Selected Topics from the Tevatron

Nigel Lockyer

University of Pennsylvania

Ettore Majorana, Erice, September 2, 2006

CDF

A CDF Perspective

Topics To Be Covered

• “Primer” Tevatron--CDF--D0

• Jet Production

• Top

-cross section

-precision mass

• Bs oscillation frequency

• Searches

-Susy (tri-leptons)

-Signature based

-Extra dimensions

-Higgs (low mass SM)7x103

Events/fb-1

300Higgs

“Primer”

Accelerator Complex and Delivered Luminosity

Peak Luminosity 1.8 x 1032 cm-2 sec-1

Electron Cooling in Recycler a success

3 top per week

Goal ~ 4 x1032

Pbars Needed!

Recorded 1.3 fb-1

Slightly above base now

20 mA/hr at zero current

CDF and D0 have

Similar Amounts of Data

CDF

MUONS

ELECTRONS

1 inch

diameter

CDF Detector

L1 trigger

L2 trigger

L3 farm

disk/tape

42 L1

buffers

4 L2

buffers

1.7 MHz crossing rate

40kHz L1 accept

1 kHz L2 accept

100 Hz L3 accept

Hardware tracking for pT 1.5 GeV

Muon-track matching

Electron-track matching

Missing ET, sum-ET

Silicon tracking

Dedicated

hardware

Hardware +

Linux PC's

Linux farm (200)

2.4 THz

Jet finding

Full event reconstruction

Refined electron/photon finding

The trigger is critical at hadron colliders

DØ trigger:L1: 1.6 kHzL2: 800 HzL3: 100 Hz40-80 MB/s

Very Different Approaches by CDF and D0 CDF triggers onB mesons at L1

Both experiments write about 100 Hz to tape- offline cost driven

Typical CDF Triggers and their Usage• Unprescaled triggers for primary

physics goals (>150 trigger paths)

• Examples:– Inclusive electrons, muons pT>18 GeV:

• W, Z, top, WH, single top, SUSY, Z’

– Dileptons, pT>4 GeV:

• SUSY

– Lepton+ , pT>8 GeV:

• MSSM Higgs, SUSY, Z

• Also have +MET: W->

– Jets, ET>100 GeV

• Jet cross section, Mono-jet search

• Lepton and b-jet fake rates

– Photons, ET>25 GeV:

• Photon cross sections, Jet energy

scale

• Searches (GMSB SUSY)

– Missing ET>45 GeV

• SUSY

• ZH-> bb

• Dynamic Prescale triggers because:– Not possible to keep at highest luminosity

– Needed for monitoring

– Prescales depend often on Lumi

• Examples:– Jets at ET>20, 50, 70 GeV

– Inclusive leptons >8 GeV

– B-physics triggers

– Backup triggers for any threshold, e.g. Met,jet ET, etc.

CDF

An Unfortunate reality: CS vs lum

Complex trigger strategies necessary: Table n is from n-1 etc. Incremental

Complex Collisions to Untangle—LHC worse

Proton AntiProton

“Hard” Scattering

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event Underlying Event

Initial-State

Radiation

Final-State

Radiation

Multiple collisions (Tevatron several—LHC 20+)

Lose forward going particles down beamline

Valence quarks:

Gluons

Sea quarks

Exact mixture depends on:

Q2: ~(M2+pT2)

X: fractional momentum carried by parton

W Charge

Asymmetry

CDF

Effect of quark PDF’s easy to see

Strong Interaction

Central Jets Probe Quark Sub-Structure

Probe Q2~O(106) GeV2

No evidence of structure

0.1<| jet|<0.7

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

100

101

102

103

104

105

106

107

108

109

fixed

targetHERA

x1,2

= (M/1.96 TeV) exp(±y)

Q = M

Tevatron parton kinematics

M = 10 GeV

M = 100 GeV

M = 1 TeV

422 04y =

Q2

(G

eV2

)

x

Bs Mixing

Mission Accomplished

The Measurement Principle

vertexing (same) side

“opposite” side

• reconstruct Bs decays----decay flavor from decay products

• infer Bs production flavor (production flavor tagging)

