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

Top Physics at CDF

Gervasio GómezInstituto de Física de Cantabria

Seminari del IFIC, 3-May-2005

Gervasio Gomez/CDF IFIC, 3-May-2005 2

History I• 1964: CP violation in Kaon system• 1973: Kobayashi & Maskawa predict 3 quark generations• 1970-73: Standard Model (SM)• 1975-77: discovery of lepton (3rd generation)• 1977: resonance observed in p+nucleon+-: (b-bbar)

discovererd– Study of b quark properties

• Qb=-1/3 (1978) y (1982)

• I3=-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!

( ee ) Qb2 and R

(ee hadrons)

(ee ) 3Qq

2

quarks

wwA

ww

wV

AVFB

cs

Ig

cs

QsIg

fZggfbb

bbbbeeA

2;

2

2

)(;)2/,()2/,(

)2/,()2/,()(

32

3

5

bsc

du ?


Why must top exist?Once determined

2/13 bI 3/1bQ

t

b

NcI3f Q f

2

f

0

ww

ff

a cs

Ig

23

Requires existence of a t quark with: 2/13 tI 3/2tQ

Cancellation of anomalies such as:

0

6

1

3

2

2

10

All anomalies cancel exactly if, for each family:

03

1

3

2310

LQ


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<MZ/2– Top is almost certainly the last SM fermion

• 1995: precision EW measurements– Mtop inferred from higher order EW corrections which depend on the fermion masses– Mtop 178 GeV/c2

• 1995: discovery of top in CDF and D0– Mtop 175 GeV/c2

– By far the heaviest fundamental particle• about 200 times heavier than the proton!• Mass EW scale• Special role in EWSB? (origin of fermionic mass)

– Higgs is the only SM particle which has so far eluded detection


The Standard Model (SM)SM Fermions

Fermion masses are free parameters of the SM. For quarks:

~330 MeV

~330 MeV

~1.5 GeV

~500 MeV

~175 GeV

~5 GeV


Mass in the SMMechanism through which fermions acquire mass not fully understood

In SM, Higgs mechanism: “doublet” of scalar fields weak isospin space

0

With potential: 22 )()()( V

)(2

1 VVTL

with 2<0 ground state=minimum=vev: /2v

GeV2462

2

1

2

2

2

g

MvWWvgLD W

EW scaleMass term in lagrangian

ground state does not have original L symmetry: spontaneous EWSB

wF

WG

M

2sin2

w

WZ

MM

cos

2

vym f

f

Boson masses:

Fermion masses:Yukawa couplingfor each fermion

Scalar particle (spin 0): Higgs (not yet observed)


Tevatron

Main Injectorand Recycler

p source

Booster

DD

• P-Pbar• Collisions every 396 ns• Beam energy 980 GeV s = 1.96 TeV

• Inst. Lum. ~5x1032 cm-2s-1


CDF Detector


Top Production at Tevatron

15%

Tevatron: TeV96.1@ spp

85%

top-antitop pairs: single top:

~1 pb

~2 pb

( p p tt ) 6.1 pb

inel ( pp X) 60mb 1010 (pp tt ) 6 pb

~ one top event every 10 BILLION inelastic collisions


Top Decay

e- e(1/81)

mu- mu (1/81)

tau- tau (1/81)

e - mu (2/81)

e - tau(2/81)

mu- tau (2/81)

e+jets (12/81)

mu+jets(12/81)

tau+jets(12/81)

jets (36/81)

final state given by W+ W- decays

s10GeV1GeV120M

s10MeV)100(23

ttt

23-11

QCD

Hadronization time

NO top hadrons

Br(t Wb) 100%

Event Classificationttllbb dilepton 5%ttlqqbb lepton+jets

30%ttqqqqbb hadronic

45%here lepton = e or


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 ET b-jets– Displaced secondary vertex– Soft lepton inside jet

Possible additional jets from gluon radiation (isr,fsr)


