XENON1T 1 Tonne-year of Exposure Jacques Pienaar Recontres de - - PowerPoint PPT Presentation

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XENON1T 1 Tonne-year of Exposure Jacques Pienaar Recontres de Moriond University of Chicago Electroweak Session Kavli Institute of Cosmological Physics March 16-23, 2019 On Behalf of the XENON Collaboration XENON Collaboration ~160

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SLIDE 1

XENON1T

1 Tonne-year of Exposure

Jacques Pienaar University of Chicago Kavli Institute of Cosmological Physics On Behalf of the XENON Collaboration Recontres de Moriond Electroweak Session March 16-23, 2019

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SLIDE 2

XENON Collaboration

~160 Scientists @ 27 Institutions

2 Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 3 3 Jacques Pienaar, jpienaar@uchicago.edu

Dual Phase Time Projection Chambers

Full 3D reconstruction of interaction Discrimination between ER/NR events Sub-keV energy threshold Scalable to multi-tonne low background detectors

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SLIDE 4 4 Jacques Pienaar, jpienaar@uchicago.edu

Dual Phase Time Projection Chambers

Full 3D reconstruction of interaction Discrimination between ER/NR events Sub-keV energy threshold Scalable to multi-tonne low background detectors

Ideal for WIMP (and rare process) Searches

Fiducialization and Surface Bkg Suppression Suppression of 𝛿/β backgrounds Low energy threshold Sensitivity Larger Exposures Sensitivity

XENON1T Instrument Paper

  • Eur. Phys. J. C (2017) 77: 881
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SLIDE 5

Surface Homogeneous NR Neutrons CEνNS Other Surface (210Pb) Accidental Coincidence ER Materials (𝛿, β)

85Kr, 222Rn

Reduce by fiducializition Reduce through S2/S1 discrimination

5

!! WIMP-Like Background !!

Backgrounds

Jacques Pienaar, jpienaar@uchicago.edu

arXiv:1604.03858

8B Solar neutrino signal looks like a 6 GeV WIMP

Electronic Recoil (ER)

𝛿,β Backgrounds

Nuclear Recoil (NR)

WIMP signal, neutrons, CEνNS

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SLIDE 6

Surface Homogeneous NR Neutrons CEνNS Other Surface (210Pb) Accidental Coincidence ER Materials (𝛿, β)

85Kr, 222Rn

Backgrounds

6

Origin

  • Materials
  • Environment
  • Cosmic rays

Mitigation

  • Reject multiple scatter events
  • Cosmogenic events tagged using muon

veto

  • Passive water shielding
  • Fiducialization
  • Use detected multiple scatter NR

events and MC to constrain bkg.

JCAP04 (2016) 027

Induce NR

Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 7

Surface Homogeneous NR Neutrons CEνNS Other Surface (210Pb) Accidental Coincidence ER Materials (𝛿, β)

85Kr, 222Rn

Backgrounds

Degraded Reconstruction

Origin

  • From plate out of 210Pb on PTFE walls
  • f TPC
  • Some of charge quanta are lost,

reducing S2 size

  • Results in event being shifted into NR

band. Mitigation

  • Data driven background model used to

develop PDF for likelihood

Jacques Pienaar, jpienaar@uchicago.edu 7
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SLIDE 8

Surface Homogeneous NR Neutrons CEνNS Other Surface (210Pb) Accidental Coincidence ER Materials (𝛿, β)

85Kr, 222Rn 8

Backgrounds

https://github.com/XENON1T/pax

Degraded Reconstruction

Origin

  • Random pairing of lone S1 and S2

signals

  • Accidental pairing of small S1 and S2

signals produce events reconstructed within the search region Mitigation

  • PDF derived from data and used in

likelihood estimation

Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 9 9

Backgrounds

Origin

  • Environment
  • Detector Materials

Mitigation

  • Use ultra-pure materials as well as

passive water shielding

  • Reject multi-hit events (for 𝛿)
  • Fiducialization
  • Reject through S2/S1 (50% NR

acceptance for >99.75% ER rejection) Surface Homogeneous NR Neutrons CEνNS Other Surface (210Pb) Accidental Coincidence ER Materials (𝛿, β)

85Kr, 222Rn

Induce ER

Nuclear Recoils Electronic Recoils

Induced ERs, [1.4-15keVee], with diffused Rn220 calibration Induced NRs,[5-50keVR],with neutron source/generators

Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 10 10

Backgrounds

Origin

  • From contaminants in the liquid Xe

target Mitigation

  • 85Kr : remove by distilling the xenon

down to sub-ppt concentrations of

natKr/Xe
  • 222Rn: Selecting radiopure material and

with as low Rn emanation as possible

  • S2/S1 discrimination

Induce ER

Surface Homogeneous NR Neutrons CEνNS Other Surface (210Pb) Accidental Coincidence ER Materials (𝛿, β)

85Kr, 222Rn

(0.17 ± 0.01) events / (tonne·day·keVee) in 1300 kg FV WIMP search region: (82-6+8) events / (tonne·yr·keVee) Of which: ~8 events / (tonne·yr·keVee) from 85Kr ~56 events / (tonne·yr·keVee) from 214Pb (inferred from Bi-Po time coincidences)

Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 11 11

Mass 1.3t 1.3t 0.9t (S2, S1) Full Reference Reference ER 627 ± 18 1.62 ± 0.3 1.12 ± 0.21 Neutron 1.43 ± 0.66 0.77 ± 0.35 0.41 ± 0.19 CEνNS 0.05 ± 0.01 0.03 ± 0.01 0.02 AC 0.47 +0.27 0.10 +0.06 0.06 +0.03 Surface 106 ± 8 4.84 ± 0.4 0.02 BG TOTAL 735 ± 20 7.36 ± 0.61 1.62 ± 0.28 WIMPs best-fit (200GeV) 3.56 1.70 1.16 Data 739 14 2

