Possible Higgs searches at LHCb A preliminary study investigating the feasibility of finding the SM Higgs at LHCb Jonathan Anderson (UCD)

Outline What are the possible Higgs discovery channels at LHCb? What about the gold-plated channel? Gold-plated channel and its backgrounds Cross-sections and branching ratios for this channel The effects of the small LHCb angular acceptance Kinematic cuts used and their effects Overall conclusions

Higgs decay modes In the range 130 Gev < M H < 300 Gev, H  WW and H  ZZ dominate. While for M H < 130 Gev H  bb dominates. The QCD backgrounds swamp the hadronic final states so we must look for final states containing leptons or photons. A possible exception at LHCb might be H  bb. _ _

The Gold Plated channel H  ZZ  4L is known as the ‘gold plated’ Higgs decay channel. It divides into two regions, 130Gev < M H < 2MZ  Contains one real Z and one off mass shell Z  Branching ratio is smaller  Background elimination more difficult M H > 2M Z  Contains Two real Z’s  Higher branching ratio  easier to eliminate background H  ZZ  4μ was investigated

Backgrounds for gold-plated channel Reducible backgrounds gg  (Z/  )bb  4  gg, qq  tt  WbWb  4  gg, qq  bb  4  Irreducible backgrounds gg, qq  (Z/  )(Z/  )  4  _ _ _ _ _ _ _

Cross-sections and branching ratios Process  x BR (fb) H  4  (M H =130 GeV) H  4  (M H =150 GeV) H  4  (M H =180 GeV) H  4  (M H =200 GeV) H  4  (M H =250 GeV) H  4  (M H =300 GeV) (Z/  )(Z/  )  4  * (Z/  )(Z/  )  2 µ 2  * (Z/  )bb (Z  2 µ ) 5.63 x 10 3 bb  4   m > 200 Gev) x 10 4 tt  WbWb (W   ) x 10 3 All processes generated in pythia (One year of running equates to 2 fb -1 ) * Includes factor (1.3) to account for gg  (Z/  *)(Z*/  *) ^ __ _ _

LHCb angular acceptance The  acceptance for LHCb is  0.245

LHCb   acceptance ProcessPercentage within acceptance H  4  (M H =130 Gev) H  4  (M H =150 Gev) H  4  (M H =180 Gev) H  4  (M H =200 Gev) 1.08 H  4  (M H =250 Gev) 0.53 H  4  (M H =300 Gev) (Z/  )(Z/  )  4  2.91 (Z/  )bb (Z  2 µ ) bb  4   m > 200 Gev) tt  WbWb (W   ) 1.72 ^ __ _ _

Muon pair wise invariant masses Higgs (200 Gev)ZZ Zbbtt _ _

Muon four wise invariant masses Zbb tt Higgs (200 Gev) ZZ __

Kinematic cuts for M H > 2M Z M H (Gev) |M 12 – M Z | < and |M 34 – M Z | < |M 1234 – M H | < All muon impact parameters < 30μm

Effectiveness of high mass cuts Process200 Gev250 Gev300 GevEvents H  4  (M H =200 GeV) ± 2.6% 200k H  4  (M H =250 GeV) ± 2.9% 200k H  4  (M H =300 GeV) ± 2.9% 200k (Z/  )(Z/  )  4  ± 0.001% 6.55 ± 0.001% 5.14 ± 0.001% 100k (Z/  )bb (Z  2 µ ) 0 ± % 0 ± % 0 ± % 600k bb  4   m > 200 Gev) 0 ± % 0 ± % 0 ± % 1M tt  WbWb (W   ) 0 ± % 0 ± % 0 ± % 600k _ _ __ ^

Overall signal against background For 2 fb -1 of data (equivalent to one year) M H (Gev)SignalBackgroundSignificance ± ± ± ± ± ±

Gold-plated channel does not have any discovery potential at LHCb However it seems as though H  bb is more promising Work to be done Investigate H  bb more fully, starting with LHCb thesis… Conclusions and further work - -