mssm h 0 3 prong using vertexing at cms

MSSM H03 prongusing vertexing at CMS

Helsinki b/tau workshop30.05.-01.06.2002

Lauri A. Wendland / HIP

Helsinki b/tau workshop 30.05.-01.06.2002: MSSM H03 prong using vertexing at CMS - Lauri A. Wendland 2

Outline

• Motivation• Tools & methods• Secondary vertex (SV) reconstruction• Charge reconstruction• Effective mass reconstruction• Conclusions• Future plans


Motivation

• If 3-prong events can be used in addition to 1-prong decays, a factor of 1.7 of signal events are gained


Tools & methods

• Software– ORCA_5_4_1– CMSIM 123

• Reconstruction– Lvl1,2 calo selections (L2cut = 3.4 GeV

(lowlumi))

– Lvl3 pixel selection (RS = 0.07, RM = 0.1, RI = 0.4)

– full tracker reconstruction (Reco)• pixel lines from Lvl3 used as seeds• at least 8 hits per track demanded


H200 events

3-prong ratio %

H500 events

3-prong ratio %

QCD 80-120

L1 4464 26.3 ± 0.5 4724 24.2 ± 0.5 13492

L2 3661 25.5 ± 0.6 3836 23.4 ± 0.6 2194

L3 1st jet

2662 2777 255

L3 both jets

1827 24.8 ± 0.7 1841 23.8 ± 0.7 10

Reco both jets

1607 26.1 ± 0.8 1644 24.1 ± 0.7 8

Events produced with ORCA_4_5_0, L=2·1033 cm-2s-1

Used event samples


SV reconstruction

SVRECO

PVMC

SVMC

-jet axis

axis

a

xis

• The residual of the SV is divided into components along and transverse to the jet axis

• A double gaussian fit is used to estimate the tails of the residuals


SV residual along -jet axis

= 5.4 ± 0.5 mms = 1.3 ± 0.1 mm±2 = 62 %

H5002, 3 tracks

H2002, 3 tracks = 1.6 ± 0.2 mm

s = 0.65 ± 0.03 mm±2 = 69 %

= 5.9 ± 2.4 mms = 1.0 ± 0.1 mm±2 = 73 %

H5003 tracks

H2003 tracks = 1.4 ± 0.4 mm

s = 0.60 ± 0.04 mm±2 = 80 %

cm cm

cm cm


Why are there tails?

cm cm

R = sqrt(2 + 2)

Tails come predominantly from jets with low R Hit mismatching because of narrowness of jet?

H5002, 3 tracks

H5002, 3 tracks


Track reconstruction efficiency

number of tracks

H500 H200

number of tracks

Initial number of prongsNumber of pixel linesNumber of reconstructed tracks (at least 8 hits)

0.50.5


SV residual transverse to -jet axis

= 50 ± 11 µms = 25 ± 3 µm±2 = 78 %

H5002, 3 tracks

H2002, 3 tracks = 43 ± 66 µm

s = 22 ± 2 µm±2 = 87 %

s = 21 ± 1 µm±2 = 93 %

H5003 tracks

H2003 tracks s = 20 ± 1 µm

±2 = 93 %

cm cm

cm cm


Flightpath reconstruction

3D reconstructed flightpath in cm Background efficiency

Signal efficiency

• Signed flightpath is fine for making cuts• D-mesons could be a concern


Charge reconstruction

q q

• Low reliability, because currently tracks are lost

H500,3-prong

H500

Reconstructed charge - MC charge Total charge of two -jets

bin 0: 55 %others: 45 %


Effective mass reconstruction

• meff = sqrt(( sqrt(pi2 + m

2))2 - pi2)

• QCD background should contain heavier particles

m cut-off

GeV GeV

m m

H500,3-prong

QCD,80-120 GeV


Conclusions

• SV resolution (without tails) of– 600-1000 µm can be reached in jet axis

direction for 200 and 500 GeV Higgs events respectively

– 20-21 µm can be reached transverse to jet axis– resolution dominated by high boost of the -jets

• More efficient track reconstruction method has to be used– The signal resolution as well as background

rejection will improve if efficiency of reconstructing all 3 prongs is high


Future plans

• Move to ORCA_6_x_x• To use regional track finding instead of

pixel seeds• To use deterministic annealing filter

(DAF)

mssm h 0 3 prong using vertexing at cms

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