Soft Lepton Taggingsemileptonic B hadron decay

Tagging B-jets

B hadrons are long-lived

Vertex displaced tracks

Top events contain B hadronsOnly 1-2% of dominant W+jets background contains heavy flavorGreat S/B improvement

Top Event Tagging Efficiency

False Tag Rate (QCD jets)

55%

0.5%15%

3.6%


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


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” jlepton

control signal

Nobs Bkg

Ldtincludes kinematical and geometric acceptance andbranching fraction

CDF most precise:

7.0 2.12.4 (stat) 1.2

1.7(sys) pb

Ldt 197 pb 1


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:

8.10.9(stat) 0.9(sys) pb

Ldt 318 pb 1


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:

6.30.8(stat) 1.0(sys) pb

Ldt 347 pb 1


Cross Section MeasurementsMeasurements consistent with each other…..

… and with theory

dilepton

lepton+

jets

hadronic

error bars: red=stat, blue=total


Top MassMt 175 GeV Yukawa coupling 1 Special role in EWSB?

Dominant parameter in radiative corrections:

quadratic in mt , logarithmic in mH

GeV166181

),(,sin,, 2

top

WFBZZ

M

MZAM

GeV100070 HiggsMHiggstop MEWM

Mt from precision EW measurements


Top Mass in Run-I

mH (GeV)

Mtop all-jets D result is not included in Tevatron average: Mtop = 178.015.7 GeV/c2

Weight in

average

6%

7%

22%

58%

7%


Measuring MtopLO ME final state:

CDF sees:

•Lepton+jets•Undetected neutrino

•Px and Py from Et conservation•2 solutions for Pz from MW=Ml

•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


Jet Energy CorrectionsDetermine 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


Jet Energy Uncertainty

•New (2005) systematic uncertainty•Significant Improvement•Redoing mass analyses•Improved results soon

•2004 uncertaintyused for most mass results shown here•Dominant systematic uncertainty

~factor of 2 decrease!Run II 2004

Run I

Fractional Systematic Uncertainty vs PT

Central region

Run II 2005


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 Pi (x;Mtop)– 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

P( x;M top ) 1

dn(y;M top ) dq1 dq2 f (q1) f (q2)W ( x,y)

W(y,x) is the probability that a parton level set of variables y will be measured as a set of variables x

dn is the differential cross section: LO Matrix element

f(q) is the probability distribution that a parton will have a momentum q


Mtop: DLM• “Dynamical Likelihood Method” : ME technique• Likelihood vs. mt per event from LO ME for ttl+4j and

“transfer functions” for quark ET jet ET

– 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)

mt 177.8 5.04.5(stat) 6.2(syst) GeV


Template Technique• Determine mass of the top quark using a quantity strongly dependent on the

top quark mass Mtop (usually Reconstructed Mtop)

• Determine the Reconstructed Mtop 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 Mtop from data with same from randomly generated and simulated signal at various input top mass (Mtop) and backgrounds using an unbinned likelihood fit

Signal Template Background TemplateData

L = Lshape x Lbackground

Best signal + background templates to fit the data


Newest Template Result

M top 173.5 2.62.7(stat) 2.5(JES) 1.7(sys) GeV/c2

Combined –Log(L)

Expected error

NEW


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

mt 168.1 9.811.0(stat) 8.6 (syst) GeV

mt 174.8 7.77.1(stat) 6.5(syst) GeV

mt 179.6 6.36.4 (stat) 6.8(syst) GeV


Best Mtop Measurements

error bars: red=stat blue=total


Single Top Search

• Direct measurement of |Vtb|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

2~ tbV

pb07.088.0 NLOt

pb21.098.1 NLOt


Single top

MC Templates

s95%CL 13.6 pb

t95%CL 10.1 pb

st95%CL 17.8 pb


W HelicitySM (V-A) prediction:tWT : left handed W (30%)

tW0 : longitudinal W (70%)

F0 (t W0b)

(t W0b) (t WTb)

