## New Particle Identified At LHC 164

Posted
by
timothy

from the particularly-new dept.

from the particularly-new dept.

First time accepted submitter m4ktub writes

*"A team of researchers working with the ATLAS experiment at the LHC have published an article in arXiv where they describe what is believed to be the first observation of a new particle: the boson Chi-b (3P). Professor Roger Jones, Head of the Lancaster ATLAS group, said 'While people are rightly interested in the Higgs boson, which we believe gives particles their mass and may have started to reveal itself, a lot of the mass of everyday objects comes from the strong interaction we are investigating using the Chi-b.'"*
## Re:"Observed"? (Score:5, Informative)

This guy explains things pretty well:

http://profmattstrassler.com/ [profmattstrassler.com]

## Re:"Observed"? (Score:3, Informative)

You look at the decay modes. The know what the put in and they see the end result of the decay. With energy, mass, momentum conversation, they can reconstruct the decay. And if you find enough statistical evidence to support your claim, they you have found a 'new' particle.

## A new particle or a new state of known particles? (Score:2, Informative)

stateof a pre-existing organ. Sorry for not using a car analogy; I'm just trying to understand how physicists think of the difference between states and things, or if this dichotomy even makes sense on that level.## Re:A new particle or a new state of known particle (Score:5, Informative)

beautyflavour. Other flavours of pair have been observed before, but its the fact that this one consists of beauty quarks that makes it "new"## Re:Amazing time to be a physicist (Score:5, Informative)

However it could be argued that is is also becoming worse to be a physicist. We need larger and more expensive methods of discovering the next step. The discoveries of old can be done in a normal college lab. With say a million dollars worth of equipment enough for a normal institution to invest in. The new stuff is taking billions of dollars, to find. So discoveries are limited to what large governments are willing to pay for.

## Re:A new particle or a new state of known particle (Score:4, Informative)

The second link is hosed, but the abstract says they discovered "a new chi_b state" of quarkonium. This is well beyond my physics comfort zone, and maybe there is no real difference between states and particles in this realm, but intuitively it seems like there should be one.

Combinations of fundamental particles like quarks themselves behave as particles. The most familiar examples of such composite particles [wikipedia.org] are the proton and neutron, but there are many others consisting of various excited quantum states of various combinations of quarks. Quark/antiquark pairs are called "mesons", and combinations of three quarks are called "baryons". Since energy and mass are pretty much interchangeable in these systems, excited (higher energy) states, act like particles with a larger mass.

## Re:Quark and anti-quark? (Score:2, Informative)

Let's start by understanding that many of the subatomic particles we believe exist have never been "seen", per se. We have indirect observations, combined with mathematical models which appear to make good predictions about what we may observe when specific interactions occur.

In many cases, the mathematical models are created to explain a given observation and then tested by predicting what may be observed under different circumstances. Quark

theoryis just one such set of mathematical models. It appears to correctly predict what certain subatomic interactions will look like when we manage to experimentally create the right circumstances. Within quark theory, quark/antiquark annihilation is not defined, as that has not been necessary to explain the phenomena we have observed nor does it lead to any verifiable predictions.At this point, I feel obliged to point out that merely because the mathematics produces good results and seems to model the real world well, that does not mean that the real world obeys the mathematics - only that we are evolving better and better tools for making predictions. When (if) it ever becomes necessary to model quark/antiquark annihilation to explain an observation the mathematics will be worked out and predictions made of what other interactions may look like. If the math results in a contradiction, the reasoning leading to that math will be reevaluated until it makes accurate predictions without resulting in contradictions.

In short, quark/antiquark annihilation does not take place because we have not defined that as a property of quarks. Until there is an observation which requires that definition, it will not be made. It is not a natural part of the mathematics of quark theory.

## Re:Quark and anti-quark? (Score:5, Informative)

Within quark theory, quark/antiquark annihilation is not defined, as that has not been necessary to explain the phenomena we have observed nor does it lead to any verifiable predictions.

