Particle body-count 2


As a result of today’s talks, here’s the updated body-count (all four experiments with a lot of overlap):

Particle Original discovery Method of observation in the LHC experiments
Electron/positron 1896 (e), 1932 (e+) Peak at 1.0 in calorimeter energy to track momentum ratio, also observed in pairs from photon conversions in matter (X γ → X  e+e where X is a nucleus)
Photon 1900 (Planck’s quanta) Photon conversions and π0→ γγ
Proton 1911 Energy loss charged particle’s trajectory (dE/dx)
Deuteron 1931 Also seen in dE/dx
Muon 1936 Specialized muon detectors
Pion 1950 (π0) Neutral pion in π0→ γγ, charged pions in dE/dx
Eta meson 1961 η → γγ
Kaon 1947 (KS) Neutral kaon in KS → π+π, charged kaons (K+ and K) in dE/dx and ring-imaging Cerenkov detectors
Phi meson 1962 φ → K+ K
Lambda 1947 (Λ0) Λ0→ π+p / Λ0→ πp+
Xi baryon 1964 Ξ → π Λ0

Dark matter WIMPs not yet two candidates in the unblinded signal region of the Cryogenic Dark Matter Search (CDMS) (not an LHC experiment)

The last entry is for yesterday’s CDMS paper, which shows two candidate events surviving all analysis cuts, set prior to looking at the result (unblinding).  The probability for background fluctuating up to account for these two events is 20-23%, so no one is calling it a signal.  Both are close to the edges of the analysis cuts, so even if the observed events had significantly exceeded the background estimates, there would be room for doubt.  This may be the tip of the iceberg for direct dark matter detection, but then again, it may not.

9 Responses to “Particle body-count 2”

  1. Michael Schmitt Says:

    Hi Jim,

    this is a nice way to organize the first signals from the LHC experiments. I wonder what the next ones will be – care to venture a guess?


    • Jim Pivarski Says:

      I’ve been found out!

      My guess would be either Sigma+ -> proton pi0 (1953) or Sigma0 -> Lambda photon (1956), since these have the same strangeness content as the Lambda and therefore a similar rate of production in proton collisions. Also, a Sigma signature can be constructed from already-established components (the proton, pi0, Lambda, and photon).

      — Jim

  2. bennymay Says:

    a story with a difference

  3. Michael Schmitt Says:

    Hi Jim,

    any chance you will make another nice post? Perhaps I can suggest one: concerning alignment, how would we recognize and error in which all dimensions were mis-measured by 0.5%? I’m talking about a complete rescaling of all length scales by a factor close to but not equal to one? I have one idea, but I’ll bet you have better ideas, and this may interest readers of your blog. 🙂


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