Towards kg-scale Ultra-Low-Energy Ultra-Low-Background Ge Detector Starting Points (Collaboration ; Laboratories ; Scientific Program) Potential Physics with ULE-ULB-Ge Lessons and Experience from ULE-ULB-Ge Prototypes Status & Plans & Discussions @ Henry T. Wong Academia Sinica , Taiwan. Canberra-Eurisys, Lingolsheim, Sept 2006

Objectives for this Visit : Establish stronger collaborating relationships. US : learn the technologies and future evolution in details Canberra : understand/comment on our special needs and plans & how we use the detectors Learn status of segmented 20 g and discuss how to use it optimally for our goals. Discuss various aspects of possible scale-up to O(1 kg) : how realistic, how much, how long, how to fund …. Etc. Personal scientific curiosity …..

Leading government-funded basic research organization in Taiwan physical & biological sciences, humanities in ~30 institutes Like Max Planck Institutes in a centralized campus. One of the biggest institutes in AS ; ~ 300+ staff with ~40 research faculties Work on nano-science, biophysics, complexities & nuclear+particle physics

Program: Low Energy Neutrino & Astroparticle Physics TEXONO Collaboration Taiwan EXperiment On NeutrinO Collaboration : Taiwan (AS, INER, KSNPS, NTU) ; China (IHEP, CIAE, THU, NJU) ; Turkey (METU) ; India (BHU) ; USA (UMD) Program: Low Energy Neutrino & Astroparticle Physics Kuo-Sheng (KS) Reactor Neutrino Laboratory (Taiwan)  Neutrino properties & interactions ; Axion Searches Yang-Yang Underground Laboratory (S. Korea) [with KIMS Coll.]  Dark Matter Searches Diversified R&D Projects Trace Radiopurity Techniques with AMS Sonoluminescence ………

Extended collaboration ~30 people Part of the group at AS Extended collaboration ~30 people

 Poineering Efforts : “Zero-Background Experiment” ! KS Expt: 1st large-scale particle physics experiment in Taiwan TEXONO Coll. : 1st big research Coll. % Taiwan & China 

Kuo-Sheng Nuclear Power Plant KS NPS-II : 2 cores  2.9 GW KS n Lab: 28 m from core#1

Kuo Sheng Reactor Neutrino Laboratory Front Gate Front View (cosmic vetos, shieldings, control room …..) Configuration: Modest yet Unique Flexible Design: Allows different detectors conf. for different physics Inner Target Volume

Shielding Structures : Schematics

Reactor Neutrino Interaction Cross-Sections mass quality Detector requirements R&D : Coh. (nN) T < 1 keV Results : mn(ne) T ~ 1-100 keV On-Going Data Taking & Analysis SM s(ne) T > 2 MeV 1 counts / kg-keV-day

KS Expt: Period I,II,III Detectors ULB-HPGe [1 kg] CsI(Tl) Array FADC Readout [16 ch., 20 MHz, 8 bit] Multi-Disks Array [600 Gb]

Achieved:  A 10-keV threshold kg-scale experiment at reactor site with “cpd”-background comparable to underground lab. Evidence of cosmic-ray activation through various Ga-decays

Magnetic Moment Searches : Highlights simple compact all-solid design : HPGe (mass 1 kg) enclosed by active NaI/CsI anti-Compton, further by passive shieldings & cosmic veto TEXONO data (571/128 days) ON/OFF) [PRL 90, 2003 ; hep-ex/0605006] background comparable to underground CDM experiment : ~ 1 day-1keV-1kg-1 (cpd) DAQ threshold 5 keV analysis threshold 12 keV mn(ne) <7.2 X 10-11 mB (90% CL) [preliminary]

Next Goals: Develop 1) kg-scale experiment at 2) 100-eV threshold at the 3) same cpd-background level Scientific subjects: 1) first obseravtion of nN coherent scattering ; 2) Dark Matter searches at low-mass range ; 3) improve on magnetic moments First choice of Detector Technology : Ge  1) built on existing experience ; 2) LN2 instead of He temperature ; 3) more matured (??) at industry for scale-up.

Neutrino-Nucleus Coherent Scattering : Expected Interaction Rates at KS @ different Quenching Factors for Ge e.g. at QF=0.25 & 100 eV threshold Rate ~ 11 kg-1 day-1 c.f. nN @ accelerator ~ 1000 ton-1 yr-1 ne-p (water) @ KS ~ 1 kg-1 day-1  nN sensitive region : T < 500 eV  by-product : T>500 eV gives mn(ne)  ~ 10-11 mB at ~ 1 cpd background

TEXONO  KIMS @ Y2L Yangyang Lab (Y2L) [700 m of rock overburden] in S. Korea Install 5 g ULB-ULEGe at Y2L Study background and feasibility for CDM searches may evolve into a full-scale (1 kg) CDM experiment Expected sensitivity Y2L

Quenching Factor Measurement for Ge at CIAE’s 13 MV Tandem Facility: Goals for Oct 06 Run : Get to sub-keV Improve on present sensitivities

“Ultra-Low-Energy” HPGe Prototype ULEGe – developed for soft X-rays detection ; easy & inexpensive & robust operation Prototypes built [Canberra-Meriden] and studied : (I) 5 g at Y2L ; (II) 4 X 5 g at KS ; (III) 10 g at AS Prototype being built [Canberra-Lingolsheim] : segmented 20 g Scale-up options to O(1 kg) in multi-array or integrated form (??) threshold <100 eV after modest PSD ULEGe@KS ULEGe@Y2L

