Evidence for a Particle Produced in Association with Weak Bosons and Decaying to a Bottom-Antibottom Quark Pair in Higgs Boson Searches at the Tevatron

Abstract

We combine searches by the CDF and D0 Collaborations for the associated production of a Higgs boson with a W or Z boson and subsequent decay of the Higgs boson to a bottom-antibottom quark pair. The data, originating from Fermilab Tevatron pp collisions at √ s = 1.96 TeV, correspond to integrated luminosities of up to 9.7 fb −1 . The searches are conducted for a Higgs boson with mass in the range 100-150 GeV/c 2 . We observe an excess of events in the data compared with the background predictions, which is most significant in the mass range between 120 and 135 GeV/c 2 . The largest local significance is 3.3 standard deviations, corresponding to a global significance of 3.1 standard deviations. We interpret this as evidence for the presence of a new particle consistent with the standard model Higgs boson, which is produced in association with a weak vector boson and decays to a bottom-antibottom quark pair.

A fast track towards the ‘Higgs’ spin and parity

“…The new particle X with mass ∼ 125 to 126 GeV that has been discovered by the LHC experiments ATLAS [1] and CMS [2], with support from the TeVatron experiments CDF and D0 [3], has similarities to the long-sought Higgs particle H. The X particle is a boson that does not have spin one, and its couplings to other particles depend on their masses in a way very similar to the linear dependence expected for the Higgs boson of the Standard Model [4]. However, the spin and parity J P of the X particle remain to be determined, and this should be regarded as an open question, with the pseudoscalar hypothesis J P = 0 − and the tensor hypothesis J P = 2 + being important possibilities to exclude.…”

“…However, we note that figure 2 indicates that the backgrounds would be negligible if the X particle has J P = 2 + , and would also have a very different M ZX distribution from a 0 − signal. The signal and backgrounds would be more similar in the 0 + case, but figure 2 of [3] indicates that the statistical uncertainty in the background is small for log 10 (s/b) > −1.5 also in the 0 + case.…”

“…These demonstrate that they may (soon) be able to discriminate between different J P assignments for the X particle using the V + X invariant mass distribution. The TeVatron experiments have observed 'Higgs'-strahlung with ∼ 3 − σ significance [3], and the backgrounds are expected to peak at low invariant masses, giving hope that this mechanism could provide a 'fast track' towards determining its spin and parity.…”

“…Encouraged by the differences seen in (2.1) and in figure 1, we have made simulations of the possible signals in the TeVatron and LHC experiments. We have not analyzed further the backgrounds in the experiments, which would require more extensive simulations beyond the scope of this work, in particular because [3] gives no details of the MVA analyses used by CDF and D0 in extracting evidence for 'Higgs'-strahlung. However, we note that figure 2 indicates that the backgrounds would be negligible if the X particle has J P = 2 + , and would also have a very different M ZX distribution from a 0 − signal.…”

“…The TeVatron experiments CDF and D0 have reported evidence for production of the X particle in association with Z → + − ,νν and W ± → ± ν [3]. In this section we simulate these analyses using Delphes.…”