MEG. Flavio Gatti, Universita e INFN di Genova! DiFi Genova, 12 nov 2013

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1 MEG Flavio Gatti, Universita e INFN di Genova! DiFi Genova, 12 nov 2013

2 Forewords Searches for μ eγ: back to the late 1940 s BR(μ eγ) was naively calculated from μ e ν ν 1960 s: µ eγ did not occur with branching ratios above 10 6 Then: two-neutrino hypothesis and the postulate that there were two lepton flavors, each accompanied by a conserved lepton-flavor number in the decay: μ e ν ē ν μ

3 Why MEG? Neutral Leptons undergo LFV processes in the mixing The established existence of neutrino flavor violation implies that ALL so-called lepton flavor violating processes are also allowed and will occur at some order in perturbation theory.

4 The MEG detector

5 The Muon Beamline

6 The MEG experiment challenges High Intensity DC muon beam (on target) : ~3x10 7 s -1 High precision and High rate e + spectrometer: COnstant Bending RAdius (COBRA) SupC. Magnet at ~1.2T (max) High angle resolution Drift Chambers: ~ 9 mrad actual High e + timing resolution: Timing Counter - 65 ps actual High timing and energy resolution for gammas: LXe scintillating detector High stability: multiple energy and time calibration tools

7 COBRA magnet

8 Drift Chambers

9 Drift Chambers p resolution: 0.33 (80%)+1.5(2%) MeV theta: 9.3 mrad phi: 8.4(80%)+38(30%) mrad Theor. Michel Spectrum Response function Vertex Reconstruction! sigma(y)= 1.1 (86%)+5.3(14%) mm sigma(z)= 2.5 mm! Acceptance

10 Timing Counter 15 2(Upstream/Downstream) plastic scintillator bars (4 4 80cm3) Fine mesh PMTs at both ends, positron timing measurement Positron φ, z position reconstruction using charge-ratio (online) or time-difference timing resolution: 65ps actual (40 bench test at BTF-LNF)

11 LXe gamma Detector Scintillation light from 900 liter liquid xenon is detected by 846 PMTs mounted on all surfaces and submerged in the xenon Fast response (45ns) and high light yield (80% NaI at 175 nm): provide good resolutions of E,Time, Position. Kept at 165K by 200W pulse-tube refrigerators Gas/liquid circulation system to purify xenon to remove contaminants

12 Calibrations

13 Energy, Timing Resolution and Stability Corrected with calibration data

14 Position resolution in LXe with shadows

15 Improvement in run 2011 and in the analysis data! Doubled the statistics Hardware modifications: NaI detector used for calorimeter calibration run was replaced with BGO Laser tracker system for target and drift chamber initial alignment! Improvements of analysis, applied for data! Reconstruction improvements of Physics analysis per-event PDF for e +

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17 Analysis Results 09-11

18 ! MEG limit

19 runs completed in Aug 2013

20 Just a graphical compilation of the expectations plots from two models

21 Mass scale of the LF physics? A. de Gouvea, P. Vogel arxiv: v2

22 MEG2: Upgrade Overview

23 Summary MEG First limits of μ eγ in O(10-13) ( data) Sensitivity : No excess was found Double the statistics Expected sensitivity : ~ Upgrade proposal was accepted, and R&D ongoing More intense beam, double the efficiency and half the resolutions. Expected sensitivity : ~ in 3 years starting from 2016 Un experiment on μ eγ with better sensitivity seem not possible μ eee, μ e (conv.) are presently considered the new pathway for an experimental investigation of LFV processes.

24 Ringraziamenti I Direttori Corvisiero e Squarcia che hanno reso possibile tale attività a Genova. Il personale che ha partecipato attivamente: A. Bevilacqua, D. Bondi*, A. Manco, L. Parodi, F. Siccardi. I servizi Disegno (diretti da Cuneo - Cereseto), Meccanica (Cereseto(?)- Pollovio), Elettronica (Musico) * (nei primi anni)

25 HOLMES-EU Proposta di misura diretta di massa con metodo calorimetrico usando l Ho-163. Finanziata sul gruppo Genova - Mi Bicocca - LNGS per 5 anni, approvata dalla CSNII. Obiettivo: raggiungere un limite sub ev con un dimostratore tecnologico

26 HOLMES-EU Holmes-EU è la naturale continuazione di MARE-RD Inizialmente MARE-RD ha sviluppato tutte le competenze per l uso del decadimento beta del Re-187 (Q=2.45 kev) Successivamente si sono riscontrati limiti intrinseci presumibilmente dovuti ad un eccesso di fluttuazioni dei processi di trasformazione in calore dell energia primaria nei superconduttori ad alta TDebye : attese risoluzione di 1 ev FWHM, mai superata la barriera dei 10 ev FWHM Nel 2007 proposi di passare all Ho-163(EC): Q circa 2.5 kev, half-life= 4500 y (Re-187, half-life= 45 My), esperimento autocalibrato. Sono necessari solo atomi per rivelatore. Re Crystal SupC sensor

27 Ho-163: a new (old) probe for direct search of neutrino mass We have already (15 years ago) performed some test experiment with EC capture decay of Ho-163(1997). The major problem has been the preparation of the absorbers and the overall detector performance. 163 Ho! 163 Dy* + ν e 163 Dy* decays via Coster-Kronig transition ns, np 1/2 Breit-Wigner M,N,O lines limited at the Q value! finite neutrino mass provide at kink at the end-point like in beta spectra of 187-Re

28 Dal 2014 si inizia A Genova: preparazione e separazione isotopica dell Ho-163 prodotto ai reattori o fasci di protoni, costruzione e inserimento dell isotopo nel rivelatore. Un tipico prototipo di array di rivelatori calorimetrici da 1 ev FWHM che potrebbe essere realizzato per HOLMES-EU. (foto NASA GSFC)!