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The decay of a W. Date: 1997/05/23
A W particle can decay into a quark or lepton pair. What factors does one need to consider it calculating which occurs more often?
What factors am i forgetting below.
Link to thread of next article. Re: The decay of a W. Author: Georg Kreyerhoff <georg@acaxp6.physik.rwth-aachen.de> Date:1997/05/27 Forum: sci.physics.particle
ale2@psu.edu (ale2) writes: > > A W particle can decay into a quark or lepton pair. What factors does > one need to consider it calculating which occurs more often? > > What factors am i forgetting below. > > 1 You must consider the states available to quarks and leptons, the > number is different. > Yes. Each quark has 3 colors. You can have the combination red-antired, green-antigreen, blue-antiblue. For the phase-space integrals both quark and lepton masses are negligible (except of course for the top- quark, which is kinematically inaccessible in the decay)
> 2 You must consider all quark and lepton members which can be involved > in the decay. > Ok.
> 3 There may be a constant factor which favors the decay of quarks over > leptons or visa versa? >
The coupling constants are the same. The CKM-matrix elements |V_ij|^2 arising in the decay-widths W-> u_i dbar_j (u_i labels the up-like quarks and d_j the down-like ones) sum up to unity for a fixed i. So, if you sum over all quarks, you don't need to consider them. Instead of working with the mass eigenstates, you might very well work in a base, in which the charged currents are diagonal (so that there are no transitions between different families).
From this I get
Gamma(W->hadrons) = 3 * (2/3) * Gamma(W->leptons) = 2 * Gamma(W->leptons)
(The first 3 is the number of colors. The factor 2/3 is present, because there are 3 lepton generations, but only 2 kinematically allowed quark generations.)
Of course this holds true only on tree-level, but is in rough agreement with the particle data book, which states, that 31.6% of all W's decay into lepton pairs.
Georg
Finding the sweet spot in sports. Date: 1997/05/28
I had a small hatchet in one hand and a crummy(?) golf club in the other. The club seems dead and i was curious if the club head was hollow. I started whacking the club head on the side with the hammer side of the hatchet (club head seems solid). Then i whacked the club face with the hatchet head across the face of the club. All the while i was holding the club by the handle.
It was amazing how the golf club vibration died completely when the sweet spot was hit!
If you play golf i suggest that you try the above and find your clubs sweet spot and mark it with a marker. The sweet spot can be determined in a matter of seconds.
I also tried this with a tennis racket and a baseball bat. The hatchet will work for the tennis racket but use a solid piece of soft wood (2x4) with the bat.
(Thinking out loud), does the position of the sweet spot depend on the mass of the object that is struck with club, bat, or racket? No flames please,
Re: Finding the sweet spot in sports. Date: 1997/05/29
In article <338D9A3B.5F8D@hydro.on.ca> Dan Evens <dan.evens@hydro.on.ca> writes:
> ale2 wrote: > > I also tried this with a tennis racket and a baseball bat. The hatchet > > will work for the tennis racket but use a solid piece of soft wood > > (2x4) with the bat. > > You know, there is an absolutely dandy object associated with baseball > bats that is very nice for finding their "sweet spot." It's called a > baseball.
Not as efficient as using a 2x4, think about it.
Pick up your bat and hold it horizontal with the left hand and holding a three foot length of 2x4 or 2x3 in your right hand strike the bat soundly with the wood where you think the sweet spot is. Continue striking the bat until you locate the sweet spot. The vibration will be minimal when the sweet spot is struck and you can "feel" the maximum amount of energy is transmitted, try it!
Re: the standard model. Date: 1997/05/28
In article <JJT.97May27114217@hepux1.hep.uiuc.edu> jjt@lns598.lns.cornell.edu (Jon Thaler) writes:
> Gluons are not composed of quarks
Probably not, but it is fun to keep an open mind to that very idea?
Re: Invitation to the Flamerion. Date: 1997/05/29
In article <5mkb9o$f72@chronicle.concentric.net> Hitech@cris.com (Hitech) writes:
> The given-enough-time-we-can-do-it scenario you describe was typical of AI > computer scientists' thinking during the 60's, 70's and even early 80's, > but not today. The book is about the failure of mathematical *logic* when > applied to *rational* thinking.
So throw mathematical logic out the door! The job will be done, it is just a matter of how it will be done.
Just a gut feeling and my 2 cents.
Link to thread of next article. Re: Invitation to the Flamerion. Date: 1997/05/29
In article <5mhlee$e5b@chronicle.concentric.net> Hitech@cris.com (Hitech) writes:
> You might want to read Goodbye Descartes, The End of Logic and the Search > for a New Cosmology of the Mind, by Keith Devlin. Delvin asks if our > thought and language are so logical why have all efforts to re-create them > fallen short? The most advanced artificial intelligence and natural > language programs do not begin to approximate actual human abilities. > Computing machines, of any kind, cannot and probably never will think like > us.
Give the computer scientists just a little longer please. What kind of hardware will we have in 100 or 1000 years, assuming we have not destroyed civilization in that time.
Re: Invitation to the Flamerion. Date: 1997/05/30
In article <5ml98e$le5@chronicle.concentric.net> Hitech@cris.com (Hitech) writes:
> > When mathematical logic is thrown out the door, Von Neumann computers > which use mathematical logic circuits such as NAND and NOR gates are also > thrown out.
So come up with new circuits if one must. I am not suggesting the job is easy, just that mankind is very ingenious.
Re: QUALIFIERS/COMPREHENSIVES. Date: 1997/06/07
In article <Pine.SGI.3.95.970606150153.10425D-100000@umbc8.umbc.edu> Cassiopeia <naggar1@umbc.edu> writes: > > I would like tips/ advice on preparing for graduate comprehensive > qualifying examinations. I am really scared about them. Also, all my > courses had open book exams and the qualifier is totally closed book, they > don't give you anything. I am terrified at the thought of memorizing > tons of material. > In small print on a large sheet of paper write down what information you think might be useful if such a sheet were allowed at test time. The act of making such a list will be of help even if you can't use it at test time, might have worked for me?
Re: Learning Physics. Date: 1997/07/06
In article <867899376.8384@dejanews.com> daniel@gateway.surfcity.nb.ca writes:
> I am 15 years old and am going into grade 10 next year. I have always > been interested in physics and I am trying to find out how I can learn > basic physics out of school because I cannot take it next year.
Get a (used if possible or better yet borrow one from a family friend or library) college level physics text (one for engineers) and skim through it, stopping at things that interest you. You will be surprised what you can figure out by studying the worked out problems. What you don't understand will give you a handle on what you need to learn (mathematical skills?).
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