Light Sbottom at HERA

• Motivation
  Remarkable discrepancies between experimental results and theoretical predictions in the beauty sector have been observed by various experiments. For example:
  • The cross section for ep --> b \bar b X --> mu X' measured at HERA is significantly higher than the respective cross section calculated in NLO QCD.

  • The cross section for b-quark production at the TEVATRON has been measured by D0 and CDF. The results of both experiments are in good agreement. But the next-to-leading order calculation in QCD predicts a significantly lower value.

  • The cross section for charm production measured in two photon events at LEP is in good agreement with NLO QCD whereas the value for beauty production is much higher than predicted by NLO QCD.

  • The CDF collaboration found an excess of background in the channel B+ --> J/Psi K --> mu mu K. This non-resonant excess below the B signal is not understood, but could be explained by additional events which look like beauty events with two muons and a charged particle.

  • The H1 collaboration observed an excess of events with high missing transverse momentum and high energetic isolated muons. The kinematical properties of these events do not agree with the Standard Modell, but could be explained by a decaying stop quark.

  • The ratio R of hadron production and muon pair production in e+e- collisions measured by the MARKI collaboration at center of mass energies of 5GeV - 8GeV is higher than the values predicted in the Standard Modell. But an explanation can be given by the introduction of an additional quark with spin 0 and charge -1/3. The mass should be in the range of 3.5GeV - 3.7GeV.

  These results lead to the conclusion that it is promising to search in the beauty sector for hints of new physics.

• Possible Explanation

  The observed phenomena suggest to look for a beauty-like particle that shows a myonic decay:

                             New particle -> mu X 
  

  The assumption of a beautylike light supersymmetric particle sb could explain the observations. This particle would be produced at HERA like the well-known beauty-quark in Boson-Gluon fusion:

                          /e
                         /                     
             e__________/
                        \
                         \boson
                          \ ____________b
                           |
                           |
                           |____________b
                          /
                         /gluon
             p__________/
                        \
                         \ 
                          \p
  
  

• Phenomenology at HERA

  The predicted cross section for ep --> sbsbar at HERA is approximately 1pb for m(sb)=4GeV (LO calculation). This must be compared with the cross section for ep -->bbar of 7pb (H1 result).
  A sbottom with m(sbottom) of 4GeV could decay into jet(SM) sneutrino and lepton(SM). If the sneutrino is the lighest supersymmetric particle (LSP) 50% muons and 50% electrons are expected.
  For a sbottom with mass of 4GeV dimuon events should consist of 50% bbar and 50% sbsbbar. (7pb * 19% * 19%) = (1pb * 50% * 50%)
  In events with two jets and bottom tag with muon, the SM expects 19% muons in the second jet. The scenario with sbottom expects more than 19%.

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