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  • Suppose you want to discover a particle.

  • First, you need to-

  • Of course!

  • Thanks for walking us through that point, John.

  • If we're honest, we should say that the mathematical model for the Higgs was discovered in the

  • 1960s, but the particle itself wasn't dis- wasn't confirmed until 2012.

  • In fact, the Higgs boson ISN'T even the first new particle to be... "uncovered" at the Large

  • Hadron Collider: the Xi-b particle, basically a heavy version of the neutron, was actually

  • found several months earlier.

  • You probably didn't hear much about it because the Xi-b is just a combination of quarks that

  • we already know existÐ so it's not really that exciting.

  • I mean, if you know about cheese and you know about crackers, then the discovery of "cheese

  • and crackers," as delightful as it is, isn't likely to upend your universe.

  • But the Standard Model of particle physics also predicts something beyond cheese and

  • crackers - that is, about one out of every bajillion collisions should produce a Higgs

  • boson, which then decays into everyday stuff like electrons and photons, which are the

  • same crumbs we catch in the detector all the time.

  • This battle between the tiny chance for a collision to have produced a Higgs-like particle

  • versus all the trizillion other collisions that produce similar crumbs is part of why

  • we need a big machine like the Large Hadron Collider at all.

  • There were earlier accelerators that had enough energy to create Higgs bosons in principle

  • - but they couldn't actually do enough collisions to be confident they were actually seeing

  • a Higgs boson and not just an assortment of crumbs that looks by chance like it's from

  • a Higgs Boson.

  • It's kind of like trying to find out if a 20-sided die is rigged.

  • Maybe you suspect it's twice as likely to land on a three than on any of the other numbers.

  • But how can you check?

  • Well, that sounds easy enough - just roll the die a few times and if you see extra threes,

  • it's rigged, right?

  • Not so fast.

  • For example, if you roll the die ten times, there's a pretty good chance that you won't

  • get any threes at all!

  • That's because even though rolling a three is twice as likely as all the other numbers,

  • there are still a lot of other numbers you could roll.

  • So random chance and big numbers can be surprisingly deceptive - even if you roll the die a hundred

  • times and DO get an excess of threes, there's still a one in fifty chance that the die IS

  • fair and you just got this number by accident.

  • How much are you willing to bet that you actually have evidence for a new particle if there's

  • a one in fifty chance your results are simply a random fluctuation and the particle doesn't

  • actually exist?

  • What if a Nobel Prize is on the line - how sure do you want to be?

  • One in a thousand?

  • One in ten thousand?

  • Actually, physicists are even more stringent they won't say they've "discovered" a particle

  • unless the odds that they might get the same results even if the particle DOESN'T exist

  • are less than one in a millionso if you want to convince a particle physicist that

  • you've discovered an unfair die, you'll need to roll over five hundred and fifty times

  • to satisfy them!

  • And that's just to check if a twenty-sided die is riggedthere are far more than

  • twenty possible outcomes of a high-energy particle collision, so in order to be confident

  • about announcing evidence for a new particle at the LHC, you need around 600 million collisions

  • every secondfor two years.

  • Only then can you uncork the wine to go with your cheese and crackers, and claim a successful

  • discov– I mean, successful scientific fact-checking.

Suppose you want to discover a particle.


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ヒッグス粒子 第三部:粒子の発見の仕方 (Higgs Boson Part III: How to Discover a Particle)

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    林宜悉 に公開 2021 年 01 月 14 日