Monday, February 18, 2013

LHC Shut Down For Next Two Years

The Large Hadron Collider (LHC) which discovered the Higgs boson was shut down on Saturday (February 16, 2013) for maintenance and upgrading that is anticipated to take the next two years or so. 

What will LHC scientists be doing for the next two years?

The next two years of LHC physics will involve analyzing data that has already been collected in its first run, rather than collecting new experimental data.

As I noted in a previous post at this blog, Matt Strassler's has made some suggestions of fruitful kinds of data analysis that could be conducted in this time period looking for Higgs boson behavior contrary to Standard Model expectations in searches that would also be likely to reveals certain genetic classes of Beyond the Standard Model phenomena if it exists. 

I suspect that many of these data searches will be conducted.  I predict that these searches will definitvely kill off a lot of BSM theories, without supporting any beyond the Standard Model new physics.  But, the data analysis will lack the statistical power to rule out other BSM theories and will have some fluke observations that require further analysis when the experiment is restarted.

When the collider is restarted in the year 2015, the data collection algorithms and experimental parameters will be optimized to take advantage new and improved equipment specifications that will allow for higher energy experiments. 

The data collection algorithms and experimental parameters will also be reworked to pay less attention to searches for beyond the Standard Model phenomena that existing data analyzed over the previous two years already rules out a high levels of statistical significance and to instead focus on potential beyond the Standard Model phenomena (and Standard Model parameters) that still have higher levels of uncertainty, particularly in the higher energy regime.

What is likely to happen in the two year data analysis period?

Given what we know already and what is credibly rumored to be the case, I suspect that the next two years of data analysis will reveal several new conclusions strung out over a number of published articles over the next couple of years.  My predictions:

* The excess number of diphoton decay events from a Higgs boson relative to the Standard Model expectation will turn out to have been a statistical fluke.

* The Higgs boson mass which one line of experimental data shows to be about 125 GeV and another shows to be about 126 GeV will be resolved to show a consensus value much closer to 126 GeV and to strongly disfavor the possibility that there are two different kinds of Higgs bosons of very similar masses.

* The possibility of a new neutrino-like particle with a mass between 45 GeV (half of the Z boson mass) and 63 GeV (half of the Higgs boson mass), will be excluded.

* No new particles or forces will be discovered.

* No meaningful deviations between the Standard Model Higgs boson and the observed Higgs boson data will be detected at the 3 sigma level or greater.  There will probably be one or two instances of deviations at the 2 sigma levels or so from the Standard Model expectation that can't be ruled out without more data in an additional run that will generate lots of theoretical speculation but will amount to nothing when new data analyzed and reported on in 2016 and 2017 is available.

* LHC scientists will conclude that simple SM4 models (Standard Model with four generations of quarks, electrons and neutrinos, rather than the three now known), are excluded experimentally.

* LHC scientists will conclude that the Minimal Supersymmetric Model (MSSM) has been ruled out by existing evidence and cease to compare experimental results to that model.  Instead, the NMSSSM (next to minimal supersymmetric model) and perhaps some other emerging post-126 GeV Higgs boson SUSY model without perfect R-parity conservation will be sought.

What will be in LHC researchers sights in the next round of experiments?

Some of the main things that experimenters will be looking for when the LHC restarts are:

* Beyond the Standard Model additional heavy Higgs bosons, i.e. spin-0 particles that are charged, that are neutral and have odd parity, and that are neutral and have even parity like the existing Higgs boson but with a heavier mass.

* Heavy W' and Z' bosons.

* Lightest supersymmetric particles of various hypothesized kinds.

* Higgs boson decay paths that are fairly frequently but have been quantified only inaccurately so far because they involved decays where there is a lot of background noise (e.g. decay paths involving b quark, c quark and tau decays).

* Flavor changing neutral currents and lepton number violations.

Wild cards

* One of the game changing possibilities that could make a big difference in how the next two years of data analysis goes is the amount of progress that is made by lattice QCD theorists using advances like new Monte Carlo methods and improved computational power (e.g. from distributed computing algorithms) to reduce uncertainty in Standard Model theoretical backgrounds.

Progress on this front would greatly improve the statistical power of all of the LHC data collected so far.  If this happens it will probably make some anomalies in the data so far disappear because it turns out that they were due to theoretical errors in the calculation of Standard Model backgrounds.  But, it may make some low significance deviations from the Standard Model look much more significant than they did before because the central value of the experimental result and theoretical prediction are unchanged, but the number of standard deviations of uncertainty between the observed and predicted result rises as theoretical uncertainty is reduced.

* Another game changing possibility is that improvements in astronomy and reactor based neutrino experiments and in searches for neutrinoless double beta decay will allow for much more precise predictions regarding lepton physics and will greatly narrow the SUSY parameter space - making it easier for fine tuning in other parts of the next round of LHC experiments to focus on narrowing the small SUSY parameter space that remains even further.

It is basically impossible for all possible SUSY theories to be completely falsified for all parameter spaces at LHC.  The theoretical mind is too nimble for that.

* A third game changing possibility is that detailed analysis of the kinematics of the last two years of LHC data (such as the kind that determined that the Higgs boson was a spin-0 even parity particle), which takes quite a bit more thought and time to do than other kinds of LHC "bump-hunting" could reveal some unexpected relationships that while not contradicting the Standard Model do add a new rule or nuance to it.

A discovery of some new kinematic relationships in the data could point the way towards BSM physics that has received little or no theoretical attention to date.

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