Recent results from D0 · Recent results from D0 and CDF Paul de Jong And he seemed to suggest that...

transcript

Recent results

First D0 run II papers have been submitted to and accepted by PRL.Overall some 10 papers in pipeline for submission soon.

Today: some selected recent results from D0 and CDF on:

Electroweak bosons

Heavy B mesons

QCD: Jet production and b-jet production

Top quarks

Higgs searches: understanding backgrounds.

By no means complete: see CDF and D0 web pages11

Searches

I intend not to cover searches for new physics.

Not because it is not interesting,or because Tevatron would not besensitive, but because of lack of time.

Searches for SUSY, leptoquarks,Z’, extra dimensions, … are beingdone.

Limits have been set, significantlyimproving on run 1.

Collider physics

Doing hadron collider physics is likepanning for gold

in the Amazon river(and leaving no water unchecked…)

Trigger is crucial for physics

High pT leptons

Missing ET

Displaced tracks (b,c)

“Easy”

“Hard”

Electroweak bosons

W and Z bosons are the standard candles of hadron collider experiments!

Yesterday’s sensationToday’s calibrationBackground to Higgs, SUSY, …

Electroweak bosons

LEP experiments (and LEP energy group!) have measured Z mass and width.

Use for lepton energy calibration, together with J/ψ and ϒAlso: resolution and efficiency studies

Z à ee

Z à µµ

Electroweak bosons

Cross sections: very careful study of efficiencies

à trigger efficienciesà reconstruction and object IDà trackingà selection

And backgrounds…

Luminosity measured with scintillator counters àtotal inelastic cross section

CDF and D0 now agree on value of σinel(not so in run 1…)

6.5% uncertainty

Get everything from data;MC used only for acceptance

Tau reconstruction

Most difficult channel: Z à ττ (àµνν + hadrons + ν)

Discriminating variables on tau shower shape and track properties are usedin a neural network.Backgrounds estimated from data: mistags (same-signs vs opposite signs),

W à µν + jets,Z à µµ

Tau reconstruction capability important for H à ττ search 17

Good agreementwith MC, also onother variables

Electroweak bosons

Cross sections can now also be computed reliably, up to NNLO:

à A handle on luminosity measurement

W Mass

The mass of the W boson is an important Standard Model parameter.

CDF and D0 in Run 1

W à eν and W à µν provide clean final states.

Crucial element: lepton and missing ET energy scale

Statistics is huge:one expt, one finalstate, 150 pb-1 equalsfull LEP 2 sample.

Plot transverse mass:)cos1(22 νν ϕ l

TlTT EEM −=

W mass outlook

CDF and D0 have worked on the systematics, no mass result yet…

Expect CDF result quite soon (Wàµν, 200 pb-1, stat error 50 MeV, syst 70 ?)D0 by next summer

Goal: 40 MeV total accuracy per experiment for 2 fb-1

Improvement “for free”

Needs work…

(example: good descriptionof detector materialin MC crucial forelectron scale…)

W Width

Can measure W width by two methods:

Direct: tail of MT

D0, 177 pb-1 , W à eν: ΓW = 2.01 ± 0.09 ± 0.11 GeV

Indirect: use W/Z cross section ratio

CDF indirect:ΓW = 2.079 ± 0.041 GeV

(SM: 2.092 ± 0.002 GeV)22

As accurate as bestmeasurement to date

Most accurate measurement to date

W charge asymmetry

W/Z summary

Di-boson production:-gauge couplings-backgrounds to

top/Higgs/SUSY

B physics

Heavy B mesons

At the Tevatron, all kinds of B mesons are (copiously) produced: σ(bb) ~ 100 µb

Trigger: D0 relies on muon trigger (good rapidity coverage: good yields)CDF: muon trigger and displaced track trigger

Level 1: very fast trackingLevel 2: add silicon hits to recognize displaced tracks

with high impact parameters

Has revolutionized CDF’s charm and bottom physics program

D0 is commissioning such a trigger, but with emphasis on high pTphysics (top, Higgs, …)

Today: selection of B-physics results: BC, ∆Γ(BS) 26

BC first seen by CDF (1998), 20 events above bg, M = 6.4 ± 0.4 GeVOPAL (1998) saw 2 events, 0.6 ± 0.2 bg

D0: 210 pb-1 used. Look for BC à J/ψµX à µµµXBackground control sample: J/ψ + 1 track

Observe 95 ± 16 candidates(first 5σ observation)

M = 5.95 ± 0.14 ± 0.34 GeV

τ = 0.45 +0.12-0.10 ± 0.12 ps

BackgroundFeed down ψ(2S)Signal modelingMomentum binning

Bs lifetime

The Bs and the Bs-bar mix to 2 eigenstates with definite mass and width:∆m = mH – mL > 0, ∆Γ = ΓL - ΓH > 0 (H: heavy; L: light)

∆m governs oscillation frequency; ∆Γ≠0 implies different lifetimes.

