2005 Aspen Winter Conference The High Energy...

Andrey Korytov, University of Florida Aspen, February 14, 2005 1

Andrey Korytov

QCD Physics at Tevatron(for CDF and D0 Collaborations)

2005 Aspen Winter ConferenceThe High Energy Physics


QCD Physics at Tevatron

High PT QCD

Jet production (g and uds)Heavy flavor quark production (t, b, c) – Michael Weber (t), Friday Talk? (b, c?) Vector boson production (W, Z, γ) – Pasha Murat

Low PT QCD

Jet fragmentationHadron spectroscopyUnderlying EventDiffractive physics – Konstantin Goulianos


Jets

Jets areJets aremessymessyobjectsobjects

Analyses are not that simple...


Jets: concept is vague…

Calorimeter level:calorimeter towers lumped together according to an experimentalist’s favored algorithm

Hadron level:sprays of long lived observable particles

Parton level 2 (resummed pQCD):outgoing parton accompanied by a few soft QCD bremsstrahlung

Parton level 1 (NLO pQCD at Tevatron):outgoing 1 parton or 2 partons lumped together to mimic a particular experimental jet finding algorithm


Jets: jet finding algorithms

Cone Algorithm: cluster together calorimeter towers by their “angular” proximity in (η, φ) spacemerging/splitting of overlapping cones is not infrared stable (at NNLO)ad hoc Rsep=1.3 to match theory and exp.Tevatron Run I legacy

MidPoint Cone Algorithm:cone algorithm with modifications improving infrared stability

kT Algorithm:cluster together calorimeter towers by their kT proximityinfrared stable (no splitting/merging)no clusters left out underlying event contribution unclear favored choice at e+e- colliders


Jets: jet energy measurements

Jet Energy Resolution (stochastic):

Absolute Scale Uncertainty (systematic):

70% 6%( )

T

T T

EE E GeV

δ≈ ⊕

5%T

T

EE

δ≈


Jets: theory

Very large number of diagrams to tackle…• NLO calculations available… • but still very sensitive to scale choices…• NNLO “soon to become available” for many years…

Uncertainties in Parton Density Functions (PDFs)• especially g(x) at large x…

Sample of LO diagrams (2 2)


Inclusive jet production

ET spectra different η-bins…

( , )Tp p Jet E Xη+ → +


Jets: Inclusive jets in Run I

Run I data and NLO+CTEQ3MCDF: Excess at high ET?Compositness?

Run I data and NLO+CTEQ6MCTEQ6:

• New Data: H1, ZEUS, D0 (vs. η!), CDF• New methods: Systematic errors included• New features: Errors are available

no excess, anymore...

CDF


Jets: Inclusive jets in Run II data vs NLO

Quite reasonable agreement with NLO+CTEQ6.1, but...

déjà vu: “high-ET excess” again? ~20% dip at lower ET? (not present in Run I)all within systematic errors...

must beat systematic errors down:

• Theory: PDFs, NNLO?• Experiment: energy scale,

hadronization corrections?

Run II reach


Jets: Inclusive jets in Run II vs Run I

· PDF uncertainties largely cancel out· Energy scale errors are really annoying…

CDF


Jets: Inclusive jets by D0 and CDF

D0CDF


Jets: kT vs Cone algorithm

Cone

Shapes of Data/Theory differ...

Why? (work in progress)

CDF

KTCDF


Jets: dijet production

What one might want to look at:MJJ

θcm

∆φ12

…

1 2p p Jet Jet X+ → + +

ET=666 GeV

ET=633 GeV

MJJ=1364 GeV


Jets: Dijet production

statistical errors only

Look for narrow resonance peaks in Dijet Mass spectrum—seen none

Data/theory agree—within large systematic errors (jet-energy scale)


Jets: Dijet ∆φ12

LO is very poor at ∆φ∼π/2 and ∆φ∼πNLO fixes ∆φ∼π/2, but still no good at ∆φ∼π

Herwig is quite good everywherePythia needs ISR enhancement for ∆φ∼π/2

LO in ∆φ NLO in ∆φ


Jets: three-jet production

Many more variables to play with...No surprises...

1 2 3p p Jet Jet Jet X+ → + + +



High PT QCD

Jets production (gluons and light quarks)Heavy flavor quark production (t, b, c) – Michael Weber (top), Friday Talk (b) Vector boson production (W, Z, γ) – Pasha Murat

Low PT QCD

Jet fragmentationHadron spectroscopyUnderlying eventDiffractive physics – Konstantin Goulianos


Jet Fragmentation: intrinsically soft QCD

Differential probabilities of gluon emission:

Perturbative methods will NOT work for kT<1 GeV

( )QCDTS

T

TS kk

dkkdkdw

Λ=

/ln92 ,~ παα

k, gluon momentum

kT=k⋅sinθgluon transverse momentum

θ

Cone 0.280

MJJ=82 GeV (lower set)

MJJ=628 GeV (upper set)MJJ=229 GeV (middle set)

DATA (points) vs Herwig/QFL(line)

CDF Preliminary

dN/d

k T

kT (GeV)

1 GeV

From data we know that most particles have kT<1 GeV

ANY HOPE?

