l. perera lpc physics meeting 11/17/2005 1 search for h/a → lalith perera rutgers university for...

L. Perera LPC physics meeting 11/17/2005 1

Search for H/A →

Lalith PereraRutgers University

for

Rutgers CMS GroupAmit Lath, Keith Rose, Sunil Somalvar, Steve

Schnetzer, Bob Stone, Alik McPerson, Dimity Hits, (Eva Halkiadakis)


Why H→ • At LHC MSSM higgs are expected to produced by

• gg →bbH , gg →H qq→ H• Dominant decay modes of H:

• B(H→ ) ~ 8% , B(H→ bb) ~90%• bb channel is affected by large dijet background

• could tag associative b to lower backgrounds

• Dominant back ground to from Z/*:• can be estimated ( # of Zs from Z→e e, ..)

channel could be equally promising


→e →e 3 High DY → ee BG

→ → 3 High DY → BG

→e → 6 low QCD BG

→e →h 23 promising

→ →h 23 promising

→h →h 41 multi jet BG

mode fraction % comments

H→ Decay Modes


CDF results on H

•Rutgers CDF group did CDF run II, Hanalysis


• B/ group (and others) already working on this channel

• Rutgers group plan to concentrate on low mass higgs

low mass higgs search is challenging due to overlap with Z


CMS hadronic taus• Level 1: narrow hadronic jet with ET cut

• Level2 (HLT): • Localized energy in ECAL – isolation 0.4

• Level 25: • isolation in tracker (Calo+pixel, Si)

• signal cone 0.07, isolation cone, 0.4, ET , PT

• Offline taged tau jets:• Isolation using fully reconstructed tracks


• 1 tau jet ET > 93 GeV (104 high L)

• 2 tau jets ET > 66 GeV (76 high L) ….

• This is good at rejecting Z back ground

2 1

ET of from Z →

GeV

L1 tau trigger:


But also rejects low mass higgs

M(H) = 120GeV M(H)= 140GeV

2 1 2 1

ET ET


L1 efficiency for H→

1 or 2 tau bit

L1 global efficiency Any L1 tau bit

Any: tau 1, tau 2, tau+gamma


L1 Trigger ratesData L1 Accept 1 or 2 Tau “Any” Tau

Z->ee 16.8% 0.2% 8.0%

Z-> 55.8% 0.9% 3.7%

Z-> 65.9% 0.1% 3.0%

H(120)-> 38.1% 0.8% 11%

H(140)-> 44.0% 1.0% 15%

H(180)-> 53.2% 2.8% 25%

H(250)-> 67.7% 15% 41%


Possible ways to improve sensitivity to low mass higgs

• Understanding/estimating back grounds

• Tau reconstruction: to reject jet backgrounds, improve energy resolution

• Use tau Impact parameter

• Any other signatures of →– angular distributions. H scaler, Z-vector


Number of tracks in tagged tau jets . (from H→ m(H) =140)

(fewer 3 prong taus likely a bug in Exroot)

Tau mass reconstruction

→ h 0 25.9%

→h 11.8%

→3h 10%

→h20 9.4%

→h30 4.5%


Tau mass Calculation

Case study with 140GeV →

• Use tau tagged jets with a single track (→ n0)

• Add energy in ECAL and HCAL cells within 0.25 of jet axis

• exclude cells 0.04 (ECAL)/0.15 (HCAL) from track

• Calculate the momentum of photons and take the sum

• Add track momentum and energy

• Calculate invariant mass


Angle between pion and gammas in the tau decay (from MC)


Visible tau mass from generator e/p of tau decay particles except neutrinos.

(what is possible with an ideal detector )

Reconstructed Tagged tau jet Invariant mass

(for single track tau jets)


Improving tau mass reconstruction• Is it track energy In ECAL MIP or more?

Can we identify?

Opposite form what is expected ?

CAL

CAL


fraction of energy in HCAL, f <0.05 f > 0.05

Again, does not look right ?

Investigating!

Reconstructed visible tau mass single track tau jets


Reconstructing higgs mass

Calculate energy, momentum in collinear approx.

add to to the visible e-p to get mass.

Method used by CERN (Higgs PRS) group:


H/A mass generator level

Reconstructed 2 mass from MC parameters of t decay products

Use energies of s to get ET

Use e-p of tau decay particles as jet/track energyA 30% minimum loss for 140 GeV H

Testing Collinear approximation


Alternate method (CDF)

• Use missing ET (Ex, Ey) from calorimeter and

• Take neutrino E =ET Px=Ex; Py=Ey; Pz= 0

GeV

For m(H)=140 GeV

Generater level p-E from tau decays particles

ET from neutrinos

No loss of efficiency, Lower reconstructed mass


Future Plans

• More trigger and background studies (more MC)

• Improvements to tau mass reconstruction

• Looking at other possible parameters, …


Back up slides

l. perera lpc physics meeting 11/17/2005 1 search for h/a → lalith perera rutgers university for...

Documents