Search for the Higgs bosons in supersymmetric extensions of the SM

Giorgos Dedes

Seminar : Physik am Large Hadron Collider (LHC)

Outlook

ATLAS - CMS SUSY – MSSM Higgs sector Higgs masses Production and Decay Benchmark scenarios Higgs searches Summary

ATLAS Inner Detector: Highly segmented silicon

strips, determine very accurately charged particles trajectories

Solenoid Magnet: Solenoid coil that generates a 2T magnetic field in the region of the Inner Detector

Electromagnetic Calorimeter: Electron and photon energies are measured through electromagnetic showers

Hadronic Calorimeter: Hadrons interact with dense material and produce a shower of charged particles

Toroid Magnets: 8 toroidal coils that create a 0,4T magnetic field in the area of the Muon Spectrometer

Muon Spectrometer: Muons traverse the rest of the detector and are measured in its outer layers

CMS Tracker: Cocentric layers of silicon

sensors, measure charged particles trajectories

Electromagnetic Calorimeter: Lead-Tungstate crystals, electrons – positrons – photons interact there and their energy is measured

Hadronic Calorimeter: Hadrons interact brass layers and produce a shower of charged particles

Solenoid Magnet: Largest solenoid ever built, creates 4T field that bends the charged particle trajectories

Return Yoke: Magnetic field created from the solenoid is returned in the iron yoke. Offers support structure for the detector

Muon Chambers: Located in the iron yoke, measure energy of muons

SuperSymmetry (motivation from Higgs sector)

Hierarchy problem in the SM Higgs sector:

Quantum corrections to the H mass have quadratic divergencies

By introducing supersymmetric partners for the SM particles

quadratic divergencies are cancelled

SuperSymmetry By introducing superparticles, the SM particle spectrum is doubled.

MSSM (in a nutshell)

MSSM is the minimal extension to the standard model that realizes supersymmetry.

It imposes an extra symmetry, R parity

Sparticles enter interactions in pairs, with particles having R parity of 1 and sparticles of -1

Sparticles are produced and annihilated in pairs

MSSM Higgs sector In order to implement electroweak symmetry breaking into the MSSM, two Higgs

doublets (H1, H2) that couple to up and down type particles, are needed.

8 degrees of freedom3 are absorbed from the H mechanism and give masses to W± and Z

5 physical Higgs bosons

2 CP even (h, H),1 CP odd (A) and 2 charged H±

The MSSM Higgs sector (at tree level) is determined by 2 free parameters

MA and tanβ=v2/v1 (ratio of the vacuum expectation values of the 2 Higgs doublets)

In CP conserving scenarios mass eigenstates are equal to CP eigenstates.

In CP violating scenarios additional free parameters appear.

Non vanishing phases mix the CP eigenstates to 3 mass eigenstates

2

2*1

222

2

2

1

22

21212

2

2222

2

1211 28

'.. HH

gHH

ggchHHmHmHmV ji

ijH

Higgs masses At tree level:

and for

This gives us an upper limit for the h mass

Modifications to tree level due to top loops give additional contributions to Mh

So Mh < 133 GeV

2cos2cos42

1 2222222, ZhZAZAHh MMMMMMM

222WAH

MMM ZA MM

t

t

m

m~

log~

For the decoupling limit MA>>MZ

A and H have similar couplings and are degenerate in mass

while h resembles standard model Higgs

Higgs production (neutral)

d

Main production mechanisms:

gluon fusion and associated production with b-quarks which is dominant at high values of tanβ

Vector boson fusion and Higgs-strahlung are suppressed for h/H/A (suppressed coupling to W±, Z)

With respect to the SM, cross sections are enhanced with rising tanβ

Higgs production (charged)

Three main production processes in LHC, for single H±

From tt via gg fusion

In association with top and b quarks

In association with t quark

Higgs decays

For large tanβ, the dominant decay channels for h/H/A are bb and ττ

H± branching ratios are divided to 2 regions:

dominant decay to τν for MH± <Mt

and decay to tb for MH± >Mt

Benchmark scenarios

Due to the large number of free parameters, the MSSM Higgs search is performed in 4 CP conserving (CPC) and 1 CP violating (CPV) scenarios