The two states are also very nearly CP-eigenstates: L CP-even, H CP-odd.

In Bsà J/ψφ à µµKK the two states can be separated by looking atdecay amplitudes of different polarization states à angular distributions

Theory: ∆Γ/Γ = 0.12 ± 0.05

PDG: ∆Γ/Γ < 0.54 at 95% CL leaving Bs lifetime free (DELPHI, ALEPH,L3)< 0.23 at 95% CL if Bs width equals Bd width

HQET: true to within ~1%(PDG: true to within ~4%)

τs/τd = 0.98 ± 0.07 (D0) (220 pb-1, 337 signal events)0.89 ± 0.07 (CDF) (240 pb-1, 256 signal events)

Run 2 Measurement: (τd from J/ψK*):

Bs lifetime

CDF result: ∆Γ/Γ = 0.65 +0.25-0.33

( Γs free)

0.71 +0.24-0.28

( Γs = Γd)

Compatibility with ∆Γ/Γ=0 is 0.3%, compatibility with ∆Γ/Γ=0.12 is 1.2%

Would correspond to ∆mS = 125 +69-55 ps-1

(CKM fit: 18.3 ± 1.6 ps-1)

D0 will have a number soon.(It will be smaller than CDF’s, but for both expts errors are still sizable)

CDF do a multidimensional fitto mass, lifetime and angles

Surprise!very fast Bs oscillations!

Main Interest:

• Very high ET jets: anysigns of quark substructure?Resonances?

• Tevatron gives input to PDFfits in unique region ofx and Q2

• Heavy quark production:just standard model ornew physics?

(Further: diffraction and studies of underlying event models)31

Jet energy scale

The hard part: jet energy scale (cone jets used)

Ejet = (Emeasured – offset)/(response x out-of-cone-correction)

NoiseUnderlying eventOther interactions

Calorimeter property

Showers havefinite size

minimum-bias events

photon+jet events

energy in cones+ MC correction

Often a dominating systematic error

W/Z à jets?

Jet production

Fattest event:jet pT = 616 GeVjet-jet mass

= 1206 GeV

Di-jet mass:

Jet production

CDFDØØ

Data/theory

B-quark production

Run 1 results on b-quark production were a surprise:σ(data) >> σ(NLO QCD)

Experiment wrong?

Theory predictionincomplete?

New physics?

b-quarks

B+ mesons

Theory developments beyond NLO calculations:• MC@NLO: match to parton shower Monte Carlo’s• FONLL: resummed logarithms beyond fixed order calc.• be very very careful in unfolding/manipulating data…

Have brought data and theory in better agreement.But data statistics will improve a lot in run 2…

Stefano Frixionetalked about thishere in March

B-quark production

Recent CDF Run 2 result:

Select J/ψ à µµ10-40% are from B decay, look at J/ψ

production vertex

Data and theory agree very well(But theory error needs to decrease!)

MC like PYTHIA has LO ME for FCR

Other production mechanisms hidden in PS

GSP FEX

Disentangle and try to tune PYTHIA36

Top quarks

Top quark production

(Also single top production through electroweak processesHowever: cross section ~1 pb, larger backgrounds,

will need >1 fb-1 to observe)38

Why are the cross sectionsfor backgrounds at theLHC 10 times larger thanat the Tevatron,but the cross section fortop production 100 times?

It’s all about x…(and the gluon pdf)àYou need partons with

a certain x

Top quark is on the heavyside for Tevatron…

Still, we get 100 t pairs/week

2 leptons, 2 b-jetsmissing ET11% of events

6 jets (of which2 are b-jets)

45% of events

1 lepton, missing ET4 jets (of which 2 b)15% e + jets15% µ + jets15% τ + jets

Leptons + jets:- topological variables- b-tags

All hadronic top decays: (at least) 6 jets!

Backgrounds from QCD multijet production

Analysis uses topological variablesand b-tagging in a neural network

2-leptons: clean butsmall statistics

1 b-tag 2 b-tags

Most difficult decay channel:

Most powerful decay ch.

Cross section measured to 25% accuracy

42Agrees with NNLO-NNLL prediction

CDF, 162 pb-1: F0 = 0.89 +0.30-0.34 ± 0.17

Top quark decay properties

Test of V-A coupling in top decays: in SM W couples only to LH particlesThis together with angular momentum conservation allows top to decay into LH(negative helicity) or longitudinally-polarized (0 helicity) W bosons

In SM F-=0.30, F0 =0.70, F+ =0

Helicity of W manifests itself indecay product kinematics

D0, 160 pb-1: F+ < 0.24 @ 90% CL

Assuming three-generation CKM matrix unitarity, |Vtb|~1.0

R = BR(t→Wb)/BR(t→Wq) ~1.0

Can measure ratio by checking the b quark content of the top sample decay products

CDF: R = 1.11 ± 0.20 (>0.62 @ 95% CL) D0: R = 0.65 ± 0.32 ± 0.14 43

Is the particle we observe reallythe Standard Model top quark?

