Search for New Physics in Jets plus Missing Transverse Energy Final

States at CDF Monica D’Onofrio

IFAE-Barcelona

On behalf of the CDF collaborationsXXXIV International Meeting on Fundamental Physics

IMFP06, Madrid 5th April 2006

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Motivations The Standard Model has been a great success but ...

hierarchy problemhow to explain dark matter, etc.

Tevatron is currently only place to search for new high pT physics!

• Monojet + MET configuration:

Possible signature for Large Extra Dimensions (LED)• Multijets + MET configuration:

Golden signature to search for squarks and gluinos in SUSY scenario

Expecting small excesses from SM many studies has to rely on simulation to test standard model prediction

One of our best handles: transverse energy imbalance (Missing ET, or MET)

MET associated with jets is a very good signature to search for New Physics beyond Standard Model

Outline

SupersymmetryExtra Dimensions……

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Large Extra Dimensions (ADD scenario)Proposed as a solution to the hierarchy problem Extra dimensions are compactified or inaccessible to some part of SM Model of Arkani-Hamed, Dimopoulos, and Dvali (ADD)

n extra dimensions (≥ 2) compactified at radius R SM constrained to a 4-d brane in higher dimensional space Gravity exists in (4+n)-d “bulk” Effective Planck scale:

M2Planck ~ Rn(MD)n+2 , MD ~ 1 TeV

Gravitons appear to have mass, m2=m0

2+p2

Tower of KK modes with splittings m ~ 1/R

Each mode couples with strength, MPl

-1 , but there are many: cross section summed over all modes

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Hadron Collider Signatures of LEDReal Graviton undetected lead to Missing Transverse energy + one recoiling jet Monojet

CDF event:- ET (jet) = 361 GeV- Missing ET = 350 GeV

Graviton production mechanism

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Current results on monojet search at CDFCurrent limit based on ~ 370 pb-1

ET (leading jet) > 150 GeVMissing ET > 120 GeV

Results:

• 265 ±30 events predicted • 263 events observed

No excess observed

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Analysis strategy

SM Backgrounds that also produce Jet(s)+MET Z + jets with Z (looks just like the signal) W + jets with Wl and the lepton undetected

W is the most significant, followed by W QCD dijets, where one jet is lost or mismeasured Z

Z is irreducible: Important to have good Monte Carlo simulation Use data to evaluate it, considering Z e+e-

Using the ~1fb-1 now available: LED would give an overall excess

above SM contributions explore lower jet/MET region

make data-driven estimates of the major backgrounds.

Effect due to pT cut in MC generation

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Z + ≥ 1 jets event topology

Z0 =0

transverse plane

tracks

Jet fragmentation + Underlying Event

Pythia is the simulation that better reproduces the jet fragmentation

• Dominated by UE.• Independent of the pT of the jets.

MC samples: Z( e+e-) + 1 parton Pythia

pThat > 5 GeV/c Tune A, LQCD = 0.146

Alpgen+Herwig MadGraph+Pythia

No Tune A

Using tracks with:• pT > 0.5 GeV/c• nHits > 20• |z0| < 1.5 d0 < 2.0

PT profile in in Z+≥1 jets events

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Jet Shapes in Z+≥1 jets events

jets T

T

jets Rprrp

rNr

,011

jets T

T

jets Rprp

Nr

,0,01

Energy distribution within jets

Using the ET of the calorimeter towers in jets with pT > 25 GeV/c and |Y|< 2.1

Differential shape in steps of R = 0.1

Integral shape

Pythia more accurate than Herwig in reproducing jet fragmentation + effects due to UE

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Inclusive pjetT distributions

Pythia pT of the jets for Z + ≥ n jetsEvery MC distribution is normalized to the data shape comparison only Alpgen+Herwig

Good agreementwith Pythia MC

Alpgen+HerwigLess jets at low pT due to lack of UE in Herwig MC

Further investigation on going using Alpgen+Pythia MC First results expected for Summer 2006

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Strong interaction large production cross section

for M(g) ≈ 300 GeV/c2: 1000 event produced

for M(g) ≈ 500 GeV/c2: 1 event produced

Consider mSUGRA scenario: A0 =0, m < 0, tan = 3 or 5 5 flavors degenerate

Squarks and Gluinos At the Tevatron: mainly Squarks

and Gluinos pair production Golden signature at LHC

~

~

Missing ET

Missing ET

Multiple jets

Investigated decays: energetic jets + MET (from LSP)

