Transcript Determination of Yukawa Couplings at LHC and ILC

Searches for Neutral Higgs Bosons in
Supersymmetric Extensions of the SM
Markus Schumacher
Klausurtagung Feldberg, 13. 12. 2008
 Motivation
 Standard Model (SM)
 Structure of Higgs Sector
 Minimal Supersymmetric
 Theoretical Constraints
 Status of Searches
 Prospects for Discovery
Extension of the SM (MSSM)
 Next-to-Minimal Supersymmetric
Extension of the SM (NMSSM)
Particle
masses andconstraints
their “problem”
Theoretical
 Experiment: all particles massive (except g + gluon)
 Theory: forces described via gauge symmetries
 Problem: SU(2)LxU(1)Y-Symmetrie: no masses for
- gauge bosons: W und Z
- fermiones: (l=Dublett, r=Singlett)
„ad hoc“ mass terms destroy:
 renormalizibility  no precision predictions e.g. mtop
 good high energy behaviour: e.g. WLWL-Streuung
violates unitarity
at ECM ~ 1.2 TeV
2
The Brout-Englert-Hagen-Higgs-Kibble-Mechanismus
The „Standard“-Solution:
doublet of 4 skalar fields with
appropiately choosen potential
V = -m2 |f+f| + l |f+f|2
m2,l > 0
minimum not at f=0  spontaneous symmetry breaking
Higgs field has two components:
1) omnipresent, homogeneous background field v= 247 GeV
2) Higgs-Boson H with unknown mass MH ~ l v
H restaures unitarity if
gHWW ~ MW
gHff ~ Mf
and MH not too large
3
Mass generation and Higgs boson couplings: F = v + H
 interaction with v=247 GeV
x
x
 interaction with Higgs-Boson H
2
ggauge
Higgs
W/Z boson
x
vg2
gauge
W/Z boson
W/Z Bosonen MV ~ g v
gauge coupling
Fermions
Yukawa coupling
m f ~ gf v
 VVH coupling ~ vev: only exists after electroweak symmetry breaking
 observation of VBF yields indirect hint to background field
 only one free parameter: MH or l
4
Theoretical constraints on the Higgs boson mass
 Unitarity in VV scattering: < 1 TeV
 energy /temperature dependence of quartic coupling l
Left diagram: increasing l
require l < 1 up to energy L
 upper bound on MH=l(MH)v
triviality/pertubativity bound
Right diagram: decreasing l if mt large
require l >0 up to energy L
 lower bound on on MH=l(MH)v
vacuum stability bound
5
Experimental constraints on MH
 indirect prediction in SM:
MW(Phys) =
W
MW(Born) +
t
b
… mt2
W
W
+
H
W
W
… ln(MH)
MH < 154 (185) GeV
(incl. dir. limit)
direct search at LEP: MH < 114.4 GeV excluded at 95% CL
direct search at Tevatron:
MH ~ 170 GeV excluded
at 95% CL
6
Signal rates for SM Higgs boson production
Preliminary
Preliminary
NLO (in QCD)
(except ttH)
HIGLU, ... (SPIRA)
HDECAY (Djouadi,Spira et al.)
 Vectorboson fusion qqqqH: 2nd dominant production
but additional signature from outgoing quarks
 Hbb not selectable in ggH and VBF
H tt not selectable in gg->H
 VBF Htt promising channel close to LEP limit
our group: H tt  ll + 4 n (l=e, m)
7
Vektor boson fusion ppqqH with Htt  ll 4n
 signal characteristics:
- 2 forward jets with rapidity gap
- Higgs decay products in central detector
ttll (l=e ,m): 40fb
 background:
reducible ---------------------------------- irreducible
833 pb
MC@NLO
NNLO:770(ll)+170(tt)pb
ALPGEN/SHERPA
kinematics, colour flow, …
1.7pb (tt)
SHERPA
mass reconstruction
8
VBF:Challenges and our plans
 reconstruction of taggings jets
Preliminary
 central jet veto (pt>20 GeV, |h|<3.2)
EW
Preliminary
QCD
 mass reco. in collinear approximation
sM/M~12to 14% dominated by Emiss
20% worse for low lumi. pile-up
 optimise algos and study influence of pile up and underlying event
- investigate minimum bias and Zmm+jets
- use of tracking information
9
Mass distribution and background estimate
 mass distribution after all cuts
peak on shoulder of dominant Z BG
 estimate from data needed
Zjj
H
tt
 Zjj shape from data
jjZmm and jjZttmm identical topology
1) select Z  mm events
2) manipulate ms to look like Z  tt  ll4n
3) apply standard selection
 develop similar method for tt background
e.g. b-veto vs. b-tag, impact parameter cuts, …
10
Discovery potential
 all current ATLAS studies
 VBF H tau tau
Preliminary
Preliminary
 optimise selection (especially for ll final state):
- supress reducible BGs (tt much larger than in previous study)
- multivariate techniques
- sophisticated statistical tools
11
Exclusion potential
Preliminary
Preliminary
 for exclusion need signal efficiency and its systematic uncertainty
 dominant influences by:
- jet energy scale
 Z+jets
- parton shower + underlying event model
 Z+jets, Minimum Bias
- central jet veto eff. from data
 single top?, Z+jj?
