Search for New Physics in Jets plus Missing Transverse Energy Final States at CDF Monica D’Onofrio IFAE-Barcelona On behalf of the CDF collaborations XXXIV International Meeting on Fundamental Physics IMFP06, Madrid 5 th April 2006

Monica D'OnofrioIMPF06, Madrid 5/4/20062 Motivations The Standard Model has been a great success but... hierarchy problem how to explain dark matter, etc. Tevatron is currently only place to search for new high p T 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 E T, or MET)  MET associated with jets is a very good signature to search for New Physics beyond Standard Model Outline Supersymmetry Extra Dimensions ……

Monica D'OnofrioIMPF06, Madrid 5/4/20063 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: M 2 Planck ~ R n (M D ) n+2, M D ~ 1 TeV  Gravitons appear to have mass, m 2 =m 0 2 +p 2  Tower of KK modes with splittings  m ~ 1/R  Each mode couples with strength, M Pl -1, but there are many: cross section summed over all modes

Monica D'OnofrioIMPF06, Madrid 5/4/20064 Hadron Collider Signatures of LED Real Graviton undetected lead to Missing Transverse energy + one recoiling jet  Monojet CDF event: - E T (jet) = 361 GeV - Missing E T = 350 GeV Graviton production mechanism

Monica D'OnofrioIMPF06, Madrid 5/4/20065 Current results on monojet search at CDF Current limit based on ~ 370 pb -1 E T (leading jet) > 150 GeV Missing E T > 120 GeV Results: 265 ±30 events predicted 263 events observed No excess observed

Monica D'OnofrioIMPF06, Madrid 5/4/20066 Analysis strategy  SM Backgrounds that also produce Jet(s)+MET Z + jets with Z  (looks just like the signal) W + jets with W  l 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 p T cut in MC generation

Monica D'OnofrioIMPF06, Madrid 5/4/20067 Z + ≥ 1 jets event topology Z 0  =0 transverse plane tracks Jet fragmentation + Underlying Event Pythia is the simulation that better reproduces the jet fragmentation Dominated by UE. Independent of the p T of the jets.  MC samples: Z(  e+e-) + 1 parton Pythia  p T hat > 5 GeV/c  Tune A, LQCD = Alpgen+Herwig MadGraph+Pythia  No Tune A Using tracks with: p T > 0.5 GeV/c nHits > 20 |z 0 | < 1.5 d 0 < 2.0 P T profile in  in Z+≥1 jets events

Monica D'OnofrioIMPF06, Madrid 5/4/20068 Jet Shapes in Z+≥1 jets events  Energy distribution within jets Using the E T of the calorimeter towers in jets with p T > 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

Monica D'OnofrioIMPF06, Madrid 5/4/20069 Inclusive p jet T distributions Pythia p T of the jets for Z + ≥ n jets Every MC distribution is normalized to the data  shape comparison only Alpgen+Herwig Good agreement with Pythia MC Alpgen+Herwig Less jets at low p T due to lack of UE in Herwig MC  Further investigation on going using Alpgen+Pythia MC  First results expected for Summer 2006

Monica D'OnofrioIMPF06, Madrid 5/4/  Strong interaction  large production cross section for M(g) ≈ 300 GeV/c 2 :  1000 event produced for M(g) ≈ 500 GeV/c 2 :  1 event produced  Consider mSUGRA scenario: A 0 =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 E T Multiple jets  Investigated decays: energetic jets + MET (from LSP) Phys.Rev.D59:074024,  (pb)

Monica D'OnofrioIMPF06, Madrid 5/4/ 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 s35 s41 s46 Signal region (blind box) determined by optimizing S/√B

Monica D'OnofrioIMPF06, Madrid 5/4/ 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 W  l 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

Monica D'OnofrioIMPF06, Madrid 5/4/ Backgrounds (2)  Generated with PYTHIA in different p T 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 PROCESSMC generatorK-factormethod Z+jetsALPGEN+Herwig1.18NLO MCFM W+jetsALPGEN+Herwig1.09NLO MCFM WWALPGEN+Herwig1.4NLO MCFM ttbarHerwig- 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

Monica D'OnofrioIMPF06, Madrid 5/4/  Selection: 3 jets with E T >125 GeV, 75 GeV and 25 GeV Missing E T >165 GeV H T =∑ jet E T > 350 GeV Missing E T not along a jet direction  Avoid jet mismeasurements Event selection Signal region MET distribution after applying all the cuts except MET >165 GeV H T distribution after applying all the cuts except HT >350 GeV

Monica D'OnofrioIMPF06, Madrid 5/4/ Missing E T = 223 GeV E T (1st) = 172 GeV E T (2nd) = 153 GeV E T (3rd) = 80 GeV E T (4th) = 65 GeV H T = E T (1st) + E T (2nd) + E T (3rd) = 404 GeV XY view of event with large MET

Monica D'OnofrioIMPF06, Madrid 5/4/  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 BBMET (GeV)HT (GeV) Event Event Event Results

Monica D'OnofrioIMPF06, Madrid 5/4/ 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

Monica D'OnofrioIMPF06, Madrid 5/4/ The Tevatron Peak luminosity  1.8 *10 32 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

Monica D'OnofrioIMPF06, Madrid 5/4/ 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.  m G = x n k exp(-πkr c )  The only scenario with extra dimensions implemented in Pythia.  Free parameters: Graviton mass (m G ) Dimensionless coupling (k/M Pl )

Monica D'OnofrioIMPF06, Madrid 5/4/ Reference SUSY points for squark/gluino SampleNLO Sigma (pb)M0M0 M 1/2 M(q)M(g) M(  1 ) M(LSP) s s s