Charged Higgs Prospects with CMS

Prospects of Cherged Higgs Discovery at Colliders, Uppsala,13-16 September 2006, Uppsala,13-16 September 2006

R. KinnunenHelsinki Institute of Physics

Charged Higgs Prospects with CMS


Prospects for Charged Higgs Discovery at CollidersUppsala, 13-16 September 2006Uppsala, 13-16 September 2006



ContentsContents

- - IntroductionIntroduction- CMS full simulationCMS full simulation- Searches for the light charged Higgs bosons with the Searches for the light charged Higgs bosons with the H± -> decay decay channel in the tt eventschannel in the tt events- Searches for the heavy charged Higgs bosons:Searches for the heavy charged Higgs bosons: with the with the H± -> decay channel decay channel with the with the HH± -> tb -> tb decay channel decay channel- Other possible search channels- Other possible search channels



Production and decay channels

Production of the H± at the LHC mainly through the processes- tt, t ->bH± for mH+ < mtop – mb

- gb -> tH± and gg -> tbH± for mH+ > mtop

Main decay channels: H± ->, H± -> tb, H± -> Wh, H± -> ±



CMS full simulation

- GEANT4 based detector simulation (OSCAR) - Full event reconstruction (ORCA)- All predictions include the pile-up corresponding to the low luminosity of 3x1033cm-2s-1

- In the following expectations only for low luminosity are shown



Search for light charged Higgs bosons

Signal process defined as gg -> tt -> W±H±bb->lbb, l = e or

Minimum of BR(t->bH±) at tan ~ 6

Signal generation with PYTHIABR(H± -> ) with HDECAY decays with TAUOLA

For mH+ = mtop the off-shell contribution included with the process gb->tH±

and compared to the results from gg -> tbH± - Generation of the gb -> tH± and gg -> tbH± processes with PYTHIA



Backgrounds

Main backgrounds from tt and W+3 jet production with a jet faking hadronic decay, 3 final states from tt: pp ->tt->W+W-bb, W+->, W-l pp ->tt->W+W-bb, W+->jj, W-l pp ->tt->W+W-bb, W+->l, W-l’

Generation of tt events with PYTHIA, cross section normalization to 850 pb

W+3jets,Wlgenerated with MadGraph, ET > 20 GeV, || < 2.5, Rjj>0.5Wt,W1lW2or qq, generated with TopRex, normalization of xBR to 1.8 pb

tq+tb,t->Wblb, generated with TopRex, normalization of xBR to 78.1 pbWbb, Wlgenerated with TopRexZbb, Zllgenerated with MadGraph



Search strategy, selection chain

Event selectionone lepton passing the Level-1 and HLT triggersat least 3 jets with ET > 40 GeVexactly one b jet tagging with track counting method and impact parameter measurement Efficiency for mH+ = 140 GeV : signal 47%, tt background 45%, W+3jets 16%

one identified jet, ET > 40 GeVQl x Q = -1Missing ET > 70 GeV



Offline identification

Definition of identification variables:- Matching cone Rm around the jet direction for searching the leading track- Signal cone Rs around the leading track- Isolation cone Ri around the signal cone

For this channel: Rm = 0.1, Rs = 0.07, Ri = 0.4 with veto on tracks with pT > 1 GeV in the isolation coneECAL isolation for jet: ET

cell (0.13<R<0.4) < 5.6 GeV, R defined around the jet direction Electron contamination suppressed with a cut on maximal HCAL cell (ET > 2 GeV) inside the jet cone pleading track / E > 0.8, to exploit the opposite helicity correlations in in the H± -> and W± -> decays, leading to harder pions from H± ->

Identification starts from canditates provited by the L1+HLT trigger

Efficiency: signal 11-15%, tt->WWbb -> bbl 5%, W+3jets 1%, tt->WWbb -> bbl’’l 2%



Examples of event selection variablesExamples of event selection variables

Signal/background difference in the hadronic channels due to helicitycorrelations

Missing ET > 70 GeV cut can suppress only the W+3jet backgroundtt events 50-60%W+3 jets ~40%

A r b i t r a r y n o r m a l i z a t i o nA

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xBR(fb) selection efficiency events for 10fb-1

tt, t ->bH±, mH+= 140 GeV

10700 0.48% 510


5060 0.50% 254


1830 0.50% 92


157 0.51% 8

gb->tH±, mH+= 170 GeV

140 0.71% 10

gg ->tbH±, mH+=170 GeV

297 0.54% 16

tt->WWbb->lbb 25.8x103 0.20% 516

tt->WWbb->ll’’’bb 39.8x103 7.4x10-4 293

tt->WWbb->ljjbb 2.5x105 1.5x10-4 366

W+3 jets,W->l 8.4x105 1.3x10-5 107

Wt->lb 1800 3.7x10-4 20

Selection efficiencies for signal and backgrounds

Other signal sources in tt events, like H± ->tb,cs,su,cb and H±->,->l,W->jj, also studied and the contribution is found to be smallBackgrounds from ofher sources (Zbb, Wbb) negligible Good agreement for the events from tt + gb->tH± and gg->tbH± at mH+= 170 GeV



