Overview of GERDA simulation activities with MaGe Luciano Pandola INFN, Laboratori del Gran Sasso MaGe Joint Workshop, Munich, January 2010

Main activities in GERDA that are using MaGe Simulation of the main GERDA set-up (Phase I, Phase II, with segmented/BEGes) Total expected background rate and spectrum Many contributions to be taken into account (require a coherent approach and infrastructure) Calibration system Activity and position of calibration sources Pulse shape simulation Study expected background rejection performances, provide realistic “data” to test reconstruction algorithms Test stands and prototypes Interpretation of data and validation of simulations BeGes (Hd, LNGS, Zurich) and segmented (Munich) Some topics will be described in dedicated talks

GERDA geometries selectable in MaGe - 1 Top muon veto Neck Cryostat Water tank Detector array Directory /gerdageometry Used to simulate the main GERDA setup all infrastructure in place water tank, cryostat, detector array, holders Detector array can be customized in number, type and size of crystals (can be set individually) within the 95 positions available: any combination of segmented, BeGes, non-coax, natGe, enrGe and dimensions (provide they are not too big!)

GERDA geometries selectable in MaGe - 2 Directory /munichteststand Contains about 20 geometries for test stands and screening facilities at Munich, LNGS, Heidelberg and Hades Work performed for data interpretation (e.g. with BEGes) and Monte Carlo validation (e.g. Munich prototypes)

GERDA output schemes The directory /gerdaio contains 12 GERDA specific output schemes Most of them are ROOT-based (+ possibly ASCII outputs) 3 output schemes are related to the main GERDA setup change for the amount/type information they store (radioactive isotopes, neutrons, all hits) Other schemes to be used with tests stands and other GERDA geometries some of them are general enough to be used with other geometries, e.g. file-based geometries tools to dump hit information on ASCII files  interface to external software for pulse shape simulation

MCC2 Campaign - 1 Simulations run for Phase I and Phase II arrangements Phase II array contains: 8 enrGe unsegmented detectors (HdM-IGEX), 14 enrGe 18-fold segmented detectors and 8 natGe unsegmented detectors (GTF) Phase I array has HdM-IGEX-GTF. Individual dimensions considered. Main contributions of energy depositions in crystals: Contamination of materials Neutrons-induced Muon-induced Various physics processes contributing to the energy spectrum are simulated using MaGe

MCC2 Campaign - 2 Final goal: get expectation of full energy spectrum of both phases of GERDA (rate & shape) can also be used “a posteriori” (with a fit) to evaluate contaminations of materials Assumptions: Core and segment thresholds = 10 keV Resolution: 2.5 keV FWHM at 1.332 MeV GTF detectors are considered only for anti-coincidence (not for the energy spectrum) Need to keep track of (many) individual contributions, each with parameters, as half-lifes, activities, etc. ( NEST)

Example: 0nbb decay 0nbb decay of 76Ge in the active volume and dead layer for Phase I and II arrays. Spectrum in the assumption of DBD mediated by massive Majorana neutrinos. Dead layer: 0.8 mm for p-type detectors and negligible for n-type For T1/2 = 1.2 · 1025 y (KK) active volume dead layer bck goal Signal efficiency vs. anti-coincidence cuts (Phase II array) No cuts: 92.0% Det anti-coinc: 91.3% Seg anti-coinc: 87.2%

Example: Prompt m-induced background Prompt m-induced background simulated again with MaGe in the MCC2 framework (Phase I & II). Derived info for new estimate of m-induced delayed background (e.g. 77mGe, 38Cl) Notice: the previous simulation [NIM A 570 (2007) 149] run with different geometry. Used MUSUN to simulate explicitely energy-angle correlation No cut Segment anti-c Results qualititatively consistent with the previous work. For Phase II (at Qbb): 9·10-3 counts/(keV·kg·y) without cuts and 4·10-4 counts/(keV·kg·y) with segment anti-coincidence. Cherenkov veto needed and allows for < 10-5 counts/(keV·kg·y)

Example: n-induced background Water buffer absorbs effectively all external neutrons: main contribution comes from neutrons produced in the setup (specifically, the stainless-steel cryostat!). Global limit to bck from external neutrons: 10-7 cts/(keV·kg·y) nuclear recoils (n,n’g) 1000 kg·y exposure Spectrum due to interactions of n from cryostat Prompt background at Qbb: 7·10-6 cts/(keV·kg·y) with no cut. Reduction by factor of 4 by segment anti-coincidence

Other applications: background from 222Rn in LAr Measurements of the 222Rn cryostat emanation triggered a new Monte Carlo campaign for the background estimate  simulated effect of 222Rn daughters (214Bi and 214Pb) for the Phase I & II arrays Phase II array [uniform 222Rn distribution]: 214Bi no cut 214Pb no cut segmentation segmentation Segmentation cut: factor ~2 at Qbb

Conclusions GERDA Monte Carlo group (aka TG10) uses/develops MaGe as the main simulation tool main GERDA set-up precisely coded, with proper shapes and dimensions customizable in terms of shape, number and dimensions of detectors also many test-stands and prototypes available in MaGe used for data analysis and MC validation other home-made codes used for cross-check and/or as quicker solutions for intensive jobs Ongoing simulations to produce: full background spectrum (not only at Qbb) requires infrastructure to keep track of individual contribution pulse shapes for candidate Phase II detectors