2 GeV

kT distribution of particles in jets

THEORY EXPERIMENT


Jet Fragmentation: doing it analytically

Jet fragmentation in pQCD:parton shower development: resummed NLL approximations

e.g., MLLA, Modified Leading Log Approximation with single parameter Qeff=Qcutoff=ΛQCD

hadronization: no coherent theory

LPHD, hypothesis of Local Parton Hadron Duality with one parameter KLPHD=Nhadrons/Npartons

MLLA+LPHD:cannot describe all details…but all analytical…does it work at all?

R~1/MJJR~1/QcutoffR~1/Λ~1/mπ~1 fm


Jet Fragmentation: data vs resummed pQCD

Charged particles in jetsTwo parameter fit:

Qeff = 230±40 MeV kT-cutoff can be set as low as ~ΛQCD

KLPHD(± ) = 0.56 ± 0.10 number of hadrons ≈ number of partons

particle

jet

px

E=

CDF


Jet Fragmentation: Gluon vs Quark jets

Difference of Gluon and Quark jets:r = Nhadrons(gluon jet) / Nhadrons(quark jet)calculations (for partons): various extensions of NLLA (r=1.5-1.7) data: 15+ papers from e+e-, not all self-consistent (r = 1 to 1.5)CDF: r=1.6±0.2

jet coneQ E θ=



High PT QCD


Low PT QCD



Hadrons: Λb mass

Tevatron is THE heavy flavor hadron factory (not very clean though...)Secondary vertex trigger allows to fish them outWorld largest sample of Λb

M(Λb)=5619±1.2±1.2 MeV/c2

PDG2002: 5624 ± 9


Hadrons: X(3872)

Aug 2003: Belle announced discovery of X(3872) J/ψ π+π−

M=3872.0±0.6 ±0.5 MeVΓ < 2.3 MeVππ masses are always high (>500 MeV)

Confirmed by CDF, D0, BaBar

Interpretation still remains unclear:3D2 charmonium? cc

• too heavy for it (expected M~3810-3840)• also, not seen to decay to χ1γ

M(X)~M(D0)+M(D*0) = 1864.6 + 2006.7 = 3871 MeV• DD* molecule? cu-cu

Quadra-quark? cu-cu

Μ(J/ψ)+Μ(ρ) = 3097+770 = 3867 MeV• ???


Hadrons: X(3872) at CDF

M=3871.3±0.7 ±0.4 MeVΜ(ππ) invariant masses are all high (>500 MeV)high yield:

• ~1/8 of ψ(2S)• ~85% are prompt, not B-decays!


Hadrons: pentaquarksPenta-quark states predicted byDiakonov, Petrov, Polyakov(1997):Θ+ : uuddsMass ~ 1530 MeVWidth ~ 15 MeV Decays equally to nK+ and pK0

10 experiments report evidence: see above3 experiments report no observation: HERA-B, PHENIX, BES

In addition,

NA49 at SPS/CERN (pp collider, Ecm = 17.2 GeV): ssddu(1862)

H1 at HERA ep collider: D*- p state: Θc=uuddc(3099)

/ / /3/ 2 π++ −− + − + −Ξ →Ξ

STATISTICAL SIGNIFICANCE VARIES FROM ~4σ to ~8σ


Hadrons: Ξ–hyperon track sample at CDF

• CDF developed tracking of long lived hyperons (Ξ and Ω) in the SVX detector

Two Track Trigger Jet 20 Trigger

]2[GeV/c1.24 1.26 1.28 1.3 1.32 1.34 1.36 1.38

2N

/ 2

MeV

/c

0

2000

4000

6000

8000

CDF Run II Preliminary

]2[GeV/c1.24 1.26 1.28 1.3 1.32 1.34 1.36 1.38

2N

/ 2

MeV

/c

0

2000

4000

6000

8000

)πΛM(

-πΛ+πΛ

-1L = 220pb

track found in SVX

N=36,000

Ξ

]2[GeV/c1.25 1.30 1.35 1.40

2N

/ 2

MeV

/c0

500

1000

CDF Run II Preliminary

]2[GeV/c1.25 1.30 1.35 1.40

2N

/ 2

MeV

/c0

500

1000

)-πΛM(

-πΛ+πΛ

-1L~220pb track found in SVXΞ

Two Track Trigger: NTTT ~ 18 times larger than NA49 dataJet20 Trigger: NJet20 ~ 2 times larger than NA49 data


Hadrons: Ξ-- (1860) is not found at CDF

TTT Jet20

~0.21<0.0757+/-51Ξ−π+

~0.45<0.0847+/-70Ξ−π+/−

~0.24<0.04-54+/-47Ξ−π−

R(Ξ1860/Ξ1530) NA49R(Ξ1860/Ξ1530) U. L. 95% C.L.

