Search for neutral Higgs bosons in e+e- collisions at sqrt{s} = 196 GeV

a r X i v :h e p -e x /9908016v 2 24 A u g 1999
P R E L I M I N A R Y
4August 1999
Search for neutral Higgs bosons
in e +e −collisions at
√
1Summary of preliminary results
The analyses designed for the189GeV data,described in detail in[1],have been applied without any modifications to the data collected by ALEPH up to July27,1999.The data
√s=195.6GeV. sample comprises29.0pb−1at
The expected numbers of background events,the expected signal for a Higgs boson with m h=100GeV/c2and the numbers of selected candidates are listed in Table1for the hZ analyses and in Table2for the hA analyses.The reconstructed mass of the candidates selected by the NN-and cut-based hZ searches are displayed in Fig.1(a)and(b).No departure from the Standard Model expectations is observed.This leads to improved 95%confidence level limits when the latest data are combined with those collected by ALEPH at lower energies.The confidence levels for the data in the background only hypothesis or the background and signal hypothesis are shown in Fig.2(a)and(b).The limit obtained for the Standard Model Higgs boson is m h≥98.8GeV/c2,with an expected limit of99.9GeV/c2.The limit is calculated as described in[1],with the proper treatment of the overlap between the hZ and hA four jet andτ+τ−selections.The stand-alone hZ observed limit from the cut-based set of analyses is97.6GeV/c2,with98.7GeV/c2for the expected limit.For the CP-even boson h of the MSSM,the limit is85.2GeV/c2,for all values of tanβabove1,with86.1GeV/c2expected.Fig.3shows the excluded domain in the m h–tanβplane.
N bkg N obs
q(NN/cut) 4.6/3.9
ν(NN/cut) 1.8/1.4
10.47
hττ+ττq 2.52
32.3/30.327/26
Channel N sig
b b 2.3
bττ0.4
Total 2.7
Table2:Number of background events expected,expected signal for m h≈m A= 85GeV/c2and observed candidates in the1999ALEPH data with the hA selections.
1
reconstructed Higgs mass (GeV/c 2
)
e v e n t s /3 G e V /c 2
reconstructed Higgs mass (GeV/c 2
)
e v e n t s /3 G e V /c
2
Figure 1:Distribution of the reconstructed Higgs boson mass of the selected events (dots)in the hZ searches by the NN-based (a)and cut-based (b)sets of selections.The histograms show the Standard Model expectations.
Higgs mass (GeV/c 2
)
c b
188.6+191.6+195.6191.6+195.6 GeV sin 2
(β-α)=1
ALEPH
PRELIMINARY
0.10.20.30.40.50.60.70.80.9186
88
90
92
94
96
98100102104
Higgs mass (GeV/c 2)
c s
expected observed sin 2(β-α)=1
ALEPH
PRELIMINARY
10
-10
10-9
10-810
-710-610-510-410-310-210-1186
88
90
92
94
9698100102104
(a)(b)
Figure 2:(a)Background-only confidence level curves (c b )as a function of the Higgs mass hypothesis for the 191.6and 195.6GeV data alone (dashed)and combined with the lower energy ALEPH data (solid)for sin 2(β−α)=1.(b)Expected (dashed)and observed (solid)confidence level curves for the Standard Model signal hypothesis using all ALEPH data up to 195.6GeV.
2
t a n β
Figure 3:Expected (dashed)and observed (solid)95%confidence level curves in the [m h ,tan β]plane of the MSSM.The dark regions are not allowed theoretically.The com-bined experimentally excluded region is essentially identical in the case of no stop mixing,for which the theoretically forbidden region is also indicated (dashed-dotted curve).
3
References
[1]aleph Collaboration,“Search for the Neutral Higgs Bosons of the Standard Model
√
and the MSSM in e+e−Collisions at。