12
Stability of the Higgs boson mass
 the hierarchy problem: why is v=246 GeV <<Mplanck or MGUT
 large corrections to Higgs mass
without new symmetry: fine tuning to level 10-34 needed or cut off at 1 TeV
 divergence cancelled by particle with: D spin = ½, ~ same mass, same coupling
if mass correction ~ O(100 GeV)
 MSUSY~O(1TeV)
13
Other arguments for SUSY
 largest symmetry of a unitary, interacting field theory =
Lorentz invariance x gauge symmetry x supersymmetry
 link to gravity: most string models are supersymmetric
local Supersymmetry incorporates gravity
 Grand Unification (GUT) possible:
sin θ
2 SUSY
W
= 0.2335(17)
sin 2θexp.
W = 0.2315(2)
Cold Dark Matter (CDM): lightest SUSY particle (LSP) might be stable
Baryon asymmetry in universe (BAU): can maybe explained
14
Parameters in SUSY (with R-Parity)
 Minimal SUSY: one spartner for each SM particle, no new parameters
only freedom in Superpotential
„the problem“: SUSY broken in nature: (e.g. no spin 0 partner of electron)
no „real“ model for SUSY breaking yet  parametrise
105 additional parameters to describe SUSY breaking
in specific models: mSUGRA, GMSB, AMSB,… ~5 parameters
15
The MSSM Higgs Sector in the Nutshell
 SUSY requires 2 Higgs doublets
– masses for up and down type fermions
- anomaly free
 5 Higgs bosons: 3 neutral + 2 charged
 scalar potential w/o SUSY breaking
„lH4" given by gauge couplings, no EW-symmetry breaking
 scalar potenital after SUSY breaking
 different m1, m2 evolution  m2 negative  triggers EW-symmetry breaking
2
after EWSB: two free parameters in Higgs sector (v21 + v22 = vSM
)
16
The MSSM Higgs Sector in the Nutshell
 at Born level:
- 2 parameters: tanb=v2/v1 and MA
- CP conserved  2 neutral CP-even h,H
+ 1 CP-odd A
- upper mass bound (quartic coupling = gauge couplings): Mh < MZ
 large loop corrections from SUSY breaking sector esp. top/stop
mh < 133 GeV (+-3GeV)
for mtop=175 GeV, MSUSY=1TeV
in constrained MSSM a la LEP/LHC corrections depend on 5 SUSY parameters:
Xt mixing in stop sector
M0 common sfermion mass at EW scale
M2, SU(2) gaugino mass at EW scale, M1 from GUT relation
Mgluino gluino mass
m Higgs mass mixing parameter
5 parameters fixed in the benchmark scenarios considered
 mSUGRA: Xt, M0 for Higgs and sfermion, M1/2 for gauginos, sign m, tanb
17
MSSM Higgs Bosons Phenomenologie
 modified couplings gMSSM = x gSM
x
t
b/t
W/Z
h
cosa/sinb
-sina/cosb
sin(a-b)
H
sina/sinb
cosa/cosb
cos(a-b)
A
cotb
tanb
-----
 no coupling of A to W/Z
 small a  small BR(htt,bb)
 large b  large BR(h,H,Att,bb)
a = mixing btw. CP-even neutral Higgs bosons
 Higgs boson mass pattern
 new production mode: b(b)Higgs
18
Constraints on the Higgs sector
 MSSM bounds
Constrained MSSM:
Mh<133 GeV for mtop=175 GeV, MSUSY=1TeV
General MSSM:
Mh<150GeV
 EW precision data, dark matter density, am, bsg in CMSSM = mSUGRA
precision from DM,
am, bsg constraints
19
Constraints on the Higgs sector: direct searches
 LEP: investigated 5+3 benchmarks
Mh/A<~ MZ excluded at 95% CL
 TEVATRON:
largest sensitivity at large tan b
via bbH, Htt
20
„Old“ MSSM Scans based on LO TDR and VBF-SN results
4 CPC benchmark scenarios considered: Carena et al. , Eur.Phys.J.C26,601(2003)
 MHMAX scenario
 Nomixing scenario
maximal mh < 133 GeV  conservative LEP exclusion
small mh < 116 GeV  difficult for LHC
 Gluophobic scenario
small gh,gluon
mh < 119 GeV
theo. aim: harm discovery via
gg h, hgg and hZZ4 l
 Small a scenario
small ghbb and ghtt mh <123 GeV
theo. aim: harm discovery via
VBF, htt tth, hbb
 mainly influence masses and couplings of h
 phenomenology of heavy states very similar
21
Some technicalities
1) SM LO production cross sections (Spira) times MSSM correction factors (FH)
Mt= 175 GeV
2) branching ratios from FeynHiggs (T. Hahn et al.)
