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)

L. Perera LPC physics meeting 11/17/2005 2

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

L. Perera LPC physics meeting 11/17/2005 3

→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

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CDF results on H

•Rutgers CDF group did CDF run II, Hanalysis

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• 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

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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

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• 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:

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But also rejects low mass higgs

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

2 1 2 1

ET ET

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L1 efficiency for H→

1 or 2 tau bit

L1 global efficiency Any L1 tau bit

Any: tau 1, tau 2, tau+gamma

L. Perera LPC physics meeting 11/17/2005 10

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%

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

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

L. Perera LPC physics meeting 11/17/2005 12

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%

L. Perera LPC physics meeting 11/17/2005 13

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

L. Perera LPC physics meeting 11/17/2005 14

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

L. Perera LPC physics meeting 11/17/2005 15

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)

L. Perera LPC physics meeting 11/17/2005 16

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

Can we identify?

Opposite form what is expected ?

CAL

CAL

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

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

L. Perera LPC physics meeting 11/17/2005 18

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:

L. Perera LPC physics meeting 11/17/2005 19

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

L. Perera LPC physics meeting 11/17/2005 20

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

L. Perera LPC physics meeting 11/17/2005 21

Future Plans

• More trigger and background studies (more MC)

• Improvements to tau mass reconstruction

• Looking at other possible parameters, …

L. Perera LPC physics meeting 11/17/2005 22

Back up slides

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L. Perera LPC physics meeting 11/17/2005 24