sage
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Anybody notice Changhai's post: origin of mass III
It contains a very good intro to Higgs mechanism.
| 发表时间：2005-06-17, 13:23:12 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
昌海学友的这篇质量起源是很好的科普。尤其是从概念和
历史上讲清楚了Higgs机制是怎样被引进场论来产生其它粒子
的质量项的。
不过，我对Higgs机制有点怀疑。按现在的说法，Higgs粒子要在
能量更高的加速器上才能找到，可是W和Z粒子在现在的加速器上
已找到，而W和Z粒子的质量就是由Higgs机制产生的，那么为什么
可以认为Higgs粒子要在更高能区才能找到呢？
道可道非常道
名可名非常名
| 发表时间：2005-06-17, 18:43:55 |
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kanex
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Re: Anybody notice Changhai's post: origin of mass III
因为higgs很重。
江畔何人初见月`江月何年初照人`
| 发表时间：2005-06-18, 02:09:52 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
Higgs很重说明了在现有能量区内不能产生，我可以接受
这个讲法。但是，这也就意味着W正负和Z粒子无法通过
“吃”掉Higgs粒子来获得质量，那么，它们的质量从何
而来呢？弱电统一模型是否要修改呢？
道可道非常道
名可名非常名
| 发表时间：2005-06-18, 07:37:43 |
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kanex
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Re: Anybody notice Changhai's post: origin of mass III
为什么就不能吃掉了。
不过，说到这个，我目前暂时没看过higgs粒子本身的质量是怎么解释的。
对这方面关注不是很多，因为一切都要等LHC实验结果才能做。
江畔何人初见月`江月何年初照人`
| 发表时间：2005-06-19, 10:31:12 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
不是不能吃掉，而是没有Higgs粒子可吃。
因为按照Higgs粒子太重的说法，在现在的能量标度
下不能有Higgs粒子产生，因而也就没有Higgs粒子
让W正负和Z粒子通过Higgs机制来获得质量。
我想有一点要注意的是，在弱电模型提出来时，没有
Higgs粒子太重的说法。只是在W正负和Z粒子的找到后，
而Higgs粒子却找不到的情况下，才出来Higgs粒子太重
的说法。
这是一个解释，但是这个解释与原来的弱电模型有矛盾之处，
是不是这样呢？
道可道非常道
名可名非常名
| 发表时间：2005-06-19, 11:49:50 |
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dolphin
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Re: Anybody notice Changhai's post: origin of mass III
Higgs机制是很迷人的,象是一种质量产生机制的美妙解释,只能期待LHC在07年后的运行了.
| 发表时间：2005-06-19, 20:39:08 |
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sage
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Re: Anybody notice Changhai's post: origin of mass
因为按照Higgs粒子太重的说法，在现在的能量标度
下不能有Higgs粒子产生，因而也就没有Higgs粒子
让W正负和Z粒子通过Higgs机制来获得质量。
我想有一点要注意的是，在弱电模型提出来时，没有
Higgs粒子太重的说法。只是在W正负和Z粒子的找到后，
而Higgs粒子却找不到的情况下，才出来Higgs粒子太重
的说法。
这是一个解释，但是这个解释与原来的弱电模型有矛盾之处，
是不是这样呢？
well. maybe changhai will mention it in his later series. let me briefly explain it as following.
Yes, Higgs should be roughly at the same scale as W and Z bosons. However, adding up all the collider experiment we have so far, we are still exploring the neighbourhood of weak scale. Therefore, the wording 'roughly' is very important.
masses of W and Z roughly scales like gv where g is gauge coupling and v is the VEV of the Higgs.
On the other hand, the mass of Higgs goes like \lambda v (or sqrt(lambda) v depending on the definition of lambda) where lambda is some coupling in the Higgs potential and v is Higgs VEV.
you see at the level, it is not very hard to have order 1 splittlings between Higgs mass and W and Z masses because they depend on different coupling constants, although it is true that they are both proportional Higgs VEV. For the reason you have said, we do not expect them to be very different.
Now, more importantly, let look a little further to see how do we discover them.
