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Author Topic: Is the Higgs mechanism a load of cods?  (Read 7237 times)

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« on: 26/06/2007 12:01:12 »
The Higgs mechanism was devised to account for the mass of certain particles. However, it seems that applying this mechanism causes another, equally intractable, problem; that being, the mass of the Higgs particle would be far too high. To make it work, physicists need to apply a fudge factor (fine tuning, as they euphemistically call it). Now, this isn't just a little fudge. It needs to be accurate to 16 decimal places.

I've read that the Higgs mechanism is the only way that these particles can gain mass. That seems to me to be a very arrogant, if not ignorant, statement. Surely, all that can be said is that it is the only theory so-far devised that even sort-of maybe can account for the mass of particles even though it needs to be botched quite a bit.

Can the truth be that the Higgs mechanism doesn't, in fact, exist? Or is there something very fundamental that I'm not understanding that means the Higgs mechanism must be correct?
« Last Edit: 26/06/2007 12:02:56 by DoctorBeaver »


 

paul.fr

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Is the Higgs mechanism a load of cods?
« Reply #1 on: 26/06/2007 12:34:31 »
have a coffe and give this a read, Doc.
http://www.exploratorium.edu/origins/cern/ideas/higgs.html
 

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« Reply #2 on: 26/06/2007 13:22:37 »
Paul - I've read that - & a lot more stuff that goes into a lot more detail. I know what the Higgs mechanism is & what it's supposed to do. But my problem with it remains unanswered. It solves 1 problem at the expense of creating another equally intractable problem. So, is it just a red herring?
 

paul.fr

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Is the Higgs mechanism a load of cods?
« Reply #3 on: 26/06/2007 13:26:29 »
Isn't this what the LHC at CERN is trying to prove?
 

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« Reply #4 on: 26/06/2007 13:39:45 »
Among other things, yes(ish). But it quite possibly won't give any definitive answers. The reason being that according to the theory, the light Higgs particle should have a mass equal to the weak scale mass (250GeV) & colliders have had that capability for quite a while now (the LEP at CERNE and the Tevatron at Fermilab to name 2 of them). Thus far, the light Higgs particle has not been found.

The LHC will work at much higher energy (about 7 times that of the LEP) but if the light Higgs particle has a mass of 250GeV it should already have been found. If a particle is found at a higher mass then it won't be the light Higgs particle; unless, of course, the theory is fudged yet again to allow for a heavier mass.

The heavy Higgs particle is way beyond our hopes of ever detecting directly as its mass is predicted to be equivalent to the Planck mass, which is 1013 times the weak scale mass; i.e. the energy level required for a GUT.
« Last Edit: 26/06/2007 13:41:20 by DoctorBeaver »
 

paul.fr

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Is the Higgs mechanism a load of cods?
« Reply #5 on: 27/06/2007 09:40:23 »
As we all know, my memory and attention span is rather weak...so, Just why do we need there to be light Higgs particle?

Also, it seems not many people are posting here. So, if you could enlighten us all Doc, that would be splendid.
 

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« Reply #6 on: 27/06/2007 14:56:42 »
I was hoping Ian may be able to shed some light.

Enlighten you? Hmmm... OK, I'll try.

It's to do with gauge bosons. Gauge bosons are the particles that carry (or mediate, as it's known) the electromagnetic, weak & strong forces. There are 3 gauge bosons - the W, Z & the photon (although the W can be W+ or W-). For some reason, physicists love symmetry; but symmetry says that all of these bosons should have zero mass. Experiments have shown that not to be the case. All bosons apart from the photon have mass. So, the symmetry needs to be broken by a process known as Spontaneous Symmetry Breaking. That's where the Higgs particle comes in.

Higgs particles interfere with the W & Z bosons to give them mass - at least, that's what the theory says. The problem arises because, according to Quantum Field theory, Higgs particles should be equivalent to the Planck mass; whereas, to cause spontaneous symmetry breaking they need to be 10 million trillion times lighter. That's where the 16 decimal place fudge factor comes into it.

