Transcript Search for NMSSM Higgs at LHC in h→aa →mmmm signature

Search for NMSSM Higgs at LHC
in h→aa →mmmm signature
Alexander Belyaev
(South Hampton)
Jim Pivarski, Alexei Safonov, Sergey Senkin
(Texas A&M)
Motivation
• NMSSM is a viable extension of MSSM
–
–
–
–
Additional singlet superfield
Elegant solution to m problem of MSSM
Much less fine tuning and little hierarchy problem of MSSM
Fifth neutralino “singlino” can be consistent with WMAP
• Expanded higgs sector
– If Br(h1→a1a1) significant, softening of direct LEP limits on higgs
• Large parameter space
– Mostly explored region ma>2mt
• Need large luminosity to directly detect (10-100 ifb), challenging
experimentally
– Region of ma<2mt not thoroughly explored
• Clean signature of two pairs of collimated muons
• Could be a near zero background early LHC search
Motivation II
• Studies of the region ma>2mt show that this is a difficult
analysis
– Collimated pairs of tau or b jets make it challenging from
experimental point of view, large backgrounds force to use VBF
production
– Need 10-100 ifb
• Strictly speaking, there is no reason not to explore the
ma<2mt region
• Process pp→h1+X→a1a1+X
– Can rely on muons if Br(a1→mm) is large enough
– Experimentally very easy analysis (although a few tricks are
required), low backgrounds, can use all higgs production modes
– Lack of missing energy allows direct measurement of ma1, mh1
Analysis Strategy
• In the region of interest these events appear as two
collimated di-muon pairs
• Relatively simple topology
• Many constraints:
– m(mm)=m(a1) m(mmmm)=m(h1)
• Benchmark using CMS detector TDR
• Also note sensitivity to dark matter light bosons
* Analysis does not have to change if considering various
production mechanisms, only acceptance will
Acceptance Estimates
• Calculate acceptance using Pythia gg→h1 →a1
a1→mmmm
– Grid in ma = 0.5-5 GeV, mh=60-120 GeV
• Simple selections:
– Require a muon w/ pT>20 GeV within |h|<2.4
– 3 more muons w/ pT>5 GeV within |h|<2.4
– Sort nearby opposite charge muons into pairs using
DR(mm)
• Large acceptance
– of the order of 30-40%
• Many ways to increase
– e.g. tracks instead of some
of the muons
Signal Shape
• Signal: narrow 3D bump in
(m12, m34, m1234) space
• Background: mostly smooth
function (next slide)
m1234
– Symmetrize in m12 and m34
m34
m12
Backgrounds
• E/weak pp->4l: CalcHEP
– Negligible
• QCD:
– 2->2 Pythia
• Leptons from heavy flavor,
including J/psi
• 20 events/100 ipb
– Direct J/psi+X production
(also Pythia)
• Negligible
– Fakes from QCD with
misidentified muons
• Use 2->2 Pythia with 3
leptons+track smearing with
decay probabilities
• Also around 20 evts/100 ipb
•
Background numbers normalized
to “large” region
– 0.5<m12<4
– 60<m1234<120
Sensitivity
m1234
• Fit directly in 3D using
binned likelihood for:
– aS(m12, m34,m1234)
+bB(m12, m34,m1234)
– Fit looks for excess on the
diagonal
– There the background is
tiny
m12
Exclusion limit with 100 ipb
12
10
Sigma*B(h->aa)
• Background function
comes from
parameterizations on last
page
• Note that 0.4 background
evts/ipb in full space
m34
8
Ma=3 GeV
6
Ma=2 GeV
4
Ma=1 GeV
2
0
60
80
100
m(h) GeV
120
140
Branching of a to muons
Obtained using
NMSSMTools
package
• Branching to muon is fairly independent of
anything else
• Muons compete with a→gg and lower with
lighter quarks
D-Zero Limit
• D-Zero: direct 4mu search,
similar to what we do:
• Limit on sigma x BR of the
order of 0.1pb
• About 40 times smaller xsection given everything
else equal (and
acceptances are very
similar):
– 100 ipb LHC = 4 ifb TeV
• LHC should quickly surpass
Tevatron due to much
higher x-section
Phenomenology
• Now let’s look at what this means for
NMSSM
• Zoom into the region where ma is small
• We started with gg→h1→a1a1
– Use NMSSMTools package for couplings
– FeynHiggs for SM x-section
Parameter Space
Controls coupling of
new superfiled to SM
• Navigate to the
region with
small ma and
high Br(h→aa)
– Avoid fine
tuning, sort of
go with the flow
and see what
happens
h1 Production and Decay
40-120 GeV
• Scan in the selected
range for production xsection of the lightest
CP-even higgs h1 and
Br(h1→a1a1)
– Range used for the plot is
mh=40-150 GeV
• Scale SM Higgs xsections (FeynHiggs)
using couplings from
NMSSMTools
)~120
Two distinct scenarios for light aM(h
1: 1
When m(h1) is light, it has strong
coupling to light a1, decouples from
SM; h2 is SM-like (~120 GeV)
If m(h1) is a bit heavier, then it
becomes SM-like higgs
CP-odd Higgs Decay
• BR(a→mm)~10-20%
for ma<2mt threshold
– Largely independent
of other parameters
• Factoring in
Br(h→aa), overall
Br(h → 4m)~2-3%
Gluon Fusion x-section
• We cut somewhat into the allowed space, but
the preferred region has very small crosssection through gluon/b-fusion
Conclusions and Plans
• Attractive and technically simple analysis, LHC
will surpass Tevatron with just ~200 ipb
• Have taken a look at the low m(a) scenario:
– Still need to finalize the results, but it look like in the
NMSSM parameter space allowing light ma, h1
becomes a singlet
• Looking now into the pp→h2→h1h1
– If the branching ratio is large, may be able to see both
a1 and h1 at LHC
– If small, h1 will be hard to detect
Production Cross Section
• NLO FeynHiggs:
– NLO cross-section and width for SM higgs:
 SM ( gg  H ),  SM (bb  H ), HSMgg
• NMSSMTools:
– Branching ratio for h1→gg, h1 width, reduced bbh1
NMSSM
coupling: Br(h1  gg), hNMSSM
,
G
bbh1
1 total
 NMSSM gg  h1    SM ( gg  H )
hNMSSM
1  gg
HSM gg
  SM ( gg  H )
Br(h1  gg)hNMSSM
1 total
NMSSM 2
 NMSSM (bb  h1 )   SM (bb  H )(Gbbh
)
1
HSM gg