Detection of Cerenkov light emission in LAr

1. Detection of Cerenkov light emission in LAr Ettore Segreto University of L’Aquila Cryodet International Workshop Laboratori Nazionali del Gran Sasso 13-14 March 2006

2. OUTLINE • Detection of visible light in coincidence with cosmic ray muons in the ICARUS 10m3prototype during a dedicate test run at Gran Sasso Laboratory external facility. • Geometrical features of the 3D reconstructed muons tracks. • Monte Carlo simulation of the detector and of the cosmic muon flux. • Comparison of Data with Monte Carlo results. • Cerenkov radiation in a next generation large mass LAr TPC (?) Cryodet workshop

3. Cryodet workshop Nuclear Instruments and Methods in Physics Research A 516 (2004) 348-363

4. 128 ICARUS 10m3 prototype • The module : • ~ 10m3 of LAr (14 tons). • TPC (2.00m (w) x 3.26m (h) x 0.35m( l) drift length) with two read-out planes: two independent representations of the ionizing event (and possibility of 3D reconstruction). • 2” quartz windowed PMT (EMI 9814BQ) -spectral sensitivity: 160 nm-600 nm- not sensitive to 128 nm LAr scintillation radiation. Cryodet workshop

5. Data sample • The detector was exposed to cosmic ray flux at surface during a complete test (cryogenics, electronic, acquisition system…) held in the external facility (Hall di Montaggio) of LNGS (January-May 2000). • The installation inside the 10m3 LAr volume of the EMI 9814BQ PMT was designed in order to check any possible light emission phenomena, apart from VUV scintillation emission, accompanying ionization processes. • In a limited period during the test run a sub-sample of the collected data have been acquired using the PMT signal as trigger for the detector. In principle, if no visible light emission is registered by the PMT in coincidence with the passage of particles in the liquid, no events are recorded. Indeed, we acquired a large sample of events during this dedicated test, indicating that visible light signals are associated to through-going particles. • About 1200 events produced by single penetrating muons have been selected for the present analysis Cryodet workshop

6. Events selection and reconstruction (I) Collection view Typical event produced by a crossing muon in the 10m3 detector triggered with the internal PMT Induction view Each view of each selected event is linearly fitted to obtain the geometric parameters of the two 2D projections of the event. PMT Cryodet workshop

7. Events selection and reconstruction (II) • The analytic combination of the two 2D projection of the events allows to obtain a complete 3D reconstruction of the muon track: • Entry point in the detector. • Zenith (and Azimuth (angles. Hall di Montaggio Cryodet workshop

8. Geometrical features of selected tracks (I) • The peak position in distributionmeans that muons propagating towards the PMT window are strongly favored, i.e. strong directionality (characteristic of Cerenkov radiation) • The left-right asymmetry(white histogram) is mainly due to the geographycal location of the detector. The presence of the Gran Sasso massif strongly suppresses the cosmic muon flux with larger values of zenith angles (>450) in the region  ~ [2000,3400]. • A cut was applied: only vertical muons are considered (<450) to remove asymmetry (yellow histogram). The residual asymmetry is due to the PMT position, not perfectly symmetric with resepect to the wire chamber Cryodet workshop

9. Geometrical features of selected tracks (II) Track Impact parameter w.r.t. the PMT optical window Most of the events are broadly distributed between 5 cm and 20 cm. The average value is < d > ≈ 10 cm. Cryodet workshop

10. Cerenkov radiation in LAr by cosmic muons. A cosmic muon (z= ±1) in ultra-relativistic regime ( 1) propagating in LAr (n 1.22) radiates visible Cerenkov photons with an angle w.r.t. its direction: The spectrum is continuous: Average number of Cerenkov photons detectable by the installed PMT (160nm-600nm): Cryodet workshop

11. Monte Carlo simulation • Simulation code based on the GEANT 3 package. • Precise description of the geometrical features and of the materials constituting the detector. • Exact spectrum (energy, azimuth and zenith angles) for cosmic muons. • Cerenkov photons production and propagation. • Optical properties of the materials: • Refelectivity of the internal structures (aluminium/stainless steel). • Rayleigh scattering in LAr (and no absorption). • PMT response (Quartz window transmittance and photo-cathode quantum efficiency). Cryodet workshop

12. Real data vs. MC simulation YellowData Red MC The detected light is consistent with Cerenkov radiation emission by cosmic muons. Cryodet workshop

13. From Carlo Rubbia talk Cryodet workshop

14. Single detector: charge imaging, scintillation, Cerenkov light Charge readout plane GAr E ≈ 3 kV/cm LAr Electronic racks Extraction grid E-field E≈ 1 kV/cm Field shaping electrodes UV & Cerenkov light readout PMTs Cathode (- HV) Cryodet workshop

15. Cerenkov photons: additional discrimination Idea: use combination of charge readout and Cerenkov light to determine mass of particle (hep-ph/0402110 A. Rubbia) Drift The track in the LAr TPC + with 500 MeV of kinetic energy Spectrum: 200nm<  <600nm Full GEANT-4 simulation Cryodet workshop

16. Example: / discrimination in beta beams Signal  e   Background  e e The combination of the information from the tracking and calorimetric measurements with the Cerenkov light provides improved particle identification. For example one can separate in this way pions from muons, a very important tool in the context of beta-beams 20% coverage and 20% Q.E. Cryodet workshop

17. Conclusions • Ionizing tracks from cosmic ray muons crossing the ICARUS 10m3 active volume have been collected in coincidence with visible light signals from a PMT immersed in liquid argon. • By means of a detailed Monte Carlo simulation we have shown that the geometrical characteristics of the events are compatible with the hypotesys of Cerenkov light emission as the source of the PMT signals. Cryodet workshop

18. Backup Slides Cryodet workshop

19. Combinig Cerenkov and charge read-out (I) • Non destructive multiple read-out of a LAr TPC allows to reconstruct particle tracks with bubble-chamber quality. • Fine granularity allows precise calorimetric measurements. • Tracking and calorimetry provide momenta, particle identification, clean e/separation … Cryodet workshop

20. Why detect Cerenkov radiation in a LAr TPC of next generation? Electronic crates f≈70 m h =20 m Max drift length Passive perlite insulation A “general-purpose” detector for superbeams, beta-beams and neutrino factories with broad non-accelerator physics program (SN n, p-decay, atm n, …) Cryodet workshop

21. Neutrino detection: LAr TPC vs water Cerenkov Multi prong event detection not possible with water Cerenkov K2K ICARUS 50 liters Cryodet workshop

22. Pion contamination for 90%muon acceptance Cryodet workshop