Estimation of systematic uncertainties

jet energy scale 3% +jet events and hadronic W mass in tt events, 10% for pT < 20 GeV

Missing ET scale 10% derives mainly from the low pT part of the jet energy scale

b tagging 5% study with the tt events

tagging 4% Z-> jet+X / Z-> ratio

lepton identification 2% estimation

b mis-tagging 5% estimation

mis-tagging 2% estimation

luminosity 3% W and Z based measurements, 5% for 1fb-1

Measurement uncertainties affecting the event selection efficiencyand methods for their measurement

Expectations for 30 fb-1



For the estimate of the tt uncertainty the theoretical cross section is usedwith a total theoretical uncertainty of 5.6% from PDF uncertainty 2.5%and scale uncertainty 5% (luminosity uncertainty 5%):

W+3 jet background uncertainty is assumed to be measured from data.For an estimate a signal-free ”area” is defined with selection cuts similar to the signal selection with:- one lepton (Level-1 and HLT)- 3 non-b jets- no jets- including pixel isolation for an electron to avoid QCD background- substraction of the tt contribution



Expected H± discovery reach from gg -> tt -> W±H±bb->lbb

in mhmax scenario with = 200 GeV



Searches of heavy Charged Higgs bosons with H± -> in the associated production

Fully hadronic events selected with the -> hadrons + and t -> qqb decays to exploit helicity correlations and to reconstruct the H± transverse mass with missing ET from H± ->

Event genaration with the gg -> tbH± process - allows predictions close to the tt threshold

Signal generation with PYTHIA decays with TAUOLA Normalization to the NLO cross section by T. Plehn et al. normalization of BR and MSSM mass relations with FeynHiggs



Backgrounds, generator and normalization

tt, t1 -> , t2->qqb PYTHIA 840 pb

Wt, W1 -> , W2->qq TOPREX 63 pb

W± +3jets, W± -> MadGraph

ET > 20 GeV, || < 2.5, Rjj>0.5 for jets

3.55 nb

QCD multi-jet, 120 < pT < 380 GeV PYTHIA 640 nb

decays with TAUOLA



Event selection

Trigger: Level-1: jet, ET > 93 GeVHLT: Missing ET > 67 GeV, primary vertex reconstruction with pixel lines, regional reconstruction inthe full tracker around the Level-1 jet pT > 25 GeV for the leading track, isolation in a cone around the leading track

Offline analysis: Veto on isolated leptons from W->lto ensure missing ET from H± -> lepton identification with tracker isolation, and with ECAL/track matching, shower shape, ECAL/HCAl ratio for electrons, ”BR(W->)” = 8.9%, ”BR(W->e)” = 7.9% with good purity

Identification of one hadronicjet Missing ET > 100 GeV W and top mass reconstruction tagging of one b jet veto on addional central jets with ET > 25 GeV transverse mass reconstruction from the jet and Missing ET



Off-lineOff-line identification identification

Hadronic decay modes found after trigger:n dominates at this level

-> Calorimeter reconstruction usedEnergy flow algorithms under study in CMS forthe possibility for a more precise tracker reconstruction of the hadronic decay

Offline Offline identification:- jet reconstruction in the direction of the triggeredjet, ET > 100 GeV- leading track within R < 0.1 around the jet direction- small signal cone around the leading track, r=0.04- one or three tracks in the signal cone- isolation of the signal cone in 0.04<R<0.4- addional quality cuts for the leading track: transverse impact parameter < 0.3 mm and at least 10 hits in the tracker (signal efficiencies ~95%)- ET of maximal HCAL cell in the jet > 2 GeV to remove electron contamination- pleading track/E jet > 0.8, exploits the helicity correlations

-> 26.3%

n

52.1%

+ X 27.5%



Helicity correlations in Helicity correlations in H± -> and W± -> harder pions from H± -> than from W± -> in the decay and in the decays through longitudinalcompoments of and a1 mesons

Distributions affected by the trigger selection! Distributions affected by the trigger selection!

