KArlsruhe TRI:um Neutrino (KATRIN) neutrino experiment hup:// T1/2=12.32 y

Size: px

Start display at page:

Download "KArlsruhe TRI:um Neutrino (KATRIN) neutrino experiment hup://www.katrin.kit.edu T1/2=12.32 y"

Shavonne Snow
6 years ago
Views:

1 KArlsruhe TRI:um Neutrino (KATRIN) neutrino experiment hup:// T1/2=12.32 y Deviations around the endpoint due to nonzero neutrino mass hups://neutrino.ikp.kit.edu/owncloud/data/katrin/ﬁles/public/videos/

2 The KArlsruhe TRI:um Neutrino (KATRIN) experiment searches for a neutrino mass between 0.2 ev and 2 ev. Assuming that the endpoint energy for zero neutrino mass in tri:um beta decay is Q β-, find the expected rela:ve error of electron energy determina:on by KATRIN.

3 If we assume that the matrix element does not depend on E e-, and amer taking out the strength g of the weak interac:on, one obtains: 2π 3! 7 ft = g 2 m 5 e c 4 ˆM, ˆM ' 2 fi gm ' fi ' fi ( ) = F Z D, w 2 1 ( ) 2 wdw f-function f Z D,w 0 w 0 1 ( ) w 2 1 w 0 w where w = E e / m e c 2 and w 0 is the reduced max. electron energy. electrons positrons

Beta decay: microscopic view On a more fundamental level, beta decay of

another through exchange of charged weak currents (W bosons carry net

p e - _ e - ν ν e n W - The flavor of quarks is conserved in strong

4 Beta decay: microscopic view On a more fundamental level, beta decay of hadrons can be viewed as the transforma:on of one type of quark to another through exchange of charged weak currents (W bosons carry net charges; Z boson is neutral - it is the source of neutral weak current). p e - _ e - ν ν e n W - The flavor of quarks is conserved in strong interac:ons. However, weak interac:ons change flavor! d u + e +ν u d + e + e +ν e e - Z 0 ν

5 Three generations of matter There are three "sets" of quark pairs and lepton pairs. Each "set" of these par:cles is called a genera:on, or family. The up/down quarks are first genera:on quarks, while the electron/electron neutrino leptons are first genera:on leptons. up type (q=+2/3e) down type (q=-1/3e) par:cles of higher genera:ons to decay to the first genera:on (everyday mauer is made of par:cles from the first genera:on) neutral charged (q=-e) mass 12 matter particles suffice in nature? hup://journals.aps.org/prl/abstract/ /physrevleu The result of the sta:s:cal analysis is that the existence of further fermions can be excluded with a probability of percent (5.3 sigma). The most important data used for this analysis come from the recently discovered Higgs par:cle.

Beta decay: mass and weak eigenstates When a quark beta-decays, the new quark does not have a definite flavor.

02º However, the observed weak transi:ons are between quarks of definite flavor.

interac:on eigenstates: " u% " # d' ' c %" # s' ' t % # b' ' A quark of charge +2/3 (u,c,t) is always

6 Beta decay: mass and weak eigenstates When a quark beta-decays, the new quark does not have a definite flavor. For instance (Cabibbo 1963): u d ' = d cosθ c + ssinθ c Cabibbo angle θ c =13.02º However, the observed weak transi:ons are between quarks of definite flavor. In general, the strong-interac:on quark eigenstates: " u% " # d ' c %" # s ' t % # b ' are different from weak interac:on eigenstates: " u% " # d' ' c %" # s' ' t % # b' ' A quark of charge +2/3 (u,c,t) is always transformed to a quark of charge -1/3 (d,s,b) and vice versa. This is because the transforma:on proceeds by the exchange of charged W bosons, which must change the charge by one unit.

7 Kobayashi and Maskawa generalized the Cabbibo matrix into the Cabibbo Kobayashi Maskawa matrix (or CKM matrix) to keep track of the weak decays of three genera:ons of quarks! # # # " d ' s' b'! # = # % # " weak eigenstates Beta decay: CKM Matrix U ud U us U ub U cd U cs U cb U td U ts U tb! # # # %" d s b % mass eigenstates The current determination: Cabibbo-Kobayashi-Maskawa (CKM) matrix The choice of usage of down-type quarks in the defini:on is purely arbitrary and does not represent some sort of deep physical asymmetry between up-type and down-type quarks. For nuclear beta-decay, we are mainly concerned with the transi:on between u- and d- quarks. As a result, only the product enters into the process. G V = G F cosθ c

What are the consequences of parity viola:on in beta decay? h =! σ p! p helicity The eigenvalue of h is v/c.

In general, the par:cle with h>0 is called right-handed h<0 is called lem-handed Experimentally, h(ν e ) 1, h(ν e ) +1 Beta decay: helicity (helicity

edu The global characteriza:on in terms of handedness is not meaningful for other par:cles, like electrons.

8 What are the consequences of parity viola:on in beta decay? h =! σ p! p helicity The eigenvalue of h is v/c. For a massless par:cle, the eigenvalues of h can be only +1 or -1. In general, the par:cle with h>0 is called right-handed h<0 is called lem-handed Experimentally, h(ν e ) 1, h(ν e ) +1 Beta decay: helicity (helicity flips under parity) hup://journals.aps.org/pr/abstract/ /physrev left-handed or right-handed? hup://hyperphysics.phy-astr.gsu.edu The global characteriza:on in terms of handedness is not meaningful for other par:cles, like electrons. An electron could have spin to the right and be traveling right and therefore be classified as righthanded. But from the reference frame of someone traveling faster than the electron, its velocity would be to the lem, while its spin would be unchanged. This would mean that the electron is a lemhanded par:cle with respect to that reference frame.

Beta decay: helicity

Beta decay: helicity What are the consequences of parity viola:on in beta decay? h =! σ p! p helicity The eigenvalue of h is v/c. For a massless par:cle, the eigenvalues of h can be only +1 or -1. In general, the par:cle with