Phys.Rev.D59:074024,1999

)0.2(~~ TeVsgqpp

)(2/)( ~~ GeVMM gq

103

1 (p

b)

10-3

10-6

10-9

300 500 700

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Analysis strategy

“Blind Analysis”1) Define a signal region (Blind Box)2) Make sure MC is in agreement

with data outside this region (Control Region)

3) “Open” the Blind Box

Chosen region not excluded by other experiments

Use Isajet but moving on for PYTHIA

third generation removed from 2 2 process

Chosen 3 bench-mark points to optimize analysis selection criteria

s35s41

s46

Signal region (blind box) determined by optimizing S/√B

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Backgrounds fb

Backgrounds dominate Need to be specifically rejected:

QCD multijets: reject jet close to MET direction

Z+jets with Z->e+e-(+-)

W/Z+jets with Wl or Z, DiBoson:

reject isolated electrons and muons

Top: Signatures similar to W+jets (rejection more challenging)

MET due to jet energy mismeasurements

MET physics backgrounds

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Backgrounds (2)

Generated with PYTHIA in different pT bins

Selected region dominated by Jet events in the data with low MET

Compared distributions MC events to data to find NLO factor and obtained scale factor to the MC ~1.0 CDF Run II preliminary

MULTIJET BACKGROUND ESTIMATIONS

PROCESS MC generator K-factor methodZ+jets ALPGEN+Herwig 1.18 NLO MCFMW+jets ALPGEN+Herwig 1.09 NLO MCFM

WW ALPGEN+Herwig 1.4 NLO MCFMttbar Herwig - NLO cross section

Hadron Jets(QCD) Pythia ~1.0 DATA

Dedicated study to verify the LO to NLO scale factors for the normalisation of the samples “k-factors”

OTHER BACKGROUNDS:estimations from Monte Carlo

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Selection: 3 jets with ET>125 GeV, 75 GeV and 25 GeV Missing ET>165 GeV HT=∑ jet ET > 350 GeV Missing ET not along a jet direction Avoid jet

mismeasurements

Event selection

Signal region

MET distribution after applying all the cuts except MET >165 GeV

HT distribution after applying all the cuts except HT >350 GeV

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Missing ET = 223 GeV

ET(1st) = 172 GeV

ET(2nd) = 153 GeV

ET (3rd) = 80 GeV

ET(4th) = 65 GeV

HT = ET(1st) + ET(2nd) + ET(3rd) = 404 GeV

XY view of event with large MET

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No evidence for excess of events: Exclude squarks and gluinos for bench-mark masses values D0 excluded gluinos up to 230 GeV (VERY PRELIMINARY, no PDF unc. included) CDF:

Limit expected in one week Expected similar to D0

In L = 245 pb-1 of data Background expectations inside the Blind Box: 4.1 0.6 1.4 events. Opening the blind box 3 events have been found

Inside BB MET (GeV) HT (GeV)

Event 1 223.3 404.2Event 2 195.6 470.1Event 3 166.6 362.3

Results

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Conclusions In 2005, Tevatron achieved the 1 fb-1 goal Delivered total luminosity 1.6 fb-1

1.2 fb-1 on tape ready for data analyses! Very rich searches physics program ongoing at CDF

Tevatron is currently the only place to search for new physics

Missing transverse energy is one of our best handles: in association with jet(s) constitute i.e. good signature for

Large Extra Dimension (monojet) Supersymmetry (multijets)

Final results foreseen for Summer Conferences Very important for the LHC

Back up

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The Tevatron

Peak luminosity 1.8 *1032 cm-2

s-1

Integrated luminosity/week

about 25 pb-1

Analyses shown here use 0.3 – 1.0 fb -1

Highest-energy accelerator currently operational

CDF and D0: ~1.2 fb-1 on tape

date

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Randall-Sundrum Scenario Only one extra dimensions limited by two 4-

dimensional brains. SM particles live in one of the brains. Graviton can travel in all 5 dimensions. mG = xn k exp(-πkrc)

The only scenario with extra dimensions implemented in Pythia.

Free parameters: Graviton mass (mG) Dimensionless coupling (k/MPl)

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Reference SUSY points for squark/gluino

Sample NLO Sigma (pb) M0 M1/2 M(q) M(g) M(1) M(LSP)

s35 0.26 144 148 340 357 110 59

s41 0.17 149 156 375 394 116 62

s46 0.03 153 164 390 414 122 65