Background Prediction

Background models in 4 dimensions: S1, S2, r, z Numbers in table for illustration Statistical inference done with PLR analysis in 1.3t fiducial volume and full (S1,S2) space

Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 12

SR0+SR1 Combined Results

Energy Space

12
  • Events that pass all cuts are shown.Small (single coloured)

charts correspond to unambiguously bkg events. Larger Pie Charts represent larger WIMP probability

  • Events are shown as pie charts showing relative PDF from

each component for the best fit model of a 200 GeV WIMP (σ=4.4⋅10-47 cm2)

Surface Background NR Referecence Region 200 GeV WIMP Signal ER Background

Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 13

SR0+SR1 Combined Results

Spatial Distribution

13
  • Performed unbinned profile likelihood. Model uncertainties

included as nuisance parameters.

  • Maximum radius of FVs set by surface event contributions
  • Corners due to constraining radio-impurity contribution to ER

to be sub-dominant to uniform 222Rn bkg

Jacques Pienaar, jpienaar@uchicago.edu
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SLIDE 14

SR0+SR1 Combined Results

Spin Independent Limits

14
  • Safeguard to protect against spurious mis-modeling of

backgrounds

  • No significant >3σ excess
  • Background only hypothesis is accepted although the p-value
  • f ~0.2 at high mass (200 GeV and above) does not disfavor a

signal hypothesis either

Jacques Pienaar, jpienaar@uchicago.edu
  • Phys. Rev. Lett. 121, 111302
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SLIDE 15

SR0+SR1 Combined Results

15 Jacques Pienaar, jpienaar@uchicago.edu

Spin Dependent Limits

101 102 103

WIMP mass [GeV/c2]

10−42 10−41 10−40 10−39 10−38 10−37 10−36

WIMP-neutron σSD

χn [cm2] LUX (2017) P a n d a X
  • I
I ( 2 1 8 ) X E N O N 1 ( 2 1 6 ) XENON1T (1 t×yr, this work) 101 102 103

WIMP mass [GeV/c2]

10−42 10−41 10−40 10−39 10−38 10−37 10−36

WIMP-proton σSD

χ p [cm2] LUX (2017) P a n d a X
  • I
I ( 2 1 8 ) X E N O N 1 ( 2 1 6 ) PICO-60 (2019) XENON1T (1 t×yr, this work)
  • Same event selection criteria and event corrections as

applied to SI search

  • Most stringent limit on WIMP-Neutron scattering cross

section

  • Exclude new parameter space in isoscalar theory with axial-

vector mediator

101 102 103 104 WIMP mass [GeV/c2] 102 103 Mediator mass [GeV/c2] CMS (2018) ATLAS (2018) PICO-60 (2017) X E N O N 1 T Axial-vector mediator Dirac WIMP gq=0.25, gχ=1.0 arXiv:1902.03234
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SLIDE 16

SR0+SR1 Combined Results

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  • Coupling of WIMP with virtual pion-current between

two nucleons

  • Same featureless falling exponential differential

recoil spectrum as WIMP-nucleon interaction

  • Limit setting performed in same manner as SI

results on 1 tonne-year exposure

Jacques Pienaar, jpienaar@uchicago.edu

Pion Coupling

  • Phys. Rev. Lett. 122, 071301
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SLIDE 17 17 Jacques Pienaar, jpienaar@uchicago.edu

XENONnT

Minimal Upgrade

The XENON1T infrastructure and sub- systems were designed to accommodate a larger TPC.

Fiducial Xe Target

XENONnT TPC features: total Xe mass = 8 t target mass = 5.9 t fiducial mass = ~4 t

Background

Identified strategies to effectively reduce 222Rn by ~ a factor 10. Decrease neutron background thanks to new active neutron veto.

Fast Turnaround

Use XENON1T sub- systems, already tested Fast pace: Installation summer 2019, 
 commissioning by end 2019

x4 10

1

x

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SLIDE 18 18 Jacques Pienaar, jpienaar@uchicago.edu

Backup Slides

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SLIDE 19 19 Jacques Pienaar, jpienaar@uchicago.edu

Combined Data Set

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SLIDE 20 20 Jacques Pienaar, jpienaar@uchicago.edu

Energy Resolution

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SLIDE 21 21 Jacques Pienaar, jpienaar@uchicago.edu

Calibration Fits

Rn220 AmBe NG

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SLIDE 22 22 Jacques Pienaar, jpienaar@uchicago.edu

Model/Data Comparison

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SLIDE 23 23 Jacques Pienaar, jpienaar@uchicago.edu

Lone S1/S2 Rate

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SLIDE 24 24 Jacques Pienaar, jpienaar@uchicago.edu

Electron Lifetime

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SLIDE 25 25 Jacques Pienaar, jpienaar@uchicago.edu

Light/Charge Yield Stability

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SLIDE 26 Jacques Pienaar, jpienaar@uchicago.edu

Future Sensitivities of LXe Detectors

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SLIDE 27 Jacques Pienaar, jpienaar@uchicago.edu

XENON Infrastructure

www.xenon1t.org

Cryogenics & Purification DAQ & SC Xe Storage & Recovery Kr distillation column & Xe Analytics Cryostat & LXeTPC Muon Veto