Measurements of jet rates with the anti

Measurements of jet rates with the anti

Measurements of jet rates with the anti-kT and
SISCone algorithms at LEP with the OPAL
detector
Andrii Verbytskyi
Rencontres de Moriond, QCD and High Energy Interactions,
La Thuile, Italy
19 - 26 March 2016
1 / 34
The LEP Accelerator
OPAL
The world most famous
e + e − collider running
1989-1995(LEP-I),
1996-2000(LEP-II). Now
tunnel hosts LHC.
Energy ranges
≈ 91 GeV(LEP-I) and
91 − 208 GeV(LEP-II).
Host of four big
experiments: OPAL,
ALEPH, DELPHI, L3.
2 / 34
The OPAL Collaboration and Detector
Hadron calorimeters
and return yoke
Electromagnetic
calorimeters
Muon
detectors
Jet
chamber
Vertex
chamber
Microvertex
detector
Omni-Purpose Apparatus
at LEP
Advanced
multipurpose detector
with almost 4π solid
angle coverage.
Collaboration of more
than 300 people.
y
θ
z
Z chambers
ϕ
x
Presampler
Forward
detector
Silicon tungsten
luminometer
Solenoid and
pressure vessel
Data available for
re-analysis.
Time of flight
detector
3 / 34
Jets at OPAL: motivation
e + e − → γ ∗ /Z 0 → hadrons is perfect for studying QCD.
New algorithms, never used before at LEP, can produce
valuable results:
SISCone1 ;
anti-kT 2 .
Compare new algorithms for e + e − , validate them and their
implementation.
Expect to produce an input for αs determination with reduced
uncertainties.
Study hadronisation corrections.
1
2
G. P. Salam and G. Soyez, “A Practical Seedless Infrared-Safe Cone jet algorithm”, JHEP 0705 (2007) 086
M. Cacciari et al., “The Anti-k(t) jet clustering algorithm”, JHEP 0804 (2008) 063
4 / 34
Jet rates: OPAL Coll.,“Determination
of αs using jet rates at LEP with the
OPAL detector,” EPJC 45 (2006) 547
Jet Fraction
Similar studies elsewhere
1
OPAL (91 GeV)
Durham
0.8
2-jet
3-jet
4-jet
5-jet
PYTHIA
HERWIG
10
kT (x 100)
10
3
anti-kT
(x 10)
10
2
SIScone
0.4
-1
jet
dσ/dE T,B (pb/GeV)
0.6
4
ZEUS 82 pb
0.2
0
NLO ⊗ hadr ⊗ Z
0
10
-4
10
-3
10
-2
10
-1
ycut
10
1
10
2
-1
Q > 125 GeV
-2 < ηjet
B < 1.5
|cos γh| < 0.65
2
hadronisation correction
jet energy scale uncertainty
1.1
hadronisation uncertainty
kT (+0.05)
1
anti-kT
0.9
0.8
SIScone
5
10
15
20
25
30
35
40
45
50
55
Comparison of algorithms:
ZEUS Coll., “Inclusive-jet
cross sections in NC DIS at
HERA and a comparison of
the kT , anti-kT and
SISCone jet algorithms,”
PLB 691 (2010) 127
jet
E T,B (GeV)
5 / 34
Data and MC samples
√
Full LEP data sample with 12 energies: s = 91.2 − 207 GeV.
MC samples with simulated detector level:
e + e − → γ ∗ /Z 0 → hadrons KK2f 3 signal samples hadronised
with Pythia6 and Herwig6.
e + e − → leptons + hadrons grc4f 4 and KoralW5 background
samples hadronised with JETSET7.4.
For some plots the samples are merged:
91 → 91 GeV
161 − 189 → 177 GeV
130 − 136 → 133 GeV
192 − 207 → 197 GeV
3
S. Jadach et al., “The precision Monte Carlo event generator KK for two fermion final states in e + e −
collisions”, CPC 130 (2000) 260, also PRD 88 (2013) 11, 114022.
