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Top Physics at CDF Gervasio Gómez Instituto de Física de Cantabria Seminari del IFIC, 3-May-2005.

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Presentation on theme: "Top Physics at CDF Gervasio Gómez Instituto de Física de Cantabria Seminari del IFIC, 3-May-2005."— Presentation transcript:

1 Top Physics at CDF Gervasio Gómez Instituto de Física de Cantabria Seminari del IFIC, 3-May-2005

2 Gervasio Gomez/CDFIFIC, 3-May History I 1964: CP violation in Kaon system 1973: Kobayashi & Maskawa predict 3 quark generations : Standard Model (SM) : discovery of  lepton (3rd generation) 1977: resonance observed in p+nucleon  +  - :  (b-bbar) discovererd –Study of b quark properties Q b =-1/3 (1978) y (1982) I 3 =-1/2 (1984) Implies existence of an additional quark (top): 3rd generation weak isospin partner of the b quark A long search for the TOP quark begins!

3 Gervasio Gomez/CDFIFIC, 3-May Why must top exist? Once determined Requires existence of a t quark with: Cancellation of anomalies such as: All anomalies cancel exactly if, for each family:

4 Gervasio Gomez/CDFIFIC, 3-May History II 1983: Discovery of W, Z with masses as predicted in SM 1994:  (Z) in LEP & SLC exclude a 4th generation neutrino with M

5 Gervasio Gomez/CDFIFIC, 3-May The Standard Model (SM) SM Fermions Fermion masses are free parameters of the SM. For quarks: ~330 MeV ~1.5 GeV ~500 MeV ~175 GeV ~5 GeV

6 Gervasio Gomez/CDFIFIC, 3-May Mass in the SM Mechanism through which fermions acquire mass not fully understood In SM, Higgs mechanism: “doublet” of scalar fields weak isospin space With potential: with  2 <0 ground state=minimum=vev: EW scale Mass term in lagrangian ground state does not have original L symmetry: spontaneous EWSB Boson masses: Fermion masses: Yukawa coupling for each fermion Scalar particle (spin 0): Higgs (not yet observed)

7 Gervasio Gomez/CDFIFIC, 3-May Tevatron Main Injector and Recycler  p source Booster P-Pbar Collisions every 396 ns Beam energy 980 GeV  s = 1.96 TeV Inst. Lum. ~5x10 32 cm -2 s -1

8 Gervasio Gomez/CDFIFIC, 3-May CDF Detector

9 Gervasio Gomez/CDFIFIC, 3-May Top Production at Tevatron 15% Tevatron: 85% top-antitop pairs: single top: ~1 pb ~2 pb ~ one top event every 10 BILLION inelastic collisions

10 Gervasio Gomez/CDFIFIC, 3-May Top Decay final state given by W + W - decays Hadronization time NO top hadrons Event Classification tt  l l bb dilepton 5% tt  l qqbb lepton+jets 30% tt  qqqqbb hadronic 45% here lepton = e or 

11 Gervasio Gomez/CDFIFIC, 3-May Top Detection  Events are energetic –Large total transverse energy: Ht  Events are central and spherical –|  |< 2.0, aplanarity  High energy jets and isolated leptons –missing Et from neutrino in leptonic modes –High Et jets  Two high E T b-jets –Displaced secondary vertex –Soft lepton inside jet  Possible additional jets from gluon radiation (isr,fsr)

12 Gervasio Gomez/CDFIFIC, 3-May Soft Lepton Tagging semileptonic B hadron decay Tagging B-jets B hadrons are long-lived Vertex displaced tracks  Top events contain B hadrons  Only 1-2% of dominant W+jets background contains heavy flavor  Great S/B improvement Top Event Tagging Efficiency False Tag Rate (QCD jets) 55% 0.5% 15% 3.6%

13 Gervasio Gomez/CDFIFIC, 3-May Top Pair Cross Section Measure in different samples –Understand top kinematics –Understand heavy flavor content –Cross check results –Validate top samples for other top measurements Test of SM predictions Sensitivity to physics beyond SM –Background to Higgs and SUSY searches

14 Gervasio Gomez/CDFIFIC, 3-May Cross Section: dileptons Selection: 2 leptons (e,  ), 2 jets, high MET –Second lepton can be “loose” -- even an isolated track Main backgrounds: DY, dibosons, & “fakes” j  lepton controlsignal includes kinematical and geometric acceptance and branching fraction CDF most precise:

