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

Experimental Study of Neutralino ProductionExperimental Study of Neutralino Productionin SPS 1a: a First Lookin SPS 1a: a First Look

Markus BallKlaus DeschECFA/DESY WorkshopSUSY SessionPraha, 15/11/02

• Motivation• Analysis• Mass + Cross section estimation• Summary+Outlook

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 2

MotivationMotivation

• 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 Phases

1M

Choi et al., hep-ph/0002033

2tan , ,M

Choi et al., hep-ph/0108117

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 3

MotivationMotivation

Choi et al., hep-ph/0108117 Idea:

But what are the experimental errors doing to this?

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 4

MotivationMotivationA guess:

need very accurate measurement of and

02m( )

0 012 1 2(e e )

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 5

MotivationMotivation

Complication: at large tanthe tends to be the NLSP,making the decay dominant!This is experimentally challenging

10 02 1

SPS1a

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 6

MotivationMotivation

Neutralino masses and branching ratios:

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 7

AnalysisAnalysis

0 0 0 01 2 1 1e e • 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

s 500 GeV

1fb

e e E

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 8

Analysis: Signal + BackgroundAnalysis: Signal + Background

process cross section(fb)

signal 65

12

105

1276

2050000

130

61

ZZ WW

* *Z / ( ) / qq

0 01 1 1 1

0 01 1

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

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 9

Analysis: Cut selectionAnalysis: Cut selection

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.

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 2(| cos | | cos |) / 2 0.8

cos (jet1, jet2) 0

m(jet1, jet2) 15 GeV

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 10

Analysis: Cut selectionAnalysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 11

Analysis: Cut selectionAnalysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 12

Analysis: Cut selectionAnalysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 13

Analysis: Cut selectionAnalysis: Cut selection

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 14

Analysis: Cut FlowAnalysis: Cut Flow

Statisitical precision on cross section(assuming SUSY backgrounds known) : 12 12/ 2.2%

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 15

Mass reconstructionMass 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

0 02 1m( ) m( )

0 02 1m( ) m( )

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 16

Mass reconstructionMass reconstruction

1: fit falling slope of invariant mass distribtion

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 17

Mass reconstructionMass reconstruction

2. Count events with high masses:

N2 N1

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 18

Mass reconstructionMass reconstruction

3. Count events with small opening angles:

Method 3 has highest sensitivity: error ~ 1.4 GeVBut background not yet considered, expect factor larger error This might be enough to tell, where to do a threshold scan…

2

N2 N1

M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 19

Summary+OutlookSummary+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