4
J. Fujimoto et al., “Grc4f v1.1: a four fermion event generator for e + e − collisions”, CPC 100 (1997) 128.
5
M. Skrzypek et al., “Monte Carlo program KORALW-1.02 for W pair production at LEP-2/NLC energies
with Yennie-Frautschi-Suura exponentiation”, CPC 94 (1996) 216.
6 / 34
OPAL √s=183-209 GeV
Event selection
1500
a)
Events
Events
1000
Preselected
750
b)
1000
500
500
250
High energy multihadron
event:
0
0
-3
-2
-1
0
750
-4
-3
-2
420
-1
10
0
CC03
Events
Events
10
c)
1000
1
5+7log “good”
tracks+clusters;
(W )
log (W
)
significant 1500
energy
deposit in the central region of calorimeter.
d)
+ W − background probability.
Low e + e − → W
1000
500
500
250
0
-4
-3
-2
0
-1
0
0.2
0.4
0.6
log10(y45)
Events
1500
0.8
1
Sphericity
e)
1000
Selected
500
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Likelihood Output
Selection of W + W − →
qqqq events as in OPAL
Coll., “Measurement of
the e + e − → W + W −
cross section and W decay branching fractions at
LEP”, EPJC 52 (2007)
767.
7 / 34
Event reconstruction
Low energy or poorly reconstructed tracks and calorimeter
clusters removed;
Calorimeter clusters and tracks combined with energy flow
algorithm to prevent double counting;
Running jet algorithms on the resulted list of objects.
SiScone in spherical coordinates with = 0.75 and Etilde
merging scheme, R = 0.3, 0.4, 0.5, 0.7, 0.9, 1.1.
e + e − version of anti-kT , R = 0.3, 0.4, 0.5, 0.7, 0.9, 1.1.
PxCone (ee) and Durham for comparison.
8 / 34
Check of the MC samples
OPAL DP(prel.) ee-anti-k R=0.7, s=91GeV
OPAL DP(prel.) ee-anti-k R=1.1, s=161GeV
Njets=3
Njets=4
0.8
Njets=2
1
Njets=3
Njets=4
0.8
Njets=2 KK2f
Njets=3
Njets=4
Njets=4 KK2f
Njets=3 KK2f
Njets=4 KK2f
0.6
0.4
0.2
0.2
0.2
0
0
20
30
40
50
Ecut,GeV
0
Njets=4 KK2f
0.6
0.4
10
Njets=2 KK2f
Njets=3 KK2f
0.4
0
Njets=2
1
0.8
Njets=2 KK2f
Njets=3 KK2f
0.6
Fraction
Fraction
Fraction
Njets=2
1
OPAL DP(prel.) SISCone R=0.7, s=207GeV
T
T
0
10
20
30
40
50
0
10
20
Ecut,GeV
30
40
50
Ecut,GeV
KK2f MC with Pythia6 hadronisation.
Good description of the data for various jet algorithms.
9 / 34
Check of the reconstruction
Comparison to previous analyses with Durham and PxCone.
Njets=3, Durham
0.6
0.5
OPAL DP(prel.) SISCone R=0.7, s=91GeV
Fraction
Fraction
OPAL DP(prel.) Durham, s=91GeV
Njets=3, SISCone
0.6
Njets=3, PxCone
0.5
Njets=3, Durham, OPAL
Njets=3, PxCone, M.A.D.
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0
0
−4
10
−3
10
−2
10
−1
10
1
10
2
10
y
cut
Data from:
JADE and OPAL Colls., “QCD
analyses and determinations of αs in
e + e − annihilation at energies between
35 GeVand 189 GeV”, EPJC 17
(2000) 19
0
10
20
30
40
50
Ecut,GeV
Data from:
"Determination of αs using
jet rates at LEP",
M.A. Donkers, PhD thesis.
