Higgs boson pair production at the LHC in the bb ̄W+W- channel

We consider Higgs boson pair production at the LHC in the bb ̄W+Wchannel, with subsequent decay of the W+Wpair into ��jj. Employing jet substructure and event reconstruction techniques, we show that strong evidence for this channel can be found at the 14 TeV LHC with 600fb-1 of integrated luminosity, thus improving the current reach for the production of Higgs boson pairs. This measurement will allow us to probe the trilinear Higgs boson coupling �. DOI: https://doi.org/10.1103/PhysRevD.87.011301 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-90739 Accepted Version Originally published at: Papaefstathiou, Andreas; Yang, Li; Zurita, José (2013). Higgs boson pair production at the LHC in the bb ̄W+Wchannel. Physical Review D (Particles, Fields, Gravitation and Cosmology), 87(1): 011301(R). DOI: https://doi.org/10.1103/PhysRevD.87.011301 ZU-TH 20/12, LPN12-094 Higgs boson pair production at the LHC in the bb̄W+W− channel Andreas Papaefstathiou, Li Lin Yang, José Zurita Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China Institut für Theoretische Physik, Universität Zürich, 8057 Zürich, Switzerland We consider Higgs boson pair production at the LHC in the bb̄W+W− channel, with subsequent decay of the W+W− pair into `νjj. Employing jet substructure and event reconstruction techniques, we show that strong evidence for this channel can be found at the 14 TeV LHC with 600 fb−1 of integrated luminosity, thus improving the current reach for the production of Higgs boson pairs. This measurement will allow to probe the trilinear Higgs boson coupling λ. PACS numbers: 14.80.Bn, 13.85.Qk Introduction. One of the aims of the LHC is to search for the agent of electroweak symmetry breaking (EWSB), which in its minimal form is the Standard Model (SM) Higgs boson (h). Recently, both the ATLAS and the CMS collaborations have observed a new state with a mass of about 125 GeV, whose properties are in substantial agreement with the SM Higgs boson [2]. The quest for understanding the mechanism behind EWSB does not end with the discovery of the Higgs boson. It is crucial to test the Higgs boson potential to its full extent, measuring the couplings of the Higgs boson to gauge bosons and matter fields, and also to probe its self interactions. After EWSB, the Higgs potential can be written as V (h) = mhh /2 + λvh + λ̃h/4. In the SM, λ = λ̃ = (mh/2v ) ≈ 0.13 for mh=125 GeV. With an extended Higgs sector, as is common in many new physics models beyond the SM, these couplings will deviate from the SM values. Therefore, measuring these two couplings is very important to reveal the true nature of the Higgs boson. At the LHC, the quartic coupling λ̃ may be probed via triple Higgs boson production. However, its tiny cross section [3] makes it very difficult, if not impossible, to do so. On the other hand, the trilinear coupling λ can be measured with Higgs boson pair production, pp → hh, which may be discovered at a large luminosity phase of the LHC. In the following we will focus on that possibility. The discovery potential of Higgs boson pair production at the LHC has been studied in [4, 5]. Ref. [4] concentrated on the decay channels hh→ bb̄γγ, bb̄μ+μ−, finding that with 600 fb−1 one expects 6 signal and 11 background events, giving a significance of about 1.5σ. In the recent years, jet substructure has been shown to be very important when dealing with hadronic decays of heavy particles [6]. In the h→ bb̄ case, this was put forward in the seminal paper by Butterworth, Davison, Rubin and Salam (BDRS) [7] in the context of Wh and Zh production, which were previously considered as challenging to probe at the LHC. With the subjet techniques, BDRS have shown that this can become a very promising discovery channel for the Higgs boson. Ref. [5] employed these new techniques, and assuming good τ reconstruction efficiency (∼ 80%), the authors claimed the bb̄τ+τ− channel as the most promising one, with 57 signal and 119 background events at 600 fb−1. In both [4] and [5], the hh → bb̄W+W− → bb̄`νjj channel was considered less promising, due to the large tt̄ background. In this Letter, we apply the BDRS techniques to this final state in conjunction with event reconstruction using mass-shell constraints, assuming that the Higgs boson mass is well-measured. We show that in the highly boosted regime, the reconstruction of both Higgs bosons present in the event allows us to distinguish the signal and background, thereby turning this channel into a potentially significant contribution in the discovery of Higgs boson pair production. Higgs pair production and decay. The main production mechanism for Higgs boson pairs at the LHC is gluon fusion, which was studied at leading order (LO) in quantum chromodynamics (QCD) in [8, 9]. Other production modes such as qq → qqhh, V hh, tt̄hh are a factor of 10-30 smaller [10, 11], and therefore we do not consider them in the rest of our analysis. We employ the code HPAIR [12] to compute the production cross section, which implements the next-toleading order (NLO) QCD corrections obtained in the heavy top quark limit [13]. We have modified the public version of HPAIR in order to use the up-to-date parton distribution functions (PDFs) present in the LHAPDF library [14]. For the LO and NLO cross sections, we employ CTEQ6L1 and CT10 [15] PDF sets with the corresponding values of αs, respectively. We adopt the pole masses for the top and bottom quarks to be mt = 174.0 GeV and mb = 4.5 GeV. For a 125 GeV Higgs boson, we have obtained an NLO cross section of 32.3 −4.7 fb, where the uncertainty reflects the variation of the renormalization and factorization scales μr = μf around the central value μ0 by a factor of 2, with μ0 being the Higgs boson pair invariant mass. In the left panel of Fig. 1 we show the scale variation of the production cross sections at LO and NLO. One can observe that there is a large K-factor (∼ 2) on the cross section, and that the scale uncertainty is still high (about 20%). Either an NNLO computation or performing QCD ar X iv :1 20 9. 14 89 v2 [ he pph ] 1 0 Ja n 20 13