Uploaded by minutephysics on 26.07.2012

Transcript:

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 million… so 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 rigged – there

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 second… for 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.

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 million… so 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 rigged – there

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 second… for 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.