N=1 single element (5 g & 10 g) : Schematics

4 X 5 g N=4 array : Schematics

Segmented 20g : Schematics ♥ Under construction at Canberra-Eurisys

Auto LN2 Refill system for N=4 array Segmented 20 g : larger dewar , single reservoir ; prefer AMI-186 Series

System Schematic Diagram Typical signals: HPGe High gain (0~9keV) HPGe Low gain (0~100keV) CsI(Tl) channel (current signal)

CAEN VME: 4 Channel 12 bit 40 MHz ADC

System configuration Dataset configuration Dataset 1 Dataset 2 Academia Sinica data Dataset 2 Power Plant Data FADC sampling rate (MHz) 20 MHz FADC sampling time (bins / μs) 1800 bins / 90 μs 1424 bins / 71.2 μs Amp#1 Gain Shaping time (μs) 80 12 Amp#2 750 6

ULEGe Calibration Peaks: Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray  random trigger for zero ♥ Would hope to have sub-keV calibration point (HOW ??)

PSD I : Correlate two gains & shaping time sh=6us, high gain sh=12us, super gain

Events near threshold sh=6us, high gain y-axis sh=12us, super gain x-axis energy=114.7283eV noise energy=137.8089eV signal

PSD II : Correlate with pre-trigger pulse shapes sh=6us, super gain sh=12us, high gain

KS events: signal sh=12us, high gain x-axis sh=6us, super gain y-axis energy=217eV energy=373eV

KS events: noise sh=12us, high gain x-axis sh=6us, super gain y-axis energy=151eV energy=177eV

ULE-HPGe Prototype Results PSD Cut Threshold ~ 100 eV Calibrations by keV lines & “0” from random trigger Single channel readout : PSD by two shaping times & gain Achieved threshold < 100 eV : lowest for bulk radiation detectors ! – at regular background Background measurements under way at KS & Y2L

Intensive studies on sub-keV background Background Measurements & Comparisons Intensive studies on sub-keV background Similar background at KS & Y2L Apparent difference between 5 g & 1 kg due to scaling with surface area instead, reproduced in simulations i.e. background can be ~ O(1 cpd) at > 1 keV range for 1 kg ULEGe in compact array form Intensive studies of sub-keV background under way

Background comparison

Threshold Vs Background Plots AS better electronics noise levels Scale up to compact 1 kg ; understand background source (g/n) ; improved shielding design Improved PSD ; dual-readout coincidence

R&D Program towards Realistic O(1 kg) Size Experiments (both nN & CDM) : measure & study background at sub-keV range at KS & Y2L ; design of active & passive shielding based on this. compare performance of various prototypes devise calibration scheme at sub-keV range measure quenching factor of Ge with neutron beam develop advanced PSD techniques to further suppress noise-edge  reduce threshold studying scale-up options ULEGe-detector Discrete elements Vs segmented Ge dual readout channels to suppress electronic noise keep other detector options open

3X3X5 elements @ 20 g each (i.e. 900 g) Dual readout per element A Possible Design : 3X3X5 elements @ 20 g each (i.e. 900 g) Dual readout per element veto ring  lids 2D Projection 1X1 + ring , dual readout prototype available Oct 06.

Time Scale & Plans : To Demonstrate with segmented 20 g : give 100 eV treshold (after all analysis work), project background ~cpd level at 100-500 eV (with Ge-active-veto) Can submit proposal for 1-kg ULEGe by then (summer 2007 ??) Construction can start as soon as end 2007 depending on a) prototype results; b) AS funding approval ; and c) any flexibilities in staging of construction & payment (to be discussed). Scientific Goals  R&D plans/results were known and viewed with anticipation in the field of neutrino physics presentations in numerous international conferences [WIN05-Delphi ; TAUP05-Zaragoza ; n06-Santa Fe ; ICHEP06-Moscow ; NDM06-Paris ……]

Summary & Outlook Kuo-Sheng Neutrino Lab.: Established & Operational  Modular & Flexible Design ※ Unique HPGe Low Energy Data (@ 10 keV threshold) ※ Bkg Level ~ Underground CDM Expt. Results on mn (Gn)  Other Program under way Future goal : an O(1 kg)+100 eV threshold expt.  observe neutrino-nucleus coherent scattering  perform LE-CDM experiment  improve on magnetic moment sensitivity R&D program pursued : optimization of prototype ULEGe’s @ ~100 eV threshold first background measurement in the 100 eV – 1 keV region investigate scale-up options  Open up a New Detection Channel & New Detector Window

Some Output from 2006/9/1 Discussions : Optimization of detector volume constrained by a) perimeter and b) thickness Constraints : diameter < 85 mm ; thickness < 10 mm Keen to see how to dual-channel-correlation studies work out Try studying pulse shapes of raw pre-amp pulse AFTER AC-coupling Can HV side be a single channel ? i.e. what’re its roles : for PSD or PSD+energy Minimize length to bring out contacts : i.e. prefer no “inland” channels Expect new product in 2007 on electrical-cryo-system that can go below liquid nitrogen temperature.