10 / 34
Anti-kT with R = 0.7
OPAL DP(prel.) ee-anti-k R=0.7, s=91GeV
OPAL DP(prel.) ee-anti-k R=0.7, s=133GeV
Njets=3
Njets=4
Njets=3
Njets=4
0.8
Njets=2 KK2f
0.6
Njets=2
1
Njets=3 KK2f
Njets=4 KK2f
Njets=4 KK2f
0.6
Njets=3
Njets=4
Njets=3 KK2f
0.4
0.4
0.2
0.2
0.2
0
0
10
20
30
40
50
Njets=4 KK2f
0
0
Ecut,GeV
Njets=2 KK2f
0.6
0.4
0
Njets=2
1
0.8
Njets=2 KK2f
Njets=3 KK2f
T
Fraction
Fraction
Fraction
Njets=2
0.8
OPAL DP(prel.) ee-anti-k R=0.7, s=177GeV
T
T
1
10
20
30
40
50
0
Ecut,GeV
10
20
30
40
50
Ecut,GeV
OPAL DP(prel.) ee-anti-k R=0.7, s=197GeV
Fraction
T
Njets=2
1
KK2f +Pythia6 describes the data well.
Njets=3
Njets=4
0.8
Njets=2 KK2f
KK2f +Herwig6(not shown) describes
the data well.
Njets=3 KK2f
Njets=4 KK2f
0.6
0.4
Both tuned by OPAL.
0.2
0
0
10
20
30
40
50
The uncertainties are statistical only. Full uncertainties are in the backup.
Ecut,GeV
11 / 34
SISCone with R = 0.7
Fraction
Fraction
Njets=2
1
Njets=3
Njets=4
0.8
Njets=3
Njets=4
0.8
Njets=2 KK2f
0.6
Njets=2
1
Njets=3 KK2f
Njets=4 KK2f
Njets=4 KK2f
0.6
Njets=3
Njets=4
Njets=3 KK2f
0.4
0.4
0.2
0.2
0.2
0
0
10
20
30
40
50
Njets=4 KK2f
0
0
Ecut,GeV
Njets=2 KK2f
0.6
0.4
0
Njets=2
1
0.8
Njets=2 KK2f
Njets=3 KK2f
OPAL DP(prel.) SISCone R=0.7, s=177GeV
Fraction
OPAL DP(prel.) SISCone R=0.7, s=133GeV
OPAL DP(prel.) SISCone R=0.7, s=91GeV
10
20
30
40
50
0
Ecut,GeV
10
20
30
40
50
Ecut,GeV
Fraction
OPAL DP(prel.) SISCone R=0.7, s=197GeV
Njets=2
1
KK2f +Pythia6 describes the data well.
Njets=3
Njets=4
0.8
Njets=2 KK2f
KK2f +Herwig6(not shown) describes
the data well.
Njets=3 KK2f
Njets=4 KK2f
0.6
0.4
Both tuned by OPAL.
0.2
0
0
10
20
30
40
50
The uncertainties are statistical only. Full uncertainties are in the backup.
Ecut,GeV
12 / 34
Scaling of the jet rates with the visible energy, R = 0.7
OPAL DP(prel.) Scaling with E , N =3
jets
133GeV anti-k T R=0.7
0.8
177GeV anti-k T R=0.7
197GeV anti-k T R=0.7
0.6
OPAL DP(prel.) Scaling with E , N =4
jets
1
vis
91GeV anti-k T R=0.7
133GeV anti-k T R=0.7
0.8
177GeV anti-k T R=0.7
197GeV anti-k T R=0.7
0.6
133GeV anti-k T R=0.7
0.4
0.2
0.2
0
0
0.4
0.5
OPAL DP(prel.) Scaling with E , N =2
vis
0.1
0.15
vis
91GeV SISC. R=0.7
133GeV SISC. R=0.7
0.8
0.05
0.2
0.25
0.3
0.35
177GeV SISC. R=0.7
133GeV SISC. R=0.7
177GeV SISC. R=0.7
197GeV SISC. R=0.7
0.4
0.4
0.2
0.2
0
0
0.5
Ecut/Evis
177GeV SISC. R=0.7
197GeV SISC. R=0.7
0.2
0.4
91GeV SISC. R=0.7
197GeV SISC. R=0.7
0.4
0.3
0.25
Ecut/Evis
133GeV SISC. R=0.7
0.6
0.2
0.2
jets
0.8
0.6
0.1
0.15
1
0.6
0
0.1
vis
91GeV SISC. R=0.7
0.8
0.05
OPAL DP(prel.) Scaling with E , N =4
jets
1
0
Ecut/Evis
OPAL DP(prel.) Scaling with E , N =3
jets
1
197GeV anti-k T R=0.7
0
0
Ecut/Evis
Fraction
0.3
177GeV anti-k T R=0.7
0.6
0.4
0.2
91GeV anti-k T R=0.7
0.8
0.2
0.1
jets
1
0.4
0
Fraction
Fraction
vis
91GeV anti-k T R=0.7
Fraction
Fraction
vis
1
Fraction
OPAL DP(prel.) Scaling with E , N =2
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Ecut/Evis
0
0.05
0.1
0.15
0.2
0.25
Ecut/Evis
Evis is a sum of energies of all objects in the event.