CPC scenarios:1. mh – max scenario (MSUSY = 1TeV, μ=200GeV, M2=200GeV, Xt=√6MSUSY, Ab=At, Mgluino=0,8MSUSY)

2. no - mixing scenario (MSUSY = 2TeV, μ=200GeV, M2=200GeV, Xt=0, Ab=At, Mgluino=0,8MSUSY)

3. gluophobic scenario (MSUSY = 350GeV, μ=300GeV, M2=300GeV, Xt=-750GeV, Ab=At, Mgluino=500GeV)

4. small α scenario (MSUSY = 800GeV, μ=2TeV, M2=500GeV, Xt=-1100GeV, Ab=At, Mgluino=500GeV)

CPV scenario:the CPX scenario (MSUSY = 500GeV, μ=2TeV, M2=200GeV, Ab=At, Mgluino=1000GeV)

Benchmark scenarios mh-max scenario: Designed to maximize the h

mass. Gives a limit for the Mh (133 GeV) that strongly depends on Mt

no-mixing scenario: Similar to mh-max but with no mixing in the stop sector.Designed to explore the effect of no stop mixing, results to Mh < 116 GeV (Difficult for LHC)

gluophobic scenario: Coupling of h to gluons strongly suppressed. Designed to affect the processes gg→h , h→γγ and h→ZZ →4l. Yields a Mh < 119 GeV

small α scenario: Coupling of h to b and τ is suppressed. Mh < 123 GeV. Designed to affect the channels h→ττ and tth, h→bb

CPX scenario: CP eigenstates do not coincide with mass eigenstates. So h, A, H mix to mass eigenstates H1, H2, H3. CPX has maximal mixing (90 degrees)

Suppressed h-gluon coupling

Status of previous Higgs searches The search for MSSM H bosons has been performed at LEP

and is an ongoing effort at Tevatron

LEP: 8 scenarios scanned at LEP1 and LEP2

No discovery but limits for the masses and tanβ have been set.

tanβ exclusion 0,7 – 2.0 and Mh , MA > 90 GeV

Tevatron: Still no discovery,

a large part of the tanβ - MA

parameter space will be covered

with 5 fb-1 of data (2007-2008)

Higgs searches in LHC ATLAS and CMS will cover a large variety of

different final states and a big part of the (MA, tanβ) plane

The channels investigated during the last years in ATLAS and CMS are:h/H/A→γγh/H/A→bbh/H/A→ττh/H/A→μμH→ZZ , tt , hhA→ZhH±→τν , tbH/A→χo

2 χo2

h / H / A → γγ The expected MSSM rates for h and H decaying to γγ

are generally suppressed with respect to SM case. For this rare decay, A boson is only observable in a limited region of the parameter space.

Optimistic scenario: Branching ratio is estimated assuming that all SUSY particles have a mass higher than 1TeV (there can be stop-quarks , charginos and neutralinos lighter than 1TeV)

The same kinematic cuts are applied as in the case of the SM

2 photon candidates ordered in PT (starting from PT1 > 40GeV and PT2 > 25GeV for h and reaching PT1 >

125GeV and PT2 > 25GeV for the heavy Higgses

Both photon candidates in |n|<2,4 and events with more than one γ in transition region in an interval Δn = 0,15 are rejected

Backgrounds: γγ pair production, γ-jet, dijet and Z→ee

ATLAS

h / H / A → bb

More promising channel is h / H / A → bb , due to the high branching ratio (~90%) especially for high values of tanβ

For the low mass Higgs best sensitivity is achieved in the tth, h→bb

ATLAS

For high mass region bbH/A, H/A→bb Quite challenging to trigger a 4 jet final state Require 2 hard jets from Higgs decay and 2 softer

tagging jets Enormous QCD background Complex final state, 20% combinatoric background

