PERFORMANCE OF THE MACRO LIMITED STREAMER TUBES IN DRIFT MODE FOR MEASUREMENTS OF MUON ENERGY

1. 7 International Conference on th ADVANCED TECHNOLOGY AND PARTICLE PHYSICS Villa Olmo, Como, 15-19/10/2001 PERFORMANCE OF THE MACRO LIMITED STREAMER TUBES IN DRIFT MODE FOR MEASUREMENTS OF MUON ENERGY M. Giorgini for the MACRO Collaboration Goal : energy estimate of upgoing muons with a Multiple Coulomb Scattering (MCS) analysis Experimental procedure • Use of the MACRO limited streamer tubes in drift mode - Check of the electronics with 2 dedicated “test beam” - Study of drift velocity in He/n-pentane mixture • Use of a neural network (NN) to estimate the muon energy • event by event Conclusions

2. SECTION OF THE MACRO DETECTOR m nm 7 rock absorbers 3 liquid scintillators 14 horizontal planes of limited streamer tubes filled with a mixture of He (73%) / n-pentane (27%) The upthroughgoing muons are induced by neutrino interaction in the rock below the detector The oscillation probability is a function of En P(nm nt) = sin22Q sin2(1.27 Dm2 L/En) It is IMPORTANT to estimate the induced-muon energy

3. 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 X sYa pm X0 pm = muon momentum X0 = radiation length of the material ~ The saturation occurs when sY = space resolution of the detector For MACRO: sY = 10cm/Em(GeV) The space resolution of the tracking system is ~ 1 cm corresponding to Em ~ 10 GeV, not enough to study neutrino oscillations with parameters ~ Dm2 ~ 10-3 eV2 and sin2 2Q = 1

4. THE MACRO LIMITED STREAMER TUBES Cross section : 3X3 cm2 Length : 1200 cm About 5600 chambers and ~ 50000 wires Mixture : He(73%) / n-pentane(27%) MACRO is non equipped with a TDC system Time informations can be obtained from theQTP (Charge and Time Processor) System (designed for the search for slow magnetic monopoles) ADC/TDC system with a 640 ms memory Frequency of the clock : 6.6 MHz TDC bin size : Dt =150 ns Ultimate space resolution :s =Vdrift. Dt/ 12 ~2mm

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

6. 3 liquid scintillators 7 rock absorbers beam 4 streamer tubes 10 streamer tubes (MACRO lower part) (MACRO attico) 60 RUNS with 2 GeV < Em < 12 GeV (~ 105 muons) 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

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

8. m r = 50 mm wire r STUDY OF DRIFT VELOCITY IN He- n-PENTANE 50 mm < r < 1.5 cm dN/dt = dN/dr * dr/dt • 3cm vdrift constant

9. COMPARISONGARFIELD MC – REAL DATA Good agreement between MC and real data

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

11. 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

12. STUDY OF THE MACRO SPACE RESOLUTION Analysis of the downgoing muon (<Em> ~ 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 Vdrift measured at the “test beam”, obtaining the drift radius The track is reconstructed as the best fit of the drift circles

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

14. VARIABLES SENSITIVE TO MS Average abs(residual) Maximum residual of residuals distribution s Difference of residuals relative to the 3 more distant tubes Slope and intercept of ‘progressive fit’ (see below) Dx 100 GeV Dx = 1 2 3 Np 4 1 GeV Dx Np 5 6 7 8 9 Np 10 Np = progressive number of s.t. of MACRO lower part Absorber

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

16. OUTPUT OF THE NEURAL NETWORK The response is linear with event energy up to Em ~ 40 GeV

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

18. RECONSTRUCTION OF THE MUON ENERGY INVERTING THE CURVE JUST SHOWN FOR 4 DIFFERENT Em VALUES

19. 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 s = 1cm to s = 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 Em ~ 40 GeV The test beam data are in agreement with the MC expectations with 1s error This method can be applied to estimate the energy of neutrino-induced upgoing muons in MACRO to study the neutrino oscillations hypothesis