# Hypernuclei physics experiment

1. Feb 1, 2004

### jimmy p

A new particle physics experiment has created as many "hypernuclei" in its first three months of operation as have been produced in the 50 years since the exotic particle was first discovered. Scientists announced the achievement on Friday at a meeting in Bormio, Italy.

Hypernuclei are atomic nuclei combining not just the usual protons and neutrons but also rare particles called hyperons. About 100,000 have been created in an experiment called FINUDA, on the Dafne accelerator at the National Laboratory of Frascati.

Hypernuclei are incredibly short-lived, surviving for less than a billionth of a second. But by studying them scientists hope to learn more about the weak force, one of nature's four fundamental forces, as well as the first moments of the Universe's existence.

The FINUDA experiment has so far churned out 35 varieties of hypernuclei already known to science. But in future months, scientists hope to fashion completely new hypernuclei, such as a hydrogen-7-lambda, comprised of one proton, five neutrons, and one exotic lambda particle, a hyperon that includes a strange quark. Normally, hydrogen contains zero, one, or two neutrons, but the massive lambda particle allows the nucleus to bind to additional neutrons.

"There is a general consensus that we had abundant production of strange quarks at the Big Bang," says FINUDA spokesman and nuclear physicist Tullio Bressani. "If we demonstrate objects like hydrogen-7-lambda are stable, it would be a bridge to answer questions about the strange nuclear matter in the early Universe."

Hypernuclei are only rarely produced in the natural world, when a high-energy cosmic ray strikes a nucleus on Earth under just the right conditions. "It's like you are trying to catch a rare fish," Bressani told New Scientist. But the accelerator provides a steady supply of hypernuclei.

The FINUDA experiment has produced many more hypernuclei than other attempts around the world because its detectors were designed specifically to create and study hypernuclei.

However, creating hypernuclei is a difficult, multi-stage process in which researchers must swap a lambda particle for a proton or neutron in a nucleus. "It isn't easy to do this," says Peter Meyers, a nuclear physicist at Princeton University, New Jersey, US. "You have to make the exotic particle, get it into the nucleus, have it stick there, and know all this has happened."

First the researchers smash an electron and its antimatter counterpart, a positron, together to produce a medium-weight elementary particle called a phi meson. This then decays into charged kaons. Shooting the kaons at paper-thin targets of lithium, carbon, vanadium, or aluminium produces the hypernuclei.

Researchers know they have created a hypernucleus when they measure the energy of one of its decay products, a negatively charged particle called a pion.

QUOTED FROM NEW SCIENTIST

Does anyone know much about hyperons? How will it help with researching about the weak force?

2. Feb 5, 2004

### Orion1

hypernuclei...

hyperons
hypernucleus
hypernuclei

hyperon:
. any baryon that is not a nucleon; unstable particle with mass greater than a neutron

In the classification of subatomic particles according to mass, the heaviest of such particles. Compare lepton, meson, nucleon. Some large and highly unstable components of cosmic rays are hyperons.

hydrogen-7-lambda, comprised of one proton, five neutrons, and one exotic lambda particle, a hyperon that includes a strange quark.

1 proton +1 - 938.3 Mev
5 neutrons 0 - 5(939.6 Mev)
1 lambda 0 - 1115.6 Mev

hydrogen-7-lambda +1 - 6751.9 Mev

According to the strong semi-empirical binding energy formula, a hydrogen-based nucleus can only stablize between 1.7 to 3.4 amu.

A hydrogen-7-lambda hypernucleus is not cohesive by strong nuclear cohesion, but by the weak nuclear cohesion.

A hydrogen-7-lambda hypernucleus is actually repelled by its strong nuclear cohesion effects by -5.870 Mev/u.

In order for a hydrogen-7-lambda hypernucleus to stabalize, its weak nuclear cohesion must exceed its strong nuclear repulsive anti-cohesion.

The weak semi-empirical binding energy formula may have a cohesive resonance peak around 7 u.

Ew > Es
Ew > 5.870 Mev/u

Hydrogen:
nucleus stability region: 1.7 to 3.4 u
Deuterium: 2.014 u
Tritium: 3.024 u
Hydrogen-2-lambda: 2.204 u
Hydrogen-3-lambda: 3.213 u

Hydrogen-7-lambda
strong binding energy: -5.870 Mev/u
weak binding energy: >+5.870 Mev/u???
mass: 7.248321 u

According to my calculations, a Hydrogen-2-lambda or Hydrogen-3-lambda nucleus is more 'stable' than a Hydrogen-7-lambda nucleus...

Does anyone know what the equasion and energy constants are for the weak semi-empirical binding energy formula?

Reference:
http://www.lnf.infn.it
http://www.newscientist.com/news/news.jsp?id=ns99994626

Last edited: Feb 5, 2004
3. Feb 5, 2004

### LURCH

Re: Hypernuclei

Just speculatin', but the Weak Force dirves radiative decay in most cases. Thess particals have a lifespan less than a billionth of a second, and then they decay. It would seem that observing these particals would be like observing the Weak Nuclear Force at its greatest concentration (so to speak). It must be the dominant factor in the lives of hypernuclei.

4. Feb 6, 2004

### Norman

Re: hypernuclei...

5. Feb 6, 2004

6. Feb 6, 2004

### Norman

I am assuming that by large they mean mass, not the percent of composition of cosmic rays... every paper I have read on GCR composition has never mentioned them (that doesn't mean I am right though). The composition of galactic cosmic rays is fairly relative to the abundance of the particle in the universe. There are well understood deviations from this that are well explained by theory. I would still like to know exactly what is meant by "large".
Cheers,
Ryan

7. Feb 6, 2004

### Orion1

Hyperion Flux...

In 1952 Professors Danysz and Pniewski observed a cosmic ray interaction in emulsion, in which one of the nuclear fragments contained a hyperon. Such fragments were called hyperfragments. In other words, a hyperfragment (or hypernucleus) is a nucleus in which one or more nucleons are replaced by hyperons.

The $$K^-$$ meson and the $$\Lambda^0$$ hyperon are two commonly encountered unstable particles. For example, they are commonly produced in air showers by cosmic rays at a detectable flux rate.

Reaction:
$$K^- + p^+ \rightarrow \Lambda^0 + \pi^0$$

The reaction can be used to make $$\Lambda^0$$'s at rest in the laboratory by scattering $$K^-$$ mesons off a stationary proton (Hydrogen) target.

Reference:
http://auger.ifj.edu.pl/Historia-k/HistoriaA.htm
http://aka-ocw.mit.edu/NR/rdonlyres/Physics/8-20Introduction-to-Special-RelativityJanuary--IAP-2003/
ref #1:
74E9D1C8-B5E4-42A3-AB43-F274CC8721D7

8. Feb 8, 2004

### Norman

Re: Hyperion Flux...

Detecting them in air showers as end products of cosmic ray interactions is quite different then hyperons being components of the GCR. Infact their short lifetime excludes them. That is why I was wondering... it is the same reason we don't find other short lived resonance states existing in the GCR...

Once again, this is in the lab setting... actually detecting lambdas in the GCR spectrum would be quite a different thing. In addition, you do not even find kaons in the GCR spectrum due (most likely) to their short lifetime. They are much more likely to decay into muons and neutrinos.
Cheers,
Ryan