SUPERSYMMETRY SEARCHES AT CDF

Transcription

1 SUPERSYMMETRY SEARCHES AT CDF Xavier Portell Freiburg, 8 th Nov

2 OUTLINE Tevatron and CDF Supersymmetry (SUSY) SUSY models phenomenology SUSY analyses at CDF: Squarks and Gluinos (Missing E T +jets) Chargino and neutralino (3-leptons) Neutralinos in GMSB (delayed photons) RPV chargino and neutralino (3- or 4-leptons) RPV stop (tau signatures) RPV tau sneutrino (eµ signatures) MSSM Higgs searches Indirect searches Final Notes RPV R-parity Violation 2

3 THE TEVATRON Chicago s = 1.96 TeV Booster p p CDF DØ Tevatron p source Main Injector Inst. Luminosity vs Time 36x36 bunches at 396 ns crossing time Main injector: 150 GeV proton beam 06 Antiproton recycler: used as accumulator Electron cooling implemented ( L~40%) In 2009: Base Goal 4.4 fb -1 Design 8.5 fb Current record: cm -2 s -1

4 THE CDF DETECTOR CDF was highly upgraded in Run II Had Calorimeter Em Calorimeter η=1 Muon system η=0 B field: 1.4 T Great performance: ~2.0 fb -1 delivered Efficiency ~ 85% ~1.7 fb -1 to tape Drift chamber Inner tracker (Si) The analyses presented here include luminosities from fb -1 4

5 THE STANDARD MODEL The SM works very well... Precision EWK measurements SM Mass hierarchy problem (quadratic divergences)...but there exist some unresolved problems Unification of forces Dark Matter Matter-antimatter asymmetry 5

6 SUPERSYMMETRY SUSY: Q Boson> = Fermion Q Fermion> = Boson The introduction of SUSY have very interesting implications: SM With SUSY Provides a natural solution to the hierarchy problem Electromagnetic, weak and strong couplings unified at the GUT scale. Can provide a candidate for cold dark matter. 6

7 SUSY: NEW PARTICLES But SUSY also imply new undiscovered particles... h 0, A 0, H 0 Particles not discovered SUSY is a broken symmetry The Minimal Supersymmetric Standard Model (MSSM) introduces ~ 100 new parameters... Taking some theoretical assumptions important reduction 7

8 SUSY BREAKING Different models predict how the symmetry is broken determines phenomenology One of the preferred models: msugra Symmetry broken via gravitational interactions Hidden sector visible sector (ewk) Soft SUSY breaking Only 5 parameters that determine whole phenomenology. m 0 : common scalar mass at GUT m 1/2 : the common gaugino mass at GUT tanβ: Ratio of Higgs vaccum expectation values A 0 : Trilinear coupling Sign(µ): Higgs mass term 8

9 R-PARITY Most general SUSY lagrangian Leptonic and Baryonic number violation in the superpotential u ~ s + e W W L= 1 B= 1 = = 1 ijk λ LL i j e 2 1 ijk λ'' ui d 2 k j + λ d k ijk i j LQ d k l i i + µ LH λ ijk i u l j d - u ijk denote the families involved ν k New symmetry postulated: R p =(-1) 3(B-L)+2s SM particles: R p =1 Superpartners: R p =-1 When R p is conserved (RPC): Superpartners produced in pairs Lightest SUSY Particle (LSP) is stable (Dark matter candidate) 9

10 CROSS-SECTIONS Tevatron: 1.96 TeV LHC: 14 TeV T. Plehn, PROSPINO Cross Section (pb) T. Plehn, PROSPINO Cross Section (pb) q ~, g ~ ± ~χ 1 0 ~χ 2 increase by 3-4 orders of magnitude w.r.t. Tevatron. comparable to Tevatron. 100 events per fb -1 10

11 R P CONSERVING SCENARIO msugra MODEL 11

12 SQUARKS AND GLUINOS DIRECT SQUARK-GLUINO PRODUCTION: DECAY: Strong interaction: large production rate expected Missing E T Need to carefully understand the backgrounds, detector effects... Multiple jets background reduction Missing E T Missing E T (MET) + jets (3 or more) Diboson L=371 pb -1 + jets 12 E T

13 SIGNAL: SQUARKS/GLUINOS Grid in m 0 -m 1/2 (~100 points) µ < 0 tan β = 5 A 0 = 0 4 flavours considered (no sbottom or stop in 2->2 process) Samples generated using ISASUGRA in PYTHIA Parton-Shower and Underlying Event modeled using Pythia-TuneA Squarks and Gluino production 4 cases: squark-antisquark squark-squark (and c.c.) gluino-gluino squark-gluino (and c.c.) Each sub-process is normalised using PROSPINO: Q M gluino or M squark or 1 2 (M gluino + M squark ) 13

