The Mainz LXe TPC MC simulations for a Compton scattering experiment

Transcription

1 The Mainz LXe TPC MC simulations for a Compton scattering experiment Pierre Sissol Johannes Gutenberg Universität Mainz 12 November / 24

2 Outline 1 Dark Matter 2 Principle of a dual-phase LXe TPC 3 The Mainz LXe TPC 4 MC simulations for a Compton scattering experiment 5 Summary and Outlook 2 / 24

3 Hints to a new kind of matter "discovery": galaxy dynamics in COMA Cluster "Es ist natürlich möglich, dass leuchtende plus dunkle (kalte) Materie zusammengenommen eine bedeutend höhere Dichte ergeben,..." Fritz Zwicky, 1933 galaxy rotation curves Cosmic Microwave Background (CMB) and cosmology Temperature Fluctuations [µk 2 ] Multipole moment l Angular Size 3 / 24

4 The WIMP as DM candidate Properties of Dark Matter: non-baryonic (from primordial nucleosynthesis and cosmological models) high mass GeV c 2 TeV c 2 gravitational and (hopefully) weak interaction no SM particle can fulfill requirements (mass, interaction) candidate: Weakly Interacting Massive Particle SUSY provides us "automatically" with a stable particle with WIMP properties simulations suggest that galaxies are located in large halos of Dark Matter 4 / 24

5 Searching for DM Direct Detection f χ f χ χ χ Production in colliders Indirect Detection f f χ f χ f XENON100 5 / 24

6 Principle of a dual-phase LXe TPC Scattering of a WIMP in LXe leads to excitated and ionized Xe atoms Xe and Xe + + free e LXe scintillation: de-excitation of Xe excimers Xe 2 Xe is transparent to scintillation light LXe ionization: e drift upwards in electric field extraction into gas phase and proportional scintillation example: XENON100 TPC with 3D resolution 6 / 24

7 Background discrimination background discrimination is crucial for DM search 7 / 24

8 Motivation for Mainz experiment understanding of Xe scintillation and ionization signals for low-energy deposits necessary to improve background discrimination in LXe TPC experiments also: examination of pulse shape discrimination possibility? Bottom line: We need a small TPC which can probe low-energy Xenon scintillation for scintillation and ionization yield measurements 8 / 24

9 Setup in Mainz idea: use small scatter volume with high light yield and 3D-position reconstruction (background discrimination) size: 55 mm in diameter only 2 PMTs (one TOP, one BOTTOM) 8 APDs for x-y resolution minimized amount of passive materials prototype of flexible PCB electric field cage 9 / 24

10 Dark Matter 2-phase LXe TPC The Mainz LXe TPC Simulations on Compton scattering Summary and Outlook Electric field cage Motivation: uniform electric field with minimal passive materials design and development during diploma thesis flexible printed circuit board choice of materials depending on surrounding holding structure / handling / environment / cleanliness SMD resistors with 100 MΩ currently in testing phase 10 / 24

11 Outline of simulation topics Implemented setup and source energies Angular uncertainty Doppler broadening Comparison of potential secondary detectors Background 11 / 24

12 Implemented setup source hν [kev] 22 Na ,5 137 Cs 661,6 60 Co 1173,2 1332,5 88 Y 897,5 1836,6 gamma ray source in collimator TPC in cryostat and vacuum chamber secondary detector to measure scattered gamma rays 12 / 24

13 Angular uncertainty deviation from TPC center (3D) deviation from detector center (3D) LXe TPC θ real difference between θ real and θ nom simulation smearing source d s θ nom y [mm] average error d LXe-Det detector x [mm] average error in measuring x-y coordinates with APDs (simulation) 13 / 24

14 Doppler broadening E free = E 0 1+ E 0 mc2 (1 cos θ) calculated deposited energy: E Calc = E 0 E free broad energy spectrum due to bound and moving electrons electron momentum distribution leads to energy distribution source energy E 0 = kev, scattering energy E nom = 60 kev p z = pγ p electron p γ Modified Compton formula: p z = mc E 0 E E 0E mc 2 (1 cos θ) E0 2 + E 2 2E 0 E cos θ 14 / 24

