PERFORMANCE OF THE MACRO LIMITED STREAMER TUBES IN DRIFT MODE FOR MEASUREMENTS OF MUON ENERGY - Use of the MACRO limited streamer tubes in drift mode -Use of a neural network (NN) to estimate the muon energy event by event - Check of the electronics with 2 dedicated “test beam” Conclusions ADVANCED TECHNOLOGY AND PARTICLE PHYSICS 7 International Conference on th Villa Olmo, Como, 15-19/10/2001 M. Giorgini for the MACRO Collaboration Goal : energy estimate of upgoing muons with a Multiple Coulomb Scattering (MCS) analysis Experimental procedure - Study of drift velocity in He/n-pentane mixture

SECTION OF THE MACRO DETECTOR 14 horizontal planes of limited streamer tubes filled with a mixture of He (73%) / n-pentane (27%) 7 rock absorbers 3 liquid scintillators   The upthroughgoing muons are induced by neutrino interaction in the rock below the detector The oscillation probability is a function of E P(    ) = sin 2 2  sin 2 (1.27  m 2 L/E ) It is IMPORTANT to estimate the induced-muon energy

MACRO is not equipped with a magnet: the ONLY way to estimate muon energy is by the Multiple Coulomb Scattering (MCS) in the absorbers The r.m.s. of the lateral displacement of a muon crossing a depth X of material is : X 0 p  p  = muon momentum X 0 = radiation length of the material The saturation occurs when  Y = space resolution of the detector ~ For MACRO:  Y = 10cm/E  (GeV) The space resolution of the tracking system is ~ 1 cm corresponding to E  ~ 10 GeV, not enough to study neutrino oscillations with parameters  m 2 ~ eV 2 and sin 2 2  = 1 ~ X Y Y 

THE MACRO LIMITED STREAMER TUBES Cross section : 3X3 cm 2 Length : 1200 cm About 5600 chambers and ~ wires Time informations can be obtained from the QTP (Charge and Time Processor) System (designed for the search for slow magnetic monopoles) ADC/TDC system with a 640  s memory Frequency of the clock : 6.6 MHz TDC bin size :  t =150 ns Mixture : He(73%) / n-pentane(27%) Ultimate space resolution :  =V drift.  t/ 12 ~2mm MACRO is non equipped with a TDC system

THE MACRO CERN PS-T9 “TEST BEAM” Main goals : MAIN GOALS : Absolute calibration of energy reconstructed by multiple scattering Study of drift velocity in He / n-pentane mixture Study of the QTP-TDC linearity : comparison of QTP-TDC (150 ns/div) and standard TDC Lecroy 2228A (250 ps/div) Test of the software used for muon tracking

10 streamer tubes (MACRO lower part) 4 streamer tubes (MACRO attico) 7 rock absorbers 3 liquid scintillators beam 60 RUNS with 2 GeV < E  < 12 GeV The analog output of each chamber is sent to a QTP channel The digital output is sent to a TDC Lecroy Trigger : fast coincidence of S1,S2,S3 scintillators HV : 4050 V (~ 10 5 muons)

STUDY OF QTP-TDC LINEARITY Comparison between the response of the MACRO The TDC-QTP response is linear within 10 % QTP system and standard TDC’s ( Lecroy )

STUDY OF DRIFT VELOCITY IN He- n-PENTANE 3cm r = 50  m wire 50  m < r < 1.5 cm  r dN/dt = dN/dr * dr/dt constant v drift

Good agreement between MC and real data COMPARISON GARFIELD MC – REAL DATA

1 dedicated run with rock absorbers away: QTP-TDC  150  ns/div  ~ 2 mm Standard Lecroy TDC (250 ps/div)  ~ 500  m SPACE RESOLUTION ( RESIDUALS DISTRIBUTION) In MACRO the space resolution is expected to be spoiled by  rays produced in the rock absorbers and by gas mixture variation. 2 mm is our best resolution !

RESULTS OF THE CERN PS-T9 “TEST BEAM” The QTP electronics can be successfully used to operate the streamer tubes in drift mode The QTP-TDC response is linear within 10% The drift velocity in He/n-pentane mixture is in good agreement with GARFIELD MC The software is adequate to perform a good muon track fit The space resolution of the MACRO streamer tubes in drift mode is ~ 2 mm

STUDY OF THE MACRO SPACE RESOLUTION Analysis of the downgoing muon ( ~ 300 GeV) tracks with the standard tracking (no QTP) Selection of the hits with a single fired tube For each hit, the corresponding TDC value is multiplied by the V drift measured at the “test beam”, obtaining the drift radius The track is reconstructed as the best fit of the drift circles

MACRO RESIDUALS DISTRIBUTION Without QTP (streamers in digital mode)  ~ 1 cm With QTP  ~ 3 mm Improvement of the space resolution of a factor 3.5 !

VARIABLES SENSITIVE TO MS Average abs(residual) Maximum residual Slope and intercept of ‘progressive fit’ (see below) of residuals distribution  Difference of residuals relative to the 3 more distant tubes 100 GeV 1 GeV Np Np = progressive number of s.t. of MACRO lower part Absorber Np xx xx  x =

USE OF A NEURAL NETWORK (NN) TO SEPARATE SAMPLES OF DIFFERENT ENERGIES Average residuals Max residuals Neural Network 0. < Output < 1. Training: Fixed energy Different zenith angle  of residuals distribution Slope of ‘progressive fit’ Intercept of ‘progressive fit’ Diff. of residuals for the 3 more distant tubes This procedure allows to estimate event by event the energy of upgoing muons

The response is linear with event energy up to E  ~ 40 GeV OUTPUT OF THE NEURAL NETWORK

The comparison data-MC shows a good agreement in the E  range from 2 to 100 GeV The CERN PS-T9 “test beam” allows to calibrate the NN output ONLY up to E  =12 GeV A second “test beam” was performed at the SPS-X7 with 15 GeV < E  < 100 GeV

RECONSTRUCTION OF THE MUON ENERGY INVERTING THE CURVE JUST SHOWN FOR 4 DIFFERENT E  VALUES

CONCLUSIONS The MACRO streamer tube system can be used in drift mode for measurements of muon energy The QTP system allows to improve the MACRO space resolution of a factor 3.5 from  = 1cm to  = 3mm The NN approach allows to estimate the muon energy event by event The output of the NN increases with the muon energy up to E  ~ 40 GeV ~~ This method can be applied to estimate the energy of neutrino-induced upgoing muons in MACRO to study the neutrino oscillations hypothesis The test beam data are in agreement with the MC expectations with 1  error