QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 1

QCD Studies with resurrected JADE Data

Stefan Kluth

for M. Blumenstengel, P. A. Movilla Fernandez, S. Bethke,O. Biebel, C. Pahl, J. Schieck

Max-Planck-Institut für PhysikFöhringer Ring 6D-80805 Münchenskluth@mppmu.mpg.de

Outline:1 Introduction2 Data vs modern MCs

3 Scaled Momentum ξ=ln(1/x)4 Extended Power Correction Fits

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 2

1 Why low energy e+e− data?

Running strong coupling:

αS(Q) = α

S(µ)/(1+2β

0ln(Q/µ))

�

C

�

= Acα

S(Q) + B

Cα

S

2(Q) + PC/Q

�

Interplay between hard and softQCD best studied at 'medium'energies

�

JADE data!

Eur. Phys. J. C22 (2001) 1-15

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 3

1 The JADE Detector and Data

JADE @ PETRA/DESY 1979 - 1986

�

s = 12 to 46,8 GeV

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 4

1 The JADE Software

Detector simulation (pre-GEANT) and reconstructionrunning on IBM RS6000 AIXsystem

�

generate physics usingmodern generators, e.g.PYTHIA, HERWIG,ARIADNE (LEP 1 tunes)�

pass through JADEsimulation/recontruction�

compare with data orderive corrections

Hadronic event in JADE at 35 GeV

P.A. Movilla Fernandez, PhD Thesis,RWTH Aachen, PITHA 03/01

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 5

2 Background from b-productionPYTHIA b-event at 14 GeV

Subtract b-background (~9%), present data at udsc hadron-level

P.A. Movilla Fernandez, PhD Thesis,RWTH Aachen, PITHA 03/01

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 6

2 JADE Data vs MC: ThrustGenerators: PYTHIA 5.7, HERWIG 5.9, ARIADNE 4.08, COJETS 6.23 with OPAL (-based) LEP 1 tunes, JETSET 6.3 with JADE tuneData at hadron-level corrected for bb-background

P.A. Movilla Fernandez, PhD Thesis,RWTH Aachen, PITHA 03/01

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 7

2 JADE Data vs MC: y23

(Durham)

PYTHIA/ARIADNE generally ok, HERWIG too hard at low

�

s, JETSET6.3(J) ok too, COJETS fails at low

�

sP.A. Movilla Fernandez, PhD Thesis,RWTH Aachen, PITHA 03/01

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 8

3 Scaled momentum ξ = ln(1/x)

Shape of ξ=ln(1/x) distribution around peak: skewed Gaussian MLLA (Q

0

� Λ) calculation for partons

�

LPHD

�

hadron spectra

Nucl. Phys. B355 (1991) 54

σ: width, S: skewness, k: kurtosis, ξ0: peak position

D � �

N y2 � � y

exp k y8

�

S y �

2

�

2 � k y � 2

4� S y � 3

6

� k y � 4

24

� � � � � y � y , y � log s2

eff

, � 0 � � �

11 � 2n f

932C A

, � � F y � O 1

S � � � � 3 � 3, k � � � � 4 � 4 � 3

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 9

3 Measurements and Fits

Fit MLLA (Fong/Webber): Λeff

, N, and <ξ>, O(1) or ξ0

�

results for Λeff

, N stable w.r.t. <ξ>, O(1) or ξ0

M. Blumenstengel, PhD Thesis, RWTH Aachen

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 10

3 Peak Fit Results

Peak position <ξ> or ξ0 and Ndepend on √s

Λeff

and O(1) constant

M. Blumenstengel, PhD Thesis, RWTH Aachen

s GeV � 0 N �

effMeV

22 2.74 � 0.09 11.6 � 0.4 136 � 2835 3.06 � 0.05 14.1 � 0.2 142 � 2544 3.19 � 0.06 16.4 � 0.6 110 � 38

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 11

3 MLLA Peak Position Fits

Λeff

= 206

�

3 MeV

Reasonable description of data(similar result from OPAL)

M. Blumenstengel, PhD Thesis, RWTH Aachen

� 0 y �

12

y � Cy � C

y � log s2 �

eff

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 12

3 Flavour (Mass) Effects

M. Blumenstengel, PhD Thesis, RWTH Aachen

�

c , b0 � �

uds0 � 0.5 log

�c , b

�

uds

Fit with Λb, Λ

c and Λ

uds with

data from OPAL for ξ0

b, ξ0

c

and ξ0

uds as constraints

�

uds184 � 33MeV

�

c239 � 90MeV

�

b247 � 28MeV

Mass effects about 20 � 30%

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 13

4 Extended Power Correction FitsDMW model:

�

assume integrable αS at very low Q

�

analyse renormalon ambiguities

y Dy

1 � T 2

M H2 1

C 3 �

BT ln 1

�

BT

�

DBTBT , �

S

BW12

ln 1

�

BW

�

DBWBW , �

S

y � y PT Dy P

d �

dy

�

d �

PT

dyy � Dy P

P M

I

Q

�

0

I

� �

S

R

�

0

I

� 1

I0

�

I �

S k dk

Nucl. Phys. B469 (1996) 93

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 14

4 Extended Fits with BW

pQCD is O(αS

2)+NLLA,

�

s<MZ

χ2(pQCD+DMW) = 65.5/24

χ2(pQCD+DMW+A11

) = 22.2/23

Evidence for additional terms, probably behaving like ln(Q)/Q

P.A. Movilla Fernandez, PhD Thesis,RWTH Aachen, PITHA 03/01

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 15

4 Extended Fits with y23

(D)pQCD is O(α

S

2)+NLLA

�

extended fit ranges

�

DMW prediction is

�

y23

�

~ ln(Q)/Q2

χ2(pQCD) = 151/107

χ2(pQCD+A20

/Q2) = 71.2/106

Evidence for additional terms, probably behaving like 1/Q2

at low

�

s

Analysis with restricted fit rangesis consistent too

P.A. Movilla Fernandez, PhD Thesis,RWTH Aachen, PITHA 03/01

QCD Studies with resurrected JADE Data Stefan Kluth Moriond QCD '03 16

Summary

� Modern MC generators with LEP 1 tunes generally agree with JADE data down to 14 GeV

� Quantitative QCD studies at 14 to 44 GeV

� Ideal laboratory for interplay hard � soft QCD

� Measured ξ=ln(1/x) 22 to 44 GeV with JADE

� Test MLLA QCD predictions (together with OPAL)

� Study flavour (mass) effects (together with OPAL)

� Extended DMW power corrections fits

� BW additional A

11ln(Q)/Q contribution?

� y23

(D) additional A20

/Q2 contribution?