15 Gervasio Gomez/CDFIFIC, 3-May Cross Section: l+jets+B-tag Selection: 1 lepton (e,  ), >=3 jets, high MET Btag Main backgrounds: W+HF, QCD, W+jets (mistags) CDF most precise:

16 Gervasio Gomez/CDFIFIC, 3-May x-sec: l+jets+kinematics Selection: 1 lepton (e,  ), >=3 jets, high MET NO Btag: higher statistics, worse S/B Main backgrounds: W+jets, QCD, EW kinematic distributions: likelihood or NN CDF most precise:

17 Gervasio Gomez/CDFIFIC, 3-May Cross Section Measurements Measurements consistent with each other….. … and with theory dilepton lepton + jets hadronic error bars: red=stat, blue=total

18 Gervasio Gomez/CDFIFIC, 3-May Top Mass Mt  175 GeV  Yukawa coupling  1Special role in EWSB? Dominant parameter in radiative corrections: quadratic in m t, logarithmic in m H Mt from precision EW measurements

19 Gervasio Gomez/CDFIFIC, 3-May Top Mass in Run-I m H (GeV) M top all-jets D  result is not included in Tevatron average: M top =  15.7 GeV/c 2 Weight in average 6% 7% 22% 58% 7%

20 Gervasio Gomez/CDFIFIC, 3-May Measuring Mtop LO ME final state: CDF sees: Lepton+jets Undetected neutrino P x and P y from Et conservation 2 solutions for P z from M W =M l Leading 4 jets combinatorics 12 possible jet-parton assignments 6 with 1 b-tag 2 with 2 b-tags ISR + FSR Dileptons Less statistics 2 undetected neutrinos Less combinatorics: 2 jets Challenging: Largest uncertainty: Jet Energy Measurement

21 Gervasio Gomez/CDFIFIC, 3-May Jet Energy Corrections Determine true “particle”, “parton” jet E from measured jet E Non-linear response Uninstrumented regions Response to different particles Out of cone E loss Spectator interactions Underlying event

22 Gervasio Gomez/CDFIFIC, 3-May Jet Energy Uncertainty New (2005) systematic uncertainty Significant Improvement Redoing mass analyses Improved results soon 2004 uncertainty used for most mass results shown here Dominant systematic uncertainty ~factor of 2 decrease! Run II 2004 Run I Fractional Systematic Uncertainty vs P T Central  region Run II 2005

23 Gervasio Gomez/CDFIFIC, 3-May Matrix Element Technique Determine mass of the top quark evaluating a probability using all the variables in the event, integrate over all unknowns Sum over all permutations of jets and neutrino solutions Background process probabilities are or not be explicitly included in the likelihood Top mass: maximize  i P i (x;M top ) –Each event has its own probability –Correct permutation is always considered (along with the other eleven) –All features of individual events are included, thereby well measured events contribute more information than poorly measured events W(y,x) is the probability that a parton level set of variables y will be measured as a set of variables x d n  is the differential cross section: LO Matrix element f(q) is the probability distribution that a parton will have a momentum q

24 Gervasio Gomez/CDFIFIC, 3-May Mtop: DLM “Dynamical Likelihood Method” : ME technique Likelihood vs. m t per event from LO ME for tt  l+4j and “transfer functions” for quark E T  jet E T –Minimize -ln L (combined likelihood from all events) Background mapping function: measured to true mass for a given bkg fraction (19% for l+4j with b-tag)

25 Gervasio Gomez/CDFIFIC, 3-May Template Technique Determine mass of the top quark using a quantity strongly dependent on the top quark mass M top (usually Reconstructed M top ) Determine the Reconstructed M top per event: Minimize a  2 expression for the resolutions and kinematic relationships in the ttbar system. Choose jet to parton assignment and P z based on best fit quality. Build signal and background templates Obtain the measurement from the data: Compare Reconstructed M top from data with same from randomly generated and simulated signal at various input top mass (M top ) and backgrounds using an unbinned likelihood fit Signal TemplateBackground Template Data L = L shape x L background Best signal + background templates to fit the data

26 Gervasio Gomez/CDFIFIC, 3-May Newest Template Result Combined –Log(L) Expected error NEW

27 Gervasio Gomez/CDFIFIC, 3-May Other template measurements Dileptons: b-tagged l+jets: b-tagged l+jets w/ multivar templates: Probability for Mt from likelihood based on MC multidimensional templates

28 Gervasio Gomez/CDFIFIC, 3-May Best Mtop Measurements error bars: red=stat blue=total

29 Gervasio Gomez/CDFIFIC, 3-May Single Top Search Direct measurement of |V tb | 2 Sensitive to new physics – W’, anomalous couplings, FCNC Final state: lepton, MET, 2 jets & at least 1 b-jet Challenging –Small cross section –tt now background –Large additional backgrounds