• measure proper time of the b-quark decay (very precisely)

e,μ

CDF-II Upgraded for Bs Mixing

• multi-purpose detector

• excellent momentumresolution (p)/p<0.1%

• Yield:

– SVT based trigger

• Tagging power (SSKT)

– TOF, dE/dX in COT

• Proper time resolution:

– SVXII, L00 (not in

trigger)

– SVX-III deadtimeless

Triggering On Displaced Tracks Critical

trigger Bs ->Ds- , Bs -> Ds

- l+

trigger extracts 20 TB /sec

“unusual” trigger requirement:

two displaced tracks: (pT > 2 GeV/c, 120 μm<|d0|<1mm)

Primary Vertex

Secondary Vertex

d0 = impact parameter

B

Lxy

Luciano Ristori Pisa

A first

Bs Mixing Basics

• Neutral B Meson system

• mixture of two states (No CPviolation case):

• BH and BL may havedifferent mass and decaywidth– m = MH – ML

(>0 by definition)

– = H - L

• The case of = 0

( )

( )BBB

BBB

L

H

=

+=

2

1

2

1

Measurement .. In a Perfect World

what about detector effects?

“Rig

ht S

ign”

“Wro

ng S

ign”

Realistic Effects

flavor tagging power,background

displacementresolution

momentumresolution

mis-tag rate 40% (L) ~ 50 μm (p)/p = 5%

Amplitude

• Oscillatory factor in pdf

+/- is flavor at production versus decay

A is amplitude of oscillation and A=1 for signal and A=0 background

D is event dilution (epsilon D^2 is about 5%)

A=1 for real signal

Width will be proportional to B lifetime

( )( )1 cosDA mt+tL

fixed value of ms, fit for Amplitude

repeat for different values of m

if a signal is found, fit for mixing frequency!

Amplitude Scanning

Signal Yield Summary: Hadronic

high statistics light B meson samples: B+ ( D0 ): 26k events B0 ( D- ): 22k events

3700Total

200Bs-> Ds3 (K*K)

500Bs-> Ds3 ( )

600Bs-> Ds (3 )

800Bs-> Ds (K* K)

1600Bs-> Ds ( )

Yield oscill. fit range

Same Side Kaon Tags

• exploit b quark fragmentation

signatures in event

• B0/B+ likely to have a -/ nearby

• Bs0 likely to have a K+

• use TOF and COT dE/dX info. to

separate pions from kaons

• problem: calibration using only B0

mixing will not work

• tune Monte Carlo simulation to

reproduce B0, B- distributions,

then apply directly to Bs0

Bs – Sufficient Proper Time Resolution

osc. period at ms = 18 ps-1

• Period=.33 ps~100 μ

• resolution ~ 26 μm

D0 Amplitude Scan

P-value=5%

CDF Amplitude Scan

Prob. of stat. fluctuation: 0.2%ms=17.31+0.33±0.07 ps-1

|Vtd/Vts|=0.208+0.001(exp) +0.008 (th.)

Big Improvement

ms measurement:

Impact on Unitarity Triangle

Experimental precision on unitarity triangle greatlyimproved => the triangle still closes!

Top Physics

Why Is the Top Quark Interesting?

• Heaviest known fundamental particle

• Is this large mass telling us somethingabout electroweak symmetry breaking?

• Related to mW and mH :

– mW~Mtop2

– mW~ln(mH)

• If there are new particles the relationmight change:

– Precision measurement of topquark and W boson mass canreveal new physics

• Precision measurements of mass,couplings, charge, spin, helicity ofW…?

