Distinguishing `Higgs' Spin Hypotheses using gamma gamma and WW* Decays

Understand

The new particle X recently discovered by the ATLAS and CMS Collaborations in searches for the Higgs boson has been observed to decay into gamma gamma, ZZ* and WW*, but its spin and parity, J^P, remain a mystery, with J^P = 0^+ and 2^+ being open possibilities.

• We use PYTHIA and Delphes to simulate an analysis of the angular distribution of gg to X to gamma gamma decays in a full 2012 data set, including realistic background levels.
• We show that this angular distribution should provide strong discrimination between the possibilities of spin zero and spin two with graviton-like couplings: ~ 3 sigma if a conservative symmetric interpretation of the log-likelihood ratio (LLR) test statistic is used, and ~ 6 sigma if a less conservative asymmetric interpretation is used.
• The WW and ZZ couplings of the Standard Model Higgs boson and of a 2^+ particle with graviton-like couplings are both expected to exhibit custodial symmetry.