Top quark decay properties

Test of V-A coupling in top decays: in SM W couples only to LH particlesThis together with angular momentum conservation allows top to decay into LH(negative helicity) or longitudinally-polarized (0 helicity) W bosons

In SM F-=0.30, F0 =0.70, F+ =0

Helicity of W manifests itself indecay product kinematics

CDF, 162 pb-1: F0 = 0.89 +0.30-0.34 ± 0.17 D0, 160 pb-1: F+ < 0.24 @ 90% CL

Assuming three-generation CKM matrix unitarity, |Vtb|~1.0

R = BR(t→Wb)/BR(t→Wq) ~1.0

Can measure ratio by checking the b quark content of the top sample decay products

CDF: R = 1.11 ± 0.20 (>0.62 @ 95% CL) D0: R = 0.65 ± 0.32 ± 0.14 43

Top quark mass

Run 1 only:

New in 2004 !

Matrix ElementMethod

Fundamental SM parameterTop mass together with EW data constrain Higgs mass

Top quark mass

Using Run I l+jets events (125 pb-1) DØØ developed the “matrix element method”

Detailed knowledge of top quark decay and detector response is required à event by event likelihood calculated vs mt

Phase space x LO ME PDFs Probability for observable x when y was produced (Ex: quark ET → jet ET)

stat. error5.6 à 3.6 GeV

syst. error5.5 à 3.9 GeV

Top quark mass

Run 2 only:

} Methods are close to theMatrix Element Method

Systematic error (mainly jet energy scale)

is becoming limiting accuracy factor

Top quark mass

Outlook:

Jet energy scale: W constraint helps for light jetsb-quark jets? Look for Z à bb

Stated goal for run 2 is 2.5 GeV per experiment.

Needs appropriate trigger. Trying to improve current triggers and use displaced track trigger.

The road to the Higgs…

Higgs search

If nature has indeed used the Higgs mechanism to generate mass, there isvery likely at least one light Higgs boson.

(The Standard Model needs a Higgs boson.Electroweak data indicates that it is light: 114+69

-45 GeV

SUSY models: MSSM and NMSSM want a light h)

The Tevatron may be in a position to discover it, or exclude its existenceover a sizable mass range.

It needs: luminosity (>2 fb-1)optimal techniques to separate signal and backgroundgood understanding of the background

Now is the time to study this

Higgs search

SM dominating decay modesMay be different in SUSY

gg à H à bb swamped by backgroundTry to see Z à bb first.

gg à H à WW feasible for MH > 140 GeV

WH and ZH are our best SM Higgs bets:H à bbZ à 2 leptons or 2 neutrino’sW à lepton + neutrino

ttH too small

bbH and H à ττ could be enhanced in SUSY

Backgrounds: W/Z+light jetsW/Z+bb

50Also important at the LHC…

Wqq and Wbb

MCFM is a NLO Monte Carlo for Wqq and Wbb but no interface to PS

MC@NLO is a NLO MC interfaced to PS but cannot yet do W+jets

ALPGEN/MADGRAPH can do Wqq and Wbb matched to PS but only at LO

Can use with total rate scaled to NLO or use MCFM

D0 analysis for Wbb: 174 pb-1

MC = (ALPGEN+PYTHIA)*0.95 à MC does a decent job

Outlook

Ambitious luminosityplans:

4-8 fb-1 by 2009

Tevatron likely torun until madeobsolete by LHC

Outlook

Layer 0

If Layer 1is dead andno Layer 0

Impact parameterresolution

Inner layer ofsilicon detectoris expected to dieafter ~4 fb-1

Also: relativelyfar from beam

In 2005 D0 intends to install a Layer 0 forits silicon detector, at R=1.6 cm from beam,inside current detector.

In addition: trigger system upgrade.54

Connection with LHC

Does all this matter for LHC physics?

What we get out of it: doing physics at the CURRENT high E frontierexperience in commissioning, computing, analysis

What the LHC physics gets out of it:

àPDF’s, jet algorithms in practice, tests of ME-PS matching, underlyingevent models and tunes, hadronization, b-tagging strategies, massresolution optimization, tau reconstruction, backgrounds, better MC’s,impact on the physics landscape and constraints on beyond SM models,….

55th and final slide…

Haringtijd…

Recent results from D0 · Recent results from D0 and CDF Paul de Jong And he seemed to suggest that...

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