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

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 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 Phases Choi et al., hep-ph/0002033 Choi et al., hep-ph/0108117

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 3 Motivation Choi et al., hep-ph/0108117 Idea: But what are the experimental errors doing to this?

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 4 Motivation A guess: need very accurate measurement of and

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 5 Motivation Complication: at large tanthe tends to be the NLSP, making the decay dominant! This is experimentally challenging SPS1a

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 6 Motivation Neutralino masses and branching ratios:

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

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 8 Analysis: Signal + Background processcross section(fb) signal65 12 105 1276 2050000 130 61 Not yet considered: Higgs non-tau backgrounds (electrons, muons)

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

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

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

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

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

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 14 Analysis: Cut Flow Statisitical precision on cross section (assuming SUSY backgrounds known) :

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

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 16 Mass reconstruction 1: fit falling slope of invariant mass distribtion

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 17 Mass reconstruction 2. Count events with high masses: N2 N1

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M.Ball/K.Desch, Experimental Analysis of Neutralino Production in SPS 1a 18 Mass reconstruction 3. Count events with small opening angles: 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… N2 N1

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