It is very important to realize that in a collider, any new particle do not come out with a little flag on it saying that 'hey, my name is ....'. Most of the particles, like Higgs or W/Z, decay before it reach any detector. Therefore, we only see their decay products. A usual practice is to detect the decay products, from them, we infer the production of a 'mother' particle.
It is also very important to realize that we have no control to select one kind of particle to produce. We product all of them according to certain probabilities. Therefore, in order to single out a channel, we have to go above the background, ie, other particle productions.
(I realized that I will need more discussion here, let me continue with another post.)
| 发表时间：2005-06-20, 13:33:21 |
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卢昌海
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Re: Anybody notice Changhai's post: origin of mass
:: Higgs很重说明了在现有能量区内不能产生，我可以接受
:: 这个讲法。但是，这也就意味着W正负和Z粒子无法通过
:: “吃”掉Higgs粒子来获得质量
W and Z do not eat Higgs, they eat Goldstone particles (BTW, the descriptive word "eat" shouldn't be taken too seriously - how can you eat something massless to become fat? :-), so there is no issue as whether Higgs is too heavy for it to be "eaten" by the W and Z particles.
:: 因为按照Higgs粒子太重的说法，在现在的能量标度
:: 下不能有Higgs粒子产生，因而也就没有Higgs粒子
:: 让W正负和Z粒子通过Higgs机制来获得质量。
:: 这是一个解释，但是这个解释与原来的弱电模型有矛盾之处，
:: 是不是这样呢？
Again, the assumption W and Z aquire mass through Higgs mechnism doesn't mean Higgs particle has to be lighter than W and Z, therefore a Higgs particle heavier than W and Z doesn't conflict with electroweak theory (of course, if Higgs is too heavy, it would conflict with certain consistency conditions set by experiments, but that's a different issue).
宠辱不惊，看庭前花开花落
去留无意，望天空云卷云舒
| 发表时间：2005-06-20, 14:08:26 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
::Again, the assumption W and Z aquire mass through Higgs mechnism
::doesn't mean Higgs particle has to be lighter than W and Z, therefore
::a Higgs particle heavier than W and Z doesn't conflict with electroweak theory
OK, "W and Z aquire mass through Higgs mechnism", so I think there has to be somehow someway a Higgs particle's participation, otherwise, what this Higgs mechnism indicates? I am not saying Higgs particle has to be lighter than W and Z,
what I mean is that when we find W and Z, we know (according to theory) there is
a Higgs mechnism, therefore, there are Higgs particles involved ( this is my understanding). Hence, Higgs particles should be there in the current collider.
I can accept what sage said, some particles may be difficult to find, what confuses
me is the saying that "Higgs particle is too heavy", that means we do not have Higgs particle in the current collider, however, we have Higgs mechnism and we found W and Z.
A higher energy collider may make it easy to find Higgs particle, that I agree.
道可道非常道
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| 发表时间：2005-06-20, 15:00:38 |
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卢昌海
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Re: Anybody notice Changhai's post: origin of mass
What makes you think the discovery of the W and Z implies "Higgs particles should be there in the current collider"? You can only say the discovery of W and Z is a strong indication for the correctness of Higgs mechanism, or a strong evidence for the existence of the Higgs particle. None of these has any contradiction with the statement "Higgs is too heavy". What we mean by "Higgs is too heavy" is the MASS of the Higgs particle is heavier than the light-energy region that has been excluded by current experiments. Such a Higgs particle can still have effects in the energy range of the current colliders. A particle's mass doesn't have to be within the scope of the current collider for it to participate in the processes on those colliders.
宠辱不惊，看庭前花开花落
去留无意，望天空云卷云舒
| 发表时间：2005-06-20, 15:32:03 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
I got that idea when I leant the weak-electro-unifying model. It predicts that the
W and Z does not have mass at the start, and then due to Higgs mechinsm, they gain mass. Later they found W and Z in a collider, that says Higgs mechinsm works, therefore, if we think the weak-electro-unifying model is right, should Higgs particles be in there, too?
