PICO 60 Results and PICO 40L Status Carsten B. Krauss for the PICO - PowerPoint PPT Presentation

PICO 60 Results and PICO 40L Status Carsten B. Krauss 
 for the PICO Collaboration TAUP 2019, Sept 09 2019 � 1

Outline • PICO 60 • Results • Electron Recoil Rejection • PICO 40L • Summary � 2

PICO 60 • PICO 60 was initially filled with 26.8kg of CF 3 I (PRD 93 , 052014, 2016) • This fill was successful, but limited by anomalous backgrounds • The chamber was subsequently filled with 52.2kg of C 3 F 8 (run 1: 3.3keV threshold, run 2: 2.45keV , blind analysis) • Particulate contamination and the water bu ff er liquid ultimately limited this chamber design • Later, we also learned that neutron backgrounds prevented background free operation for exposures larger than ~1000kg days � 3

Bubble Chambers for Dark Matter • Use moderately superheated liquid with large fluorine content to boost the spin dependent WIMP sensitivity • The bubble chambers stays expanded until the cameras detect a bubble in an image (or a timeout occurs) • Piezoelectric acoustic sensors pick up waveforms that allow to distinguish louder alpha background events from nuclear recoil events � 4

Bubble Chambers for Dark Matter • Use moderately superheated liquid with large fluorine content to boost the spin dependent WIMP sensitivity • The bubble chambers stays expanded until the cameras detect a bubble in an image (or a timeout occurs) • Piezoelectric acoustic sensors pick up waveforms that allow to distinguish louder alpha background events from nuclear recoil events � 4 Phys. Rev. D 100 , (2019) no.5, 052001

Bubble Chambers for Dark Matter • Use moderately superheated liquid with large fluorine content to boost the spin dependent WIMP sensitivity • The bubble chambers stays expanded until the cameras detect a bubble in an image (or a timeout occurs) • Piezoelectric acoustic sensors pick up waveforms that allow to distinguish louder alpha background events from nuclear recoil events � 4 Phys. Rev. D 100 , (2019) no.5, 052001

C 3 F 8 Run 1 Result (SD) The 90% C.L. limit on the SD WIMP-proton cross section from PICO-60 C3F8 plotted in blue, along with limits from PICO-60 CF3I (red), PICO-2L (purple), PICASSO (green), SIMPLE (orange), PandaX-II (cyan), IceCube (dashed and dotted pink), and SuperK (dashed and dotted black). The indirect limits from IceCube and SuperK assume annihilation to τ leptons (dashed) and b quarks (dotted). � 5 Phys.Rev.Lett. 118 (2017) no.25, 251301

C 3 F 8 Run 2 Result (SD) 90% C. L. limit on the SD WIMP proton cross section from the profile likelihood analysis of the PICO-60 C 3 F 8 combined blind exposure plotted in thick maroon, along with limits from the first blind exposure of PICO-60 C 3 F 8 (thick blue), as well as limits from PICO-60 CF 3 I (thick red), PICO-2L (thick purple), PICASSO (green band), SIMPLE (orange), XENON1T (gray), PandaX-II (cyan), IceCube (dashed and dotted pink), and SuperK (dashed and dotted black). The indirect limits from IceCube and SuperK assume annihilation to τ leptons (dashed) and b quarks (dotted). � 6 Phys.Rev. D100 (2019) no.2, 022001

PICO 60 Complete Exposure • The new results is improved by • Lower threshold (3.3 keV ➝ 2.45 keV) • Better understanding of the threshold by careful analysis of years of calibration data • The PICO 60 detector was ultimately limited by backgrounds and made space for PICO 40L � 7

ame device, beg PICO 60 PICO 40L • PICO 60 was limited by “small” pressure vessel that allowed backgrounds to enter the chamber • The bu ff er liquid and particulate contamination also created hard to reject recoil like events • To address this, PICO 40L is turned “right-side-up” to eliminate the bu ff er liquid and collect possible dust contaminants in the inactive region. PICO 40L also has a much larger pressure vessel to reduce the impact of external backgrounds • This design requires extra cooling systems in the lower part of the detector 8

ame device, beg PICO 60 PICO 40L 8

ame device, beg PICO 60 PICO 40L Superheat Cold 8

ame device, beg PICO 40L • The detector is filled with active liquid and fully instrumented • Currently in commissioning • Regular data taking will start in Fall 2019 9

PICO 40L construction • Jan - April 2019 � 10

First Bubble! • The detector was brought to temperature and the first bubbles were recorded • Temperature control trigger systems still need to be fully commissioned in the coming weeks/months � 11

Expected PICO40L sensitivity • Exploring parameter space below the Xe CE ν NS cross section (grey area) � 12

Post PICO 40L Plans • With a hydrogenated liquid for PICO 40L (after the C 3 F 8 program is complete) we can extend the range of bubble chambers to much lower masses � 13

Summary • PICO has operated 3 generations of bubble chambers since 2012 • We have been able to constantly improve the sensitivity towards spin depended dark matter with C 3 F 8 as target • PICO 40L will improve the reach once again • PICO 500 is starting to be constructed in 2020 
 ➞ see A. Noble’s talk tomorrow � 14