15 Doppler broadening (0,0) 15 / 24

16 Doppler broadening vs angular uncertainty (NaI) scattering energy E =20 kev scattering energy E =100 kev Anzahl der Ereignisse normiert auf 100 % 100 Dopplerverbreiterung Detektor bei 30 cm Detektor bei 60 cm (E - E calc ) / E real calc Anzahl der Ereignisse normiert auf 100 % 100 Dopplerverbreiterung Detektor bei 30 cm Detektor bei 60 cm (E - E calc ) / E real calc source energy E 0 =661.6 kev 16 / 24

17 Real energies in NaI scintillator E 0 [kev] ,6 E nom [kev] θ nom [ ] θ nom [ ] 2 5,08 1, ,83 10,27 Anzahl der Ereignisse n source energy E 0 =1836 kev 2 kev 10 kev 20 kev 50 kev 100 kev 50 source energy E 0 =511 kev reale Streuenergie E [kev] real Anzahl der Ereignisse n kev 10 kev 20 kev 50 kev 100 kev reale Streuenergie E [kev] real 17 / 24

18 Comparison of potential secondary detectors NaI scintillator: + easy handling + fast signal ( 250 ns) low probability of coincidences + low costs poor energy resolution of 5-10 % measurement by angular position Doppler broadening and size have influence on performance Ge detector: requires cryo-cooling inflexible handling large time uncertainty ( µs) coincidences higher costs + very good energy resolution of % (FWHM) + direct energy measurement possible + large detector sizes still feasible (reduces number of setup configurations) 18 / 24

19 Comparison of secondary detectors scattering energy E =20 kev scattering energy E =100 kev Anzahl der Ereignisse normiert auf 100 % 100 Ge-Detektor NaI-Szintillator Dopplerverbreiterung (E - E ) / E real calc calc Anzahl der Ereignisse normiert auf 100 % 100 Ge-Detektor NaI-Szintillator Dopplerverbreiterung (E - E ) / E real calc calc source energy E 0 =661.6 kev 19 / 24

20 Signal and background signal: all events that are evaluated as single-scatter events in the experiment (take into account measuring accuracy) E Xe + E Ge = E 0 background: all non-signal events that are detected and can not be ruled out E Xe + E Ge E 0 20 / 24

21 Summary & Outlook Mainz TPC: better understanding of background in Dark Matter experiments with Xenon new technological features, as for example usage of APDs for S2 detection and PCB as electric field cage (R&D) simulations on Compton scattering experiment: analyzing energy resolution decision for Germanium detector information about expected event rate estimation of expected signal-to-background started my PhD in August: "Study of the low-energy response of nuclear recoils in liquid xenon for Dark Matter applications" at the moment: ; ongoing improved tests of PMTs/APDs and fieldcage development of CSP for the APDs/comparison with commercial ones TPC design finished, manufacturing in the Workshop started first tests planned for beginning of 2013 further members of the MainzTPC project: U. Oberlack, C. Grignon, R. Othegraven, B. Beskers, T. Jennewein, E. Kjartansson, M. Morbitzer 21 / 24

22 Pierre Sissol ETAP Seminar 11 November 2012 Questions? Thanks to my collaborators in the XENON Mainz group 22 / 24

23 23 / 24

24 References NASA / WMAP Science Team MPE/V.Springel Griest, K. und Kamionkowski, M.: Supersymmetric dark matter. Physics Reports, : , Websites of CERN (LHC), PAMELA and XENON Aprile, E. und Doke, T.: Liquid Xenon Detectors for Particle Physics and Astrophysics. Rev.Mod.Phys., 82: , XENON100 Collaboration: E. Aprile et al.: Dark Matter Results from 225 Live Days of XENON100 Data. arxiv: [astro-ph.co] Phys. Rev. Lett. 107, (2011): E. Aprile et al. (The XENON100 Collaboration) Bastian Beskers [priv. comm.] 24 / 24