14 CUTS: SQUARKS/GLUINOS Cuts against cosmics & beam-halo E T > 70 GeV At least three jets E jet T η jet > 25 GeV < 2.0 ( one jet central η < 1.1) EM fraction < 0.9 Remove electrons φ(e T, jets) > 0.7 φ(e T, track) > 0.7 Remove QCD Remove muons No pairs of tracks in Z-mass window jet Apply different thresholds for MET and E T of the jets as a function of gluino mass: GeV ET H T = 3 i= 1 jets E T, i jet1 E T jet2 E T A B C

15 SQUARKS AND GLUINOS Backgrounds: QCD MC (Pythia) normalised using data (at low MET). W/Z+jets MC (ALPGEN+PS) and WW (Pythia) normalised to NLO using MCFM program. Top MC (Pythia) normalised to NLO theoretical cross-section. Total systematic uncertainty ~ 20-30% Data is in good agreement with SM 15

16 SQUARKS AND GLUINOS: LIMITS Observed limit of 387 GeV/c 2 when M gl ~M sq and M gl >220 GeV/c 2 in any case. An update with more data is currently ongoing. 16

17 3 rd GENERATION SQUARKS Mass eigenstates Mix of weak eigenstates. Mixing proportional to quark masses and Yukawa couplings large split in the mass. Specially significant for stop and sbottom, which can have one low mass state. CDF has dedicated analyses to search for these particles SBOTTOM STOP Depending on the mass: Heavy: Medium: Light: ~ ~0 t tχ ~ ~ ~0 t bχ ± bwχ ~ ~ 0 t cχ Signatures: Missing E T and Heavy Flavour jets A Light stop is preferred (consistent with baryogenesis) Balazs, Carena, Wagner (hep-ph/ ) Low-p T jets are challenging 17

18 LIGHT STOP AND SBOTTOM Remove QCD and electrons Use Heavy Flavour tagging c-jet tagging: ~17% Syst: 12% b-jet tagging: ~40% Syst: 8.6% Define three zones for Missing E T (>50 GeV) and E T of the jets: L=295 pb -1 M stop <100 GeV/c 2 M sbottom <140 GeV/c 2 100<M stop <120 GeV/c 2 140<M sbottom <180 GeV/c 2 M stop >120 GeV/c 2 M sbottom >180 GeV/c 2 stop analysis sbottom analysis 18

19 LIMITS FOR STOP/SBOTTOM No excesses found: new limits (95% C.L.) Ongoing analyses with more data 19

20 R P CONSERVING SCENARIO msugra MODEL ± χ ~ i ~0 χ i 20

21 CHARGINOS AND NEUTRALINOS 3-leptons Missing E T We have always 2 like-sign leptons (one from each superpartner) In msugra: M ~ M ~ 2 M 0 0 ~χ ± 1 ~χ 2 ~χ 1 hep-ph/ T. Plehn, PROSPINO 200 GeV/c 2 LEPII Easy to trigger and low background: GOLDEN CHANNEL 21

22 CHARGINOS AND NEUTRALINOS The third lepton tends to be very soft tanβ determines the lepton flavour composition Cuts in lepton P T : P T 1st ~20 GeV/c P T 2nd ~10 GeV/c IMPORTANT ANALYSES VARIETY - 3 leptons (ee+l, µµ+l, eµ/µe+l) - 2 leptons + track Low p T zone taus dominate - 2 like-sign (LS) leptons (ee,µµ,eµ) Different trigger paths and cut optimizations to reduce backgrounds (Drell-Yan, dibosons, conversion...) 22

23 CHARGINOS AND NEUTRALINOS Since data agrees with background expectations... Low tanβ and slepton mass degenerate A µµ+µ event M ± ~χ > 127 GeV/c 2 1 (σxbr<0.25) Beyond LEP (in these scenarios) A combination with 1 fb -1 luminosity to be finalized 23

24 R P CONSERVING SCENARIO GMSB MODEL 0 ~χ 1 24

25 DELAYED PHOTONS In GMSB: Neutralino decays into a photon and a gravitino (LSP). Lifetime: free parameter. Right and wrong vertexing for SM ~2ns Signal example If it decays inside detector: - Neutralino ~ 10 ns (e.g.) - Prompt photon ~ 5 ns Blinded signal region [2,10] ns Crucial for the analysis: EMTiming system installed end of Beam halo Cosmics L=570 pb -1 Cuts on ET of the photon (>30 GeV), ET of the jet (>35 GeV) and MET (>40 GeV) Exp: 1.3 ± 0.7 events Data: 2 events 25

26 DELAYED PHOTONS: LIMITS The analysis will continue with more data. Analysis almost background-free once beam/cosmic contributions understood. 26