30 Gervasio Gomez/CDFIFIC, 3-May Single top MC Templates

31 Gervasio Gomez/CDFIFIC, 3-May W Helicity SM (V-A) prediction: t  W T : left handed W (30%) t  W 0 : longitudinal W (70%) Kinematic distributions for the different helicity states are different SM: t W+W+ l+l+ ** Lepton Pt test of V-A tWb vertex

32 Gervasio Gomez/CDFIFIC, 3-May W Helicity dilepton and lepton+jets lepton+jets

33 Gervasio Gomez/CDFIFIC, 3-May Search for H +

34 Gervasio Gomez/CDFIFIC, 3-May Search for 4th generation t’ Same selection as kinematic top xs Fit Ht to t’,t,W+jets and QCD Likelihood for different Mt’ (one such plot for each point)

35 Gervasio Gomez/CDFIFIC, 3-May Other Top Measurements MeasurementResult (runI) ~300

36 Gervasio Gomez/CDFIFIC, 3-May Summary & Outlook All measurements consistent with SM –Recently published or submitted: “Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2)=1.96 TeV Using Dilepton Events”, Phys. Rev. Lett 93, (2004) “Search for Electroweak Single Top Quark Production in p anti-p Collisions at S**(1/2)=1.96 TeV”, Phys. Rev. D 71, (2005) “Measurement of the W Boson Polarization in Top Decay at CDF at S**(1/2)=1.8 TeV”, Phys. Rev. D71, (R) (2005) “Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2)=1.96 TeV Using Kinematic Fitting of B-Tagged Lepton+Jet Events”, hep-ex/ “Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2)=1.96 TeV Using Lepton+Jet Events with Secondary Vertex B-Tagging”, hep-ex/ “Search for Anomalous Kinematics in t anti-t Dilepton Events at CDF II”, hep-ex/ –Reduced Jet Energy Scale uncertainty –Hope for 2 fb -1 or more by end of 2007 –  ~ 10% (now ~30%) –  m ~2-3 GeV (now 4.3 GeV from RunI) –Single Top: possible observation –  F 0 reduced uncertainty (now %) –Mass limit on t’

37 Gervasio Gomez/CDFIFIC, 3-May Backup Slides

38 Gervasio Gomez/CDFIFIC, 3-May Template Result from CDF –Log Likelihood vs M top, JES M top (GeV) JES(  ) Source  M top (GeV/c 2 ) B-jets modeling0.6 Method0.5 ISR0.4 FSR0.6 Background shape1.1 PDF0.3 Other MC modeling0.4 Total1.7 Measurement is more precise than the current world average ! Systematic uncertainties Most of these can be reduced with more data

39 Gervasio Gomez/CDFIFIC, 3-May SM quick review SM quark and lepton lagrangian Predicts all experimental observations of quark and lepton interactions Covariant derivative fixed by gauge invariance under U(1)xSU(2)xSU(3) transformations: Defining:

40 Gervasio Gomez/CDFIFIC, 3-May W Helicity from lepton Pt l + jets dilepton

41 Gervasio Gomez/CDFIFIC, 3-May Publishing Mtop for 15 years

42 Gervasio Gomez/CDFIFIC, 3-May Matrix Element at D  Last result from Run I: June, 2004 Reduced the statistical uncertainty from 5.6 to 3.6 (expected error from 7.4 to 4.4) => 2.4 times more data Total uncertainty from 7.3 (lepton+jets CDF) to 5.3 (D0) Run II results from D  and CDF coming soon!

43 Gervasio Gomez/CDFIFIC, 3-May Mass: D0 RunI m t =  3.6(stat)  3.9(syst) GeV/c 2 Statistical uncertainty reduced: 5.6 to 3.6 GeV/c 2 –Equivalent to Lx2.4 ! Likelihood vs. m t for each event: Phase space x LO ME for top or BG (W+4j) PDFsProbability for observable x given parton y (Ex: quark E T  jet E T ) Likelihood gives effective weigh to each event Maximize combined likelihood to extract m t

44 Gervasio Gomez/CDFIFIC, 3-May Template Results from D  Topological – No b-tagging requirement Construct a discriminant using topological variables (D LB ) to improve S/B At least one b-tagged jet: –no requirement on discriminant D LB First top mass at D  top mass measurement with b- tagging ttbar candidates 69 S/B~3/1 ttbar candidates 94 S/B~1/1 Reconstructed M top (GeV)

