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Inclusive search for Squark / Gluino production at CDF

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Barcelona

Inclusive search for Squark / Gluino production at CDF

Gianluca De Lorenzo

(on behalf of the CDF collaboration)

Madison, WI

Pheno 2007 Symposium

> 2 fb-1 already on tape!

this analysis based on ~1.1 fb-1

(data collected up to september 2006)

Gianluca De Lorenzo, Pheno 2007

- transforms fermions into bosons and vice versa.
- provides a framework for the unification including gravity.
- explains the gauge hierarchy with the exact cancellation between fermion & boson loops for Higgs.
- if R-parity conservation is assumed SUSY particles must be produced in pairs and the Lightest Supersymmetric Particle (LSP) is stable.
- LSP is a promising candidate for the dark matter.

RP = +1 (particles)

RP = -1 (s-particles)

RP = (-1)3(B-L)+2s

Gianluca De Lorenzo, Pheno 2007

- The SUSY breaking is gravity mediated.
- Only five free parameters: the values of all the other SUSY parameters are derived with RGEs down to TeV scale
- The LSP is the neutralino →

mSUGRA signature: gluinos & squarks decaying in energetic jets + missing ET (LSP)

mSUGRA parameters

Gianluca De Lorenzo, Pheno 2007

A0 = 0 -- tanb = 5 -- m < 0

R parity conservation assumed; four 2→2 sub-processes:

gluino - gluino (and cc)

gluino - squark

squark - squark (and cc)

squark - antisquark

third squark generation removed (no stop, no sbottom).

MC samples generated using ISASUGRA in PYTHIA 6.216

different sub-processes normalized to NLO according to PROSPINO

PDF CTEQ6.1M

renormalization-factorization scale:

s

m → Mg or Mq or ½(Mg+Mq)

mSUGRA generation: grid of MC samples, generated for different values of gluino-squark masses

Gianluca De Lorenzo, Pheno 2007

- QCD processes:
- missing ET due to jet energy mismeasurement
- MC events generated with PYTHIA
- MC samples normalized to data in a low-missing ET region

SM cross sections bigger than SUSY up to a factor of108

- bosons and t-tbar decays:
- missing ET mainly due to undetected neutrinos/muons or to electrons mis-identified as jets

- dibosons:
- MC events generated with PYTHIA
- MC samples normalized to the MCFM NLO cross section

- W→ln+jets, Z→ll+jets and Z→nn+jets:
- exclusive n-parton samples generated with ALPGEN; parton shower from PYTHIA.
- samples matched with MLM method and normalized to the inclusive D/Y cross section

- t-tbar decays:
- MC events generated with PYTHIA
- mt = 172 GeV/c2
- MC samples normalized to the theoretical cross section sttbar= 7.3 pb

Gianluca De Lorenzo, Pheno 2007

TRIGGER

- trigger selection requires missing ET above 35 GeV and at least 2 jets

Cleanup Cuts

- minimum number of 3 jets per event with ET>25GeV and |h|<2
- at least one central jet with |h|<1.1
- minimum missing ET of 70 GeV
- set of basic cuts to avoid beam halo and cosmics contamination

QCD rejection

- |Df (missingET-jets)| > 0.7 to avoid events where the missing ET is due to jet energy mismeasurement.

W/Z+jets and diboson rejection

- EMF of the jets less than 90% to reject electrons mis-identified as jets
- |Df (missingET-isotrack)| > 0.7 to reject events with MET due to undetected muons
- reject events when two isolated tracks have invariant mass close to the Z mass [76GeV,106GeV]

Gianluca De Lorenzo, Pheno 2007

- further background reduction obtained selecting on five different variables:
- ET(jet1), ET(jet2), ET(jet3)
- missing ET
- HT = ET(jet1) + ET(jet2) + ET(jet3)

- The thresholds are optimized in order to maximize the signal over background separation (based on S/√B)
- Three different set of cuts are defined with increasing gluino mass to enhance the sensitivity: the three sets define three different signal regions A, B and C.

signal regions definition

Gianluca De Lorenzo, Pheno 2007

QCD dominated sample:|Df (missingET-jets)|cut is reversedto enhance the QCD contribution.

electrons dominated sample:EMF cut reversed to enhance the electron related contributions (non-QCD bkg).

muons dominated sample: cut on the isolated tracks reversed to enhance muon related contributions (non-QCD bkg).

good agreement between data and SM MonteCarlo

Gianluca De Lorenzo, Pheno 2007

good agreement data-SM prediction

number of selected events

Gianluca De Lorenzo, Pheno 2007

no evidence of SUSY has been found→→→extract EXCLUSION LIMIT

- event details:
- missing ET = 196GeV
- ET(jet1) = 236GeV, ET(jet2) = 150GeV, ET(jet3) = 84GeV
- HT = 470GeV

h-fview of the calorimeter

CDF transverse view

Gianluca De Lorenzo, Pheno 2007

Jet Energy scale: the dominant source of systematics is the ± ~3% uncertainty on the absolute jet energy scale (JES) that translates into a 10% (20%) uncertainty on the signal (background); it represents, on average, the 80% of the total systematics.

Other systematics for SIGNAL...

Renormalization/factorization scale: the nominal m value varied to ½m and 2m in the NLO PROSPINO calculation. (0.5% uncert. on efficiency)

PDF: Hessian method to estimate the uncertainty due to the choice of the PDF in the PROSPINO calculation. (2% uncert. on eff.)

ISR/FSR: ISR and FSR varied in a controlled way. (4% uncert. on eff.)

Other systematics for BACKGROUND...

Top: 10% PDF uncertainty from theory, renormalization uncertainty negligible, ISR/FSR estimated as for the signal.

Z/W+jets: 2% global uncertainty on the inclusive cross section.

diboson: 10% PDF + renormalization uncertainty from theoretical calculation.

Gianluca De Lorenzo, Pheno 2007

- limit curves obtained with a bayesian approach at 95% C.L.
- We include the statistical and all the systematic uncertainties in the limit calculation.
- Correlation between Signal and Background uncertainties are also considered.

- The mass limit is placed at the crossing between the NLO cross section and the observed limit curves.
- For Mg~Mq we exclude up to 380 GeV/c2.
- The yellow band indicates the theoretical systematics on the NLO cross section. (25-35% uncertainty on average)
- the expected limit is also shown (dashed line).

the systematic uncertainties on the NLO signal cross section are included in the limit calculation(limit with theor. uncert. excluded also calculated...)

Gianluca De Lorenzo, Pheno 2007

For nominal cross section: observed limit of ~380 GeV/c2when Mg ~ Mq .

Mg <230 GeV/c2 excluded in any case.

4-jets analysis on going to improve the sensitivity in the region Mq>>Mg.

theoretical uncertainties on the NLO cross section included

Gianluca De Lorenzo, Pheno 2007

theoretical uncertainties on the NLO cross section excluded

- theoretical uncertainties on signal NLO cross section not included in the limit calculation.
- the red region is the 95% C.L. excluded zone
- yellow band represents the effect of the theoretical uncertainties on the excluded zone.

Gianluca De Lorenzo, Pheno 2007

- CDF Run II has found no evidence of Squarks and Gluinos in 1.1 fb-1 of data.
- Mg below 230 GeV/c2 is excluded at 95% C.L. in the mSUGRA scenario (A0 = 0, tanb = 5, m < 0).
- When Mg~Mq, masses below 380 GeV/c2 are excluded at 95% C.L.
- 4-jets analysis ongoing and more than 2 fb-1 ready to be analyzed: stay tuned for further updates!

Gianluca De Lorenzo, Pheno 2007