27 R P VIOLATING SCENARIO msugra MODEL ± χ ~ i ~0 χ i 27

28 RPV: CHARGINO/NEUTRALINO ASSUMPTIONS Only first term of W RPV is considered (protect proton lifetime) Charge current universality λ <0.135 GeV RPV vertex: only in the last decay. The decay is inside the detector In general: λ 121 > λ 122 >> λ 133 CDF analysis v e e ( ) v µ e µ W RPV = λ i j ijk L L E +... i,j,k denote the leptonic families involved. χ ~ 0 1 ~ µ λ 121 k µ + νe e - 0 A pair of ~χ 1 at least 4 leptons and two neutrinos Only one RPV at a time λ eeee, eeeµ, eeµµ λ µµµµ, µµµe, µµee Also optimizing for 3 leptons to improve acceptance 28

29 RPV: 4 LEPTONS Example of bkg. Low background just for asking 4 leptons or more! Trilepton Signal Regions Dataset λ 121 : eel λ 122 : µµl Background 2.9 ± ± 1.0 RpV SUSY 3.8 ± ± 0.4 Data 5 1 Probability to see >=5 with 2.9 ± 0.8 is 17% Dataset Background RpV SUSY Data 4 Signal Region Signal ± ± Very low background! 29

30 R P VIOLATING SCENARIO msugra MODEL 30

31 RPV: STOP RPV vertex 2 b-jets 1 τ hadronic (64.8%) 1 τ semi-leptonic (35.2%) RPV vertex CHALLENGE: τ identification Jets and leptons τ misidentification Used Z ττ for hadronic τ ID: Eff ~ 56% Expected events: 2.2 Observed events: 2 (1e + 1µ) New mass limits are obtained L=322 pb -1 31

32 R P VIOLATING SCENARIO msugra MODEL 32

33 RPV TAU SNEUTRINO Motivations - Attractive signature: high p T eµ (clean) - Interpretation on other scenarios (Z ) λ 132 <0.05 λ 311 <0.16 Physics backgrounds: Z ττ, ttbar, dibosons Fake backgrounds: real e and fake µ // real µ and fake e Performed statistical checks of consistency No deviations/excesses Results depend on coupling values Control region L=344 pb -1 33

34 HIGGS SECTOR Two complex Higgs doublets needed to avoid anomalies Eight degrees of freedom W ±, Z and 5 Higgs particles: h, H, A, H +, H - At tree-level two independent parameters: m A, tanβ Five more parameters trhough radiative corrections: hep-ph/ M SUSY (squark, gaugino masses) X t (related to the stop mixing) M 2 (gaugino mass term) µ (Higgs mass parameter) m gluino (comes via loops) X t different scenarios: maximal mixing scenario (m h less constrained) no-mixing scenario (m h more constrained) 34

35 CHARGED HIGGS Direct production is very small at the Tevatron ~ 0.1 pb But if H ± is smaller than the top: t bh + Event selection: τ had e/µ At least one b-jet Missing E T Importance of τ tagging. Build a likelihood discriminant (isolation, p T...) Systematics mainly come from mistags and fakes (~20% each) Example of a two b-jet event Backgrounds: Real τ s: ttbar, diboson, Z ττ Fake τ s: W+jets... Expectation: 3.88 ± 0.52 Observation: 6 (4 electron and 2 muons) Exclusion: BR(t H + b)>0.5 Expected exclusion for 1fb -1 : BR>0.1 L=335 pb -1 35

36 Production modes (φ A, h, H): Couplings to τ, b are enhanced by tanβ: bb 90% of cases (but huge background) ττ 10% of cases (cleaner signature) Expected: ± 5.4 ± 27.7 Observed: 487 NEUTRAL HIGGS Backgrounds: Z/γ* ττ (irreducible) Dijets, W+jets, γ+jets Dibosons, ttbar, Z Extensive use of τ tagging: shrinking cone... L=310 pb -1 36

37 INDIRECT SEARCHES ± χ ~ i ~0 χ i 37

38 INDIRECT SEARCHES: B S µµ SM: Bs->µµ is heavily suppressed: BR( B s + µ µ ) = (3.5 ± 0.9) 10 (Buchalla & Buras, Misiak & Urban) New CDF result: Using B + J/ψ K + for normalisation 9 SUSY: BR enhancement by 1-3 orders of magn. (Babu, Kolda: hep-ph/ many more) High resolution! σ(mµµ) ~ 0.23 MeV R. Dermisek et al. hep-ph/ (2005) Found 1 event; expected background 0.9±0.3 New limits at 95% C.L: BR(B s µµ) < L=780 pb -1 38

39 FINAL NOTES SUSY is a well motivated theory. SUSY can manifest itself in plenty of different final state signatures. No SUSY signal has been found so far at the Tevatron. CDF (D0) will keep adding more data to the different SUSY searches until the LHC starts. 39

