25 February 2011

Baysean SUSY Parameter Odds

Baysean statistics is the art of estimating the probability of an outcome when you already have some data to guide you in knowing that the answer should be like from prior experience. Given what we know about narrowing possibilities for SUSY parameters from the LHC what seems like the most likely SUSY parameters if SUSY exists? A new paper make some guesses (multiple omissions of entire sentences from quoted material not noted individually) for leading SUSY theories:

m_{1/2} has to be raised to from 300 GeV or so to approximately 400 GeV in CMSSM [constrained minimal extension of the Standard Model], NUHM1 [model with common non-universal Higgs masses], and VCMSSM [very constrained minimal extension of the Standard Model], and 550 GeV in mSUGRA [minimal supergravity].

m_0 may remain . . . between 70 and 230 GeV.

The best tan(beta) has to be raised from 8-11 to 9-16 in the three models and stays at 28 in mSUGRA.

The preferred Higgs mass is near 115 GeV in the three models and 120 GeV in mSUGRA.

The gluino masses around 800-1000 GeV are favored in the three models while 1100-1400 GeV wins in mSUGRA.

[Compared to prior estimates,] the 800-1,000 GeV squark masses actually became more likely than before. Also, the most likely squark mass actually decreased!

SUSY starts to be strongly disfavored if no squarks are found with masses below 1500 GeV, where they are expected.

Neutralino Mass as light as 10 GeV or so is expected.

The LHC will ultimately be providing data that should reveal all particles with masses up to about 1000 GeV. This should reveal a Higgs boson, if there is one, early on. Indeed, the predictions are close to the bottom end of the range of masses where a Higgs boson has not been ruled out yet (about 114 GeV to 140 GeV).

But, any lightest supersymmetric particle other than a neutralino (a possible dark matter candidate that may be hard to observe directly because it would not have strong interactions with other particles much like neutrinos), would be expected by this analysis to be detected only towards the end of an LHC run and can't be unequivocally ruled out by LHC.

For comparison's sake, the currently measures values of the other particles in the Standard Model are as approximately as follows (in MeV/c^2 units and 1,000 MeV = 1 GeV):

Electron Neutrino: Less than 0.000007
Electron: 0.511
Up Quark: 2-8
Down Quark: 5-15

Muon Neutrino: Less than 0.27
Muon: 105.7
Charm Quark: 1,000-1,600
Strange Quark: 100-300

Tau Neutrino: Less than 31
Tau: 1777
Top Quark: 168,000-192,000
Bottom Quark: 4,100-4,500

W Particles: 80,398
Z Particle: 91,188

Photon: Zero

Gluons: Zero

Glueballs (spin zero, low energy states of strong force bosons) have been calculated to have a mass of about 630 GeV that may vary with momentum using Standard Model equations, but have not been directly observed.