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

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 Scientists @ 27 Institutions Jacques Pienaar, jpienaar@uchicago.edu 2

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 Jacques Pienaar, jpienaar@uchicago.edu 3

Ideal for WIMP (and Dual Phase Time rare process) Searches Projection Chambers Fiducialization and Surface Bkg Suppression Full 3D reconstruction of interaction Suppression of 𝛿 / β backgrounds Discrimination between ER/NR events Low energy threshold Sensitivity Sub-keV energy threshold Scalable to multi-tonne low Larger Exposures Sensitivity background detectors XENON1T Instrument Paper Jacques Pienaar, jpienaar@uchicago.edu 4 Eur. Phys. J. C (2017) 77: 881

Backgrounds Reduce through S2/S1 Electronic Recoil (ER) 𝛿 , β Backgrounds discrimination Surface Homogeneous NR Neutrons CE ν NS Accidental Nuclear Recoil (NR) Other Surface ( 210 Pb) Coincidence WIMP signal, neutrons, ER 85 Kr, 222 Rn Materials ( 𝛿 , β ) CE ν NS Reduce by fiducializition !! WIMP-Like Background !! 8 B Solar neutrino signal looks like a 6 GeV WIMP arXiv:1604.03858 Jacques Pienaar, jpienaar@uchicago.edu 5

Backgrounds Surface Homogeneous JCAP04 (2016) 027 NR Neutrons CE ν NS Accidental Other Surface ( 210 Pb) Coincidence ER 85 Kr, 222 Rn Materials ( 𝛿 , β ) Induce NR 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. Jacques Pienaar, jpienaar@uchicago.edu 6

Backgrounds Surface Homogeneous NR Neutrons CE ν NS Accidental Other Surface ( 210 Pb) Coincidence ER 85 Kr, 222 Rn Materials ( 𝛿 , β ) Degraded Reconstruction Origin • From plate out of 210 Pb on PTFE walls of 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

https://github.com/XENON1T/pax Backgrounds Surface Homogeneous NR Neutrons CE ν NS Accidental Other Surface ( 210 Pb) Coincidence ER 85 Kr, 222 Rn Materials ( 𝛿 , β ) 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 8

Backgrounds Surface Homogeneous NR Neutrons CE ν NS E lectronic R ecoils Accidental Other Surface ( 210 Pb) Coincidence N uclear R ecoils ER 85 Kr, 222 Rn Materials ( 𝛿 , β ) Induce ER Induced ERs, [1.4-15keV ee ], with diffused Rn220 calibration Induced NRs,[5-50keV R ],with neutron source/generators 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) Jacques Pienaar, jpienaar@uchicago.edu 9

Backgrounds Surface Homogeneous NR Neutrons CE ν NS Accidental Other Surface ( 210 Pb) Coincidence ER 85 Kr, 222 Rn Materials ( 𝛿 , β ) Induce ER (0.17 ± 0.01) events / (tonne·day·keV ee) in 1300 kg FV WIMP search region: (82 -6+8 ) events / (tonne·yr·keV ee ) Origin • From contaminants in the liquid Xe Of which: target ~8 events / (tonne·yr·keV ee ) from 85 Kr ~56 events / (tonne·yr·keV ee ) from 214 Pb (inferred from Bi-Po Mitigation time coincidences) • 85 Kr : remove by distilling the xenon down to sub-ppt concentrations of nat Kr/Xe • 222 Rn: Selecting radiopure material and with as low Rn emanation as possible • S2/S1 discrimination Jacques Pienaar, jpienaar@uchicago.edu 10

Background Prediction 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 CE ν NS 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 3.56 1.70 1.16 (200GeV) Data 739 14 2 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 11

SR0+SR1 Combined Results Energy Space ER Background NR Referecence Region 200 GeV WIMP Signal Surface Background • 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 cm 2 ) Jacques Pienaar, jpienaar@uchicago.edu 12

