Experimental Study of Neutralino Production in SPS 1a: a First Look

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Experimental Study of Neutralino Productionin
SPS 1a a First Look
Markus Ball Klaus Desch ECFA/DESY Workshop SUSY
Session Praha, 15/11/02

• Motivation
• Analysis
• Mass Cross section estimation
• SummaryOutlook

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Motivation

• Chargino-Neutralino sector of MSSM depends at
  tree level
• only on 4 parameters
• can be determined in
  Chargino-Sector
• accessible in Neutralino-Sector (cross
  sections, masses)
• particular interest CP-violation a Phases

Choi et al., hep-ph/0002033
Choi et al., hep-ph/0108117
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Motivation
Idea
Choi et al., hep-ph/0108117
But what are the experimental errors doing to
this?
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Motivation
A guess
a need very accurate measurement of
and
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Motivation
Complication at large tanb, the tends to be
the NLSP, making the decay
dominant! This is experimentally challenging
SPS1a
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Motivation
Neutralino masses and branching ratios
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Analysis

• in SPS 1a
• (far above threshold, WW
  very forward)
• 500 , no polarisation (yet)
• SUSYGEN for signal SUSY background
• PYTHIA for SM background
• SIMDET 4.1 for fast detector simulation
• so far only generic
  have been considered

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Analysis Signal Background

• Not yet considered
• Higgs
• non-tau backgrounds (electrons, muons)

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Analysis Cut selection

• signal topology
• two acoplanar low-multiplicity jets
• missing total transverse energy
• jet-jet angle smaller than for WW and
  charginos/staus
• (both taus come from one decay)
• Cuts

1. force event into 2 jets (low mult.) 2 E_jet(1)
lt 100 GeV 3. Abs(E_jet(1)-E_jet(2)) lt 50 GeV 4.
5. 6. cos (acoplanarity angle) gt 0 7. Visible
Energy gt 15 GeV 8.
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Analysis Cut selection
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Analysis Cut selection
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Analysis Cut selection
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Analysis Cut selection
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Analysis Cut Flow
Statisitical precision on cross section (assuming
SUSY backgrounds known)
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Mass reconstruction

• is tough (too much invisible stuff)
• in principle invariant tau-tau-mass has upper
  endpoint at
• this is still true for jet-jet-mass but only few
  events are
• at maximal mass
• tried to use 3-prong taus to reconstruct
  tau-direction and
• correct jet-jet mass for pt of neutrinos died
  statistical death
• try to estimate from
  distributions 3 methods a

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Mass reconstruction
1 fit falling slope of invariant mass distribtion
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Mass reconstruction
2. Count events with high masses
N1
N2
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Mass reconstruction
3. Count events with small opening angles
N1
N2
Method 3 has highest sensitivity error 1.4
GeV But background not yet considered, expect
factor larger error This might be enough to
tell, where to do a threshold scan
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SummaryOutlook

• first look into neutralino production in SPS 1a
• tau final states are not easy
• SM and SUSY backgrounds can be sufficienctly
  reduced to
• perform decent cross section times BR
  measurement
• (2)
• Mass reconstruction only from shape of
  distributions
• o(1-2 GeV) seems possible
• many things to be done
• - Higgs background
• - reducible backgrounds, esp. di-leptons
• - polarisation
• - include errors from other SUSY processes
  (staus,charginos)
• - simulate threshold scan