-selection efficiencies including pre-selection, trigger and off-line

mmH± (GeV) (GeV) 200 400 tt Wt W+3j QCD

Total efficiency 3.8% 9.0% 5.0x10-4 6.7x10-4 1.9x10-3 9.2x109.2x10-5-5

QCD multi-jet event: generation with 170<pt<380 GeV, no trigger simulation

selection efficienciesselection efficiencies



Minimization of = ((mjj –mW)/W)2 + ((mjjj –mtop)/top)2

with W = 10 GeV, top = 17 GeV, from all hadronic jets with ET>20 GeV,no mass window used for the reconstructed W mass

Due to the jet assignment problemany of the 3 jets tagged with aprobabilistic secondary vertex methoddiscriminator > 1.5 and Et

jet > 30 GeV

Top mass reconstruction and b taggingTop mass reconstruction and b tagging

~20% probability for p~20% probability for pTTbb(ass) > p(ass) > pTT

bb(t-(t->bqq)>bqq)

Efficiency for 140 < mtop < 210 GeV+one b jet: 25% signal (mH+=200 GeV), 1.2% W+3 jets



Transverse mass reconstructionTransverse mass reconstruction

mmT T = (2 E= (2 ETT jet jet E ETT

missmiss (1 - (1 - jet, E jet, ETTmissmiss))))1/21/2

Transverse mass distributions for the signal and background with all selection cuts

1.4 tt events at large m1.4 tt events at large mTT, with , with good missing Egood missing ETT measurement and passing track quality measurement and passing track qualitycuts,cuts, are events triggered with a hadronic jet (are events triggered with a hadronic jet (fake fake signal signal))- can be suppressed requiring strong correlation for the can be suppressed requiring strong correlation for the jet and missing Ejet and missing ETT with pT

Higgs > 50 GeV (signal efficiencies > 84% )

with pTHiggs > 50 GeV



Signal area may be defined with a cut in jet, ET

missbutmT jet, ET

miss> 100 GeV used in this study

Transverse mass reconstructionTransverse mass reconstruction



xBR (fb)

Selection efficiency

Events mT > 100 GeV

signal, mH+=170 GeV 1359 4.5x10-4 18.3 14.2

signal, mH+=180 GeV 1238 5.1x10-4 18.9 14.8

signal, mH+=200 GeV 776.0 6.7x10-4 15.5 11.6

signal, mH+=300 GeV 118.3 2.4x10-3 8.7 8.3

signal, mH+=400 GeV 37.7 3.4x10-3 3.8 3.6

signal, mH+=600 GeV 5.6 4.3x10-3 0.72 0.72

tt 1.24x105 1.2x10-5 43.0 0.86 ± 0.33

Wt 9.1x103 2.6x10-5 7.0 0.09 ± 0.04

W+3 jets 4.2x105 4.6x10-7 5.8 0.6 ± 0.6

QCD, 170 < pT < 380 GeV

1.3x108 1.2x10-7 0.14 0.14 ± 0.14

Selection efficiencies and number of events for 30 fb-1

tan = 30

Uncertainty due to MC statistics and factorization procedure

QCD background estimation with the full selection chain- estimate neglecting correlations between Missing ET and selection cuts- no trigger simulation- selection applied on the leading jet- Negligible contribution from the pT bins below pT < 170 GeV



Systematic and MC uncertainties

Including systematic and MC uncertainties total background in the signal area mT> 100 GeV: 1.7 ± 1.0 events

These measurements not yet done, the uncertainty of the dominant tt background estimated on basis of event selection efficiency and the cross section: Uncertainty in the event selection efficiency 3% obtained from the tt events with variation of the jet and missing ET scales within the expected uncertainties

Including the experimental uncertainties ( identification 8%, b tagging 5%, luminosity 5%)and the tt cross section uncertainty of 5.6%: Systematic uncertainty on the tt (and Wt) backgrounds 11% For W+3jet the present MC uncertainty (~100%) strongly dominates

Two main sources of background in the signal area mT jet, ETmiss)>100 GeV:

- tail of the tt and W+3jet backgrounds due to measurement uncertainties- fake jets, possible in all considered backgrounds

The tail of the tt and W+3jet backgrounds can be measured from data exploiting theW+3jet, W-> events with large rate and precise muon momentum measurement Fake rate may be determined with the help of the +jet events



Discovery potentialDiscovery potential



Signal and Background Simulation

Signal simulation with Signal simulation with PYTHIAPYTHIA for both processes for both processes gb -> tH± 3b selection gg -> tbH± 4b selectionNormalization to NLO gb -> tH± cross section

Background generation:For 3b selection ttjj with MadGraph/MadEvent

For 4b selection ttbb with CompHEP ttjj with CompHEPproblem of double counting of b’s b’s from gluon splitting vetoed in the ttjj background