13 / 34
Scaling of the jet rates with the visible energy, R = 0.3
OPAL DP(prel.) Scaling with E , N =3
jets
133GeV anti-k T R=0.3
0.8
177GeV anti-k T R=0.3
197GeV anti-k T R=0.3
0.6
OPAL DP(prel.) Scaling with E , N =4
jets
1
vis
91GeV anti-k T R=0.3
133GeV anti-k T R=0.3
0.8
177GeV anti-k T R=0.3
197GeV anti-k T R=0.3
0.6
133GeV anti-k T R=0.3
0.4
0.2
0.2
0
0
0.4
0.5
OPAL DP(prel.) Scaling with E , N =2
vis
0.1
0.15
vis
91GeV SISC. R=0.3
133GeV SISC. R=0.3
0.8
0.05
0.2
0.25
0.3
0.35
177GeV SISC. R=0.3
133GeV SISC. R=0.3
177GeV SISC. R=0.3
197GeV SISC. R=0.3
0.4
0.4
0.2
0.2
0
0
0.5
Ecut/Evis
177GeV SISC. R=0.3
197GeV SISC. R=0.3
0.2
0.4
91GeV SISC. R=0.3
197GeV SISC. R=0.3
0.4
0.3
0.25
Ecut/Evis
133GeV SISC. R=0.3
0.6
0.2
0.2
jets
0.8
0.6
0.1
0.15
1
0.6
0
0.1
vis
91GeV SISC. R=0.3
0.8
0.05
OPAL DP(prel.) Scaling with E , N =4
jets
1
0
Ecut/Evis
OPAL DP(prel.) Scaling with E , N =3
jets
1
197GeV anti-k T R=0.3
0
0
Ecut/Evis
Fraction
0.3
177GeV anti-k T R=0.3
0.6
0.4
0.2
91GeV anti-k T R=0.3
0.8
0.2
0.1
jets
1
0.4
0
Fraction
Fraction
vis
91GeV anti-k T R=0.3
Fraction
Fraction
vis
1
Fraction
OPAL DP(prel.) Scaling with E , N =2
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Ecut/Evis
0
0.05
0.1
0.15
0.2
0.25
Ecut/Evis
Evis is a sum of energies of all objects in the event.
14 / 34
SISCone jet rates with different R parameter
0.6
Njets=3 PxCone R=0.7
Njets=3 SIScone R=0.3
Njets=3 SIScone R=0.5
Njets=3 SIScone R=0.7
Njets=3 SIScone R=0.9
Njets=3 SIScone R=1.1
1
0.8
0.6
OPAL DP(prel.) Running of SiSCone alg. with R, s=207GeV
Fraction
0.8
Fraction
OPAL DP(prel.) Running of SiSCone alg. with R, s=91GeV
Njets=2 PxCone R=0.7
Njets=2 SIScone R=0.3
Njets=2 SIScone R=0.5
Njets=2 SIScone R=0.7
Njets=2 SIScone R=0.9
Njets=2 SIScone R=1.1
1
0.8
0.6
0.4
0.4
0.2
0.2
0.2
0
0
0
10
20
30
40
50
Ecut,GeV
0
Njets=2 PxCone R=0.7
Njets=2 SIScone R=0.3
Njets=2 SIScone R=0.5
Njets=2 SIScone R=0.7
Njets=2 SIScone R=0.9
Njets=2 SIScone R=1.1
1
0.4
0
10
20
30
40
50
Ecut,GeV
0
10
20
30
40
50
Ecut,GeV
OPAL DP(prel.) Running of SiSCone alg. with R, s=207GeV
Fraction
Fraction
OPAL DP(prel.) Running of SiSCone alg. with R, s=91GeV
Njets=3 PxCone R=0.7
Njets=3 SIScone R=0.3
Njets=3 SIScone R=0.5
Njets=3 SIScone R=0.7
Njets=3 SIScone R=0.9
Njets=3 SIScone R=1.1
1
0.8
0.6
Stable results for 2- and 3- jet rates.
