QCD: Goddammit

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QCD: Goddammit

#1  Postby twistor59 » Dec 14, 2015 7:28 pm


Already the ATLAS experiment has put out two results which are a significant and impressive contribution to human knowledge. They represent a first look at the physical behavior of quarks and gluons at the highest collision energies ever examined. And to the disappointment of many, including me, they show the existing theory’s equations work very well!
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Re: QCD: Goddammit

#2  Postby crank » Dec 14, 2015 7:58 pm

Don't you just hate it when everything works exactly as predicted? I guess no surprise, no discoveries.
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Re: QCD: Goddammit

#3  Postby DavidMcC » Dec 30, 2015 3:40 pm

I'm afraid particle physics may be dying of old age. :(
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Re: QCD: Goddammit

#4  Postby lpetrich » Jan 11, 2016 4:53 am

This is evident from the smoothness of the curves. Running into some new particle would create a jump at its production threshold, and the curves contain no such jumps. So there is no evidence of a new QCD-interacting particle between the top quark's mass of 175 GeV and about 1 TeV, where the statistics become too weak.

Also evident is the lack of evidence of compositeness of known QCD-interacting particles up to about 1 TeV of energy. This is interesting because 1 TeV is far above their rest masses. This suggests that we have gone as far as we can in compositeness for elementary particles. Any further compositeness would require some mechanism like the mechanism that gives pions their low masses, and that requires an even greater spread in particle masses than what we observe.
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Re: QCD: Goddammit

#5  Postby newolder » Feb 14, 2017 4:37 pm

Don't know if this is the right topic - move as necessary...

LHCb experimenters report the Standard Model is good at 7.8 sigma for the decay of a heavy meson (two quarks in combination - a Bottom and a Strange)
14 February 2017: First single experiment observation of the decay Bs0→ μ+μ-.

From discovery to precision measurement.

[ Branching fraction Bs0→ μ+μ- = (2.8±0.6)x10-9 ; B0→ μ+μ- < 3.4x10-10 ]

Today, in a seminar at CERN, the LHCb collaboration presented the first observation by a single experiment of the decay Bs0→μ+μ-, with a statistical significance of 7.8 standard deviations. The measured branching fraction (2.8±0.6)x10-9 is in agreement with the Standard Model (SM) prediction of (3.65±0.23)x10-9. It is the most precise measurement of this quantity to date.

LHCb source
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Re: QCD: Goddammit

#6  Postby Rumraket » Feb 15, 2017 10:13 am

Imagine if they built the Superconducting Supercollider, and it confirmed the standard model and found nothing else new.
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