# B How many photos of the Higgs were taken before 7.4.12?

1. Sep 27, 2017

### gamow99

I read once that 37 photos of the decay products of the Top Quark were taken before its existence was announced but I have forgotten where I read it. Does anyone know the number of photos of the Higgs were taken before its existence was announced? Further, why would x number of photos yield a five sigma degree of certainty but not x - 1? Seems kind of arbitrary to me.

2. Sep 27, 2017

### gamow99

Alternatively, if someone knows the number of photos that were taken of some other fundamental particle before its existence was announced then I would be happy to know that too.

3. Sep 27, 2017

### Orodruin

Staff Emeritus
You do not take photos of elementary particles. You observe their interactions and effects in particle detectors.

4. Sep 27, 2017

### gamow99

Yes, I'm aware that 'taking a photo of a particle' does not have the same properties as 'taking a photo of a human'. Nevertheless, scientists need to rev up their particle accelerator and obtain data. Many of these acquisitions of data do not contribute to the existence of the Higgs but some of them do. So how many were there for the Higgs. In the OP I mentioned that I read somewhere that for the top quark that number was 37.

5. Sep 27, 2017

Staff Emeritus

You are saying "There are 37 somethings that I will call photos that aren't photos of the top quark, but I don't know exactly what they are. How many of these same things whatever they are are there for the Higgs?" That's a hard, hard question to answer.

6. Sep 27, 2017

### Staff: Mentor

By analyzing the data of previous collisions, have there been found indications of Higgs prior to 2012, after the physicists knew what to look for?

7. Sep 27, 2017

### Staff: Mentor

We knew what to look for the whole time. The mass was unknown, but that simply means you look at all possible mass values.
The 2011 dataset was sufficient to get a hint of a possible new particle at 125 GeV already, but more collisions (from 2012) were needed to clearly confirm that it is a new particle.

At the time of the Higgs discovery, ATLAS and CMS each had about 150-200 Higgs to two photon decays and ~5 Higgs to four lepton decays in the dataset. For individual events, you can never be sure what caused them, finding the Higgs and distinguishing it from background requires a statistical analysis.
How much data you need depends on the signal strength, the detector performance, the amount of background, and a bit of randomness. The experiments updated their results once in a while with more data, at the time where the significance was close to 5 standard deviations they decided to make a press conference. A few events more or less wouldn't have changed that.

This Insights article discusses some of the concepts

8. Sep 27, 2017

### gamow99

Excellent answer. Thanks very much for your help. This is exactly what I wanted to hear.

9. Sep 27, 2017

### gamow99

Also, does "150-200 Higgs to two photon decays and ~5 Higgs to four lepton" mean that for every 2 photon decays there were "sensed" 150 Higgs, or does this mean that in the entire life of CMS only two photon decays had occurred?

10. Sep 27, 2017

### Staff: Mentor

"150-200 Higgs to two photon decays" means "150-200 events in which a Higgs decayed to two photons ($H \rightarrow \gamma \gamma$)".

Last edited: Sep 27, 2017
11. Sep 27, 2017