道可道非常道
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| 发表时间：2005-06-20, 16:01:54 |
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卢昌海
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Re: Anybody notice Changhai's post: origin of mass
You might have confused a particle's mass with its possible contribution to the physical processes at an energy scale below it's mass. A particle's mass can be "too heavy" for the current colliders to directly create and unambiguisously identify it, yet it is totally fine for such a particle to contribute to other processes on those colliders (although there will be a suppression factor for such contributions if the collider energy is low).
:: if we think the weak-electro-unifying model is right, should
:: Higgs particles be in there, too?
Yes, if electroweak theory is correct, then Higgs is already there in the sense it already contributed to the physical processes we observed on the current colliders. But - as said above - that doesn't mean Higgs mass has to be in the same range, therefore doesn't contradict to the claim "Higgs is too heavy" (which merely means Higgs mass is heavier than the low-energy region excluded by current experiments).
宠辱不惊，看庭前花开花落
去留无意，望天空云卷云舒
| 发表时间：2005-06-20, 16:11:46 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
Let me go slowly to clarify my thoughts.
1) I accept electroweak thory is right so Higgs mechnism does play a role
2) The discovery of W and Z is an indirect evidence that Higgs particle exists in the current colliders.
To here, there is no disagreement, right?
3) Now, I say if Higgs particles are there, why we can not find them?
The answer usually is that "Higgs particle is too heavy". In particle physics,
the mass and energy is used interchangebly, a particle too heavy means the energy requirement is high, therefore, a higher energy collider is needed. To me,
that statement means that the Higgs particles can not be created, if they are already there, even they are heavy, they should be found.
I guess the point here is that, if you explain this statement that "Higgs particle is too heavy" causes difficulty to observe them, then it is OK, I can accept, if "Higgs particle is too heavy" means in a low energy collider, Higgs particles can not exist, then my question stays.
So, your opinion is that, in a collider of finding W and Z particles, Higgs particles are already there, which provides Higgs mechnism and let W,Z get mass. But, since Higgs particles are too heavy, it is difficult to observe so that a higher energy collider is needed. Do I understand you correctly?
道可道非常道
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| 发表时间：2005-06-20, 18:38:55 |
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卢昌海
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Re: Anybody notice Changhai's post: origin of mass
:: if "Higgs particle is too heavy" means in a low energy collider,
:: Higgs particles can not exist, then my question stays.
This seems to be the key mis-understanding. Higgs can exist at any energy as a virtual particle, and contributes to certain physical processes. Higgs mass only sets a threshold for creating Higgs as an on-shell particle.
宠辱不惊，看庭前花开花落
去留无意，望天空云卷云舒
| 发表时间：2005-06-20, 19:29:39 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
OK, I can stop at here now. I used to think that the "Higgs particle is too heavy" is
a saying invented by some physists so that they can ask for more money to build larger collider.:-)
Anyway, let's wait and see, I think if this time the Higgs particle can not be found, all the reasons to build an even bigger collider still exist and the thory will never fail.:-)
道可道非常道
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| 发表时间：2005-06-20, 19:46:01 |
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可见光
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Re: Anybody notice Changhai's post: origin of mass III
元江兄应该注意，on-shell的Higgs粒子可能很容易衰变，或者很容易跟其他粒子发生反应，所以自然界没有现成的供我们景仰，只能靠实验室产生。
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| 发表时间：2005-06-21, 08:03:18 |
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元江
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Re: Anybody notice Changhai's post: origin of mass III
我想这样说还是合理的，能接受：-)
“Higgs粒子太重”这句话
如果归结为实验上很难观察到，所以需要更高能量的加速器来捕捉它，
那我可以理解。但是我在另一方面产生疑问，那就是这个理由是万能的。
我们化一百亿造个加速器，找到了Higgs粒子，皆大欢喜，找不到，
那就还是“Higgs粒子太重”，然后再化一千亿造个加速器，如此循环
往复，何处是个头呢？
不知道现在有没有对Higgs粒子的重量有个合理的估算？比如说，在什么
样级别的加速器中找不到，那就可以认为Higgs粒子不存在？
道可道非常道
名可名非常名
| 发表时间：2005-06-21, 09:05:30 |
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