This is total nonsense. Quark/antiquark annihilation [aps.org] is perfectly well-described in standard theory. The answer to the OP's question is that the quark and antiquark

doannihilate, which is why all mesons are unstable. But it takes a little bit of time for the annihilation to happen, which gives you the lifetime of the meson.## Re:Quark and anti-quark? (Score:4, Informative)

They can and they do, but the process does not have to occur instantly (although it will happen pretty darn fast by human time scales) and the probability of decaying via one of these processes may be very small indeed. In this case it seems (although I haven't really had a chance to read the paper) that other decay processes occur faster than any annihilation process, so those happen very rarely.

Why do they happen very rarely? Well it looks from the abstract that this is a excited state of the beauty anti-beauty system, so it probably has to shed some angular momentum before it can decay to any reasonably small number of elementary particles (angular momentum is a conserved quantity). This thing basically shoots off a photon (a quanta of light) and turns into another beauty anti-beauty meson called an Upsilon, which can then decay via an annihilation process.

In short a conserved quantity (probably angular momentum) makes it far more likely that this system will decay to a Upsilon rather than some final state which is the result of some annihilation process.

Why is angular momentum conserved? Because the laws of physics appear to be symmetric under rotations (simplifying a tad). Why is that the case? Hell if I know.

One poster has suggested that it is because the particles are not 'touching'. At this length scale the notion of a position of a particle is questionable at best. These are not localised things that are going in circular orbits. Another poster has suggested that quarks are just mathematical objects. This is true, but it is also true of every theoretical notion you have. Given that all you have in your brain is models of reality this position works just as well when applied to dogs and cats as it does to quarks and upsilons.

## Re:A new particle or a new state of known particle (Score:4, Informative)

I think the use of flavour here is quite okay, to be honest

Actually, it's not, because flavour [wikipedia.org] has a very distinct and very different meaning in this context.

## Re:"Observed"? (Score:4, Informative)

## Higgs != Gravity (Score:5, Informative)

The thing is we have the 'graviton' listed as the force carrier, but we have not seen or don't even really know what a graviton would look like, so the Higgs is almost and alternate / parallel description of the mechanism.

Sorry but this is just wrong. The Higgs mechanism has nothing whatsoever do so with gravity and is definitely not just some alternative description of it. For a start it is a scalar field with spin-0 and so cannot create a force because that requires a direction so there is no way at all that the Higgs can possibly explain gravity - although it does explain very clearly why energy and mass are related. I appreciate that you are trying to simplify things down for a more general audience but you went a little off the rails here!

## Re:Higgs, Mass and Gravity (Score:5, Informative)

I'm not sure I understand how a 115â"130 GeV/c^2 Higgs boson can give mass to a 0.5 MeV/c^2 electron.

That's because the Higgs boson itself does not give the electron mass it is the Higgs field: the Higgs boson is just a quantized vibration of the Higgs field, like a photon is a vibration of the EM field. If you think about it in terms of the surface of a lake then the Higgs boson is a ripple on the surface. However the water in the lake will produce drag even if there are no ripples e.g. if the object is moving very slowly...but things are a little difference because water waves are classical and do not have quantized energy levels.

The "drag" i.e. mass, comes from the fact that the Higgs field does not have zero value. When writing down the equations to describe this physics you end up with two terms: one describing how a Higgs boson couples to the particle and one describing how the non-zero vacuum Higgs field couples to the particle. Since the vacuum value of the Higgs field is constant, and the field is scalar, this last term looks identical to a mass term so the particle behaves exactly the same as a particle with a mass.

The Higgs boson's mass is simply the minimum amount of energy to make the Higgs field vibrate. This is a quantum oscillator effect and so it depends on the shape of the Higgs potential around the vacuum state i.e. how does the energy density in the Higgs field change as you move the field away from the vacuum groundstate.

if mass is caused by Higgs wouldn't that make gravity dependent on Higgs?

No - think of it this way. The Higgs field explains why mass and energy are interchangeable because it explains the mass of the fundamental particles as a binding energy to the non-zero "constant" Higgs field in the universe. Hence all mass is caused by "binding" energy either to the Higgs field e.g. electrons or between particles e.g. quarks in a proton.

Gravity is a force which couples to a particle's 4-momentum NOT just to its mass. This is something Newtonian gravity gets wrong: gravity will bend light which is massless but which has a non-zero 4-momentum. All the Higgs field does is change that 4-momentum. However if we lived in a universe without a Higgs field, so that the fundamental particles have no mass, the mass-less electron would still feel gravitational forces just like the photon does in ours.