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

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SIMDET 4.1 for fast detector simulation. so far: only generic have been considered ... 3. Abs(E_jet(1)-E_jet(2)) 50 GeV. 4. 5. 6. cos (acoplanarity angle) 0 ... – PowerPoint PPT presentation

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


1
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

2
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
3
Motivation
Idea
Choi et al., hep-ph/0108117
But what are the experimental errors doing to
this?
4
Motivation
A guess
a need very accurate measurement of
and
5
Motivation
Complication at large tanb, the tends to be
the NLSP, making the decay
dominant! This is experimentally challenging
SPS1a
6
Motivation
Neutralino masses and branching ratios
7
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

8
Analysis Signal Background
  • Not yet considered
  • Higgs
  • non-tau backgrounds (electrons, muons)

9
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.
10
Analysis Cut selection
11
Analysis Cut selection
12
Analysis Cut selection
13
Analysis Cut selection
14
Analysis Cut Flow
Statisitical precision on cross section (assuming
SUSY backgrounds known)
15
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

16
Mass reconstruction
1 fit falling slope of invariant mass distribtion
17
Mass reconstruction
2. Count events with high masses
N1
N2
18
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
19
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
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