3) efficiencies and background expectations from published „old“ MC studies
4) efficiency corrections for:
(a) increased total width in MSSM w.r.t SM
(b) mass degeneracy of h,H,A
5) evaluate signficance form signal and background rate
counting experiment using Poissonian statistic
no systematic uncertainties considered !
22
Corrections to Expected Signal Rates
a) for part of MSSM parameter space: large Gtot  eMSSM = K eSM
K=
h
b) signal overlap due to mass degeneracy of Higgs bosons
count signal in mass window 1
= signal 1 + signal 2 in window 1
23
Vector Boson Fusion: 30 fb-1 (old LO, SN-Study)
Preliminary
h or H observable
with 30 fb-1
 studied for MH>110GeV at low lumi running
 same conclusion in other benchmark scenarios
24
Light Higgs Boson h: 30 fb-1
observable channels: VBF
Preliminary
bbh hmm
Preliminary
(tth hbb w/o syst. error)
Preliminary
difference mainly due to
different mh in same (tanb,MA) point
( up to 17 GeV difference)
25
Small a scenario, h: 30 fb-1
 hole due to reduced branching ratio for H  tt
Preliminary
Preliminary
covered by enhanced BR to gauge bosons
complementarity of search channels
almost gurantees observation of h
26
Light Higgs Boson h: 300 fb-1
(VBF only 30 fb-1)
Preliminary
Preliminary
 also hgg, hZZ4 leptons (tthbb) contribute
 large area covered by several channels
 sure discovery and parameter determination possible
 small area uncovered @ mh = 90 to 100 GeV
 hgg sensitive in gluophobic scenario due to VBF, Wh, tth production
27
Heavy Neutral Higgs Bosons
ATLAS preliminary
 most promising: bbH/A, H/Att,mm
s ~ (tanb)2
 old LO study:
tt  lep had +  had had (M > 450 GeV)
 new NLO study: tt  lep lep
Preliminary
Preliminary
same BGs as VBF, Htt
mass reco. and BG estimate a la VBF
no forward jet and CJV
but b-tag instead of b-veto
28
Overall discovery potential in CP conserving MSSM
300 fb-1
Preliminary
 at least one Higgs boson observable
for whole parameters space
in all CP conserving benchmarks
ATLAS preliminary
 significant area where only lightest
Higgs boson h is observable
 discrimination via
- observation in SUSY cascades or
H SUSY decays?
- investigation of properties of h?
similar results in other benchmark scenarios
VBF channels , H/Att only used with 30fb-1
29
SM or Extended Higgs Sector e.g. MSSM ?
discrimination via VBF
BR(h WW)
R = BR(h tt)
compare expected measurement
of R in MSSM with SM prediction
300 fb-1
ATLAS
prel.
assumes Mh precisely known
negelects syst. uncertainties
D=|RMSSM-RSM|/sexp
 similar study by M. Dührssen et al.
incl. 13 channels and systematic uncertainties  VBF dominates
30
The CP violating complex MSSM
 MSSM Higgs sector CP conserving at Born level
 CP effects via complex couplings in loops
At, Ab
Mgluino
 mass eigenstates H1, H2, H3
not equal CP eigenstates h,A,H
„new“ Born level pars: tanb and MH+-
 why complex SUSY breaking parameters?