MW = 80.404 ± 0.030 GeV/c2

Mtop = 172.5 ± 2.3 GeV/c2

Top Production and Decay

Top production bystrong interaction

85% quark annihilation

15% gluon fusion

Final state complex

Weak decay of W-boson

Br(t bW)=100% , Br(W->lv)=1/9=11%

dilepton (4/81) 2 leptons + 2 jets + missing ET

lepton+jets (24/81) 1 lepton + 4 jets + missing ET

fully hadronic (36/81) 6 jets

Gluon radiation ISR and FSR adds more jets

t

t g

g g g

q t

t q

Tagging (not mis-tagging) b-jets is Critical

• Exploit large lifetime of the b-hadron

• reconstruct primary vertex: μm resolution ~ 30

• Form Lxy: transverse decay distance projected onto jetaxis:

– Lxy>0: b-tag along the jet direction => real b-tag ormistag

– Lxy<0: b-tag opposite to jet direction => mistag!

• Significance: Lxy >7 (Lxy) i.e. 7 sigma

Want this high Want this low

Top hadronic cross section

• NN discriminates between top andmulti-jet backgrounds

• Control in pretag sample and 4-and 5-jet bins

• Dominant syst. Uncertainty: JES

L=1 fb-1

6 jets+

Top Quark Cross section: Lepton + Jets

• Select:

– 1 electron or muon

– Large missing ET

– 1 or 2 b-tagged jets

Top Signal(tt) = 8.2 ± 0.6 (stat) ± 1.1 (syst) pb

Single tag result (OK with SM)

45 double-taggedEvents, nearly no background

b-jets lepton

missing ET

jets

Check

backgrounds

Summary of top cross sectionsCDF

Cross sections consistent across decay modes—agree with SM

Top Mass: All-jets Final State

• Background control critical:– Signal/Background=1/2

– Background checked in background richregions

• Templates used for the signal andbackground shapes

mtop=174.0 ± 2.2 (stat.) ±4.8 (syst.) GeV/c2

772 events Background control0.4<NN<0.6

P(mt; x) = d |Mtt(x,mt)|2 W(x)res.

LO Matrix Elementfor tt production

Parametrization of jet energy resolution from MC

Jet

En

ergy

Parton Energy

For each event x, form probability as function of top massmt by integrating over all unmeasured quantities:

Top Mass--Matrix Element Method

Use knowledge of top event kinematics to weight “top-like”

X: measured quantities (angles, momenta..)

Integrate over phase space (pdfs)

Top mass: Lepton + Jets(4)• Matrix-Element method

– 1 b-tag => Signal/Background=4/1

– Add jet energy scale as 2nd unknown

and fit for it:

• JES=0.99±0.02

– Constrain 2 untagged jets to

W mass (apply to b-jets also)

166 events

mtop=170.9±2.2 (stat.+JES)±1.4 (syst.)

GeV/c2

mtop=170.9±2.6 GeV/c2

Single Best To Mass Measurement

Top Mass: Dilepton Final State

• Improved matrix-element

method:

– 0 b-tag: Signal/Background=3/2

– 1 b-tag: Signal/Background=30/1

– New: Measure recoil (pT of ttbar

system) and include this

information

• A priori uncertainty improved by

10%

mtop=164.5±3.9 (stat.) ±3.9 (syst.) GeV/c2

with b-tagging: mtop=167.3±4.6 (stat.) ±3.8 (syst.)

78 events

Top Mass: Combined Result

CDF mtop=170.9 ± 2.4 GeV/c2CDF and D0 best (last updated 07/26/2006

CDF

Z b bar Enriched Sample from Trigger

Top Mass: Future

Goal: Understand b-jets

Searches

• SUSY

• Signature searches

• Extra Dimensions

• Low Mass Higgs

Supersymmetry

particle

superparticle

WMAP

Most SUSY models predict the

sparticle spectrum accessible at

TEV scale. Tevatron would be able

to discover SUSY

mSUGRA (Minimal SuperGravity)

• Gravity breaks SUSY

• Model with 5 parameters

• Masses m1/2, m0

• Coupling A0

• Higgs sector:

sgn(μ), tan

• New parity Rp is conserved

• Rp = +1 for SM particle

• Rp = -1 for SUSY particle

SUSY is (by observation) a broken symmetry

Log10Q (GeV)

