Lightest supersymmetric particle

The lightest supersymmetric particle ( English lightest supersymmetric particle abbreviated LSP ) is the hypothetical lightest elementary particles in the Super symmetry .

properties

The LSP has the R-parity characteristic of supersymmetric particles . In model theories, in which the R-parity is preserved in interaction processes , it therefore has the following properties: ${\displaystyle P_{R}=-1}$

• This particle has to be absolutely stable. The reason is that there is no lighter supersymmetric particle into which it could decay, and because of the conservation of R parity, a decay only into ordinary matter (with R parity +1) is excluded.
• Every other supersymmetric particle must sooner or later decay into an odd number of LSP,
• In particle accelerators you will (if any) can only produce an even number.

WIMP candidate

The LSP is a much discussed candidate for a dark matter forming WIMP (weakly interacting massive particle).

It is considered unlikely that the LSP will participate in the electromagnetic or strong interaction (as a carrier of color charge ). Otherwise it would have condensed with ordinary matter during the formation of matter in the early universe and would have already been discovered because of its great mass.

For example, there are narrow experimental limits on the abundance of heavy isotopes . Norman and co-authors (1987) give an upper limit for the frequency of such negatively charged “super-heavy” isotopes of 1.2 · 10 ⁻¹² per nucleon . For the relative frequency of the LSPs compared to the frequency of the proton , according to Ellis and Flores (1988), for the mass range of the LSPs from 1 to 10 ⁷  GeV / c², an upper limit of 10 ⁻¹⁵ to 10 ^{−30 results} . When participating in the strong interaction, one would expect values ​​of 10 ⁻¹⁰ and when participating in the electromagnetic interaction of 10 ⁻⁶ .

The following hypothetical supersymmetric particles remain as WIMP candidates:

Sneutrino

The sneutrino of the common MSSM is the super partner of the (normal, left-handed ) neutrino . According to previous experiments, it is ruled out ( Z boson - decay width at the LEP ).

In the form of the sterile sneutrino (super partner of the sterile or right-handed neutrino ) it is still discussed as a possibility in some extended models.

Gravitino and NSP

Gravitinos as LSP lead to cosmological problems: their interaction with ordinary matter is too weak to be considered for the dark matter observed in the early universe through the conversion of thermal energy into mass.

But it would be possible that gravitinos are the last decay product of other supersymmetric particles created at that time. The search would then apply to these likewise hypothetical NSPs or NLSPs ( next to lightest supersymmetric particles , second lightest supersymmetric particles).

Neutralino

The favored candidate is currently the lightest neutralino (also referred to as ), i.e. a mixture of different super partners of neutral gauge bosons ( i.e. Gauginos , more precisely Bino and Wino ⁰ ) and super partners of also neutral Higgs bosons ( i.e. Higgsinos ). The Particle Data Group gave 2006 as the experimental lower limit for the neutral mass 46  GeV / c²; for comparison: the mass of the proton is 0.94 GeV / c². ${\displaystyle {\tilde {N}}_{1}}$ ${\displaystyle {\tilde {\chi }}_{1}^{0}}$

literature

• Hans Klapdor-Kleingrothaus , Kai Zuber: Particle astrophysics. Teubner Verlag, 1997, p. 100.
• Klapdor-Kleingrothaus, Staudt: Particle physics without accelerators. Teubner Verlag, 1995, p. 437.

Notes and sources

1. ↑ Eric Norman, Stuart Gazes, Dianne Bennett: Searches for supermassive -particles in iron ${\displaystyle X^{-}}$ . In: Physical Review Letters , Volume 58, 1987, pp. 1403-1407, abstract .
2. ↑ John Ellis , R. Flores: Realistic predictions for the detection of supersymmetric dark matter . In: Nuclear Physics B, 307, 1988, pp. 883-908.
3. ↑ Likewise in the "constrained" MSSM. Thomas Hebbeker: Can the S-Neutrino be the lightest supersymmetric Particle? In: Physics Letters B, 470, 1999, arxiv : hep-ph / 9910326 .
4. ^ W. Buchmuller , K. Hamaguchi, M. Ratz, T. Yanagida : Gravitino and Goldstino at Colliders . 2004, arxiv : hep-ph / 0403203 .
5. ↑ PDG {{dead link | url = http://www.iop.org/EJ/article/0954-3899/33/1/001/g_33_1_001.html | date = 2018-12 | archivebot = 2018-12-01 08:12:11 InternetArchiveBot}}, the Joint LEP2 Supersymmetry Working Group, Aleph, Delphi, L3 and Opal Experiments reports 47 GeV / c²