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 , 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! X! 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 if a conservative symmetric interpretation of the log-likelihood ratio (LLR) test statistic is used, and 6 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. We simulate the present ATLAS and CMS search strategies for X! WW using PYTHIA and Delphes, and show that their eciencies

Highlights

  • A new particle X with mass ∼ 125 to 126 GeV has been discovered by the ATLAS [1] and CMS [2] Collaborations during their searches for the Higgs boson of the Standard Model

  • We find that the data already available may be able to offer some discrimination, and that the data likely to be available to the ATLAS and CMS Collaborations by the end of 2012 should be able to distinguish between the spin-zero and graviton-like spin-two hypotheses at about the 3-σ level if a conservative symmetric interpretation of the likelihood ratio (LLR) test statistic is used, or over 6 σ if a less conservative asymmetric interpretation is used

  • We find that the current ATLAS and CMS measurements favour custodial symmetry for the XW W and XZZ both if the X particle has JP = 0+ and if it has JP = 2+ and graviton-like couplings

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Summary

Introduction and Summary

A new particle X with mass ∼ 125 to 126 GeV has been discovered by the ATLAS [1] and CMS [2] Collaborations during their searches for the Higgs boson of the Standard Model. A first step towards answering this question was taken in [3] (see [4]), where it was shown that the data published in the ATLAS and CMS discovery papers [1, 2] and other public documents, in combination with results from the TeVatron experiments CDF and D0 [5], are inconsistent with mass-independent couplings to the t, Z0, W ± and b, and highly consistent with linear scaling ∼ M/v, where v ∼ 246 GeV is the expected electroweak symmetry-breaking scale. We find that the current ATLAS and CMS measurements favour custodial symmetry for the XW W and XZZ both if the X particle has JP = 0+ and if it has JP = 2+ and graviton-like couplings This result is based on simulations of the ATLAS and CMS H → W W ∗ searches using PYTHIA and Delphes, which indicate that their efficiencies are a factor 1.9 lower under the spin-two hypothesis. Extrapolation to the full expected 2012 data set suggests that it will not be able to discriminate significantly between the 0+ and graviton-like 2+ hypotheses using the ratio of X → W W ∗ and ZZ∗ decays

Possible spin-parity assignments
Pseudoscalar couplings
Tensor couplings
Toys and Statistical Procedure
Background Simulation
Log-Likelihood Ratio Test Statistic
Simulation of ATLAS and CMS event selections
Data analysis under different JP hypotheses
Findings
Overview and Prospects
Full Text
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