As Higgs bosons are extremely rare, sophisticated analysis techniques are required to spot the signal events within the large backgrounds from other processes. After signal-like events have been identified, powerful statistical methods are used to quantify how significant the signal is.
As statistical fluctuations in the background can also look like signals, stringent statistical requirements are made before a new signal is claimed to have been discovered. Eager physicists analysed the data as soon as it arrived. In the summer of , there was a small excess in the Higgs decay to two W bosons for a mass around GeV. Things got more interesting as an excess at a similar mass was also seen in the diphoton channel.
However, as the dataset increased, the size of this excess first increased and then decreased. Although neither experiment had strong enough results to claim observation, what was particularly telling was the fact that both ATLAS and CMS had excesses at the same mass. In , the energy of the LHC was increased from 7 to 8 TeV, which increased the cross-sections for Higgs boson production.
As quickly as the data arrived it was analysed and, sure enough, the significance of that small bump around GeV increased further. Seats at the seminar were so highly sought after that only the people who queued all night were able to get into the room. The ATLAS Collaboration celebrated the discovery with champagne and by giving each member of the collaboration a t-shirt with the famous plots. Incidentally, only once they were printed was it discovered that there was a typo in the plot.
After discovery, we began to study the properties of the newly-discovered particle to understand if it was the Standard Model Higgs boson or something else. In fact, we initially called it a Higgs-like boson as we did not want to claim it was the Higgs boson until we were certain. The mass, the final unknown parameter in the Standard Model, was one of the first parameters measured and found to be approximately GeV roughly times larger than the mass of the proton.
It turned out that we were very lucky — with this mass, the largest number of decay modes are possible. In the Standard Model, the Higgs boson is unique: it has zero spin, no electric charge and no strong force interaction. The spin and parity were measured through angular correlations between the particles it decayed to.
Sure enough, these properties were found to be as predicted. The discovery of the Higgs boson relied on measurements of its decay to vector bosons. In the Standard Model, different couplings determine its interactions to fermions and bosons, so new physics might impact them differently. Therefore, it is important to measure both. During Run 2, the increase in the centre-of-mass energy to 13 TeV and the larger dataset allowed further channels to be probed. Over the past year, the evidence has been obtained for the Higgs decay to bottom quarks and the production of the Higgs boson together with top quarks has been observed.
Paralysed mice walk again after gel is injected into spinal cord New mineral davemaoite discovered inside a diamond from Earth's mantle How Minecraft is helping children with autism make new friends New COP26 draft text adds caveats to fossil fuel subsidies phase-out The surprising upsides of the prions behind horrifying brain diseases.
How worried should we be about covid spreading among wild animals? The Amazon's pink river dolphin population is in freefall COP People from climate-ravaged regions say we need action now Birds in the Amazon are adapting to climate change by getting smaller COP26 news: Real progress made but more emissions cuts are needed. COP People from climate-ravaged regions say we need action now Birds in the Amazon are adapting to climate change by getting smaller COP26 news: Real progress made but more emissions cuts are needed New COP26 draft text adds caveats to fossil fuel subsidies phase-out Don't miss: Cowboy Bebop gets a live-action remake on Netflix.
Like all fundamental fields, the Higgs field has an associated particle — the Higgs boson. The Higgs boson is the visible manifestation of the Higgs field, rather like a wave at the surface of the sea.
A problem for many years has been that no experiment has observed the Higgs boson to confirm the theory. This particle is consistent with the Higgs boson but it will take further work to determine whether or not it is the Higgs boson predicted by the Standard Model. The Higgs boson, as proposed within the Standard Model, is the simplest manifestation of the Brout-Englert-Higgs mechanism.
Other types of Higgs bosons are predicted by other theories that go beyond the Standard Model. How do the elementary particles get their mass? How does the Brout-Englert-Higgs field work? The next few weeks were among the most intense I have ever experienced. One time I thought some colleagues had come into the office, but it turned out to be two stray cats fighting in the corridor. According to predictions from the Standard Model, the Higgs can transform into two of these particles when it decays, so scientists on both experiments knew that this project would be key to the discovery process.
All in all, it was the most exciting time in my career. I think the best qualities of the community came out during the discovery. At the end of June, Hard and his colleagues synthesized all of their work into a single analysis to see what it revealed. And there it was again—that same bump, this time surpassing the statistical threshold the particle physics community generally requires to claim a discovery. Hard had no idea whether CMS scientists were looking at the same thing.
It was not relevant to the tasks at hand. Still, rumors were circulating around theoretical physics groups both at CERN and abroad. Mccullough, then a postdoc at the Massachusetts Institute of Technology, was avidly following the progress of the two experiments.
It could have properties mostly consistent with the Higgs boson but still be not absolutely identical. He says they were excited but also nervous and stressed: Extraordinary claims require extraordinary confidence.
0コメント