SR0+SR1 Combined Results Spatial Distribution • 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 222 Rn bkg Jacques Pienaar, jpienaar@uchicago.edu 13

SR0+SR1 Combined Results Spin Independent Limits Phys. Rev. Lett. 121 , 111302 • Safeguard to protect against spurious mis-modeling of backgrounds • No significant >3 σ excess • Background only hypothesis is accepted although the p-value of ~0.2 at high mass (200 GeV and above) does not disfavor a signal hypothesis either Jacques Pienaar, jpienaar@uchicago.edu 14

SR0+SR1 Combined Results Spin Dependent Limits 10 − 36 10 − 36 10 − 37 10 − 37 χ n [cm 2 ] χ p [cm 2 ] ) 6 1 0 2 ( 0 0 1 N O N E X 10 − 38 10 − 38 WIMP-neutron σ SD WIMP-proton σ SD ) 8 1 0 2 ( I I - X a d n a P ) 6 1 0 XENON1T (1 t × yr, this work) 2 ( 0 LUX (2017) 0 1 10 − 39 N 10 − 39 O N E X ) 8 1 0 2 ( PICO-60 (2019) I I - X a d 10 − 40 10 − 40 n a P XENON1T (1 t × yr, this work) LUX (2017) 10 − 41 10 − 41 10 − 42 10 − 42 10 1 10 2 10 3 10 1 10 2 10 3 WIMP mass [GeV/c 2 ] WIMP mass [GeV/c 2 ] arXiv:1902.03234 Axial-vector mediator CMS (2018) Dirac WIMP • Same event selection criteria and event corrections as Mediator mass [GeV/c 2 ] ATLAS (2018) g q =0.25, g χ =1.0 10 3 applied to SI search • Most stringent limit on WIMP-Neutron scattering cross X E N O N 1 T PICO-60 (2017) section • Exclude new parameter space in isoscalar theory with axial- vector mediator 10 2 10 1 10 2 10 3 10 4 Jacques Pienaar, jpienaar@uchicago.edu 15 WIMP mass [GeV/c 2 ]

SR0+SR1 Combined Results Pion Coupling Phys. Rev. Lett. 122 , 071301 • 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 16

XENONnT 1 x4 10 x Minimal Upgrade Fiducial Xe Target Background Fast Turnaround Identified strategies to Use XENON1T sub- XENONnT TPC The XENON1T e ff ectively reduce 222 Rn systems, already tested features: infrastructure and sub- by ~ a factor 10 . systems were designed total Xe mass = 8 t Fast pace: Decrease neutron to accommodate a target mass = 5.9 t Installation summer 2019, 
 background thanks to larger TPC . commissioning by end fiducial mass = ~4 t new active neutron veto. 2019 Jacques Pienaar, jpienaar@uchicago.edu 17

Backup Slides Jacques Pienaar, jpienaar@uchicago.edu 18

Combined Data Set Jacques Pienaar, jpienaar@uchicago.edu 19

Energy Resolution Jacques Pienaar, jpienaar@uchicago.edu 20

Calibration Fits Rn220 AmBe NG Jacques Pienaar, jpienaar@uchicago.edu 21

Model/Data Comparison Jacques Pienaar, jpienaar@uchicago.edu 22

Lone S1/S2 Rate Jacques Pienaar, jpienaar@uchicago.edu 23

Electron Lifetime Jacques Pienaar, jpienaar@uchicago.edu 24

Light/Charge Yield Stability Jacques Pienaar, jpienaar@uchicago.edu 25

Future Sensitivities of LXe Detectors Jacques Pienaar, jpienaar@uchicago.edu

XENON Infrastructure Cryogenics & Purification Muon Veto DAQ & SC Kr distillation Cryostat & LXeTPC column & Xe Analytics Xe Storage & Recovery www.xenon1t.org Jacques Pienaar, jpienaar@uchicago.edu