To cause spontaneous symmetry breaking of the weak force particles, Higgs particles should have a mass of 250GeV; but, although at least 2 colliders can operate at 250GeV or above, no Higgs particles have even been discovered.

Coming from 1 direction, Higgs particles should have been detected by now but haven't been, and coming from the other direction, they should have a mass 10 million trillion times their mass calculated the 1st way.

Now, it seems to me, that something must be awry with the theory. Would you not agree?
 

Offline Soul Surfer

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Is the Higgs mechanism a load of cods?
« Reply #7 on: 27/06/2007 23:43:02 »
I havent come in on this one because I thought everything was being explained quite well as in most of the popular articles. I must also admit that I have mixed feelings about the Higgs mechanism and the way it is explained myself.  However it does seem to be the main contendder that explains why mass exists.  (in the standard model the particles are essentially massless)

As far as detecting Higgs particles there are some reports of a slight hint that they may have been detercted but the results are not strong enough to be at the acceptable level of statisitical significance because they are right at the limit of the colliders and happen quite rarely.  the LHC shluld be able to make loads of them
 

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« Reply #8 on: 28/06/2007 00:18:44 »
Ian - thanks for your reply. I'm glad I'm not the only one with doubts.
 

Offline Soul Surfer

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Is the Higgs mechanism a load of cods?
« Reply #9 on: 28/06/2007 23:11:04 »
There's quite a good article in the June issue of Scientific American that gives a bit more background illustrating the convergent thinking betweek cosmologists and particle physicists that gives the concept a bit more solidity.

Also this week's New Scientist has a very intresting article on the evolution of physical laws by Paul Davies.  (a contemporary of mine at UCL although I'm not in touch with him)
 

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« Reply #10 on: 28/06/2007 23:14:46 »
Thanks, Ian. I'll check out those articles.
 

Offline chrisdsn

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Is the Higgs mechanism a load of cods?
« Reply #11 on: 01/07/2007 09:03:59 »
Hi DoctorBeaver,

You're right to think that the Higgs mechanism isn't
obviously correct, but I think that you're wrong to
think that it's problems are equally intractable as
removing gauge symmetry from the theory.

As regards the Higgs mechanism being correct, I think
you have simply read incorrect/overly general statements.
The Higgs mechanism as given in a text-book on the
standard model is simply the easiest way to spontaneously
break the gauge symmetry. There is active theoretical
research on variations of the mechanism (supersymmetric Higgs,
multiple Higgs, "little Higgs" to name just a few), and
on alternatives such as technicolor (another way to
spontaneously break the gauge symmetry). 

The restrictions on particle interactions due to gauge
symmetry are extraordinarily well tested experimentally.
From a combined theoretical/experimental point of view the
most compelling proof is the success of this model over
large changes in the energy scale. While the theory is
constructed in terms of fundamental particles, what are
actually observed are combinations of particles. For example
the theory of the strong force, QCD, consists of point quarks held
together by gluons. At high enough energy, experiments can
see what look like almost free quarks weakly coupled to
gluons. However, there is  -- of course -- some smallest
scale that such experiments can probe, while the the theory
consists of point quarks. When you look in a "small box"
of space you actually see is a quark (say) plus a bunch
of gluons and quark-antiquark pairs. What is actually observed,
then, is a "quark" which is actually a combination a quark and a bunch
of gluons and virtual quark-antiquark pairs, and a "gluon" which
is actually as combination of gluons and quark-antiquark pairs.
There is no reason (other than gauge symmetry) that such
combinations would still look like quarks interacting with
gluons with merely some changes to the interaction strengths as
they do. Moreover, the standard model not only predicts that
the almost free quark interacting with gluons model should work
over a large energy scale, you can calculate exactly how the
interaction strengths should change as the scale probed
changes, and this has been checked by experiment.   

