Distinguishing ‘Higgs’ spin hypotheses using γγ and WW ∗ decays

Abstract

The new particle X recently discovered by the ATLAS and CMS Collaborations in searches for the Higgs boson has been observed to decay into γγ, ZZ * and W W * , 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 → X → γγ 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: ∼ 3σ if a conservative symmetric interpretation of the log-likelihood ratio (LLR) test statistic is used, and ∼ 6σ if a less conservative asymmetric interpretation is used. The W W 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. We simulate the present ATLAS and CMS search strategies for X → W W * using PYTHIA and Delphes, and show that their efficiencies in the case of a spin-two particle with graviton-like couplings are a factor 1.9 smaller than in the spin-zero case. On the other hand, the ratio of X 2 + → W W * and ZZ * branching ratios is larger than that in the 0 + case by a factor 1.3. We find that the current ATLAS and CMS results for X → W W * and X → ZZ * decays are compatible with custodial symmetry under both the spin-zero and -two hypotheses, and that the data expected to become available during 2012 are unlikely to discriminate significantly between these possibilities.

Implications of LHC data on 125 GeV Higgs-like boson for the Standard Model and its various extensions

“…For this purpose, its spin and parity [3][4][5][6][7][8][9][10][11][12] and its couplings to the SM particles should be determined as accurately as possible (see Ref. [13] for the review on the SM Higgs boson and references therein).…”

Gravity-mediated (or composite) Dark Matter confronts astrophysical data

“…Then, we can impose the similar bounds on vector dark matter from monophoton searches [87,88] as for axion or Z -mediated dark matter [29,30]. Furthermore, if the KK graviton decay into a pair of dark matter is forbidden, we should rely on the resonant production of the KK graviton via gluon fusion into diphotons [89][90][91], or vector boson or photon fusion [92]. Other decays of the graviton, such as top or W,Z boson pairs, would be difficult to be performed at low mass, as the current resonant searches are based on boosted topologies.…”

The Higgs-like boson spin from the center–edge asymmetry in the diphoton channel at the LHC

“…Many proposals have been put forward to discriminate between the spin-0 and spin-2 hypotheses basically focusing on kinematic distributions, e.g., angular distributions [12][13][14][15][16][17][18][19][20][21][22], event shapes [23] as well as other observables [24][25][26][27][28][29]. Among the latter, an interesting possibility to discriminate between the spin hypotheses of the Higgs-like particle was studied in [26,28] by means of the center-edge asymmetry A CE , where its high potential as a spin discriminator was demonstrated.…”

“…Among the latter, an interesting possibility to discriminate between the spin hypotheses of the Higgs-like particle was studied in [26,28] by means of the center-edge asymmetry A CE , where its high potential as a spin discriminator was demonstrated.…”

“…Here, we review the application of A CE to the angular study of the diphoton production process (1) at ATLAS extending the analysis done in [26,28] by accounting for various admixtures of the gg and qq production modes. Also, an optimization of the center-edge asymmetry on the kinematical parameter which divides the whole range of cosθ into center and edge regions will be performed in order to enhance the potential of A CE as a discriminator of spin hypotheses of Higgs-like resonances.…”