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Register a new userSignal-background interference in gg --> H --> VV
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Authors
Nikolas Kauer
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The resonance-continuum interference between the SM Higgs search signal process gg --> H --> VV (V=W,Z) and the irreducible background process gg --> VV is studied at leading order for integrated cross sections and differential distributions in pp collisions at sqrt{s}=7 TeV and 14 TeV for M_H=400 GeV. Leptonic weak boson decays are included, and realistic experimental selection cuts are applied.
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For the Standard Model extended with a real scalar singlet field, the modification of the heavy Higgs signal due to interference with the continuum background and the off-shell light Higgs contribution is studied for gg --> ZZ, WW --> 4 lepton processes at the Large Hadron Collider. Interference effects can range from O(10%) to O(1) effects for integrated cross sections. Despite a strong cancellation between the heavy Higgs-continuum and the heavy Higgs-light Higgs interference, the full interference is clearly non-negligible and modifies the heavy Higgs line shape. A |M_VV - M_h2| < Gamma_h2 cut mitigates interference effects to O(10%) or less. A public program that allows to simulate the full interference is presented.
We study the interference between the amplitudes for $gg rightarrow X rightarrow gg$, where $X$ is a new heavy digluon resonance, and the QCD background $gg rightarrow gg$, at the Large Hadron Collider. The interference produces a large low-mass tail and a deficit of events above the resonance mass, compared to the naive pure resonance peak. For a variety of different resonance quantum numbers and masses, we evaluate the signal-background interference contribution at leading order, including showering, hadronization, and detector effects. The resulting new physics dijet mass distribution may have a shape that appears, after QCD background fitting and subtraction, to resemble an enhanced peak, a shelf, a peak/dip, or even a pure dip. We argue that the true limits on new digluon resonances are likely to differ significantly from the limits obtained when interference is neglected, especially if the branching ratio to $gg$ is less than 1.
We study how the property of asymptotic helicity conservation (HCns), expected for any 2-to-2 process in the minimal supersymmetric model (MSSM), is realized in the processes $gg to gammagamma,gamma Z,ZZ,W^+W^-$, at the 1loop electroweak order and very high energies. The violation of this property for the same process in the standard model (SM), is also shown. This strengthens the claim that HCns is specific to the renormalizable SUSY model, and not generally valid in SM. HCns strongly reduces the number of non-vanishing 2-to-2 amplitudes at asymptotic energies in MSSM. Consequences at LHC and higher energy colliders are identified.
Signal-background interference effects are studied for H --> WW and H --> ZZ searches in gluon fusion at the LHC. More specifically, the interference in the channels with semileptonic weak boson pair decay is analysed for light and heavy Higgs masses with minimal and realistic experimental selection cuts. In the semileptonic decay modes, the interference is affected by tree-level background contributions enhanced by 1/e^2 relative to the gluon-fusion continuum background in the fully leptonic decay modes. We find that for both light and heavy Higgs masses the interference with the loop-induced weak-boson pair background dominates over the interference with the tree-level weak-boson plus jets background for a range of selection cuts. We therefore conclude that higher-order background contributions can induce leading interference effects. With appropriate background suppression cuts the interference can be reduced to the 10% level for heavy Higgs masses, and to the per mille level for the light SM Higgs.
We study the electroproduction of the LHCb pentaquark states with the assumption that they are resonant states. The main concern here is to investigate the final state distribution in the phase space in order to extract the feeble pentaquark signal from the large non-resonant background. Our results show that the ratio of the signal to background would increase significantly with proper kinematic cut, which would be very helpful for future experimental analysis.
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