45 Gervasio Gomez/CDFIFIC, 3-May Other Matrix Element based M top DLM: only a signal probability, requires b- tagging New results with decrease JES and more data coming soon! Ideogram: Uses same kinematic fit as D  template method, and includes D LB discriminant in likelihood fit Uses background probability

46 Gervasio Gomez/CDFIFIC, 3-May Implications for M Higgs New combined D0 mass: –M t = ± 5.1 GeV/c 2 New World Average: –M t = ± 4.3 GeV/c 2 Global EW fit using new average –LEPEWWG method (hep-ex ) –Best-fit M H  113 GeV/c 2 –Upper 95% C.L. : 237 GeV/c 2 Yellow region excluded (direct search) : M H < GeV/c CL

47 Gervasio Gomez/CDFIFIC, 3-May Futuro: LHC Tevatron: x~0.18 LHC: x~ to 8 ttbar/sec ¡Una verdadera fábrica de top! 1 año a baja luminosidad: 10 fb -1 : 8x10 6 sucesos ttbar

48 Gervasio Gomez/CDFIFIC, 3-May CMS y ATLAS Detectores multi-propósito adaptados al acelerador LHC: Electrónica rápida Alta granularidad Buena resolución Buena identificación de jets, muones, missing Et, vértices desplazados, trazas

49 Gervasio Gomez/CDFIFIC, 3-May Masa del top en el LHC Combinando todos los canales:  m ~1 GeV j1j1 j2j2 b-jet t Leptón+jets: Tag 2 b-jets Identificar leptón y MET Usar jets con Mjj más cercano a Mw Reconstruir Mtop=Mjjb Pares ttbar de alto Pt: Back-to-back Hemisferios opuestos Menos fondo combinatorial Menor JES sys (alto Pt de los jets) Pero los jets del W se sobreponen Sumar todos los clusters en un cono alrededor de la dirección del top Restar Underlying Event Dependencia en  R j1j1 j2j2 b-jet t

50 Gervasio Gomez/CDFIFIC, 3-May Resonancias 1.6 TeV resonance M tt Reconstrucción de M tt para búsqueda de resonancias SM Higgs (BR smaller with respect to the WW and ZZ decays) MSSM Higgs (H/A, if m H,m A >2m top, BR(H/A → tt)≈100% for tanβ≈1) Otros modelos: Technicolor, strong ElectroWeak Symmetry Breaking, Topcolor, “colorons”, …

51 Gervasio Gomez/CDFIFIC, 3-May Single top en LHC fusión Wg: 245±27 pb S.Willenbrock et al., Phys.Rev.D56, 5919 Wt: 62.2 pb A.Belyaev, E.Boos, Phys.Rev.D63, W* 10.2±0.7 pb M.Smith et al., Phys.Rev.D54, ) Determinación del vértice tWb: V tb 2) Medición independiente de la masa 3) Polarización del top Mecanismos de producción: Proceso  V tb (stat)  V tb (theory) Wg fusion0.4%6% Wt1.4%6% W*2.7%5% ProcesoSeñalFondoS/B Wg fusion27k8.5k3.1 Wt6.8k30k0.22 W*1.1k2.4k0.46 Con 30 fb -1 : determinación de cada proceso por separado

52 Gervasio Gomez/CDFIFIC, 3-May FCNC en desintegraciones de top Desintegraciones de FCNC suprimidas (Br< ) en SM t  Zq (CDF Br<0.137, ALEPH Br<17%, OPAL Br<13.7%) –tt  Wb + Zq con W  l o jj y Z  l + l - –Reconstruir t  Zq  (l + l - )j –Sensibilidad a Br(t  Zq) = 1.1 X (100 fb -1 ) t   q (CDF Br<0.032) –tt  Wb +  q con W  l –Sensibilidad a Br(t   q) = 1.0 X (100 fb -1 ) t  gq –Fondo de QCD es enorme –Buscar “like-sign” tops (ie. tt) –Fácil identificar dileptones “like-sign” –Sensibilidad a Br(t  gq) = 7 X (100 fb -1 )

53 Gervasio Gomez/CDFIFIC, 3-May Top más allá del SM En teorías SUSY+GUT, M top causa EWSB: Modelos de ruptura dinámica de la simetría electrodébil (EWSB): –Interacciones modificadas del top en varios modelos Technicolor: –Top flavor, top seasaw, top-color assisted technicolor Ventana a nueva física y al mecanismo de generación de masas


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