possible higgs searches at lhcb a preliminary study investigating the feasibility of finding the sm...
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Possible Higgs searches at LHCb
A preliminary study investigating the feasibility of finding the SM Higgs at LHCb
Jonathan Anderson (UCD)
Outline
What are the possible Higgs discovery channels at LHCb?What about the gold-plated channel?Gold-plated channel and its backgroundsCross-sections and branching ratios for this channelThe effects of the small LHCb angular acceptanceKinematic cuts used and their effectsOverall conclusions
Higgs decay modes
In the range 130 Gev < MH < 300 Gev, H WW and H ZZ dominate. While for MH < 130 Gev H bb dominates.
The QCD backgrounds swamp the hadronic final states so we must look for final states containing leptons or photons.
A possible exception at LHCb might be H bb.
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The Gold Plated channel
H ZZ 4L is known as the ‘gold plated’ Higgs decay channel.
It divides into two regions, 130Gev < MH < 2MZ
Contains one real Z and one off mass shell Z Branching ratio is smaller Background elimination more difficult
MH > 2MZ Contains Two real Z’s Higher branching ratio easier to eliminate background
H ZZ 4μ was investigated
Backgrounds for gold-plated channel
Reducible backgrounds gg (Z/)bb 4 gg, qq tt WbWb
4 gg, qq bb 4
Irreducible backgrounds gg, qq (Z/)(Z/)
4
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Cross-sections and branching ratios
Process x BR (fb)
H 4 (MH=130 GeV) 0.903
H 4 (MH=150 GeV) 1.459
H 4 (MH=180 GeV) 0.7627
H 4 (MH=200 GeV) 2.756
H 4 (MH=250 GeV) 2.2163
H 4 (MH=300 GeV) 1.7643
(Z/)(Z/ ) 4 20.618 *
(Z/)(Z/ ) 2µ2 41.236 *
(Z/)bb (Z 2 µ) 5.63 x 103
bb 4m > 200 Gev) 1.303 x 104
tt WbWb (W ) 5.637 x 103
All processes generated in pythia(One year of running equates to 2 fb-1)* Includes factor (1.3) to account for gg (Z/*)(Z*/ *)
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LHCb angular acceptance
The acceptance for LHCb is 0.015 0.245
LHCb acceptanceProcess Percentage within
acceptance
H 4 (MH=130 Gev) 2.042
H 4 (MH=150 Gev) 1.672
H 4 (MH=180 Gev) 1.284
H 4 (MH=200 Gev) 1.08
H 4 (MH=250 Gev) 0.53
H 4 (MH=300 Gev) 0.351
(Z/)(Z/ ) 4 2.91
(Z/)bb (Z 2 µ) 4.678
bb 4m > 200 Gev) 19.39
tt WbWb (W ) 1.72
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Muon pair wise invariant masses
Higgs (200 Gev) ZZ
Zbb tt_ _
Muon four wise invariant masses
Zbb tt
Higgs (200 Gev) ZZ
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Kinematic cuts for MH > 2MZ
MH (Gev) 200 250 300
|M12 – MZ| <
and|M34 – MZ| <
5
5
10
10
15
15
|M1234 – MH| < 4.5 9 13.5
All muon impact parameters <
30μm 30μm 30μm
Effectiveness of high mass cuts
Process 200 Gev 250 Gev 300 Gev Events
H 4 (MH=200 GeV) 73.87 ± 2.6%
200k
H 4 (MH=250 GeV) 71.21 ±2.9%
200k
H 4 (MH=300 GeV) 70.37 ±2.9%
200k
(Z/)(Z/ ) 4 6.136 ± 0.001%
6.55 ±0.001%
5.14 ±0.001%
100k
(Z/)bb (Z 2 µ) 0 ±0.00017%
0 ±0.00017%
0 ±0.00017%
600k
bb 4m > 200 Gev)
0 ±0.0001%
0 ±0.0001%
0 ±0.0001%
1M
tt WbWb (W ) 0 ±0.00017%
0 ±0.00017%
0 ±0.00017%
600k
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Overall signal against background
For 2 fb-1 of data (equivalent to one year)
MH (Gev) Signal Background Significance
200 0.044 ± 0.00114
0.0734 ± 0.00002
1.148
250 0.0168 ± 0.00048
0.0784 ± 0.0002
0.424
300 0.0088 ± 0.00026
0.0614 ± 0.0002
0.251
Gold-plated channel does not have any discovery potential at LHCbHowever it seems as though H bb is more promisingWork to be done Investigate H bb more fully, starting with
LHCb thesis…
Conclusions and further work
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