Jets and QCD in D0 Experiment

Jets and QCD inD0 Experiment

Physics at Extreme Energies

Hanoi, Vietnam July 23, 2000

V. Šimák

Institute of Physics ASCR, Prague

for the D Collaborations

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Hanoi, July 23, 2000

V. Šimák 2

Outline

• Inclusive Jet Cross Section :– at 1800 GeV

– at630 GeV

– Ratio of Inclusive Jet Cross Sections

• Dijet Triple Differential Cross Section

• Dijet Mass Spectrum

All theoretical

comparisons done

with JETRAD

ddE

dT

2

21

3

dddEd

T

anythingJ2)(J1

1P

2P

11Px

22Px

1jet

2jet

s

1/ xf Aa

2/ xf Bb

)(ˆ

jets) 2pp(

2/1/21

21

cdabxfxfdxdxabcd

BbAa

pp

ln [ tan (/ 2) ]

< 4.2 inttotal)

Transverse segmentationx x

Electrons: E / E = 15%

/

Pions: E / E = 45% /

p

_p

y

zx


V. Šimák 4

Inclusive Jet Cross Section at s = 1800 GeV

±


V. Šimák 5

Inclusive Jet Cross Section at s = 1800 GeV (D)

• JETRAD F= R= ETMax /2 ,

Rsep=1.3, for |||< 0.5|< 0.5

For all PDF’s probabilities

between 47-90%


V. Šimák 6


Ldt 536 nb-1


V. Šimák 7


• Some discrepancy at low ET, errors are large , but there is overall agreement.


V. Šimák 8

Ratio of Inclusive Jet Cross Sections

Same discrepancy exists in ratio of the scaled cross sections.

QCD predictions seem to be 20% higher than expected.


V. Šimák 9

Dijet Triple Differential Cross Section

1994-1995 Collider run (run 1b):

± 6 pb-1

preliminary resultsRequire at least two reconstructed

jetsTrigger Jet: ET > 60 GeV

Probe Jet : ET > 30 GeV

No restriction on additional jets.

Measurement as input to PDF’s:gluon distribution is most

interesting. Both experiments use JETRAD for

theoretical comparisons with different

PDF’s.

Ldt


V. Šimák 10

Dijet Triple Differential Cross Section (D)

• Divide data sample into four eta bins:

-- 0.0<||<0.5, 0.5<||<1.0, 1.0<||<1.5, 1.5<||<2.0

• Divide each eta bin into two subsamples:

-- events with 2 jets on the Opposite Side (OS)

-- events with 2 jets on the Same Side (SS).

• ET of both jets are measured so there are two entries per event into each of the eight the cross sections.

• JETRAD using = E/2

Note that the renormalization and factorization scale are chosen to be:

-- f = r = E/2 ( max jet )

OS SS

Beam line


V. Šimák 11

Dijet Triple Differential Cross Section (D)

0.0<||<0.5

0.5<||<1.0

1.0<||<1.5

1.5<||<2.0


V. Šimák 12

Dijet Triple Differential Cross Section (D) = ET/2

0.0<||<0.5

0.5<||<1.0

1.0<||<1.5

1.5<||<2.0


V. Šimák 13

Dijet Triple Differential Cross Section (D) = E/2

0.0<||<0.5

0.5<||<1.0

1.0<||<1.5

1.5<||<2.0


V. Šimák 14

Dijet Triple Differential Cross Section (D) = E/2

0.0<||<0.5

0.5<||<1.0

1.0<||<1.5

1.5<||<2.0


V. Šimák 15

Dijet Mass Distribution

M

M

. %

9% 100

4 5 1000

@

@

GeV

GeV

200-220 GeV: 8% Error

800-1400 GeV: 30% Error

Smeared CrossSectionUnsmeared

f M F M M M M dM

F M AMM

sB

C

,

where

1

121221

1221

cos11

cos1

iiiiii

i

iiii

EEEEM

M

EEM


V. Šimák 16

“Typical DØ Dijet Event”

ET,1 = 475 GeV, 1 = -0.69, x1=0.66ET,2 = 472 GeV, 2 = 0.69, x2=0.66

MJJ = 1.18 TeVQ2 = ET,1×ET,2=2.2x105 GeV2


V. Šimák 17


V. Šimák 19

Ra

RRa

RRR

La

LRa

RRL

Ra

RLa

LLR

La

LLa

LLL

RRRRRRLLRRRL

RRLLLRLLLLLL

qqqq

qqqq

qqqq

qqqq

qqqqqqqq

qqqqqqqq

L

22

22

22

224

1

1

1

1

00

00

2

A

V

1

0

Axial

:1

Vector

:1

nsinteractio o:

nsinteractiosinglet :

XRL

XLR

XRR

XLL

XRL

XLR

XRR

XLL

XX

XX

ctet

M cos

2ˆ

s

s

Compositeness Contact Predictions

QCD +


V. Šimák 20

TeV

TeV

TeV NLO

LO

LO

X

Compositeness CalculationsEichten et al., Rev. Mod. Phys. 56, 579 (84) Eichten et al., Phys. Rev. Lett 50, 811 (83)Chivukula et al., Phys. Lett. B 380, 92 (96)Lee, Phys. Rev. D 55, 2591 (97)Lane, hep-ph/9605257 (96)Suggested Scale: 1.6 TeV (LL) PRL 77, 438(1996)

TeV 4.2 TeV 7.2

Conclusions

1800 Inclusive Cross Sec.

No significant excess

Excellent agreement with theory630 Inclusive Cross Sec.

NLO predictions ~20% high

Experimental measurements consistent

Ratios 630/1800

NLO predictions ~20% high.

Experimental measurements consistent

Triple Differential Cross Section:

NLO QCD with recent PDF’s (CTEQ3M, CTEQ4M, CTEQ4HJ, MRST,…) with agreement

with D0 within the systematic uncertainties

Cross sections for possible inputs to PDF’s

1800 Dijet Mass

NLO QCD in agreement with the data

Compositeness Scale > 2.4 TeV

no new physics so farno new physics so far

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Jets and QCD in D0 Experiment

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