1 / 24

Background Suppression in LArGe@MPI-K: Study and Feasibility of Bare Ge Detectors in LAr

This document presents the findings from the LArGe@MPI-K project, focusing on the study and quantification of background suppression using liquid argon (LAr) scintillation. The experimental setup and operational parameters are outlined, including the performance of bare Ge detectors in LAr without energy resolution deterioration. Background spectra were characterized using various gamma sources, and significant suppression of Compton continuum was observed. Future directions and outlook for LArGe@LNGS are discussed, highlighting the system's potential for further advancements in neutrino physics.

verna
Télécharger la présentation

Background Suppression in LArGe@MPI-K: Study and Feasibility of Bare Ge Detectors in LAr

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Results from LArGe@MPI-K goal: study and quantify background suppression with LAr scintillation M. Di Marco, P. Peiffer, S. Schönert Thanks to Davide Franco and Marik Barnabe Heider Gerda collaboration meeting, Tübingen 9th-11th November 2005

  2. Outline • Resolution of bare Ge in LAr • Experimental Setup of LArGe@MPI-K • DAQ • Operational parameters • Background spectrum • Characterization with various -sources • 137Cs, 60Co, 226Ra, 232Th • bkgd suppression in RoI • Outlook on LArGe@LNGS • Conclusions

  3. Proof of feasibility: bare p-type detectors in LAr Data taken at DSG in Mainz  No deterioration of energy-resolution for p-type detectors in LAr !

  4. Schematic system description System is designed to be air tight to prevent quenching of LAr scintillation by O2 or H2O Continously flushed with gaseous Argon Filling and emptying Ge-crystal (∅ 5.1 cm, h=3.5 cm) LAr in Dewar (∅ 29 cm) WLS and reflector (VM-2000) PMT 5 cm lead + underground lab (15 mwe) Trigger on Ge-signal Record Ge-signal and LAr-signal simultaneously Shaping 3 µs Gate width = 6 µs No hardware veto Monitor filling level (with temperature sensors) Calibrate PMT (trough optical fibre with UV-LED) Internal source External source

  5. Operational parameters PMT threshold set at ~1 single photoelectron (spe) Canberra p-type crystal (390 g) Running stable since several weeks 1 spe ≈ 5 keV energy deposition in LAr • Stability monitoring by: • peak position • resolution • leakage current • Not optimized for energy resolution: • long signal cables • FET outside system • pickup of external noise Energy resolution OK: ~4.5 keV FWHM w/o PMT ~5 keV with PMT At 1,3 MeV 60Co-line Gain in background suppression is not compromised by signal loss due to random coincidences !

  6. Background spectrum 40K 40 counts/h Ge signal (no veto) Ge signal after veto: fraction of the signal which „survives“ the cut 208Tl 10 counts/h energy in Ge (MeV)

  7. Background spectrum 40K 40 counts/h 93% survival 208Tl 10 counts/h 93% survival baseline: 41% survival energy in Ge (MeV)

  8. Calibration with different sources full energy peak : no suppression with LAr veto • 137Cs : single  line at 662 keV Compton continuum: suppressed by LAr veto

  9. real data 137Cs 662 keV 100% survival Compton continuum: 20% survival • very well reproduced by MaGe : • shape of energy spectrum • peak efficiency • peak/Compton ratio simulations same thing for 60Co (ext), 232Th (int, ext), 226Ra (int)  geometry + basic physics processes well understood 662 keV 100% survival Compton continuum: 20% survival

  10. 137Cs for now, veto simulated as a sharp energy threshold with arbitrary value  suppression by LAr overestimated in more complex cases • next: • proper threshold for spe (Poisson statistics) • calibration of LAr scintillation

  11. Calibration with different sources full energy peaks : no suppression with LAr veto • 60Co : two  lines (1.1 and 1.3 MeV) in cascade • external : high probability that only 1  reaches the crystal  acts as 2 single  lines • internal : if one  reaches the crystal, 2nd  will deposit its energy in LAr full energy peak : suppressed by LAr veto Compton continuum: suppressed by LAr veto

  12. 60Co (external) 30% 30% 100% shielding of the source not implemented in MaGe yet ~20% ~20%

  13. 60Co (internal) 40% weak source : 208Tl from bkgd is visible 100% survival 12% 12% summation peak: both  in crystal 100% survival

  14. Calibration with different sources • 137Cs : single  line at 662 keV • 60Co : two  lines (1.1 and 1.3 MeV) in cascade • full-E peak no suppression if external • full-E peak suppressed if internal • 232Th : dominated by 208Tl • 511 keV – 583 keV – 2.6 MeV : prompt cascade • 860 keV – 2.6 MeV : prompt cascade  no suppression if external  suppressed if internal • 226Ra : dominated by 214Bi • 609 keV and 1.120 keV : prompt cascade  suppressed if internal • 1.764 MeV - 2.448 MeV : direct decay  no suppression Compton continuum: suppressed by LAr veto

  15. 232Th (external) 583 keV : 70% 2.6 MeV 83% 33% 25% 25% RoI 208Tl simulated 2.6 MeV 76% 29% 18% 19%

  16. 232Th (internal) weak souce (400 Bq over 3cm)  contribution from 208Tl bkgd in real data  30% 26% (mc 15%) 14% 9,5% 9,5% RoI 208Tl simulated 12% 4% 4%

  17. 226Ra (internal)  92%  30% (mc 23%) 19% 27% 30% RoI 214Bi simulated 13% 28% 30%

  18. Summary of background suppressionfor LArGe-MPIK setup full energy peak : no suppression by LAr veto Compton continuum: suppressed by LAr veto full energy peak : suppressed by LAr veto No efficiency loss expected for 0ßß-events Suppression factors limited by radius of the active volume. R = 10 cm  significant amount of ‘s escape without depositing energy in LAr

  19. Outlook: LArGe @ Gran Sasso Diameter = 90 cm. No significant escapes. Suppression limited by non-active materials. Examples: Background suppression for contaminations located in detector support Bi-214 Tl-208 survival: 10% LArGe suppression method and segmentation are orthogonal !  Suppression factors multiplicative 3.3·10-3 survival

  20. Conclusions • LAr does not deteriorate resolution of p-type crystals • Experimental data shows that • LAr veto is a powerful method for background suppression • No relevant loss of 0ßß signal • Results will be improved in larger setup @LNGS • MaGe simulations reproduce well the data • Work in progress

More Related