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Experimental Study of Neutralino Production in SPS 1a: a First Look. Markus Ball Klaus Desch ECFA/DESY Workshop SUSY Session Praha, 15/11/02. Motivation Analysis Mass + Cross section estimation Summary+Outlook. Motivation. Chargino-Neutralino sector of MSSM depends at tree level

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experimental study of neutralino production in sps 1a a first look
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
  • Summary+Outlook

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

motivation
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

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

motivation1
Motivation

Idea:

Choi et al., hep-ph/0108117

But what are the experimental errors doing to this?

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

motivation2
Motivation

A guess:

a need very accurate measurement of

and

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

motivation3
Motivation

Complication: at large tanb, the tends to be the NLSP,

making the decay dominant!

This is experimentally challenging

SPS1a

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

motivation4
Motivation

Neutralino masses and branching ratios:

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis
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

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis signal background
Analysis: Signal + Background
  • Not yet considered:
  • Higgs
  • non-tau backgrounds (electrons, muons)

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis cut selection
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 tau’s come from one decay)
  • Cuts:

1. force event into 2 jets (low mult.)

2 E_jet(1) < 100 GeV

3. Abs(E_jet(1)-E_jet(2)) < 50 GeV

4.

5.

6. cos (acoplanarity angle) > 0

7. Visible Energy > 15 GeV

8.

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis cut selection1
Analysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis cut selection2
Analysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis cut selection3
Analysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis cut selection4
Analysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

analysis cut flow
Analysis: Cut Flow

Statisitical precision on cross section

(assuming SUSY backgrounds known) :

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

mass reconstruction
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 tau’s to reconstruct tau-direction and
  • correct jet-jet mass for pt of neutrinos: died statistical death…
  • try to estimate from distributions: 3 methods a

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

mass reconstruction1
Mass reconstruction

1: fit falling slope of invariant mass distribtion

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

mass reconstruction2
Mass reconstruction

2. Count events with high masses:

N1

N2

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

mass reconstruction3
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…

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

summary outlook
Summary+Outlook
  • 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

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a

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