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February 25, 2005



Forgot to mention this in your post below about quarks and gluons, but your use of color in descriptions is excellent. Along with text books being more light-hearted, more color within the text would be an excellent addtion to draw attention to an interesting/important fact.


Very interesting!!! The size comparisons to atoms are quite helpful and surprising. ^_^

Alejandro Rivero

Aaron, the problem with the size comparisons to atoms is that if taken too seriously, you will notice that the (unexplained in nuclear physics) stability enhancement areas coincide with the masses of known and predicted (115 GeV, e.g.) particles. As such thing is not possible to explain (very different # of degrees of freedom, and dissimilar mathematical structures), most people seems to prefer to forgot about such comparisons.

Tommaso Dorigo

Mattew: thank you for your comment! I will try to keep my posts as colored as needed...
Aaron: yes, the "size" comparisons are surprising... That is because we tend to associate size with mass, when that can be done only with a fridge, a car, or a pencil. Not with atoms, and less so with elementary particles (for which size is zero by definition and mass can be large!). That is what makes the mass comparison between a top quark (which, with very small probability, can be found even within a mere proton!) and a whole gold atom interesting.
Alejandro: your comment is kind of cryptic, although I sort of understand what you mean. Can you elaborate a bit for the public here ?
Thanks to all!


Alejandro Rivero

Tommasso, sorry to be so cryptic. For the public: I was referring to the ad-hoc corrections to spin-orbit coupling in nuclear physics. As some of you may know, different strength of the coupling must be used at different nuclear masses, in order to fit the measured energies and to get the right magic numbers. Modelling of massive nucleus is still the empirical art we learnt in the school.

Now, if you ask for plots nuclear stability models, you will notice very clearly the effect of the spin orbit correction when you trace the "drip lines", the extreme frontier of stability of a nucleus. Here you have the plot of the drip lines for four different models: http://dftuz.unizar.es/~rivero/research/uno.gif
Blue lines are the magic numbers. Red diagonal lines join, of course, nuclei having the same mass. You can notice the pass near the discontinuities caused by the empirical adjustment, specially the three rightmost ones in the neutron dripline.

And here is where you run into trouble if you have in mind the "so much GeV = so much atomic mass" analogy. These three red lines are, cof, at 246, 175 and 115 GeV.

Tommaso Dorigo

That helps a lot!
Thank you, I think you took out of the dark many of our sporadic readers...


Alejandro Rivero

Thank you for asking, Tommasso. I do not know if we can get a moral of my brief exposition. Perhaps "analogies? Don't touch!".

Or perhaps that we will find new physics at 246. LHC will tell. Cheers.


Caro collega, sperando che la cosa non ti dia fastidio ho riciclato questa tua eccellente illustrazione per un seminario divulgativo che mi e' stato chiesto di tenere:

Se ci fossero controindicazioni al riguardo fammi sapere (via mail), provvedero' immediatamente alla sostituzione con qualcos'altro (anche se difficilmente trovero' qualcosa di altrettanto autoesplicativo!)

Un grazie anticipato.

Tommaso Dorigo

Caro Andrea,

sorry if I answer only now to your comment. Sure, the material in this web page is public, everybody can use it. If it is private pictures it is a different story - but for graphs, go for it!


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