Experimental study of neutralino production in sps 1a a first look
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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