- no a priori reason why they should be real
- complex parameters yield new source of CP violation needed
- electroweak baryogenesis (1st order) in complex MSSM still ok
if mstop<mtop and MH1<120 GeV
31
Phenomenology in the CPX scenario
H1,H2, H3 couple to W,Z
H1
H2
H3
 H2,H3  H1H1, ZH1,WW, ZZ decays
sum rule:
2
Si g2i (ZZHi)
2
2
= gSM
 no absolute limit on mass of H1 from LEP
 strong dependence of excluded region
on value for mtop
on calculation used FeynHiggs vs CPH
32
Discovery potential in CP violating MSSM
CPX scenario (Carena et al., Phys.Lett B495 155(2000))
arg(At)=arg(Ab)=arg(Mgluino)=90o,,MSUSY = 500 GeV, At=Ab=Mgluino=1 TeV, m=2TeV, M2=200GeV
300 fb-1
300 fb-1
 yet uncovered region in parameter space for light Higgs boson (not yet studied)
 promising channels: ttbbH+W-bbH1W+W-bbbblnqq
Higgs in SUSY cascades,….
33
The m-problem
 MSSM Superpotential
m: the only parameter with mass dimension bevor SUSY breaking
 m not protected by symmetry, could be MGUT
but correct EWSB requires O(.1 to 1 TeV)
 idea: replace m by condensate of new scalar complex singlet field S
which is only coupled to MSSM Higgs fields
 seven Higgs bosons: 3 CP-even, 2-CP-odd, 2 charged
5th neutralino from superpartner of S
 several variants on the market: NMSSM, MNMSSM,…
and also not SUSY singlet extensions e.g. HEIDI …
34
Investigation of sensitivity in NMSSM
 following variant considered:
 six free parameters at Born level:
 two benchmark scenarios (Iris Rottländer, M.S. in LH07 proc. hep-ph 0803.115)
(more benchmarks in PhD thesis by I. Rottländer, CERN-THESIS-2008-064)
 masses, couplings, BRs calculcated with NMHDECAY (Elwanger et al.)
 same procedure as for „old“ MSSM scans
(i.e. LO cross sections, TDR etc. efficiencies and background numbers)
35
Phenomenology in light A1 scenario
 MH1 ~ 120 GeV and SM-like
 MH2 ~ heavy and decoupled in
unexcluded region
 BR(H1A1A1)
 H3,A2,H+- too heavy
 MA1 < MH1 /2 in almost whole plane
 BR(A1 tt)
36
Discovery potential in light A1 scenario
 H1 discovery potential
 H2 sensitvity
Preliminary
H2 photons reach limited
by BR(H1A1A1) ~ 55% contour
Preliminary
H2 only in excluded region observable
 other Higgs bosons too heavy or decoupled to be observable
 need dedicated searches for HA1A1bbbb,bbtt,tttt
or maybe sensitivity in SUSY decays
37
Plans for (N)MSSM Scans
 create database for masses, couplings, BRs for various benchmark scenarios

provide consistent NLO cross sections
- simple scaling not always thrustworthy (e.g. gluon fusion)
- check approximations against dedicated programs
 include mass shapes and systematic uncertainties a la SM
 evaluate discovery poential and exclusion and significance plots for data
and possibility to discriminate SM and SUSY extensions
 perform sensitivity studies for yet uncovered regions
- need signal efficiency (and shape) in addition
 look at new scenarios propsed by our theoretical friends
I do not believe in SUSY, other extensions to SM are also welcome
38
Final words
 new studies confirm good sensitivity for discovery of Higgs bosons
in SM and CP conserving MSSM
 CP Violating MSSM and NMSSM need further studies to establish
no lose situation
 VBF with Htt important
- for low mass Higgs boson discovery
- discrimination btw. SM and extended sectors
- determination of spin/CP and maybe mass
 Higgs sensitivity starts at > 1fb-1
- due to limited signal rates (except H+-)
- required good understanding of detector
 focus for first data:
- improve and validate jet and ETMISS reconstruction (Z+jets)
- investigate and tune underlying event model
(min. bias and Z+jets)
- understand backgrounds in phase space relevant for Higgs boson searches
39
Back up
40
Discovery = significant deviation from SM expectation
 significant: probability of background fluctuation
<2.9x10-7 equivalent to „5 sigmas“ for Gauss distribution

deviation: - new peak in mass distribution
- excess in kinematic distribution
 for discovery (event counting or more info):
- only need knowledge of background
- wrong modelling of signal (rate and shape)
 non optimal search strategy  more data
 for exclusion (and discovery potential)
- need signal efficiency (and shape) in addition
determination of background:
(i) from data itself with little theory and MC input
via auxilary measurement from same data set
(ii) prediction from theory + MC + detector performance
background=lumi*cross section*acceptance*efficiency
 signal-to-background ratio vs. background uncertainty
crucial for discovery significance
41
Ist es ein Higgs-Boson?