Ru

nn

ing

Ma

ss

(G

eV

)

Chargino Neutralino--Golden Mode at TeV

μe

MET μ

Simulated SUSY event

Signature: Three leptons and Missing Energy in the Transverse plane

W,H,B mix into charginos and neutralinos ( ) --- 10 is the LSP

R-parity conserved LSP stable dark matter candidate

~ ~ ~

~ ~

Chargino Neutralino Search

Wide pT range

Soft leptons more difficult

20,10

15, 5, 4

5, 5, 5

20, 5,5

20, 5, 5

20, 5, 5

p/ET’s

(GeV/c)

μe

ee

LS μ±μ±, e±e±,

μ±e±

μμ

ee

μμ

CHANNEL

• Acceptance (three leptons difficult)

• achieved using different trigger paths

pT (GeV/c)

Leading

Third

Next to Leading

e/μ

tan

Bra

nch

ing

Fra

ctio

n

Need good mSUGRA parameter

space coverage use third lepton

CDF Results !!!

DataSMChannel

LS

ee + track

μμ + l

ee + l

μe + l

μμ + l

6.8 ± 0.5 ± 1.0

0.72 ± 0.04 ± 0.05

0.13 ± 0.03 ± 0.03

0.17 ± 0.03 ± 0.04

0.8 ± 0.1 ± 0.2

0.6 ± 0.1 ± 0.1

9

1

0

0

0

1

MET (GeV)

D0 Chargino Mass Limit

Systematic uncertainties have negligible impact---Need more statistics!

Chargino mass limit of 140 GeV

With ~ 8 fb-1, sensitive up to Chargino mass ~ 240 GeV/c2 Covers ILC Mass Range

Sneutrino Decay with R-parity violation

• Sneutrino: neutral, scalar, superpartnerof SM tau neutrino

• R-parity violating production & decay

• Lepton flavor violating decay• Final State:

– High PT muon & electron

– No MET requirement (can extend for leptonic tau decays)

• this analysis is also sensitive to the Lepton Flavor Violating decays ofnew gauge boson Z’ into eμ predicted by the Models with U(1)’ gaugesymmetry.

Increasing Interest In Flavor Violating Decays

Signature based search eμ

Excellent experimental signature—very clean

R-Parity Violating Couplings

SLB

PR

2)(3)1( +=

decay) (proton 0"or '

violating# baryon :"

violating# lepton:',

RPVof strength control ",',

=

• RP is assumed in most

SUSY models

– Not a fundamentalsymmetry

– Motivated by CDM, proton

lifetime

• With RPV, most SUSY

models do not provide dark

matter candidate

– Other source required?

R-parity Violating Couplings

Backgrounds

Standard Procedure to define a control region and predict the number ofevents in that region from data and Monte Carlo

In this case, good understanding of event yields versus pair mass

Results

Limit on sneutrino cross section x Br = 530 GeV/c2 at 95% CL

Large Extra Dimensions

• Extra Spatial Dimensions could

solve the hierarchy problem:

– Effective Planck scale is

lowered

• Good signature:

– Monojet = 1 jet + missing ET

– Main background Z+jet

+jet measured from data

• No evidence for Extra Dimensions

CDF has world’s best sensitivity for >3 dimensions

Search for High Mass Diphotons• Resonance in diphoton mass spectrum?

– E.g. predicted in Randall-Sundrum model:

• alternative ED model to solve the

hierarchy problem

• predicts and ee resonances

M>875 GeV for k/MPl=0.1

Model-Independent Searches

• New searches for anomalousproduction of:– W’s and Z’ at high HT

– Anomalous ZZ

– Diphotons+X (X= …more to come)

• A spectacular event at HT~900 GeV

Higgs Boson Searches at Tevatron

CDF & D0 mounting increasinglylarge efforts

Focus here on low mass Higgs

– Preferred by electroweakprecision measurements

– Main analysis modes:

• WH l bb

• ZH (ll)bb

• H WW* b-jets

Precision EWK fit assuming SM:

M

H= 89

30

+42GeV/c 2

MH < 175 GeV/c2 95%CL

including LEP-2 MH>114.4 GeV/c2 @95C.L.

