Aod analysis for dc2 susy sample
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AOD analysis for DC2 SUSY sample. Pavel Zarzhitsky SMU. Introduction. DC2 has a new SUSY point in the coannihilation region. The parameters of the point are: m 0 =70; m 1/2 =350; A 0 =0; tan ß =10.0 ; sgn( μ )=+; m top =175.

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Aod analysis for dc2 susy sample
AOD analysis for DC2 SUSY sample.

Pavel Zarzhitsky

SMU


Introduction
Introduction.

  • DC2 has a new SUSY point in the coannihilation region. The parameters of the point are:

  • m0=70; m1/2=350; A0=0; tanß=10.0 ; sgn(μ)=+; mtop=175.

  • The coannihilation point is in a region that is favored if SUSY is to explain dark matter. LSP is almost degenerate with sleptons. It is close to point 5 in TDR, but there are some mass differences that need to be taken into account.

  • I performed some standard analysis using AOD’s, produced using full simulated data. The data contain no noise.


Data production
Data production.

  • 400,000 events were produced and digitized. The digitized data files located at /usatlas/magdacache001/ common/doyen/A9_digi/

  • All events are made without noise.

  • AOD analysis job takes ~20 min for 100000 events on 1.5 GHz CPU.

  • To analyze AOD use a sample Athena packages PhysicsAnalysis/SUSYPhys/SUSYPhysAlgs, PhysicsAnalysis/SUSYPhys/SUSYPhysUtils, PhysicsAnalysis/SUSYPhys/SUSYPhysUser.


Physics process
Physics process.

The leading processes in coannihilation region give squark that can decay through producing slow leptons:

The similar process for tau’s is given by:

Slow leptons are produced from following sources:


Leptons p t distribution
Leptons pT distribution.

pT distribution for all electrons.

pT distribution for all muons.


Leptons p t distribution1
Leptons pT distribution.

pT for leading and soft electrons

pT for leading and soft muons

leading e

second e

leading muon

second muon

pT distribution for leading and soft electrons that are used to calculate dilepton invariant mass.

pT distribution for leading and soft muons that are used to calculate dilepton invariant mass.


Invariant mass of e e and pairs

opposite sign

same sign

Invariant mass of e-e and μ-μ pairs.

Invariant mass for electron pair.

Invariant mass for muon pair.

opposite sign

same sign

These are invariant mass plots for electrons and muons separately. As you can see there is an excess of electrons with low invariant mass. Almost all of these low mass events have two soft electrons. Used cuts are on the next slide.


Electrons with low inv mass
Electrons with low inv mass.

  • As you could see on the previous slide there is an excess of electrons with low invariant mass. These events have following properties:

  • We have low mass events for the same charge and opposite charge electrons.

  • Almost all of these low mass events have two soft electrons.

  • Both electrons in the pair are very close to each other in space. Plots with eta and phi differences for electron pairs with low invariant mass are on the next slide.

  • We believe that these low mass events are caused by fake electrons from e-gamma conversion and photon emission. Both these processes will produce two adjacent clusters in the calorimeter and one track associated with them. And this is the case.


Electrons with low inv mass1
Electrons with low inv mass.

These 2 plots show difference in eta and phi between electrons in pair with invariant mass < 5GeV. As you see, they are very close to each other.


Electrons distribution
Electrons η distribution.

Invariant mass for electron pair.

eta for all electrons passed ET and jet cuts

eta for all electrons used for inv mass calculation

eta for electrons with inv mass < 5GeV

Electrons have a strange behavior in a transition region. There are two peaks at eta +-1.5, especially for electrons with low invariant mass.


Invariant mass of e e pair

not cleaned sample

cleaned sample

Invariant mass of e-e pair.

Invariant mass for electron pair.

The electron sample was clean by requirement that distance between any two electrons must be >0.2 in eta and >0.2 in phi.

From two adjacent electrons the one with highest pT was left in the sample.

On the plot you can see a comparison of e-e invariant mass with and without cleaning.


Dilepton endpoint

other from

at 100 GeV.

Dilepton endpoint.

Invariant mass for lepton pair.

  • xET>300 GeV

  • 2 SF/OS leptons Pt>10 GeV

  • >=1 jets with Pt>150 GeV

  • Opposite sign/ Opposite flavor subtraction applied

  • events with invariant mass < 5GeV are eliminated to remove electrons with low invariant mass

  • Two endpoints are expected. One from

at 67 GeV. The

Compare with TDR plots 20-9 and 20-10.


Pt for taus
Pt for taus.

pT for leading and soft taus

leading tau

second tau

pT distribution for leading and soft taus that are used to calculate tau-tau invariant mass.

pT distribution for all taus.


Tau inv mass

opposite sign

same sign

Tau inv mass.

Invariant mass for tau pair.

  • This is the same lepton pair invariant mass for two opposite sign taus.

  • xET>300 GeV;

  • 1 tau pT > 40 GeV,

  • 1 tau pT > 25 GeV;

  • >= 1 jet with pT > 100 GeV, >= 1 jets with

  • pT > 40 GeV;


Jet ll inv mass
Jet ll inv mass.

  • Using two leptons and a jet we can form invariant mass of a squark. This is for:

  • at least four jets with pT1>100 GeV, pT2,3,4 > 50 GeV;

  • Meff > 400 GeV;

  • Etmiss > max(100 GeV, 0.2 Meff );

  • Two opposite sign leptons with pT > 10 GeV.

  • The lepton pair was combined with two hardest jets. The smaller invariant mass is on the plot. It must be smaller then the four body endpoint for squark. Mllqmax = 609 GeV. Compare to TDR Fig. 20-20. The larger invariant mass should give the same endpoint on the left edge.


Jet ll inv mass1

no cut

cut 1

cut 2

no cut

cut 1

cut 2

Jet ll inv mass.

Smaller of the two e+ e- q masses.

Only electrons are included.

Smaller of the two μ μ q masses.

Only muons are included.

cut1 means Mll < 67 GeV; cut2 means Mll < 100 GeV.


Jet ll inv mass2

no cut

cut 1

cut 2

Jet ll inv mass.

OF/OS leptons subtracted.

It is not clear that the endpoint is at 609 GeV.

Smaller of the two l+ l- q masses.


Summary
Summary.

  • AOD production for DC2 is working.

  • For coannihilation point two endpoints in l-l invariant mass can be clearly seen.

  • There is a problem with excess of soft electrons with low invariant mass that is correlated with two peaks in eta.

  • More work is needed to understand endpoints in jet-l-l invariant mass.


Effective mass
Effective mass.

  • This is so called effective mass plot.

  • Meff=pT1+pT2+pT3+pT4+Etmiss

  • where pTi are for 4 hardest jets in the event.

  • xET>100 GeV

  • 4 hard jets (pT1,2>100 GeV; pT3,4>50 GeV)

  • No isolated electrons or muons (pT>20 GeV)


Missing energy
Missing energy

Missing energy plot.


Tau likelihood
Tau likelihood.

This is a plot of a tau selection likelihood. It should be more then 0 for the candidate to be a tau jet. Shape must be much more smooth, no peaks. Compare to DC1 results.


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