Top to charged higgs decays and top properties at the Tevatron Page: 4 of 8
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H decay modes
w 18 -- ---- --- ---- --- --- M(top) = 175 GeV
160 - BF(t->Hb)>O.5
s 140 Wbb
-1 2 3
10 1 10 10 10
sample used for H+ search off in SM
CDF dilepton 8.2+34 pb
CDF lep.+jets (SVX b-tag) 6.2+1 pb
DO lep.+jets (p b-tag) 8.3 + 3.6 pb
DO lep.+jets (topological) 4.1 2.1 pb
Figure 1: (left) Regions in the MH+ vs. tan/ plane where the branching fraction B(t - Hib) is larger than 50%.
The present Tevatron data is sensitive to branching fractions of 30% or larger for this decay. At tano < 2, H+
decays both to cs and W+bb, where the W+bb mode dominates for Ms+ > 135 GeV/c2. At tan/i > 5, H+ decays
to r+v exclusively. Table 1: (right) The samples used for the H search, and the value of att extracted from the
observed number of events in each channel, assuming only SM top decays. The reconstructed atf in each channel
is consistent with the theoretical value of about 5.0 pb.
training two doublets, rather than just one as required by the minimal standard model (SM).
At the Tevatron, the primary mechanism for charged Higgs production is through the top
quark decay t -* H b, provided that the H mass satisfies My < Mtop - Mb. This decay
competes with the SM decay t -* Wlb. A key parameter in the theory is tang, which is the
ratio of vacuum expectation values of the two Higgs doublets. The parameters tan3 and MH
determine the branching fractions for both the top quark and the charged Higgs boson. The
Tevatron top data is sensitive to large branching fractions B(t -4 Hob), which occur for small
values of tan/i (tan/ < 1), and large values of tan) (tan/i > 50) - see Fig. 1.
Less than a year ago, it was believed that H+ produced in top quark decays would decay into
cs if tano < 1, and T+v if tang > 5. Recently it has been demonstrated that at tano < 1, the
three-body decay H+ -> t*b -> W+bb competes with the decay H+ -> cs, as long as the virtual
top quark t* is produced close to its mass-shell value of about 175 GeV/c2 4. Fig. 1 shows the
dominant decay modes for H in the MH vs. tanQ plane.
The Yukawa couplings of HI to fermions becomes arbitrarily large in the limits tan/ -4 0
and tan3 -* oo. The t - H - b coupling is perturbative if a = (coupling)2/47r < 1, which limits
our search to the region 0.2 < tang < 175 if 1/2 is substituted for "< 1". Outside this range,
our Monte Carlo (MC) simulations and branching fraction equations become invalid.
The large Yukawa couplings also result in top quark and H widths which become very large
at the boundaries of the perturbative region of tang. As an example, if MH = 100 GeV/c2,
then at tan3 = 0.2, Fop ti 20 GeV, and at tan/ = 175, Fop :0 8 GeV5 and FHZ ~ 6 GeV.
Two separate techniques are used to exclude HI using the top data. In our first approach,
we note that a large B(t -4 Hwb) suppresses ti decay rates to dilepton final states and lepton
+ jets final states. We use the observed number of these events and the theoretical value of c-tE
to exclude H . In our second approach, we exclude HW without assuming a value of o-tc by
exploiting the fact that a large B(t -* Hob -> csb) results in a ratio of dilepton events to lepton
+ jets events that is much smaller than the SM value. Limits from the CDF direct search 6 for
HW -> Tv decays in tt events are not discussed here.
The CDF and DO collaborations at Fermilab have established the existence of top quark pair
production via the observation of events which are consistent with the SM decay tt -* WbWb.
These include dilepton events which contain two isolated high-PT e or y, missing energy (9T) and
2 or more jets, as well as lepton + jets events which contain one isolated high-PT e or p, IT and
3 or more jets. For this analysis, both CDF and DO use the same event selection criteria which is
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Bevensee, Brendan. Top to charged higgs decays and top properties at the Tevatron, article, May 1, 1998; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc688693/m1/4/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.