Discovery of first elementary particles

Transcription

1 Lptons

2 Discovry of first lmntary particls Known particls at th nd of th 30 s Elctron Proton Photon Nutron Positron Muon Pion Nutrino: a particl whos xistnc was hypotsizd without a discovry! Faraday, Goldstin, Crooks, J. J Thomson (1896) Avogadro, Prout (1815) Einstin (1905), Compton (1915) Chadwick (1932) Convntional birth dat of Nuclar Physics Andrson (1932) Cosmic rays intraction studis. Pion/ Muon sparation

3

4 Muon dcay (1930) Dcay ltron track

5 Th msotron puzzl..

6 Convrsi, Pancini, Piccioni (1947) xprimnt

7 Convrsi, Pancini, Piccioni (1947) xprimnt

8 Convrsi, Pancini, Piccioni (1947) xprimnt

9 Convrsi, Pancini, Piccioni (1947) xprimnt

10 Convrsi, Pancini, Piccioni (1947) xprimnt

11 Convrsi, Pancini, Piccioni (1947) xprimnt

12 Pion discovry

13 Pion discovry

14 Pion discovry (1947, Latts, Powll Occhialini) Pion and Muon dcay squnc: a cascad of dcays Muon dcay Nuclar Emulsion π µ ν µ ( τ = m(π ) = MV / c 2 8 s ) µ ν µ ν ( τ = s ) Muon dcay schm m ( µ ) = MV / c 2 In all ths dcays, nutrinos ar mittd! 14

15 Pion Muon π µ Exprimntal stratgy: Exposur of Emusions to Cosmic Rays Th pion in trm of quarks 15

16 Pion Muon

17 Lptons Lptons ar s = ½ frmions, not subjct to strong intractions Th imag cannot b displayd. Your computr may not hav nough mmory to opn th imag, or th imag may hav bn corruptd. Rstart your computr, and thn opn th fil again. If th rd x still appars, you may hav to dlt th imag and thn insrt it again. m < m µ < m τ Elctron -, muon µ - and tauon τ - hav corrsponding nutrinos: ν, ν µ and ν t Elctron, muon and tauon hav lctric charg of -. Nutrinos ar nutral Nutrinos hav vry small masss For nutrinos only wak intractions hav bn obsrvd so far

18 Anti-lptons ar positron, positiv muons/tauons and anti-nutrinos ν µ ν τ µ ν τ Nutrinos and anti-nutrinos diffr by th lpton numbr. For lptons L a = 1 (a =,µ or τ) For anti-lptons L a = -1 Lpton numbrs ar consrvd in any raction Lpton lpton numbr 1 lctron 1 numbr muon numbr 0 ν µ ν µ 1 0 1

19 No n p Ys n p No No p n Ys p n µ µ ν µ ν γ µ ν ν Consqunc of th lpton nr consrvation: som procsss ar not allowd Ldrman, Schwarts, Stinbrgr Nutrinos Nutrinos cannot b rgistrd by dtctors, thr ar only indirct indications First indication of nutrino xistnc cam from β-dcays of a nuclus N A Z N A Z N ν ) 1, ( ), (

20 Elctron is a stabl particl, whil muon and tauon hav a finit liftim: τ µ = 2.2 x 10-6 s and τ τ = 2.9 x s Muon dcay in a purly lptonic mod: µ ν Tauon has a mass sufficint to produc vn hadrons, but has lptonic dcays as wll: ν µ ( a) ( b) τ τ µ ν ν ν µ τ ν τ Fraction of a particular dcay mod with rspct to all possibl dcays is calld branching ratio (BR) BR of (a) is 17.84% and of (b) is 17.36%

21 1) 1) Wak of assumptions intractions of lptons ar idntical lik lctromagntic ons ( intraction univrsality) lik lctromagntic ons (2) intraction On can nglct univrsality final stat ) lpton masss for many basic calculations Th dcay rat for a muon givn many basic Γ( µ ν ν µ ) = calculations Th dcay rat for a muon is Whr Substituting G F is m th µ with Frmi mconstant τ on givn by:, for (a) and (b). It xplains why obtains BR of sam (a) and dcay (b) hav vry clos valus G 2 F m 195π 5 µ 3

22 Using th dcay rat, th τ l = liftim of a lpton B( l Γ( l ν ν l ) ν ν ) is Sinc Hr l stands for µ and τ. hav basically : on dcay mod, B= 1 in stands cas. Using for µ and xprimntal τ. l τ τ good agrmnt with τ µ m m µ τ on indpndnt valus of B xprimntal and formula masurmnts for Γ, vry th Univrsality ratio of µ and of τ lpton liftims: In no obtains

23 Th tau sarch AntiProton into LEpton Pairs) CERN PS CERN PS of th PAPLEP (Proton- It starts th sarch for th 3 rd squntial lpton family, a rplica of th first two. " ν Th Havy Lpton and its nutrino HL % # $ HL& ' It starts th sarch for th 3 squntial family, a lpton rplica of th Sarching for acoplanar lpton rd pairs of opposit chargs