40 FINAL NOTES: LHC LHC will open a new energy frontier. Inclusive searches for squark/gluinos will be one of the very first analyses to be carried out with LHC data. Tevatron experience tells us that we will need to understand the hadron collider environment (beam conditions, detector features...) The LHC is about to start an exciting journey to the energy frontier. Experience from previous ships will be worthwhile. Illustration: Sandbox Studio; Symmetry magazine (August 06). 40

41 BACKUPS 41

42 SQUARKS/GLUINOS: FUTURE 42

43 3-LEPTONS: PROJECTIONS 43

44 HIGGS STATUS 44

45 NEUTRAL HIGGS EXPECTATION For 1 fb -1 : In addition, study: 45

46 Bs µµ: PROJECTIONS 46

47 Bs MIXING Constraints on SUSY (hep-ph/ ): Place constraints in SUSY flavour violations. Constraints at large tanβ regimes for some models with seesaw mechanisms (unless m A is very heavy). Constraints on large B S µµ contributions. 47

48 SQ/GLUINO SYSTEMATICS Systematic uncertainties considered are: Energy scale Luminosity Renormalization scale Parton PDFs ISR/FSR PROSPINO: gluino-gluino µ = Mgl gluino-squark µ = 1/2 * [Mgl + Msq] squark-squark µ = Msq squark-antisquark µ = Msq MCFM: Controlled variation of Λ QCD. Contributions comparable with luminosity uncertainty Used Hessian method. Specially important for signal (high-x gluon contribution) Z µ = M Z W µ = M W Considered variations of twice and half the scale to calculate the uncertainty. Example: ZONE B JES Ren. PDF Lum. ISR/FSR SIGNAL (when Mgl~Msq) ~8% ~0.2% ~2% 6% ~5% BACKGROUND ~21% ~0.7% ~10% 6% --- Relative to efficiency Theoretical uncertainties on the signal cross-section: ~30% 48

49 CHARGINOS AND NEUTRALINOS Requirements to reduce SM background (Drell-Yan, diboson, conversions...) Observed/Expected Events Minimum p T for the 2 leading leptons Dilepton mass and angle cuts (avoid Z and Drell-Yan) Small jet activity Missing transverse energy significant All is compatible with SM... CHANNEL L (fb -1 ) EXP. BKG. OBS. DATA ee + e/µ p T : 20, 5, 5 GeV/c µµ + e/µ (p T : 20, 5, 5 GeV/c) µe + e/µ (p T : 20, 5, 5 GeV/c) e ± e ±,e ± µ ±, µ ± µ ± (p T : 20,10 GeV/c) µµ + e/µ (low p T : 5, 5, 5 GeV/c) ee + track (low p T : 15, 5, 4 GeV/c) ± ± ± ± ± ± Use e/mu only =>Very small backgrounds No third lepton requirement => Higher acceptance Sensitive to taus as 3 rd lepton => Keeps acceptance at high tanβ 49

50 50

51 CDF 3-Leptons Control Regions Drell-Yan WZ ZZ ttbar Fakes -SUSY DATA MET SIGNAL?? REGION N events/2 GeV/c 2 L=607 pb -1 Drell-Yan Dibosons ZZ bbbar -SUSY DATA M(l l ) MET (GeV) Dielectron Invariant Mass(GeV/c 2 ) Dimuon P T (GeV/c) LS-dilepton analysis has additional Control Regions to test conversion removal 51

52 Different 3-Leptons Scenarios In Standard msugra the BR into taus is enhanced smaller acceptance 52

53 TAU IDENTIFICATION Define a (shrinking) signal cone isolation annulus Seed track (p T > 6 GeV/c) 53

54 b-tagging 54

55 EXCLUSION LIMITS: CDF vs D0 D0: 310 pb -1, A 0 =0, µ<0 and tanβ=3 CDF: 371 pb -1, A 0 =0, µ<0 and tanβ=5 CDF is doing better in the 3-jets analysis zone. D0 is doing better at large squark masses (4-jets optimization) HOWEVER, D0: Using a more conservative approach reducing the cross section by 1 sigma. Not including ISR/FSR uncertainties Opposite directions effects No big change in our limits when following D0 approach. We are now performing an additional 4-jet analysis 55

56 SQUARKS AND GLUINOS: LIMITS D0: 310 pb -1, A 0 =0, µ<0 and tanβ=3 CDF: 371 pb -1, A 0 =0, µ<0 and tanβ=5 CDF: Includes the theoretical uncertainties when calculating the observed limit D0: Reduce theoretical cross section by 1σ (more conservative) M gl > 387 GeV/c 2 (when M gl ~M sq ) M gl > 241 GeV/c 2 ; M sq > 325 GeV/c 2 56

57 SQUARKS AND GLUINOS 57