V
Jet 1
V
Signal +Untergrund für 10 fb-1
Dfjj
Jet 2
Sensitivität für Ausschluss von CPE/CPO:
HWW: ~ 5 s mit 10 fb-1
Htt:
~ 2.5 s mit 30 fb-1
(MC-Generator VBFNLO von D. Zeppenfeld et al.)
C. Ruwiedel Diplomarbeit BN 2006
42
Kein Higgs?  Anomale Eichbosonselbstkopllung
Verletzt Unitarität bei Energien von ~ 1.2 TeV
Restaurierung durch „Neue Physik“
 Untersuchung von ppjj WW jj ln ln Endzustand (VBF-Signatur)
 sensitive Observable Azimuthwinkeldifferenz zw. den Leptonen
M. Mertens Diplomarbeit BN 2006
DfllLept.1
Lept.2
vielversprechende Studie auf dem Weg
MC-Generator WHIZARD (W. Kilian, J. Reuter, …)
43
Hmm: sensitivity
Preliminary
Preliminary
Preliminary
Preliminary
44
MSSM Cross section: Charged Higgs Bosons
 light charged boson: production in top decay BR(tH+b) with Feynhiggs 2.6.2
 gbHt: calculated in NLO with program
including dominant SUSY loop corrections via Db (taken from Feynhiggs)
 decay branching ratios calcluated with Feynhiggs 2.6.2
results in mhmax scenario
 production cross sections
 decay branching ratios
45
Charged Higgs boson: search channels
 light H+- (MH+- < Mtop) (PYTHIA)
Preliminary
MH+-= =130GeV
tanb=20
 heavy H+- (MH+- >= Mtop) (MATCHIG)
Preliminary
 backgrounds: tt, single t, W+jets, QCD
 top quark production dominant background in all topologies
 systematic uncertainties:
theo: 15% for tt cross section
exp.: 15 to 40% for signal and background (E scale, b-tagging largest)
 exctract background from control sample  ~ 10% background uncertainty
46
Charged Higgs boson sensitivity in mhmax scenario
 background uncertainty: 10%
 signal uncertainty included for exclusion
 limited MC statistics for background also taken into account
mhmax scenario
mhmax scenario
Preliminary
Preliminary
 most difficult region at intermediate tanb as coupling H+-tb smallest
 if statistical uncertainties from limited MC neglected  gap closed
47
Charged Higgs Bosons
high mass: mH+-> mtop
gbH+-t
H+-tn
tbqq
low mass: mH+-< mtop
ggtt
ttH+-bW
only low lumi.
 transition region around mtop
needs revised experimental analysis
 running bottom quark mass used
new:
Wqq
H+-tn
 Xsec for gbtH+- from T. Plehn‘s program
48
bbH, Httll 4n
Preliminary
 only >=1 btag analyis for now
 mass resolution ~ 20%
 low M: Ztt dominant background
larger M: tt dominant BG
 background estimate from data a la VBF
 uncertainties considered:
Preliminary
- exp. uncertainty: 5% signal 8% tt
- Z background fom data (several %)
- theo. uncertainty for signal:
20%(100 GeV) to 10%(400GeV)
 other decays ttl had, had had
and 0 btag analysis to come
49
MSSM cross sections: neutral Higgs bosons
LH03
hep-ph 0406152
 direct production:
calculated with HIGLU
 associated production: calculated with Harlander values
for NNLO bb->H plus MSSM correction from Feynhiggs 2.6.2
 branching ratios calculated with Feynhiggs 2.6.2
 uncertainties: bbH 10% scales + 14%pdfs (MRST02/04) ggbbH 20-30% 50
Light Higgs Boson H1
30
fb-1
ATLAS preliminary
300 fb-1
 border of discovery region at low tanb mostly determined
by availability of inputs (VBF >110 GeV, ttH and gg > 70 GeV)
 border at low MH+- due to decoupling of H1 from W,Z and t
 for VBF channels: assume same efficiencies for
contribution of CP even and CP odd states (needs to be checked)
 for ttH: efficiencies for CP even and odd bosons are the same
51