24 Simplfid from Th tau discovry was Th tau was thn raction at th ADONE sarchd ring for in Frascati by Zichichi which in 1967 did not in th hav τ τ nrgy produc to a of th nw lpton nough. Th maximum ADONE nrgy was s=3 GV, blow th thrshold for production s=3.554 pair of th nw 20% lpton lss!!) A lowr limit for th havy lpton (HL) mass was obtaind Nuovo Cimnto 17A (1973) 383 HL is hr

25 Th tau discovry M. Parl co. sam ida at SPEAR ( - with E= 8 GV) τ discovry with th Mark I xprimnt Common procsss µ µ π π π π π 2 (showrs) opposit sign, collinars 2 µ (pntrating) opposit sign, collinars 2 π (hadrons) opposit sign, collinars 2 π (hadrons) opposit sign, non collinars Signal τ τ τ τ τ ν 's / τ µ ν 's τ µ ν 's / τ ν 's Topology: µ pair of opposit sign, non collinars Background: non-idntifid hadrons PLUTO and DESY confirm discovry HL is calld τ from τριτον, th third (P. Rapidis) µ

26 Nutrinos: th crisis around 1930 Mattr is mad of: Particls: γ, -, p Atoms: Small nuclus of protons surroundd by a cloud of lctrons bfor Pauli: Obsrvations: Nuclar β-dcay: 3 H 3 H- Uniqu lctron nrgy? vnts Exprimntal lctron nrgy lctron nrgy Enrgy consrvation violatd?

27 Pauli s hypothsis Pauli: Variabl lctron nrgy! Pauli's lttr of th 4th of Dcmbr 1930 Dar Radioactiv Ladis and Gntlmn, As th barr of ths lins, to whom I graciously ask you to listn, will xplain to you in mor dtail, how bcaus of th "wrong" statistics of th N and Li 6 nucli and th continuous bta spctrum, I hav hit upon a dsprat rmdy to sav th "xchang thorm" of statistics and th law of consrvation of nrgy. N am ly, th possibility that thr could xist in th nucli lctrically nutral particls, that I wish to call nutrons, w hich hav spin 1/2 and oby th xclusion principl and which furthr diffr from light quanta in that thy do not travl with th vlocity of light. Th mass of th nutrons should b of th sam ordr of magnitud as th lctron mass and in any vnt not largr than 0.01 proton masss. T h continuous bta spctrum w ould thn bcom undrstandabl by th assum ption that in bta dcay a nutron is mittd in addition to th lctron such that th sum of th nrgis of th nutron and th lctron is constant... U nfortunatly, I cannot appar in T ubingn prsonally sinc I am indispnsabl hr in Z urich bcaus of a ball on th night of 6/7 D cm br. With my bst rgards to you, and also to Mr Back. Your humbl srvant. W. Pauli

28 Frmi thory of β dcay

29 What is a β-dcay? It is a nutron dcay: n p ν Ncssity of nutrino xistnc coms from th apparnt nrgy and angular momntum non-consrva=on in obsrvd rac=ons For th sak of lpton numbr consrva=on, lctron must b accompanid by an an=-nutrino and not a nutrino! Mass limit for of th β-dcay: ν can b s=matd from th prcis masurmnts m E ΔM N m ν Bst rsults ar obtaind from tri=um dcay 3 H 3 H ν it givs mν 2 V / c 2 (~ zro mass)

30 Elctron Nutrino dtction Th most powrful availabl sourcs of nutrinos, bfor th construc=on of protosinchrotrons (60) wr th nuclar ractors. By th procsss of fission ν ar producd with a spctrum of nrgis of a fw MV. A fw tns of mtrs from th cor of a ractor of 1 GW, th flow is normous Φ m -2 s -1 Elctronic nutrinos and an=nutrinos can b rvald through th lctronic "invrs bta dcay", but th cross sc=on is microscopic σ ( ν p n) ( E ν / MV) 2 m 2

31 Elctron Nutrino dtction σ ( ν p n) ( E ν / MV) 2 m 2 Rat for p targt E ν = 1MV W 1 =Φσ s 1 So, for a total rat of: W = 10 3 Hz N p = If th targt is mad of H 2 O (10 p), in a mol (18 g) thr ar N A 10/18 = protons So, on nds about 3000 mols 50 kg Dtction fficincy, fiducial volum/total volum. Lts put 1/4 Total mass ndd 200 kg Th main problm is not th ndd mass (albit this was rmarkabl in 1958), but th control of th backgrounds : n from th ractor background inducd by cosmic rays natural radioactivity

32 Elctron Nutrino dtction (1956) Cowan & Rains Cowan nobl priz 1995 with Prl (for discovry of τ- lpton) Intns nutrino flux from nuclar ractor ν Invrs β dcay p n followd by γ γ Powr plant 0.7 GW (Savannah rivr plant USA) Producing ν

