1 NaI calibrationneutron observation NaI calibration and neutron observation during the charge exchange experiment 1.Improving the NaI energy resolution (as low as reasonably achievable!) Common noise reduction Intercalibration Clustering algorithm 2.Observation of the prompt signal of “high energy” neutrons (8.9 MeV) A “matter-of-fact” evidence, in Xe and in NaI Comparison with cross sections First look at and requirements of a MC for neutrons in LXe. Giovanni Signorelli, INFN Pisa MEG collaboration meeting, PSI 9 Feb 2004

2 1.Common noise reduction 2.Crystal intercalibration 3.Clustering for energy summation NaI calibration procedure 23%  11% 55 MeV

3 Common noise reduction Algorithm: Simplif. From E.Frlez, D. Pocanic, S.Ritt NIM A463 (2001) 1.Take the ADC of the channels which see pedestal 2.Make the average 3.Subtract it from all channels (second pedestal correction) The pedestal  ’s shrink from 5  6 to 2  3. It’s not perfect but compatible with the ALARA principle Correlation between channels due to electronics, noise in cables, ADCs…

4 Crystal intercalibration ROUGH CALIBRATION Cosmic ray runs can be used to inter- calibrate crystals Muons triggered by crystal pairs Position of the Landau peak FINE TUNING Problems for crystals at the center (the crystal are not uniformly spanned by cosmics?) Refined with monoenergetic gammas

5 Energy clustering The cluster C includes the element of the detector with the maximum energy plus all the fired elements connected to another member of the cluster by a side or a corner E =  E i iCiC

6 Results The resolution is acceptable The peak position is well reproduced 54.8 MeV83 MeV129.8 MeV 5.5%5.1%4.9% Reconstructed peak

7 A better NaI helps A cleaner separation of the two NaI peaks helps in reducing the tails on the Lxe distributions An improved collinearity requirement shows the real performance

8 Neutron observation during the experiment Evidence for a prompt signal from neutrons 8.9 MeV neutron in coincidence with the 129 MeV gamma Neutrons from the Am/Be source (  10 MeV) Comparison with cross sections (physics) Inelastic scattering Xe level excitation First look at and requirements of a MC for neutrons in LXe. Geant GCALOR Geant 4 Possible use of neutrons for calibration/monitoring purposes (  Angela) Availability – switchability Probe of the entire detector

9 Evidence Runs triggered with one of the detectors only (&S1 &RF…) E measured > 110 MeV  selection of the  - p   n events No timing cut (implies an energy/position cut!) XeNaI  50% efficiency

10 Neutron-induced prompt signal in Xe For fast neutrons (1  10 MeV) the total and scattering cross sections are similar for all isotopes  = 1 barn  = 72 cm in LXe

11 Neutron cross section

12 Processes A COMPLETE MONTECARLO CALCULATION IS NEEDED FOR COMPUTING THE NEUTRON EFFECTS IN THE CALORIMETER : efficiency for fast and thermal neutron detection determination of the energy spectrum in the calorimeter energy released as a function of time energy density  (x,y,z) dependence on threshold and n-energy ALL THE RELEVANT NEUTRON CROSS-SECTIONS CAN BE INCLUDED IN GEANT 3.21 AND ARE INCLUDED IN GEANT4 information from medical physics…….! KERMA COEFF. (Kinetic Energy Released per unit Mass) and  tr /  (mass energy transfer coefficient) tabulated for neutrons

13 MC for neutrons in liquid Xenon Though the most reliable simulation today is GEANT4, some quick results were obtained with GEANT GCALOR 8.9 MeV neutron simulated impinging a 10 x 10 cm 2 window of the Lproto (time cut-off at 600ns) coming from the LH 2 target GCALOR (MICAP, E n < 20 MeV) takes care of n cross sections (ENDF VI B) N,n n,2n … If the residual nucleus is left in an excited state the deexcitation photon is generated (this is not done in the n,Xe  n’Xe case. Bug? We generated these photons by hand) Some refinement still possible In GEANT4 the code for the neutron transportation is automatically embedded in the package and is “benchmarked” with a comparison to real data!

14 Neutron Monte Carlo event sample Incoming neutron 8.9 MeV neutron 10 x 10 cm 2 window Coincidence with the 129 MeV photon

15 MC spectrum 2.2 MeV capture on protons Xe levels A neutron edge is present Low energy lines due to Xe and/or other nuclear levels High energy tails: n capture and isotope production The comparison with the data is good but not excellent

16 Conclusion A calibration procedure for the NaI has been estabilished and coded in the (Pisa version of the) analyzer, obtaining a fairly good E resolution for this detector The neutron prompt signal was identified in Xe and NaI and the understanding of the process is under way. We’ll do our best to reproduce the experimental result… A new window is open, a new handle is present. To us the difficult task to exploit it (calibration, monitoring…)!

17 …timing

18 neutron gamma n2n n 1 n 2 nn

19 Xe 129  TOT  SC

20 Xe 129  n2n  n3n Initial energy degradation and neutron duplication

21 Xe 129 nuclear level excitations  n1  n2 etc. Levels MeV energy degradation and kinetic energy into  energy

22 Xe 129 nn

23 Xe 132 nuclear level excitations  n1  n2 etc. Levels MeV

24 Xe 132 nn