Given that there seems to be good evidence that gauge
symmetry in particle interactions is well respected at the energies
currently probed by experiment, this leads to the need to break
the symmetry not in the interactions, but by the choice of
vacuum (another way to say spontaneously). Such situations
are not uncommon in other quantum systems : magnets are symmetric
between positive and negative, but under the right situation all
the spins in a system will align together and choose one or
the other as the ground state; The Miesner effect in superconductors
(which says that magnetic fields are excluded, leading to the
their very cool "levitation" effect), theoretically is almost
identical to the Higgs mechanism: the ground state within the
superconductor is breaks the U(1) symmetry of electromagnatism,
leading to the photons effectively becoming massive, and
therefore, short range.   

However, you are correct to point out that there is a
fine tuning problem, but unfair to mention the plank mass.
As with measuring a "quark", you can never observe a Higgs
in an experiment; you'll see a Higgs + gluons + virtual
particle anti-particle pairs. This "effective Higgs" will
have different couplings to the other particles (and a
different mass) depending on the scale at which you observe
it. The problem with the Higgs is that as higher and higher
energies are probed the "effective mass" of the Higgs grows
very fast (power law, rather thah the usual logarithmic
dependence), eventually rising to infinity. Obviously, an
infinite mass doesn't make sense, so before that energy scale
is reached something has to happen. Examples would be new
particles/forces. These would modify what should be included
in the "effective Higgs" and so the scaling of it's mass.   

If you assume that there is only the Standard model forces
and Gravity, then the only thing that can save the Higgs
theory from an infinite mass is Gravity, which starts to
become important around the Plank scale. In this case you would
have the 16 digit fine tuning problem. However, if you simply
require that fine tuning should not occur you get the
requirement that some new particle/force should be seen
when we probe ~2TeV. This is a range as yet unstudied by
experiment, and one which most high energy particle physcists
I've talked with (I am one, so I've talked with a few) are
expecting something to new to be seen (an argument that
was used to justify the -- sadly canceled -- super-conducting
super-collider).

best,

chrisdsn

ps. My memory is that the expected higgs range has not yet been probed
(i though the limit was ~> 110; maybe you're confusing the detector main beam
energy with the 95% confidence level on the Higgs mass?)
     


 




 
 

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« Reply #12 on: 01/07/2007 09:39:16 »
Chrisdsn - Thank you for that very comprehensive reply. You have clarified a couple of points I wasn't sure about.

As you may, or may not, know, I am not a physicist of any kind. I am, however, fascinated by particle physics and I take a very keen interest in it.

I started this thread as a result of re-reading a book called "Warped Passages" by Lisa Randall (you've probably heard of her) and the figures I quoted came from that book. It is, though, quite possible (probable, even) that I misunderstood what she wrote. The reason being that a lot of the theories she explains, she does so in very basic terms that don't really say a lot. She then adds footnotes to further explain, but these are often in very technical or advanced mathematical form which I often find difficult to follow.

Also, as her book is primarily about warped higher dimensions & branes, she skips over many other theories; she will merely state that "...according to whatever-theory, so-and-so is such-and-such." or whatever, without explaining what it all means.

Quote
For example
the theory of the strong force, QCD, consists of point quarks held
together by gluons. At high enough energy, experiments can see what look like almost free quarks weakly coupled to gluons. However, there is  -- of course -- some smallest scale that such experiments can probe, while the the theory consists of point quarks. When you look in a "small box" of space you actually see is a quark (say) plus a bunch of gluons and quark-antiquark pairs. What is actually observed,then, is a "quark" which is actually a combination a quark and a bunch of gluons and virtual quark-antiquark pairs, and a "gluon" which is actually as combination of gluons and quark-antiquark pairs.

Would these be anything to do with jets?
 

Offline Soul Surfer

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Is the Higgs mechanism a load of cods?
« Reply #13 on: 02/07/2007 10:42:45 »
Thanks too chrisdn. 

