About the INPA Seminars

All seminars are on Fridays (unless otherwise noted) and start at 12:00 (noon) with a brief presentation of the weekly scientific news. Typically the talks end by 13:00. The seminars take place in Bldg. 50A, room 5132.

The committee members are:

The following Seminar schedule for the Institute for Nuclear and Particle Astrophysics is tentative. The seminar becomes final usually a few days before the Friday of the talk.

If you have questions, comments, or suggestions please contact Paris Gordon at 510-486-4903 pcgordon@lbl.gov

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Speaker: Ann-Kathrin Schutz – Eberhard Karls University of Tubingen

January 31 @ 12:00 pm - 1:00 pm

Title: Full analysis of the background for the search of neutrinoless double beta decay in Gerda

Abstract: The GERmanium Detector Array (Gerda) experiment aims for the discovery of neutrinoless double beta decay (0νββ) decay in 76Ge. It uses HPGe detectors enriched in the isotope 76Ge, which are directly immersed into liquid argon (LAr). In second phase (Phase II) of Gerda, the radio-pure cryogenic liquid acts not only as cooling medium for the detectors and passive shielding but also as active shielding. Phase II started data taking in Dec 2015 with the design goal of increasing the sensitivity to T 0ν1/2 = O1026 yr by reducing the background by one order of magnitude. Due to the active veto system detecting LAr scintillation light, the superior energy resolution and an improved background recognition, the initial release of Phase II already showed a background rate in the energy region of interest (ROI), after pulse shape discrimination (PSD) and liquid argon veto cuts, in the range of a few counts/(ROI·ton·yr). This made Gerda the first 0νββ experiment being background free up to its design exposure of 100 kg·yr. With the latest data release in mid 2018, comprising a total exposure of 82.4 kg·yr, Gerda remained in the background free regime and it is the first experiment to surpass a median sensitivity on the half-life of 1026 yr for 0νββ decay.

In this talk, a full analysis of the background is presented where all available information on the background has been incorporated in order to develop a detailed background model describing the decomposition of the measured energy spectrum. For the first time, the single- and two-detector data have been combined in a multivariate Bayesian fit approach. Additionally, the background model focuses further on two prominent features in the energy spectrum: the α events dominating the high energy part of the spectrum and the count rates of the potassium γ-lines at 1525 keV and 1461 keV. Thanks to the granularity of the detector array, a study of the coincident events in the two-detector data which can provide further information regarding the location of contaminations has been integrated. Using the background model, important information on the main sources and their locations contributing to the background around
the Q-value of the decay (Qββ) can be deduced. Besides, the spectral shape of the total background around Qββ can be extracted. Both are crucial input informations for reliable results on the 76Ge 0νββ signal search.

Details

Date:
January 31
Time:
12:00 pm - 1:00 pm

INPA guests from campus can now come up to the lab early on Fridays. The INPA Common Room (50-5026) is reserved for our guests from 10:00 am to 12:00 noon, and from 1 pm to 5 pm. Note that the seminars are now held in 50A-5132 to accommodate a larger number of attendees.

Also, on Fridays from 1:00 pm to 2:00 pm you are welcome to join the INPA Speaker for a brown-bag lunch in the small Pers Hall conference room, 54-130B.

INPA Tea Series

The Physics and Nuclear Science Divisions have together been leaders in revolutionary changes in our understanding of neutrinos and cosmology. Everyone is welcome to attend the open forum. Tea and light refreshments will be served.

INPA Common Room (50-5026)
Fridays
3:30 pm

Access to the Lab

For a shuttle pass please email Paris Gordon. Please note: the pass is only valid for the day of the seminar.

If you have questions, comments, or suggestions please contact, preferably via email, Paris Gordon.