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New ATLAS result weighs in on the W boson

57 点作者 JohnHammersley大约 2 年前

12 条评论

buildbot大约 2 年前
Very cool. Unrelated, but the technology and engineering behind ATLAS is immense. ~98 million data channels streaming out at 2Ghz (at least that is what I recall). Cut down to a manageable level by hundreds of FPGAs in the L1 trigger.<p><a href="https:&#x2F;&#x2F;cds.cern.ch&#x2F;record&#x2F;2745767&#x2F;files&#x2F;ATL-INDET-PROC-2020-003.pdf" rel="nofollow">https:&#x2F;&#x2F;cds.cern.ch&#x2F;record&#x2F;2745767&#x2F;files&#x2F;ATL-INDET-PROC-2020...</a>
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hislaziness大约 2 年前
&quot;For this new analysis, ATLAS physicists revisited its data collected in 2011 at a centre-of-mass energy of 7 TeV (corresponding to 4.6 fb-1, also used in ATLAS’ previous measurement). Researchers employed improved statistical methods and refinements in the treatment of the data, enabling them to reduce the uncertainty of their mass measurement by more than 15%.&quot;
filmor大约 2 年前
Hah, my Bachelor thesis from 2009 explored a measurement channel for the W and Z bosons a bit (qq-&gt;WZ-&gt;llνl, so two quarks become a W and a Z which then decay into in total 3 charged leptons and a neutrino, &quot;Di-Boson Events with Leptonic Final States&quot;), sadly with simulated data as the restart after the issues from 2008 was delayed. The simplest way to measure the W and Z masses was to &quot;pattern match&quot; potential events in the data (which were already heavily preprocessed with &quot;pseudo particles&quot; derived from the tracks in the inner detector, myon detection and calorimeters), in my case Z-&gt;µµ or Z-&gt;ee, try ones best to filter out parallel channels (e.g. Z-&gt;t tbar) and then derive information from the histograms of the &quot;transverse mass&quot;, which is essentially the effective mass with the momentum component longitudinal to the beam deducted (<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Transverse_mass" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Transverse_mass</a>).
pierrebai大约 2 年前
This is ludicrous, but this kind of thing have been going on in science and physics in particular for a long time. Let&#x27;s call the phenomenon maths side-blinders.<p>One experiment finds the mass of thw W boson to be 80370 +&#x2F;- 19 MeV, another 80434 +&#x2F;-9 MeV. Clearly, both results are incompatible, their rnage don&#x27;t overlap. Of course, these are statistical ranges. But even with 95% certainty, their differences is <i>many times</i> the uncertainty, so it&#x27;s not just that they&#x27;re a bit off. IOW, we can be 100% (not 95%) sure that at least one, if not both, are incorrect.<p>Yet they are boldly reported with those uncertainty ranges, even though, clearly , those ranges cannot be correct. And then ATLAS double down by &quot;apply more statistical analysis&quot; to narrow their uncertainty range!<p>There should not be work on &quot;improved stats analysis&quot;, but more work on finding where the systemic error between the two experiment lies. I truly don&#x27;t see the point of retreading the same data set to change the value and uncertainty range when clearly there is something wrong with the data, the science, the experiment or all of the above.<p>PS: what I&#x27;d like to see, is the labs to say something along the line: given result A and B being incompatible, statistically there is a (say) 99.99% chance that one or both experiment has a hidden flaw or that there is a major flaw in the standard model.
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bmitc大约 2 年前
What are the current implications of the experiments at CERN and for ATLAS? My current interpretation is that these are massive engineering marvels that are basically just data generators for some physicists to run statistics on. That is a pessimistic view, but I am just not aware of what&#x27;s all going on there.<p>Compare this to LIGO, where one could make a similar argument, but LIGO is producing very explicit data that is driving tons of research and discoveries and is providing tandem support for electromagnetic observations.
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heywhatupboys大约 2 年前
Ever noticed how physicists were all the rage in late 2000&#x27;s, but now not so much? seems like the world has stopped caring about elementary particles.
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beezle大约 2 年前
Anyone with a good link on why CDF is the outlier?
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ttpphd大约 2 年前
Would love to have an explanation of statistical vs total uncertainty, how they are quantified and how they are different.
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Idiot_in_Vain大约 2 年前
If you want a short introduction on why physicists care so much about the weight of the W boson: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=G0Q4UAiKacw">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=G0Q4UAiKacw</a>
kzrdude大约 2 年前
I didn&#x27;t notice the scale of the X axis at first, it seems like the difference between measurements is not that great.
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qwezxcrty大约 2 年前
tldr: The ATLAS Collaboration has measured the W boson mass and it&#x27;s in agreement with the Standard Model.<p>Unfortunately, no new physics yet and we can now forget about the previous excited reports.
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Pulcinella大约 2 年前
I know this is anthropomorphizing, but the Weak force always seemed like the weird hack or cludge of the fundamental forces. Yeah it works, but do we really need two different W bosons and also a Z boson? The electromagnetic force does just fine with just the photon.<p>More anthropomorphizing, the fact that there are three generations of matter feels like a premature optimization or someone applied too much abstraction and extensibility to the universe. One or two generations makes sense, but three feels like someone thought the system would need to scale to an infinite number of generations and then that didn’t happen.
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