# of eventsChannel(TTT)


Hadrons: Pentaquark Searches

CDF Collaboration have searched for Θ⁺, Θc⁰, Ξ3/2

No evidence for these states have been found



High PT QCD


Low PT QCD



Underlying Event: introductory remarks

Underlying Event (UE) ≈(whole event) – (hard part), i.e.:

--initial state radiationmultiple parton interactionsproton remnantsnot completely independent from the hard scattering part…

Whole Event: hard scattered partonsfinal state radiationinitial state radiationmulti-parton interactions, if anyproton remnantswhole thing is entangled with color connections…

UE Physics is poorly understood:MC Generators implement UE

differently (many parameters)even when tuned to current data,

MC predictions for LHC vary wildly (factor of 3)

UE event pollutes many analyses (source of systematic errors)


Underlying Event: studies with charged tracks

Leading Jet ∆φ

“Transverse” “Transverse”

“transverse” particlesas a probe of the underlying event

ET(jet) Charged tracks:

• d2N/dφdη• d3N/dφdηdPT

• d2ET/dφdη

Charged Particle Density: dN/dηdφ

0.1

1.0

10.0

0 30 60 90 120 150 180 210 240 270 300 330 360

∆φ (degrees)

Cha

rged

Par

ticle

Den

sity

Back-to-BackLeading JetMin-Bias

CDF Preliminarydata uncorrected

Charged Particles (|η|<1.0, PT>0.5 GeV/c)

30 < ET(jet#1) < 70 GeV

"Transverse" Region

Jet#1

Min-Bias0.25 per unit η-φ

Run II


Underlying Event: default Pythia and Herwig

Default Pythia and Herwig fail to reproduce data one way or another, e.g.:

Pythia 6.206 underestimates number of tracks in transverse direction…

Herwig 6.4 gives too soft spectrum for particles in transverse direction, especially in events with small ET jets (missing MPI now have been added)

"Transverse" Charged Particle Density: dN/dηdφ

0.00

0.25

0.50

0.75

1.00

0 5 10 15 20 25 30 35 40 45 50PT(charged jet#1) (GeV/c)

"Tra

nsve

rse"

Cha

rged

Den

sity

CTEQ3L CTEQ4L CTEQ5L CDF Min-Bias CDF JET20

1.8 TeV |η|<1.0 PT>0.5 GeV

Pythia 6.206 (default)MSTP(82)=1

PARP(81) = 1.9 GeV/c

CDF Datadata uncorrectedtheory corrected

Charged Particle Density

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

0 2 4 6 8 10 12 14

PT (GeV/c)

Cha

rged

Den

sity

dN

/dηdφ

dPT

(1/G

eV/c

)

|η|<1CDF Preliminary

Min-Bias Data, 1.8 TeV

HW "Soft" Min-Biasat 0.63, 1.8, and 14 TeV


UE: tune Pythia to match CDF data

Pythia: CDF Tune A vs. Default 6.206

• Enhanced Initial State Radiation (ISR)

• Smoothed out probability of Multi-Parton Interactions (MPI) vs. impact

• MPIs are more likely to produce gluons than quark-antiquark pairsand MPI gluons are more likely to have color connection to p-pbar remnants

• …


UE: Pythia Tune A at work

"Transverse" Charged PTsum Density: dPTsum/dηdφ

0.00

0.25

0.50

0.75

1.00

1.25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

PT(charged jet#1) (GeV/c)

"Tra

nsve

rse"

PTs

um D

ensi

ty (G

eV)

CDF Run 1 Min-BiasCDF Run 1 JET20CDF Run 2PY Tune A

CDF Preliminarydata uncorrectedtheory corrected

|η|<1.0 PT>0.5 GeV/c

"Transverse" Charged Particle Density

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 2 4 6 8 10 12 14 16 18 20

PT(charged) (GeV/c)

Cha

rged

Den

sity

d3 N

/dη d

φdP

T(1

/GeV

/c)


PYTHIA Tune A 1.96 TeV

30 < PT(chgjet#1) < 70 GeV/c

70 < PT(chgjet#1) < 95 GeV/c

"Transverse" Charged Particle Density: dN/dηdφ

0.00

0.25

0.50

0.75

1.00

1.25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

PT(charged jet#1) (GeV/c)

"Tra

nsve

rse"

Cha

rged

Den

sity

CDF Run 1 Min-BiasCDF Run 1 JET20CDF Run 2PY Tune A

|η|<1.0 PT>0.5 GeV/c



Summary

High PT QCD

– all checks within systematic errors– we must beat systematic errors down to move towards

precision QCD measurements

Low PT QCD

– interesting developments despite all the challenges for applying pQCD in this domain

Progmatic

– new physics is likely to be born in a QCD process– QCD is likely to be the nastiest background for the Signal– we’d better tame this beast...

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2005 Aspen Winter Conference The High Energy...

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