How to Exploit t Polarization in Charged Higgs Boson Searches

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

R. KinnunenHelsinki Institute of Physics

How to Exploit Polarization in Charged Higgs Boson Searches


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



A method to use polarization to enhance the signal for thecharged Higgs bosons in the H± -> decay channel (in tt and gb->tH± production) was first proposed by DP. Roy, Phys. Lett. B459 (1999) 607.

- The method was applied by the CMS and ATLAS collaborationsin several studies on charged Higgs bosons:R. Kinnunen, CMS Note 2000/045; K.A. Assamagan and Y. Coadou, Acta Phys. Polon. B33 (2002)707; M. Baarmand, M. Hashemi and A. Nikitenko, CMS Note 2006/056; R. Kinnunen, CMS Note 2006/100 (only some examples mentioned)

Background for polarization studies



H± -> decay dominates for mH+ < mtop and is large also for mH+ > mtop at large tan

H± and decay modes

Hadronic decay modesBR±±12.5%BR± ±± 026%

BR± a1±± 007.5%

1-prong decay modes ~ 50%3-prong decay modes ~15%



Background suppression in the charged Higgs bosons searches with the H± -> decays channel

The search channels with H± -> are a subject of background fromgenuine ’s and from hadronic jets faking ’s

Hadronic jets faking jets from QCD multi-jet events, from W/Z+jet and tt events can be suppressed with the hadronic decay properties;narrow jet in calorimeters and 1 or 3 charged particles in the tracker

Mass reconstruction of , track impact parameter measurements andsecondary vertex reconstruction can be used to improve this selection

The backgrounds with genuine ’s from tt and W+3jet backgrounds with W->can be also efficiently suppressed due to the opposite helicity correlations in the H± -> and W± -> decays

The basic event selection requirements, like large ET for the liketrigger jet, already exploit the polarizationSelection can be enhanced with special selection cuts



Helicity correlations

Center of mass angular distributions of into a meson or a vector meson (,a1) in terms of polarization

L and T are the longitudinal and transverse polarization states of the vector meson. In the laboratory frame

p,V / p =

Harder jet for signal with P = +1 than for the background with P = -1 from the L and a1L contributions, and the opposite from the T and a1T



Illustration with simple spin arguments for formH+ -> and W+ -> :

HH++

WW++

Helicity correlations



Energy charing in the vector meson decays

Energy fraction carried by the charged pion in the vector meson decays: ±

L,T -> ±0 and a±1L,T -> ±0 0

from D.P. Roy, Phys. Lett. B459 (1999) 607

For ±L and a±

1L: E± ~ 0 or E± ~ Ea1

for ±T and a±

1T: E± ~ E0



Exploiting helicity correlations in 1-prong decays

Example of helicity correlations in 1-prong decays in the gb->tH±, H± -> signal and in the tt background with fast simulation and calorimeter smearing

A hard cut, R1 = p / p > 0.8 suppresses efficietly the background from tt, W->

ET jet > 100 GeV

ET jet > 100 GeV



Helicity correlations in full simulationHelicity correlations in full simulation

Full selection efficiency: signal 11-15%, tt->bbl 5%, W+3jets 1%

Search for light charged Higgs bosons with mH+ < mtop

in gg -> tt -> W±H±bb->lbb, l = e or

one jet with off-line identification: - ET > 40 GeV- tracker and ECAL isolation- 1 or 3 prongs in the signal cone- pleading track/E jet > 0.8

pleading track/E jet forETjet

> 40 GeVandpleading track > 20 GeV

All hadronic decays channels included



identification:

Trigger cuts: ETjet

> 93 GeV (Level-1), pTleading track > 25 GeV(HLT)

Main cuts for the off-line selection:- ET

jet > 100 GeV

- 1 or 3 tracks in a small signal cone of R = 0.04- isolation of the signal cone in 0.04<R<0.4- pleading track/Et jet > 0.8

Search for heavy charged Higgs bosons with mH+ > mtop

in gg -> tbH±, H± ->

Helicity correlations in full simulationHelicity correlations in full simulation

All hadronic decays channels included



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

Signal and background distributions for pleading track/E jet

Large suppression of backgrounds with genuine ’s

±




1) M. Guchait, R. Kinnunen, D.P. Roy, hep-ph/0608324.

The 1-prong selection with pleading track/Et jet > 0.8 suppresses the 3-prong decays from 15% to 3% in the full simulation of thegg -> tbH±, H± -> channel

New idea1) of exploiting more efficiently the 3-prong decaysbased on the decay mode without any accompanying 0’s:

-> ±±±2/3rd the 3-prong decays (10% of total)

This mode can be selected with matching of tracker momentum andcalorimeter signals or by a veto on accompanying in ECAL

The a1L contribution can be enhanced with a cut in the momentumfraction carried by the like-sign pair R3 < 0.4 or R3 > 0.8, R3 = p±±/p-jet



R3 = p±±/p-jet distributions for -> 3± with ET jet > 100 GeV

Study for the gb -> tH±, H± -> channel Event generation with PYTHIA, decays with TAUOLA Background from tt events Fast simulation of CMS detector, jet and missing ET reconstruction No trigger simulation




”Standard” selection used for 1-prong decays only




New selection for 3-prong decays


Selection of->±±±withE = |Etrktot - Ecal

tot|<10 GeV ~ calorimeter resolution

For R3 < 0.4 the event is triggered at HLT with the 3th opposite sign (hard) pion



30 fb-1

100 fb-1

Discovery potential with 3-prong selection

Effect of trigger simulation estimated to increase the discovery limits in tan with 25%

gb -> tH±, H± ->



Conclusions

Oppositehelicity correlations in the H± -> and W± -> decays allow suppression of the backgrounds with genuine ’s from tt andW+3jet events to a low level with the requirementpleading track/p jet > 0.8 in the 1-prong decays

The discovery reach can be enlarged by ~ 18-12% in tan witha 3-prong selection demanding the like-sign pion pair to carrymore than 80% or less than 40% of the jet momentum

How to Exploit t Polarization in Charged Higgs Boson Searches

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