1

1 2(mW /mt )2 0.70

Kinematic distributions for the different helicity states are different

SM: 0.3+0.7+0

left handed

1

41 cos* 2

longitudinal

1

21 cos2 *

right handed

1

41 cos* 2

t

W+

l+* Lepton Pt

test of V-A tWb vertex


W Helicity

F0 0.27 0.240.35(stat) 0.17(sys)

dilepton and lepton+jets

F0 0.88 @ 95% CL

F0 0.89 0.340.30(stat) 0.17(sys)

lepton+jets

F0 0.25 @ 95% CL


Search for H+

BR(t Hb) 0.7 @ 95% CL

(for 80 < M H 150 GeV)

ttSM (th)

(t Wb t Hb)

N expected vs N obs

L(m,BR(t Hb),BR(H cs ,Wbb ))


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)


Other Top Measurements

Measurement Result

162

126

193

193

109 (runI)

~300

BR(t Wb) /BR(t Wq)

dilepton / l jets

1.45 0.550.83

0.62 @ 95% CL

BR(t b) /BRSM(t b)

5.0 @ 95% CL

Search for Anomalous Kinematics

dilepton low Pt excess

consistency with SM 1 - 4 %

V A in tWb

fV A 0.61

f 0.18

@ 95% CL

Ldt (pb 1)

Search for tt resonances

in progress


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, 142001 (2004)• “Search for Electroweak Single Top Quark Production in p anti-p Collisions at S**(1/2)=1.96 TeV”,

Phys. Rev. D 71, 012005 (2005)• “Measurement of the W Boson Polarization in Top Decay at CDF at S**(1/2)=1.8 TeV”, Phys. Rev.

D71, 031101(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/0409029• “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/0410041• “Search for Anomalous Kinematics in t anti-t Dilepton Events at CDF II”, hep-ex/0412042

– 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– F0 reduced uncertainty (now 50-100%)– Mass limit on t’


Backup Slides


Template Result from CDF–Log Likelihood vs Mtop, JES

Mtop (GeV)JE

S(

)

Mtop 173.5 3.63.7(stat JES) 1.7(syst) GeV/c2 173.5 4.0

4.1GeV/c 2

Source Mtop(GeV/c2)

B-jets modeling 0.6

Method 0.5

ISR 0.4

FSR 0.6

Background shape 1.1

PDF 0.3

Other MC modeling 0.4

Total 1.7

Measurement is more precise than the current world average!

Systematic uncertainties

Most of these can be reduced with more data


SM quick reviewSM quark and lepton lagrangian

RRLR duQeL

fermions DiL,, ,,

Predicts all experimental

observations of quark and leptoninteractions

aa

ii

GigWigBY

igD 222 321

Covariant derivative fixed by gauge invariance under U(1)xSU(2)xSU(3) transformations:

221

22

012

L

L

Ygg

WYgBgA

Defining:

221

22

021

L

L

Ygg

WgBYgZ

22

21

1singg

gw

22

21

2cosgg

gw

L eQ f ( f f )A g2

coswf ,e,u,d

f L fL (I f

3 Qf sin2 w ) f R fR ( Qf sin2 w ) Zf

g2

2(u L

dL eLeL )W

h.c. color terms

22

21

21

gg

gge

2/)(; 2130 iWWWWW


W Helicity from lepton Pt

F0 0.88 0.470.12(total)

F0 0.24 @ 95% CL

F0 0.52 @ 95% CL

l + jets

dilepton


Publishing Mtop for 15 years


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!


Mass: D0 RunI

mt = 180.1 3.6(stat) 3.9(syst) GeV/c2

• Statistical uncertainty reduced: 5.6 to 3.6 GeV/c2

– Equivalent to Lx2.4 !

