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

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Outline

• PICO 60
• Results
• Electron Recoil Rejection
• PICO 40L
• Summary

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PICO 60

• PICO 60 was initially filled with 26.8kg of CF3I

(PRD93, 052014, 2016)

• This fill was successful, but limited by

anomalous backgrounds

• The chamber was subsequently filled with

52.2kg of C3F8 (run 1: 3.3keV threshold, run 2: 2.45keV, blind analysis)

• Particulate contamination and the water buffer

liquid ultimately limited this chamber design

• Later, we also learned that neutron

backgrounds prevented background free

• peration for exposures larger than ~1000kg

days

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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

• Phys. Rev. D 100, (2019) no.5, 052001

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

• Phys. Rev. D 100, (2019) no.5, 052001

4

C3F8 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).

Phys.Rev.Lett. 118 (2017) no.25, 251301

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C3F8 Run 2 Result (SD)

90% C. L. limit on the SD WIMP proton cross section from the profile likelihood analysis of the PICO-60 C3F8 combined blind exposure plotted in thick maroon, along with limits from the first blind exposure of PICO-60 C3F8 (thick blue), as well as limits from PICO-60 CF3I (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).

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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

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ame device, beg

PICO 60 PICO 40L

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• PICO 60 was limited by “small” pressure vessel that allowed

backgrounds to enter the chamber

• The buffer 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 buffer 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
• f the detector

ame device, beg

PICO 60 PICO 40L

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ame device, beg

PICO 60 PICO 40L

Superheat Cold

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PICO 40L

• The detector is filled with active

liquid and fully instrumented

• Currently in commissioning
• Regular data taking will start in Fall

2019

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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 CEνNS cross

section (grey area)

12

Post PICO 40L Plans

• With a hydrogenated liquid for PICO 40L (after the C3F8

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 C3F8 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

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