ATLAS

h / H / A → bb In more recent study performed for the CMS detector, this channel is

considered as cross check after discovery in H / A → ττ

CMS

CMS

At least 4 jets are required

within the detector acceptance |n|<2,4

with the hardest 2 passing PT thresholds dependant on the Higgs mass

Additional selection in CMS analysis

the centrality variable

Discovery possible for tanβ>30 (largely dependant on background uncertainties)

7,0

22

Z

T

EE

EC

h / H / A → ττ For h main production mechanism is VBF while for H/A associated

production with b-jets All τ decay modes have been considered

(lepton-lepton / lepton – hadron / hadron - hadron)

Due to the escaping neutrinos mass reconstructions is done by using the collinear approximation

ATLAS

Mass resolution dependant on Δφ between the visible decay products and sensitive to ET

miss resolution

h / H / A → ττ

Is considered a discovery channel for heavy neutral Higgs, especially in mass range 150 – 300 GeV

h / H / A → μμ

Same coupling as for ττ channel, but BR scales as (mμ/mτ)2 ≈ 1/300

For high tanβ, associated production with b-jets is dominant

Clean signature in the detector

Excellent mass resolution, can provide the best mass and width measurement for H/A

ATLAS

H→ZZ(*) →4l , H→tt

h/H→ZZ(*): Not thoroughly searched, extrapolated results from SMFor high tanβ suppressed HZZ coupling, rise of hh ttIf observed identified from the low rate

H→tt: Suppressed coupling with gauge bosons, tt becomes interesting

Observed as peak over the continuous tt background

Mass reconstruction from the decay channel bWbW→blνbj

ATLASMH=370GeV

tanβ=1,5

H→hh , A→Zh Would allow simultaneous observation of 2 Higgs bosons For H→hh, possible decays are: bbbb (largest rate-difficult trigger),

bbττ (can trigger on leptonic tau), bbγγ (easy to trigger – low rate)

For A→Zh with final state: μμbb or eebb , require 2 leptons with Z mass constrain and 2 bjets well separated from the leptons

Signal

Zbb

tt

Z+jets

H± → τν / tb 2 prominent decay modes, τν / tb for MH lower/higher than tb production

threshold MH < Mt : tt→H±Wbb→(τν)(lν)bb→(hνν)(lν)bb , trigger from W leptonic decay

MH > Mt : gg→tbH± →(bW)b(τν)→(bjj)b(hνν) , disentangle τ-jet from light jets

t mass constraint

tb decay channel opens gg→tbH± →tb(tb)→WWbbbb→qqμνbbbb

gb→tH± →t(tb)→WWbbb→qqμνbbbhas large tt+jets background , multivariate techniques used

CMS , 30fb-1

3-tags

A/H →χo2 χo

2

MSSM Higgs can be also searched in decays to supersymmetric particles Can give us a handle on the low and intermediate tanβ region not

accessible by A/H→ττ Promising decay into the next to lightest neutralinos , χo

2→l+l- χo1

Main backgrounds: squarks and gluinos cascade decays , ZZ(*), Zbb Apply lepton isolation , jet and Z veto

No mass peak reconstruction, excess of events

Overall discovery potential

In LHC MSSM Higgs could be discovered within the first years (30 fb-1)

At 300 fb-1, the biggest part of the parameter space will have been scaned

A challenge for both theorists and experimentals : A region where only one Higgs can be seen, is it SM or MSSM ?

Conclusions

Supersymmetry and MSSM in particular are favorite candidates for extension of the SM

Searches for the MSSM Higgs have been started at LEP, continue at Tevatron and will start soon in LHC experiments

A large number of processes provide us the capability to scan a large area of the parameter space

Tevatron could surprise us, otherwise LHC can give as indications during the first 3 years and discovery afterwards

Backup slides

Production cs at low tanb

A BR also in SUSY particles

MSSM Higgs sector

h/H/A couplings

CPV mixing

SM – MSSM discrimination

Other contributions in cs

h discovery potential ….dependence

on scenarios…

CPV discovery potential