• Likelihood vs. mt for each event:

P(x,mt ) 1

(mt )d (x,mt )dq1 dq2 f (q1) f (q2)W (x, y)Phase space x

LO ME for top or BG (W+4j)

PDFs Probability for observable x

given parton y(Ex: quark ET

jet ET)

• Likelihood gives effective weigh to each event

• Maximize combined likelihood to extract mt


Template Results from D• Topological

– No b-tagging requirement

• Construct a discriminant using topological variables (DLB) to improve S/B

• At least one b-tagged jet:– no requirement on

discriminant DLB

• First top mass at D top mass measurement with b-tagging

ttbar candidates 69 S/B~3/1

ttbar candidates 94S/B~1/1

Reconstructed Mtop (GeV)

Reconstructed Mtop (GeV)

M top 173.5 5.8(stat) 7.17.8(syst) GeV/c2

M top 170.6 4.2(stat) 6.0(syst) GeV/c2


Other Matrix Element based Mtop

• 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 DLB discriminant in likelihood fit

• Uses background probability

M top 177.8 5.04.5 (stat) 6.2(syst) GeV/c2

M top 177.5 5.8(stat) 7.1(syst) GeV/c2


Implications for MHiggs

• New combined D0 mass:– Mt = 179.0 ± 5.1 GeV/c2

• New World Average:– Mt = 178.0 ± 4.3 GeV/c2

• Global EW fit using new average– LEPEWWG method (hep-ex 0312023)– Best-fit MH 113 GeV/c2

– Upper limit @ 95% C.L. : 237 GeV/c2

Yellow region excluded (direct search): MH < 114.4 GeV/c2 @95% CL


Futuro: LHC

2/s

mx t Tevatron: x~0.18

LHC: x~0.025

TeV14sTeV96.1 s

pb8307:)( tt

12343332 scm101010: L

0.8 to 8 ttbar/sec

¡Una verdadera fábrica de top!

1 año a baja luminosidad: 10 fb-1: 8x106 sucesos ttbar


CMS y ATLAS

Detectores multi-propósitoadaptados al acelerador LHC:Electrónica rápidaAlta granularidadBuena resoluciónBuena identificación de jets,muones, missing Et, vértices desplazados, trazas


Masa del top en el LHC

Combinando todos los canales: m ~1 GeV

j1j2

b-jett

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

j1

j2

b-jet

t


Resonancias

1.6 TeV resonance

Mtt

Reconstrucción de Mtt para búsqueda de resonancias

SM Higgs (BR smaller with respect to the WW and ZZ decays)

MSSM Higgs (H/A, if mH,mA>2mtop, BR(H/A→tt)≈100% for tanβ≈1)

Otros modelos: Technicolor, strong ElectroWeak Symmetry Breaking, Topcolor, “colorons”, …


Single top en LHC

fusión Wg: 245±27 pbS.Willenbrock et al., Phys.Rev.D56, 5919

Wt: 62.2 pbA.Belyaev, E.Boos, Phys.Rev.D63, 034012

W* 10.2±0.7 pbM.Smith et al., Phys.Rev.D54, 6696

1) Determinación del vértice tWb: Vtb

2) Medición independiente de la masa

3) Polarización del top

Mecanismos de producción:

Proceso Vtb (stat) Vtb (theory)

Wg fusion

0.4% 6%

Wt 1.4% 6%

W* 2.7% 5%

Proceso Señal Fondo S/B

Wg fusion

27k 8.5k 3.1

Wt 6.8k 30k 0.22

W* 1.1k 2.4k 0.46

Con 30 fb-1: determinación de cada proceso por separado


FCNC en desintegraciones de top

•Desintegraciones de FCNC suprimidas (Br<10-13-10-10) en SM

t Zq (CDF Br<0.137, ALEPH Br<17%, OPAL Br<13.7%)

– ttWb + Zq con W l o jj y Z l+l-

– Reconstruir t Zq (l+l-)j– Sensibilidad a Br(t Zq) = 1.1 X 10-4 (100 fb-1)

t q (CDF Br<0.032) – tt Wb + q con W l – Sensibilidad a Br(t q) = 1.0 X 10-4 (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 10-3 (100 fb-1)


Top más allá del SMEn teorías SUSY+GUT, Mtop causa EWSB:

GeV175si0)(ln)()( 2222

tWh

GUTthGUTh mMM

Q

MmQMMM

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

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

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