Detector simulation for the 3b selection with parametrized fast simulation FAMOS



Event reconstruction and selection

L1 + HLT single muon trigger muon reconstruction and isolation with dicriminator method for muons from t -> W->, pT > 20 GeV/c b -jet identification with likelihood-based secondary vertex algorithm 3 jets with discriminant > 1

Event selection: at least one muon with at least 5 (6) jets for the 3(4)b selection with ET > 25 GeV at least 3 (4) b-tagged jets for the 3(4)b selection with ET > 25 GeV Kinematic fit in the top system with - both W mass constraints - both top mass constraints - jet and muon resolutions as function of pT

- transverse and longitudinal momentum of neutrino taken from fitS/B ratio after selection ~1% for mH+ = 300 GeV



Jet association

Likelihood ratio S/(S+B) for each variable, S=correct associations, B= wrong associationsLikelihood ratio S/(S+B) for each variable, S=correct associations, B= wrong associationsBest possible jet association chosen with the highest value of a combined LikelihoodBest possible jet association chosen with the highest value of a combined Likelihoodratioratio



Mass reconstruction



Observables for background separation:- PT of the softest q jet from the W decay 2 probability of the kinematic fit,- b-jet discriminator for the b originating directly from the H±

- the ratio of the ET of the sixth over the fifth jet

Statistical significance as a function of combined Likelihood ratiofor signal-background separation, optimized for each mass point

Background suppression



H± Observability in the H± ->tb decay

Mistag uncertainty for b not estimated yet, assume 0%, 1% and 3%

Similar analysis performed for the 4 b-tag channel

3 b-tag channel 4 b-tag channel



Fast simulation study at mH+ = 180 GeV, tan = 2.5 with full reconstruction of the event (leptonic and hadronic W, associated top and H±)

Main event reconstruction problem: correct jet association difficult

No discovery even with high luminosity and assuming known mh

Other possibilities for searchessearches

H± -> Wh, h -> bb decay channelin gb -> tH± production, with the final state of one isolated lepton, 3 b jets and 2 non-b jets



gg -> tH±,HH±± -> -> iijj

-> 3 leptons + X -> 3 leptons + X

Fast simulation study with 3 sets of parameter values in MSSM:Fast simulation study with 3 sets of parameter values in MSSM:Set A: MSet A: M22 =210 GeV, =210 GeV, = 135 GeV, m= 135 GeV, mllRR = 110 GeV, m = 110 GeV, mgg = 800 GeV, m = 800 GeV, mqq = 1 TeV = 1 TeVSet A: MSet A: M22 =280 GeV, =280 GeV, = 150 GeV, m= 150 GeV, mllRR = 130 GeV, m = 130 GeV, mgg = 900 GeV, m = 900 GeV, mqq = 1 TeV = 1 TeVSet A: MSet A: M22 =300 GeV, =300 GeV, = -150 GeV, m= -150 GeV, mllRR = 150 GeV, m = 150 GeV, mgg = 1 TeV, m = 1 TeV, mqq = 1 TeV = 1 TeV

Event selection mainly by:- 3 isolated leptons, pT>20,7,7 GeV- Reconstruction of the associated hadronic top- Missing ET > 40 GeV

Small , light sleptons favoured,dominant decay modes in the 5region of Set A: H± -> 1

2, 2

2, 1

4

2-> -> slepton+lepton->ll1

1

-> -> sneutralino+lepton -> l1

Discovery in an interesting region of medium tanbut for a limited area of parameter space

high luminosityexpectations

Backgrounds: tt, ttZ,ttBackgrounds: tt, ttZ,tt*,tth, *,tth, neutralino and chargino pair production, neutralino and chargino pair production, squark and gluino productionsquark and gluino production



Discovery Potential for charged Higgs Bosons

with full simulation, including systematic uncertainties



Conclusions

The H± -> decay channel in the tt production and in the associated gg -> tbH± production remain discovery channels with large parameter space reach for the charged Higgs bosons with full simulation and reconstruction of the CMS detector response

For H± -> in the tt production inclusion of systematic uncertainties resultsin a decrease of the mass reach by 5-10 GeV

For H± ->in in the fully hadronic channel at mH+ > mtop suppression of fake signals in the backgrounds, including the QCD multi-jet production, requires- strong isolation- high quality measurement for the leading track- large Missing ET cut even for the low mass range (due to QCD multi-jet background)Minor reduction of the discovery potential for the gg -> tbH±, H± -> channel as compared to the earlier fast simulation results

No discovery with H± ->tb at low luminosity

Charged Higgs Prospects with CMS

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