual energy spectra after40 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

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 incharge by the Geomagnetic Field (it carries informationon charge ratio at verylow energies)

=0 is theGeomagnetic

North

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...