33 Schm of th Rins and Cowan xprimnt 2m 2m Obsrvd: 3±0.2 vnts/h Background small Cross sction xpctd valu Targt = 200 l of H 2 O immdiatly annihilats in two γ s at 180 btwn thm, which go in two diffrnt containrs of liquid scintillator adjacnt. Compton lctrons produc a flash of light. H 2 O is a good modrator and in a fw tns of µs a nutron is thrmalizd. H 2 O dopd with 40 kg of Cd which has a larg cross sction for captur of thrmal n. Th rtardd γ s ar rvald in th scintillator. Dtctor at 10 m blow a building (cosmic) lot of car in shilding

34 Nutrino dtctd, finally Scinc 124 (1956) 104 W now know it was lctron antinutrino 6-Nov-17

35 Muon Nutrino dtction B. Pontcorvo (in Russia) and M. Schwartz (in US) proposd indpndntly th us of nutrino bams producd in acclrator (thy show that intnsitis should b nough). Which nutrinos: π µ ν? π µ ν? L Yang. Should b diffrnt from th lctron nutrino othrwis: Schwartz, Ldrman, Stinbrgr xprimnt. Th proton bam xtractd from th AGS at BNL is snt against a targt. Hadrons and µ ar filtrd by13.5 m of F and nutrons with paraffin µ ± ± γ

36 Muon Nutrino dtction photomultiplir 20 kv scintillator discriminators R L C coincidnc spark gap R photomultiplir scintillator a muon track particl trajctory A numbr of paralll plats ar mountd in a gas filld volum (typically, a mixtur of H and N) Plats ar altrnativly connctd to ground and to a high voltag supply Th high-voltag puls is triggrd by a coincidnc btwn two scintillation countrs placd abov and blow th spark chambr Gas amplification btwn 10 8 and 10 9 rsults in a spark discharg along th trajctory of th particl.

37 Muon Nutrino dtction 34 singl muon vnts obsrvd Additional 8 vnts compatibl with background No lctron obsrvd Conclusion: th nutrino that is born togthr with a µ in th π dcay whn intracts produc a µ, not. Two diffrnt consrvd quantitis xist, lpton flavours: n and n µ 6-Nov-17

38 Muon Nutrino dtction How do lctrons look lik Exposur of th chambrs at th 400 MV lctron bam at Cosmotron

39 Classification of lmntary particls, µ, µ γ Th photon p = ( u, u, d) n = ( u, d, d) Lptons (havir copis of th lctron) π = ( u, d ), π = ( d, u) ν Th nutrino, postulatd to xplain bta dcay and obsrvd in invrs bta dcay, is always associatd to a chargd lpton. Th hadrons, particls mad up of quarks and obying mainly to strong nuclar intraction 39

40 Anti-nutrino s vs nutrino s Davis & Harmr If th nutrino is sam particl as anti-nutrino thn clos to powr plant: ν p ν n n 37 ν 17 Cl p Ar -615 tons kitchn claning liquid -Typically on 37 Cl 37 Ar/day -Chmically isolat 37 Ar -Count radio-activ 37 Ar dcay Nobl priz 2002 (Davis, Koshiba and Giacconi) Raction not obsrvd: Nutrino-anti nutrino not th sam particl Littl bit of 37 Ar obsrvd: nutrino s from cosmic origin (sun?) Rumor sprad in Dubna that raction did occur: Pontcorvo hypothsis of nutrino oscillation ν 37 Cl - 37 Ar

41 Flavour nutrino s Nutrino s from π µν idntifid as ν µ Two nutrino hypothsis corrct: ν and ν µ Ldrman, Schwartz, Stinbrgr (nobl priz 1988) For th nutrino bam mthod and th dmonstration of th doublt structur of th lptons through th discovry of th muon nutrino

42 Discovry of τ-nutrino (2000) DONUT collaboration Production and dtction of τ-nutrino s cτ τ Δ s τ ν τ ν Τ ν τ

43 Nutrino flavours Nutrinos cannot b dirctly dtctd Th chargd lpton producd by th nutrino intraction in th dtctor idntifis th nutrino flavour

44 Nutrino flavour CHANGES In th last 15 yars w larnt that nutrino chang flavour, providd tim (flight distanc) is givn thm to do so Oscillations and flavour convrsion in mattr, prov that nutrinos, contrary to th Standard modl hav non-zro mass Flavour stats ar suprposition (mixing) of mass ignstats

45 Flavour Mass Liftim 0.5 MV µ 106 MV 2.2 µs τ 1777 MV 0.29 ps W obsrvd thr coupls of lptons (tr familis, gnrations ) On lpton is chargd (, µ, τ ), th othr is its nutrino (ν, ν m, ν t ), µ τ hav all th sam charactristics, xcpt for th mass Chargd lptons maks gravitational, lctromagntic and wak intractions. Nutrinos maks gravitational and wak intractions.

46 LEP ( ): th 3 nutrino familis Dtrmination of th Z 0 linshap: Rvals th numbr of light nutrinos Fantastic prcision on Z 0 paramtrs Corrctions for phas of moon, watr lvl in Lac du Gnv, passing trains, N ν 2.984± M Z 0 Γ Z ± GV ± GV Existnc of only 3 nutrinos Unlss th undiscovrd nutrinos hav mass m ν >M Z /2