The Proton Decay and Experiments

Transcription

1 The Proton Decay and Experiments Astroteilchenphysik Vortrag Carlos Ayerbe Gayoso

2 Contents 1- Summary of the Standard Model 2- Beyond Standard Model - Grand Unified Theories 3- The Proton Decay 4- Detecting the proton decay 5- The Counting Test Facility at Grand Sasso

3 Summary of the Standard Model Particles Spin 1 / 2 fermions and anti-fermions 3 Generations or families of quarks (d,u), (s,c), (b,t) 3 Generation of leptons ( e, νe),( µ, ν µ ),( τ, ντ ) Spin 1 gauge bosons 1 massless electronweak boson, the photon g + 3 massive electronweak bosons W, W, Z 8 massless coloured gluons, g Spin 0, Higgs boson, H 0 Interacctions Electromagnetic with coupling e (or α ΕΜ ) Weak with coupling G F Strong with coupling α S The first two are unified via two couplings g and g 0

4 BUT... Standard Model can t explain Values of the couplings e, g and α S Why there are 3 generations of quarks and leptons Why the quark generations are mixed but not the leptons The masses of the quarks and leptons And other open questions Is there a relationship between the strong force and the electroweak force? Is there a relationship between quarks and leptons? i.e. Why do the proton and electron have exactly opposite electrics charges but seem different in their properties What is the origin of CP violation? What about gravity?

5 Beyond Standard Model To answer some of these questions one needs to go beyond Standard Model to: Grand Unified Theories (GUTs) Composite Models Supersymmetry String Models...

6 Grand Unified Theories The basis of this theories is the behavior of the coupling constants: a EM increases with energy a S decreases with energy The couplings would come together at the so-called Unification Mass of about GeV

7 A little bit of mathematical foundation... Current theories are asociated with certain groups of the groups theory The Electromagnetic group U(1) has one gauge boson (the photon) The QCD group SU(3) has 3 colour charges and 8 gauge bosons (gluons) The electroweak interaction are represented by the product of the groups SU(2) U(1) So, the Standard Model is represented by the product of the groups SU(3) SU(2) U(1) The simplest GUT is labelled SU(5) and has 24 gauge bosons We have already 12 bosons There would also be: 3 bosons with electric charge 1/3 and color (Y R, Y G, Y B ) 3 bosons with electric charge 4/3 and color (X R, X G, X B ) And their 6 anti-particles These X and Y bosons are called leptoquarks

8 The Proton decay The bosons X, Y can change quarks into leptons and vice-versa It violates lepton (L) and baryon (B) conservation but still conserve B-L

9 The Proton decay This means that the proton could decay to mesons and leptons!! p p e π + π ν e With these desintegrations and assuming M X»10 14 GeV/c 2 this predicts a life time betweem 2x10 28 and 6x10 30 years

10 Detecting the proton decay One can t watch a proton for years and see if it decay (is bored!!) But we can watch protons for one year We need: A large mass (to provide the protons) A tracking capability for charged particles A way to mesure visible energy and identify particles Shielding against background (natural radiactive, cosmic rays)

11 The Counting Test Facility at Grand Sasso The CTF counting as a calorimetric liquid scintillator detector The active detector is 4.8 m 3 of a binary liquid scintillator (1,5 g PPO/L pseudocumene) The scintillator is held in a nylon vessel shielded by 1000 tons of purified water 100 PM surrounding the detector are used to mesure time and charge for each event

12 The Counting Test Facility at Grand Sasso The CTF is located at the Gran Sasso underground laboratories, it provides 3500 m water equivalent shielding from cosmic radiation It gives approximately 25/d/m 2 of muons flux Background radiation and shielding Inside the hall there is a g-rays flux of 10 8 /d/ m 2 from natural radiation The water shield provides 4,5 m of shielding from g-rays on all sides The phototubes contributes with additional g-rays of approx 2x10 6 d/ m 2 but they are 2,3 m away from scintillator Simulations suggest the water should reduce the external g-rays from natural radiation and PM to less than 100/d in the energy range of kev U, Th and K concentrations in the water contributes a BG of 100/d, those are the major sources of BG contribution (of the order os thousand scintillation events per day) BUT... With the PMT s and readout electronics they allow the identification of the excitation source for events and spatial reconstrucction, so we can identify those sources

13 The Counting Test Facility at Grand Sasso The CTF Subsystems The scintillator Scintillator Containment Vessel Scintillator Handling Scintillator Purification System Water Tank and Clean Room The Water Purification System The Photomultiplier System Data Acquisition Electronics Nitrogen System Ancillary Facilities

14 The Counting Test Facility at Grand Sasso Scintillator It consists of 1,5 g PPO (diphenyl oxazole) per liter of pseudocumene (1,2,4, trimethylbenzene) The density is 0,88 g/l at 15 C Refractive index is 1,5 at 420 nm Scintillator Containment Vessel The scintillator containmet vessel confines the scintillator within the water buffer It is made by a flexible ball of 0,5 mm thick and 1,05 m radius, made of an amorphous nylon from Bayer Chemicals It sustains the 570 kg bouyant force associated with the 12% density difference between water and scintillator It supports 3,5 MPa (but it was designated to support 14 MPa) In air, the wall have a optical trasmittance of 80% at 365nm It is attached by a system of 16 nylon strings

15 The Counting Test Facility at Grand Sasso Scintillator Containment Vessel

16 The Counting Test Facility at Grand Sasso The Photomultiplier System There are 100 PMT of 0,20 m of diameter (Thorn EMI 9351) They have a cathode eff of»25% (peak eff at 380nm) Transit time spread of 1 ns Dark noise of 500 Hz Low afterpulsing (»2,5%) Amplification of 10 7 They was choosed for their low radiactivity The dynodes are shielded against magnetic fields with mu-metall The PMT are coupled to truncated string cone light concentrators The Geometrical coverage of the active scintillator region is 21%

17 The Counting Test Facility at Grand Sasso The Photomultiplier System

18 The Counting Test Facility at Grand Sasso Background sources The main goal of the CTF is identify the radiactive sources of the scintillator to demostrate the feasibility of the facility The principal sources from scintillator are 85 Kr events/d 210 Po from the decay of 222 Rn events/d 210 Bi (events are expected in the energy window of interest, but its b-decay not have a monoenergetic signature to identify) Ra(U) < 4 x 10-9 Bq/kg and Th <10-9 Bq/kg 14 C» 3x10-4 Bq/kg (isotopic abundance 14 C/ 12 C 2x10-18 The 85 Kr is removed by nitrogen stripping Water extraction removed the 210 Po The internal radiactive BG was reduced to <40 events/d 14 C, U and Th remained stable for over a year. 85 Kr and 210 Po did not reappear Low intrisic BG was stable for several months

19 The Counting Test Facility at Grand Sasso Outlook and conclusions The CTF had demostrated the feasibility of a large scale low background liquid scintillator detector Online purification of a liquid scintillator achivied levels below detection and maintained the optical properties Radiopurity of a liquid scintillator at the level of 10-9 Bq/kg above 250 kev and 10-3 Bq/kg below 250 kev has been demostrated Since this facility main purpouse is not the detection of the proton decay, it have all the necesary for its detection

20 Conclusions The proton decay has not been detected yet, but there are a lot of facilities with the necesary to detect it Proton decay is a important piece in GUT but it is not the only Liquid scintillators detectors demostrated their capability to detect rare events as proton decay

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