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

Experimental Study of Neutralino Productionin SPS 1a: a First LookMotivationAnalysisMass + Cross section estimationSummary+OutlookMarkus BallKlaus DeschECFA/DESY WorkshopSUSY SessionPraha, 15/11/02

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

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


MotivationChoi et al., hep-ph/0108117 Idea:But what are the experimental errors doing to this?


MotivationA guess: a need very accurate measurement of and


MotivationComplication: at large tanb, the tends to be the NLSP,making the decay dominant!This is experimentally challengingSPS1a


MotivationNeutralino masses and branching ratios:


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


Analysis: Signal + BackgroundNot yet considered: Higgs non-tau backgrounds (electrons, muons)

processcross section(fb)signal65121051276205000013061


Analysis: Cut selection1. force event into 2 jets (low mult.)2 E_jet(1) < 100 GeV3. Abs(E_jet(1)-E_jet(2)) < 50 GeV4. 5.6. cos (acoplanarity angle) > 0 7. Visible Energy > 15 GeV8.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:


Analysis: Cut selection


Analysis: Cut FlowStatisitical precision on cross section(assuming SUSY backgrounds known) :


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


Mass reconstruction1: fit falling slope of invariant mass distribtion


Mass reconstruction2. Count events with high masses:N2N1


Mass reconstruction3. 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 scanN2N1


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


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