The XENON Project. M. Selvi The XENON project

Transcription

1 The XENON Project M. Selvi Assemblea di Sezione 2011

2 Dark matter in the Universe

3 Dark matter properties: what we know

4 Direct WIMP search

5 Direct WIMP search

6 Direct WIMP detection

7 Why Xenon?

8 A double-phase Xenon TPC Active veto Gas Xe Liquid Xe 3D localization (millimeter precision) => fiducial volume and single scatters PMTs sum WIMP TPC E S1 Nuclear recoil S2 PMTs TPC e - E PMTs sum S1 time Electronic recoil S2 PMTs Veto (S2/S1) WIMP << (S2/S1) time

9 Localization / discrimination

10 XENON program XENON100

11 XENON100 is watching you 242 PMT 1 x1 Low activity (Hamamatsu R8520) QE 175nm kv 98 PMT top array 80 PMT bottom array -16 kv Veto PMTs

12 XENON100 design 161 kg Xe, 62 kg inside the TPC TPC : diameter 30 cm height 30 cm Drift field : 530 V/cm Téflon around the TPC for the light collection Cryogenic system outside the shield Pulse Tube Refrigerator (160W) Constant recirculation Shield : Lead 20 cm Polyethylene 20 cm Copper 5 cm + Water 20 cm on 4 sides

13

14 XENON 100 Results

15 XENON 100 Results

16 New limit on the SI elastic dark matter live days, 48 kg fiducial mass arxiv: , submitted to PRL preliminary Profile Likelihood method arxiv: Using new Leff measurements (Plante et al, 2011 arxiv: ) WIMP velocity: v 0 = 220 km/s v esc = 544 km/s The best limit on spin independent dark matter to date: cm 2 at 50 GeV/c 2 We start to explore the predicted region for SUSY candidates

17 The next steps: XENON1T

18 XENON1T design

19 XENON1T at LNGS

20 XENON1T time schedule 2011: approval by INFN : construction at LNGS 2014: commissioning : science run

21 The XENON collaboration 60 scientists 13 institutions 9 countries

22 Bologna people and tasks M. Garbini, F.V. Massoli, R. Persiani, G. Sartorelli (PI), M. Selvi 4 FTE Study of the performances of the water shield and muon veto (MC) Test of the PMTs Design and construction of the muon veto system

23 Impegno dei servizi Servizio FTE Periodo Elettronica 0.2 Servizio Tecnico Generale 0.2 Officina Meccanica 0.3 Calcolo e reti 0.1

24 Water shield at LNGS

25 Veto and shield at LNGS 10 m

26 Muon Veto PMTs: 8 Hamamatsu R5912 in the water-proof version. Reflector foil: ER2000MA by 3M, reflectivity 98%.

27 Muon veto Nb PMT >= 3

28 Neutron interactions in LXe LNGS Water shield Phys. List. QGSP_BIC_HP LSM Poly-Pb shield Rate of single scatter, nuclear recoils, in the fiducial volume in [9,45] kev: 0.02 per year 0.09 per year

29 PMT test at Bologna

30 XENON at The Big Bang Theory

31 XENON at The Big Bang Theory

32 XENON at The Big Bang Theory

33 The XENON Project Light on Dark Matter! M. Selvi Assemblea di Sezione 2011

34 A very low and understood background Physical Review D 83, , 2011

35 Spares

36 Dark matter analysis Blind analysis = cuts are defined using only background events outside the WIMP region (below the lower 10% quantile of the electron recoil distribution) + Calibrations Cuts Data quality: - keep period with stable detector operation parameters - remove period with high electronic noise Physical events: - require two-fold coincident S1, - S2>300 pe - reject electronic noise Single scatter: - only one S1 and one S2 - no veto coincidence - S1 PMT hit pattern - S2 PMT hit pattern (good xy reconstruction) Fiducial volume = - event inside the inner volume ( 48 kg) + 1 post-unblinding cut to reject events which passed the two-fold S1 cut only because noise

37 100 live days of data arxiv: , submitted to PRL Background (within the fiducial volume) Nuclear recoil calibration preliminary preliminary 3 physical events in the WIMP search region Bkgd prediction = 1.8+/- 0.6 events => No observation of a WIMP signal 48kg fiducial volume

38 Dark Matter Search

39 Background predictions

40 Detector Calibration Several sources : 137 Cs, 60 Co, 232 Th (gammas) AmBe (neutrons) nuclear recoils + gammas ( 129m Xe, 131m Xe and inelastic scattering) AmBe preliminary preliminary Nuclear recoils/electronic recoils discrimination The discrimination power is ~99.5% at low energies for a 50% neutron acceptance