MH < 207 GeV/c2 95% CL

(pb)

e/μ

b jet

b jet

SM Higgs Production and Decay

Search strategy:

MH <135 GeV: associated production WH and ZH with H bb decay

Backgrounds: Wbb (CDF just measured), Zbb, top, WZ (must see) ,QCD

MH >135 GeV: gg H production with decay to WW* Backgrounds: WW, DY, W/ZZ, tt, tW,

Higgs: ZH bb

• Signature:

– 2 b-jets + missing ET

• Many improvements lead to

effective luminosity gain of

(S/ B)2=6.3

– Improved lepton veto

– Separate single and double b-tags

– Include WH as signal

– Use fit to dijet mass spectrum

• Plus inclusion of full data

luminosity:

– No evidence for deviation from

background

Exp. Limit / SM rate=14.2 (at mH=115GeV)

Higgs: WH l bb

• Lepton, missing ET and 2 jets:

– One or two b-tags

• New since last year:

– NN b-tagger

– Include double-tag

– Include full 1 fb-1 dataset

– Luminosity equivalent gain:

• (S/ B)2=1.252=1.6

e/μ

b jet

b jet

Exp. Limit / SM rate=23.0 (at mH=115 GeV)

Search for H WW* l l

) (rad)μ (e, φ Δ0 0.5 1 1.5 2 2.5 3

-210

-110

1

10

HIGGS MASS 160 GEV (After Cuts 1-7) data

ττ →Z

QCD fakes

W W

ν l→W

μ e→tt

μμ →Z

WZ/ZZ

160 GeV Higgs (x10)

HIGGS MASS 160 GEV (After Cuts 1-7)

Higgs mass (GeV)100 120 140 160 180 200

) (p

b)

(*)

WW

→B

R(H

×σ

-110

1

10

210

Ex

clu

de

d a

t L

EP

Standard Model

4th Generation Model

νμν, eνeνe→(*)

WW→H

95% CL LimitExpectedObserved

-1 ~950 pbDØ Run II Preliminary,

Higgs mass (GeV)100 120 140 160 180 200

) (p

b)

(*)

WW

→B

R(H

×σ

-110

1

10

21095% C.L. limits4th Generation

Model starts to beexcluded

10x 160 GeV Higgs

All CDF and DØresults nowcombined for the

first time

Combined CDF & D0 Ratio wrt SM

Luminosity equivalent=(S/ B)2

14.426.617.8All combined

2.02.02.0CDF+DØ combination

7.213.38.9Product of above

1.02.71.0WH signal in ZH

1.01.751.75NN selection

1.61.01.4Track-only leptons

1.61.01.3Forward leptons

1.11.11.1Forward b-tag

1.51.51.5Continuous b-tag(NN)

1.71.71.7mass resolution

ZH->llbbZH->vvbb

WH->lvbb

Improvement

100 105 110 115 120 125 130 135 140

1

10

SUSY/Higgs Workshop ('98-'99)

discoveryσ5 evidenceσ3

95% CL exclusion

mH (GeV)

Higgs Sensitivity Study ('03)

statistical power only

(no systematics)

inte

gra

ted

lu

min

os

ity

(fb

-1/e

xp

.)

PRELIMINARYProspects Compelling

Expect to exceedLEP limit

with about 2 fb-1

D0 Neural Net b-jet Tagger

increase efficiency by 30%

or purity by 30%

Summary Conclusion

• Both CDF and D0 running well

• D0 upgraded to improve b-tagging (Higgs)

• Significant prospects for major discovery

at Tevatron in next 2-3 years

• Luminosity and high efficiency detectors

• Areas to watch: SUSY, low mass Higgs