Probing CP Violation in h→τ−τ+ at the LHC

Abstract

We propose a novel method to reconstruct event by event the full kinematics of the cascade decay process, h → τ + τ − → (π +ν )(π − ν), which allows us to measure the τ + τ − spin correlation, a measure of the CP property of the Higgs boson. By noting that the τ ± momenta lie on the plane spanned by the accurately measured impact parameter and momentum vectors of charged pions, we can obtain the most likely momenta of the two missing neutrinos by using the probability distribution functions of the p / T vector and the location of the primary vertex. A simple detector level simulation shows an excellent agreement between the reconstructed and the true kinematics, both in the τ + τ − and the π + π − rest frames. The method can be tested in Z → τ + τ − events, which should exhibit no correlation.CP property of the observed Higgs particle h(125) [1, 2] is a window of the physics of mass generation. In general the mass eigenstate h(125) can be a mixture of CP-even and CP-odd scalar particles. While only one CP-even scalar particle exists in the Standard Model (SM), many of its extensions not only modify the Higgs couplings to gauge bosons and fermions, but also predict additional scalars and pseudo-scalars. If the Higgs sector is CP conserving, all the neutral mass eigenstates should have definite CP parity. The pure CP eigenstate assumption has been investigated experimentally by both ATLAS and CMS collaborations [3][4][5], and the CP-odd hypothesis is disfavored by nearly 3σ.However, if the h(125) particle is a mixture of the CPeven and CP-odd states, the bound on the mixing parameter is rather weak and a large mixing in the Higgs sector is still allowed [6][7][8]. (For the recent review see [9] and references there in.) There are several channels that can be used to measure the CP property of h(125). The golden channel h → ZZ

Measuring the CP state of tau lepton pairs from Higgs decay at the ILC

“…The sensitivity of the LHC experiments to measure CP effects in H → τ + τ − has been investigated in a number of phenomenological studies. In [20] a precision on the CP mixing of 4 • is predicted with an integrated luminosity of 3 ab −1 , while [17] and [21] both suggest a precision of ∼ 11 • using the same integrated luminosity. In [22] it is argued that the analysis of [17] is significantly affected by experimental effects, and that even and odd CP hypotheses can be distinguished at no better than 95% confidence level with an integrated luminosity of 1 ab −1 .…”

Probing the CP-Violation effects in the hττ coupling at the LHC

“…The VBF signal is generated with Powheg [28] at NLO accuracy in QCD and PDF set NNPDF30NLO [29], and interfaced to Pythia8 [30] for resonance decays, parton shower and hadronization. The QCD and EW Z+jets background 1 In [6], the authors use the ggF channel to check the precision of the measurement. In our opinion, it can be improved by using the VBF channel.…”

Probing the CP violating Hγγ coupling using interferometry *

“…Its source could have close relation with Higgs dynamics [3,4]. Thus the CP properties of the 125 GeV Higgs boson with spin zero is proposed to be probed in various channels at the Large Hadron Collider (LHC) [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Among them, the golden channel H → ZZ → 4 has been studied extensively and it gives relative stringent experimental constraints [19,21,22,24].…”