Strangeness

DESY - bubble chamber image: a 3 GeV photon shot in from the right most likely collided with a proton (hydrogen bubble chamber). Particles with strangeness were generated.

The strangeness (Engl.) Denotes the quantum number of the strangeness of a particle or condition in the standard model of elementary particle physics . Along with isospin , charm , bottomness and topness, it is one of the flavor quantum numbers of quarks . ${\displaystyle S\,\!}$

Its name comes from the first, in 1947 in the cosmic radiation discovered Strange particles (Engl. Strange particles ) whose life was significantly longer than the other then known unstable particles. These included kaons (mesons from a u or d quark and Strange quarks, they were the strange particles first discovered in 1947) and hyperons (baryons with a Strange quark). The strangeness quantum number was introduced by Murray Gell-Mann (1953), Abraham Pais and Kazuhiko Nishijima to explain the properties of these new particles .

Definition and choice of sign

generation	1		2		3
Up type	up		charm		Top
Quark / antiquark	u	u	c	c	t	t
Flavor quantum number	+ ½	−½	+1	−1	+1	−1
	Isospin ${\displaystyle I_{3}}$		Charm ${\displaystyle C}$		Topness ${\displaystyle T}$
Down type	down		strange		bottom
Quark / antiquark	d	d	s	s	b	b
Flavor quantum number	−½	+ ½	−1	+1	−1	+1
	Isospin ${\displaystyle I_{3}}$		Strangeness ${\displaystyle S}$		Bottomness ${\displaystyle B'}$

The strangeness of a system is equal to the negative number of Strange quarks s plus the number of associated antiparticles , the Strange antiquarks s :

${\displaystyle S=-n_{s}+n_{\overline {s}}.}$

For historical reasons, the convention is that a strange quark s, as a quark particle of the Down type , makes a contribution to the strangeness of the system (such as the hadron ) in which it is involved ; the Strange Antiquark s, however . (This sign convention applies - as well as the down-type - even for the bottom Ness of bottom quarks b with ; its antiparticle, the bottom-antiquark b has .) All other fundamental elementary particles are not "strange", ie have a strangeness of 0. ${\displaystyle S=-1}$ ${\displaystyle S=+1}$ ${\displaystyle B'=-1}$ ${\displaystyle B'=+1}$

In contrast to this, the charm quark c and the top quark t as quarks of the Up type have the opposite signs for their associated quantum numbers : the charm and the topness ; the respective antiparticles c or t have or . ${\displaystyle C=+1}$ ${\displaystyle T=+1}$ ${\displaystyle C=-1}$ ${\displaystyle T=-1}$

Physics of strange matter

Strange quarks are formed for example in the collision of protons and neutrons , protons and protons or protons and photons and have a relatively long life. This can be explained by the fact that the strong interaction is responsible for their creation , but the weak interaction is responsible for their decay . This leads to the fact that in the bubble chamber one can see so-called V-particles , V-shaped traces apparently emerging from nowhere. The decay vertex of this V-track mostly points to another (primary) vertex. The invisible connection line is created by a neutral particle with strangeness.

The strangeness remains in processes of strong and electromagnetic interaction , but can be changed with weak interaction.

Web links

• Wikibooks: Particle Physics: Particle Properties