Re higgs detection I thought that current experiments at maximum energy in fermilab just get into but do not fully encompass the range of the low mass higgs and that some slight statistical hints had been detected but the stats are not good enough to warrant a true detection.

Re jets in processes these apply on the astronomical scales and also I believe in particle physics when high angular momentum conditions are encountered.  Contrary to what one might expect a force contained object that is rotating very quickly can only loose energy from the poles and not as one might expect by things flying off the equator in all directions this means that one gets jets from the poles of a rotating object that is losing energy and not a disk from its equator
 

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« Reply #14 on: 02/07/2007 15:07:17 »
Ian - I'm talking about a different kind of jet. Gluons hold quarks together so strongly that they are never(?) seen singly. I believe the mechanism is that if 2 quarks are being pulled apart, another moves into the gap between them (similar to keeping your distance on a motorway only to have another slip in between you & the car in front). These strings of quarks are called jets.
 

Offline chrisdsn

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Is the Higgs mechanism a load of cods?
« Reply #15 on: 03/07/2007 05:28:04 »
Soul Surfer - yes, Fermilab and the previous Cern experiments (before they
were shut down for the rebuild) have both seen hints, but -- from memory --
at the 2-3\sigma level; nothing to get too excited about yet.

My previous post/Jets -  There is no such thing as a "free" quark, as the
binding between them due to gluons (and the binding of gluon to
themselves) is so strong that at low energies we only ever observe
bound states of quarks and gluons. However quarks are "asymptotically free"
at high energies (the 2004 Nobel prize). As I mentioned before, what we call a quark at a given energy scale is actually a combination of a quark, gluons and quark-antiquark pairs. This combination changes with energy
 scale such that at large energy scales the "quark" looks not free, but
only weakly coupled to the gluons (the theory that describes how the
coupling to gluons changes with energy scale is called
"renormalisation") The physics of such high energy quarks
can be studied experimentally in scattering experiments
(google "Deep Inelastic Scattering"), which probe the high energy
structure of protons, neutrons etc.

This is what I was describing before; Jets are at even lower
energies: The flip-side of asymptotic freedom of quarks at high energies
is that the coupling of quarks to gluons (and gluons to themselves)
grows at low energies, to the extent that at such low energies (and
therefore large distances) all you see is a bunch of quarks and gluons
bound together into mesons and baryons. Quark-antiquark pairs are
appearing an disappearing all the time however. Sometimes it
is energetically favorable for a meson (say) (made of two quarks,
and a bunch of gluons) to "pick up" the such a pair and become two
mesons. With the very high energy baryons and mesons that are in the
collisions in particle accelerators this can happen many times
before the detector registers/counts mesons and baryons -- leading
to them measuring a "jet" of particles, that all started with a
single -- very energetic -- particle. So DrBeavers explanation was
almost correct: the extra quarks move in in pairs, not singly.


Therefore, while the theorists have the nice task of just
working out how likely the high energy processes are to
produce a certain meson/baryon, the experimentalists will
measure a jet of meson and baryons, plus some
leptons and have to work backwards to reconstruct the high energy
vertex. It's very hard, and takes enormous amounts of computing
time (just working out how many jets the particles you measured
belong to is hard). Thankfully, I'm a theorist :).

best,

chrisdsn.
 

Offline DoctorBeaver

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Is the Higgs mechanism a load of cods?
« Reply #16 on: 03/07/2007 22:56:48 »
Chris - you said that you are a high energy particle physicist. Does that mean you don't get overly involved with string theory or extra dimensions?
 

Offline chrisdsn

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Is the Higgs mechanism a load of cods?
« Reply #17 on: 07/07/2007 13:16:42 »
DoctorBeaver - I'm not personally involved in String Theory (or extra dimensions,
it you mean the Randall-Sundrum model). I think most String theorists would count
themselves as high energy particles physicists though, so that wasn't implied
by what I said.   
 

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Is the Higgs mechanism a load of cods?
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