Search for New Physics in Jets plus Missing Transverse Energy Final States at CDF

1. 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 5th April 2006

2. 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 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 pT physics! Supersymmetry Extra Dimensions …… Outline • Monojet + MET configuration: •  Possible signature for Large Extra Dimensions (LED) • Multijets + MET configuration: •  Golden signature to search for squarks and gluinos in SUSY scenario IMPF06, Madrid 5/4/2006

3. 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: Large Extra Dimensions (ADD scenario) M2Planck ~ Rn(MD)n+2 ,MD ~ 1 TeV • Gravitons appear to have mass, m2=m02+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 IMPF06, Madrid 5/4/2006

4. CDF event: • ET (jet) = 361 GeV • Missing ET = 350 GeV Hadron Collider Signatures of LED Graviton production mechanism Real Graviton undetected lead to Missing Transverse energy + one recoiling jet  Monojet IMPF06, Madrid 5/4/2006

5. ET (leading jet) > 150 GeV Missing ET > 120 GeV Current results on monojet search at CDF Current limit based on ~ 370 pb-1 • Results: • 265 ±30 events predicted • 263 events observed No excess observed IMPF06, Madrid 5/4/2006

6. Analysis strategy Effect due to pT cut in MC generation 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. • 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t is the most significant, followed by Wm • QCD dijets, where one jet is lost or mismeasured • Ztt • Z is irreducible: • Important to have good Monte Carlo simulation •  Use data to evaluate it, considering Z  e+e- IMPF06, Madrid 5/4/2006

7. MC samples: Z( e+e-) + 1 parton Pythia pThat > 5 GeV/c Tune A, LQCD = 0.146 Alpgen+Herwig MadGraph+Pythia No Tune A Z + ≥ 1 jets event topology PT profile in f in Z+≥1 jets events • Using tracks with: • pT > 0.5 GeV/c • nHits > 20 • |z0| < 1.5 d0 < 2.0 Z0f=0 transverse plane • Dominated by UE. • Independent of the pT of the jets. tracks Jet fragmentation + Underlying Event Pythia is the simulation that better reproduces the jet fragmentation IMPF06, Madrid 5/4/2006

8. Jet Shapes in Z+≥1 jets events  Energy distribution within jets Using the ET of the calorimeter towers in jets with pT > 25 GeV/c and |Y|< 2.1 Integral shape Differential shape in steps of DR = 0.1 Pythia  more accurate than Herwig in reproducing jet fragmentation + effects due to UE IMPF06, Madrid 5/4/2006

9. Inclusive pjetT distributions pT of the jets for Z + ≥ n jets Pythia Every MC distribution is normalized to the data  shape comparison only Alpgen+Herwig Alpgen+Herwig Less jets at low pT due to lack of UE in Herwig MC Good agreement with Pythia MC  Further investigation on going using Alpgen+Pythia MC  First results expected for Summer 2006 IMPF06, Madrid 5/4/2006

10. Missing ET 103 s (pb) Multiple jets 1 10-3 Missing ET 10-6 10-9 Phys.Rev.D59:074024,1999 300 500 700 Squarks and Gluinos • At the Tevatron: mainly Squarks and Gluinos pair production • Golden signature at LHC • Investigated decays: energetic jets + MET (from LSP) • 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 b = 3 or 5 • 5 flavors degenerate ~ ~ IMPF06, Madrid 5/4/2006

11. s46 s41 s35 Analysis strategy • 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 • “Blind Analysis” • Define a signal region (Blind Box) • Make sure MC is in agreement with data outside this region (Control Region) • “Open” the Blind Box Signal region (blind box) determined by optimizing S/√B IMPF06, Madrid 5/4/2006

12. Backgrounds Backgrounds dominate Need to be specifically rejected: fb MET physics backgrounds MET due to jet energy mismeasurements • W/Z+jets with Wl or Z, DiBoson: • reject isolated electrons and muons • Top:Signatures similar to W+jets (rejection more challenging) QCD multijets: reject jet close to MET direction Z+jets with Z->e+e-(m+m-) IMPF06, Madrid 5/4/2006

13. Backgrounds (2) MULTIJET BACKGROUND ESTIMATIONS • Generated with PYTHIA in different pT bins • Selected regiondominated 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 Dedicated study to verify the LO to NLO scale factors for the normalisation of the samples  “k-factors” OTHER BACKGROUNDS: estimations from Monte Carlo IMPF06, Madrid 5/4/2006

14. Event selection Signal region • 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 MET distribution after applying all the cuts except MET >165 GeV HT distribution after applying all the cuts except HT >350 GeV IMPF06, Madrid 5/4/2006

15. XY view of event with large MET HT = ET(1st) + ET(2nd) + ET(3rd) = 404 GeV ET(1st) = 172 GeV ET(2nd) = 153 GeV ET(4th) = 65 GeV ET (3rd) = 80 GeV Missing ET = 223 GeV IMPF06, Madrid 5/4/2006

16. Results In L = 245 pb-1 of data  Background expectations inside the Blind Box:4.1  0.6  1.4 events. Opening the blind box3 eventshave been found • 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 IMPF06, Madrid 5/4/2006

17. 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 IMPF06, Madrid 5/4/2006

18. Back up

19. The Tevatron Highest-energy accelerator currently operational Peak luminosity 1.8 *1032 cm-2 s-1 Integrated luminosity/week  about 25 pb-1 CDF and D0: ~1.2 fb-1on tape Analyses shown here use 0.3 – 1.0 fb -1 date IMPF06, Madrid 5/4/2006

20. 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) Randall-Sundrum Scenario IMPF06, Madrid 5/4/2006

21. Reference SUSY points for squark/gluino IMPF06, Madrid 5/4/2006