search for the higgs boson at the lhc w. adam institut für hochenergiephysik der Öaw micro-summary...

Search for the Higgs Boson at the LHCSearch for the Higgs Boson at the LHC

W. AdamInstitut für Hochenergiephysik der ÖAW

Micro-summary of the Higgs discovery potential at LHC on the occasion of

FAKT-Tagung, Weyer, 26./27. Sep. 2004

Second “Physics at LHC” conferenceEmphasis on the physics programme &presentations by young physicistsAll 5 LHC experiments + theory

Organised by HEPHY (LOC: J.Hrubec,G.Mitselmakher, C.-E.Wulz)Held at the main building of the ÖAW~ 180 participants

The talk is based on material shown at PHLHC04 and other summer conferences

FAKT2004 Search for the Higgs Boson at the LHC 2

SM Higgs: experimental statusSM Higgs: experimental status

LEP EWWG, summer ‘04The situation after LEP:

Indirect (full EW fit)• Preferred value:

mH = 114 +69 -45 GeV(exp. errors only)

• Limit:mH < 260 GeV @ 95%CL

Precise values might still change,

but message is clear: a light Higgs

is favoured by the measurements.

Direct (LEP searches)• Observed (expected) limit

mH > 114.4 GeV (115.3GeV)• preferred value from -2lnQ ~115GeV

129GeV

114GeV



News from the Tevatron

Signatures: HWWbb(e)/()bb, HWZbb(ee//)bb (mH<130)

ggHWW* (e/)(e/) (mH>130)

(WH) x B(Hbb) for mH=115GeV < 12.4 pb (D0, e-channel)

< 5 pb (CDF)



xB(H-WW*) for mH=160GeV: < 5.7pb (D0), < 5.6pb (CDF)

Available summer ‘04: • ~400 pb-1/exp (recorded)• ~200 pb-1/exp (used)• 2009: 4.4 - 8.5 fb-1


The SM Higgs @ LHCThe SM Higgs @ LHC

Production:

mainly via gluon fusion

tt-fusion

W,Z fusion: increasinglyimportant at high masses

associated productionin the low mass region


SM Higgs: low massSM Higgs: low mass

Decay:

• bb dominates, but high multi-jet backgrounds and low mass resolution

• : BR low (10-3 to 10-4) - use small Higgs width and high resolution EM calorimetry

Material in front of calorimetry(e.g. CMS: full-Si tracker):

will need to complement withreconstruction of convertedphotons (under study)


SM Higgs: low massSM Higgs: low mass

H signal (CMS, mH=130GeV, 100fb-1)

ATL-PHYS-2003-024

Hbb much more challenging:use tt-fusion and top decay products


SM Higgs: production via VBFSM Higgs: production via VBF

Contributes ~10% at low masses, dominates at very high massesSpecial topology allows for easy tagging:• Forward jets• Central Higgs decay products

Low mass analysis decay channels:

• WW*, and

[email protected]@PHLHC04

Taus: need trigger (leptons and narrow jets) and offline enhancement (-lifetime tracking)

Contribution of VBFanalysis to total significance


SM Higgs: intermediate massSM Higgs: intermediate mass

Decay modes to WW and ZZ become important


SM Higgs: intermediate massSM Higgs: intermediate mass

HWW ll’X• strong background from top decays• need to use WW spin correlation• veto on central jets

P.Sphicas@PHLHC04

tt-background:1st jet pt vs.

For mH=170±10GeV: 10 fb-1 are sufficient for discovery

pT


SM Higgs: intermediate to high massSM Higgs: intermediate to high mass

The “easy” region: high probabilityfor decays to ZZ(*)


SM Higgs: intermediate to high massSM Higgs: intermediate to high mass

Golden channel HZZ 4

• high energy muons• Z mass constraint(s)• irreducible background: ZZ production

M.Sani@PHLHC04H 4, CMS preliminary

for high mass: decreasing sigma - need more BR: use llqq or ll


SM Higgs: summarySM Higgs: summary

Full range of Higgs boson masses can be covered - most of it already at low luminosity

CERN/LHCC 99-15 ATLAS TDR 15 CMS NOTE 2003/033


MSSM Higgs Boson MSSM Higgs Boson

5 Higgs bosons (h,H,A,H±)

• Usually parametrised using mA and tan (tree level). Stop-mixing at loop level!

• Important difference to searches at previous experiments: cascades via SUSY particles are possible! LEP HWG 2004-01

preliminaryB.Tuchming@PHLHC04


MSSM Higgs: H, AMSSM Higgs: H, A

“Decoupling regime”• High mA, high tan• decays to :

high BR, analyse leptonicand hadronic channels!

• decays to : lower BR, but ~1% mass resolution

“Intermediate regime”• mA<500GeV, tan<5-10• transition region between

couplings to u- and d-type• use AZH, H Wh,

H/A tt for very low tan

“Intense coupling regime”• Low mA, high tan• Higgses are almost degenerate

5 discovery reach


MSSM Higgses: hMSSM Higgses: h

“Decoupling regime”

• High mA, high tan

• h is SM-like (mh<150GeV!)

“Intermediate regime”

• mA<500GeV, tan<5-10

• h-couplings to VB and u-typesuppressed bb, decays

Large parts of the plane covered

VBF modes are important


MSSM Higgses: HMSSM Higgses: H±±

Production:• for low mass: tbH±

• for high mass: gb tH±

qq’ H±

gg H±H±

gg W±H±

Decay

• for mH>~130GeV: H± t(*)b dominates

• interesting for analyses: H±


MSSM Higgses: cascade decaysMSSM Higgses: cascade decays

In the MSSM Higgs bosons can decay to SUSY particles and/or be producedin SUSY decay cascades.

One scenario:

• M2 = 2*M1 = 350GeV, = 1TeV

• m(gluino) = 1200GeV• ms(squark) = 800GeV

“long” cascades via 03,4 and 0

1,2

mH<~200GeV accessible

N.Marinelli@PHLHC04

SUSY signal

SUSY bkg

SM bkg


More exotic scenariosMore exotic scenarios

Still more Higgs bosons …• CP-violation

Can add phases to MSSM parameters - major changes to all signatures• Invisible decays, e.g. to LSPs

excess would be visible, but interpretation?• Extra dimensions

e.g. Radion decays to Higgs bosons• Fermiophobic, gluophobic scenarios

Specific points in SUSY parameter space orin more general 2HDM models

Other scenarios• Technicolor

still alive .. LHC could look for decays of T to vector bosons.

• Strong VL-VL-couplingthe no-Higgs scenario: look for resonant WZ and non-resonant W+W+ scattering


Radion decaysRadion decays

Randall-Sundrum model: • warped extra dimensions; two branes (Planck & TeV plane)

Radion: scalar representation of the 5d gravitational field

Most promising channel: • hhbb : look for mass peaks

in the (narrow) and jj (broader) system• Other channels studied: bb, 4b

S.Gennai@PHLHC04


ConclusionsConclusions

In the Standard Model• LHC covers the full mass range• If discovered need to measure parameters

(mass, spin, CP, couplings, ..): major field of activity

In the MSSM:• The light Higgs is detectable in the full range• Some regions of parameter space are tricky• Analyses looking for SUSY decay chains are being developped• What’s about extensions? CP-violation?

Substantial progress also on the theoretical side, e.g.

• KNNLO for the SM Higgs production

• full one-loop + 2-loop RCs for large couplings in the MSSM

Still quite some work to be done before LHC startup!

search for the higgs boson at the lhc w. adam institut für hochenergiephysik der Öaw micro-summary...

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