Did Old LEP Data Yield New Physics?

An old study may have provided hints to new physics, but then again; it may also be a fluke. During the time period between 1989 to 2000, Arno Heister, and his team of CERN researchers ran the LHC’s predecessor — the Large Electron Positron Collider (LEP), also called “an atom smasher”. The LEP at that time was not as powerful as Large Hadron Collider is today, but it was powerful enough to register some data.  Arno Heister, a scientist at CERN, on his own time, decided to record some data between 1992 and 1995. It made some interesting discoveries before being shut down in 2000 so that the faster LHC could be built.

The LEP experiment, called ALEPH; did manage to find the W boson (the boson that carries the weak force), and it also produced muons, which are created when Z bosons decay. Muons exist for microseconds before turning into electrons or neutrinos. Sometimes, they even turn into muons or antimuons. So, what type of event occurred in the LEP?

The graph showed a ‘bump’ that peaked at 30 GeV and a long tail that trails smoothly to almost zero, which is what scientists expected to see, but this bump came with a twist. No new particles popped up. Generally the bump that show up register a peak of about 10-15 GeV (giga-electron volts). What this means is that something was happening there that the scientists didn’t expect to see. They saw that there were more muon-antimuon pairs than current theory accounted for. In the end, that means that the experiment may have revealed a new particle. The question became whether or not if the experiment finding were true, or if it was just a fluke.

In general, there are three ways to explain the bumps seen in the data:

  1. The bump may have been a statistical fluctuation, which has occurred before.
  2. It may have been an occurrence that the Standard Model already accounted for.
  3. It is a new particle or interaction that has never been seen before.

According to Matt Strassler, and independent particle physicist; the possibility of the bump representing a new particle is pretty unlikely.

In an email to Live Science, he stated that “The hump is probably nothing; the hump is too wide and comes from events that do look too much like Z bosons decaying into bottom quarks and anti-bottom quarks.”

While this is true, it certainly does not prevent scientists from looking at older data results like this one. Old data can often provide insight into new experiments, especially when the new experimental data are unanswered.

The latest run of the LHC has upped the speed for the experiment to double what it was when it discovered the Higgs boson in 2013 and it is already showing data that they originally thought was another particle that some scientists have believed to be a graviton. Follow up analysis on that initial data however, dashed those hopes when it was revealed that the jump was little more than statistical noise. Had it actually been a graviton, the implications would have been huge in that it may have proven to be the particle that carries the force of gravity throughout the universe. Depending on its mass, the graviton may even provide an explanation for ‘dark energy’ or extra dimensions. Either way, it would have provided physicists with new physics to follow since the Standard Model doesn’t have space for the graviton.

The fact is that the particles may still be out there somewhere, but unavailable to be duplicated in the LHC. Eventually, all the findings found in today’s LHC, may end up being useful in the future if not to us. Since most scientists believe that new particles would be heavy and require more energy to produce than what the LHC has now, it won’t be until a future version is created for that to be realized.

When it comes down to the past LEP experiments, the LHC did not show any similar bumps in their data screens, making it unlikely that a new particle was found in the old data, but it was certainly a fun thing to consider. As for the scientist that found the bump a decade or so ago, he is still hoping to find out what that was.

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