0.4
SISCone results close to PxCone.
0.2
0
0
10
20
30
40
50
Ecut,GeV
15 / 34
Anti-kT jet rates with different R parameter
OPAL DP(prel.) Running of ee-anti-k alg. with R, s=91GeV
T
0.6
Njets=2 anti-kT R=0.3
1
Njets=2 anti-kT R=0.5
Njets=2 anti-kT R=0.7
0.8
Njets=2 anti-kT R=0.9
Njets=2 anti-kT R=0.9
Njets=2 anti-kT R=1.1
Njets=2 anti-kT R=1.1
0.6
T
Fraction
Njets=2 anti-kT R=0.7
Fraction
Njets=2 anti-kT R=0.5
Njets=3 anti-kT R=0.5
Njets=3 anti-kT R=0.9
0.4
0.2
0.2
0
0
20
30
40
50
Ecut,GeV
0
Njets=3 anti-kT R=1.1
0.6
0.4
10
Njets=3 anti-kT R=0.7
0.8
0.2
0
Njets=3 anti-kT R=0.3
1
0.4
0
10
20
30
40
50
Ecut,GeV
0
10
20
30
40
50
Ecut,GeV
OPAL DP(prel.) Running of ee-anti-k alg. with R, s=207GeV
T
Fraction
Fraction
Njets=2 anti-kT R=0.3
0.8
OPAL DP(prel.) Running of ee-anti-k alg. with R, s=91GeV
OPAL DP(prel.) Running of ee-anti-k alg. with R, s=207GeV
T
1
Njets=2 anti-kT R=0.3
1
Njets=2 anti-kT R=0.5
Njets=2 anti-kT R=0.7
0.8
Njets=2 anti-kT R=0.9
Njets=2 anti-kT R=1.1
0.6
Similar patterns to SiSCone.
0.4
0.2
0
0
10
20
30
40
50
Ecut,GeV
16 / 34
SISCone jet rates dependence on R with Ecut = 6 GeV
1.2
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
OPAL DP(prel.) N-jet events E>6GeV with SiSCone alg., s=177GeV
1.4
Njets=2 E>6.0GeV
1.2
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
Fraction
Njets=2 E>6.0GeV
Fraction
OPAL DP(prel.) N-jet events E>6GeV with SiSCone alg., s=133GeV
1.4
1.4
Njets=2 E>6.0GeV
1.2
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
0
0.2
0.4
0.6
0.8
1
1.2
0
0.2
R
0.4
0.6
0.8
1
1.2
0.2
0.4
0.6
0.8
R
1
1.2
R
OPAL DP(prel.) N-jet events E>6GeV with SiSCone alg., s=197GeV
Fraction
Fraction
OPAL DP(prel.) N-jet events E>6GeV with SiSCone alg., s=91GeV
1.4
Njets=2 E>6.0GeV
1.2
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
Monotonic dependence on R.
0.8
The choice can be done in a wide
range.
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1
1.2
R
17 / 34
Anti-kT jet rates dependence on R with Ecut = 6 GeV
OPAL DP(prel.) N-jet events E>6GeV with ee-anti-k alg., s=91GeV
OPAL DP(prel.) N-jet events E>6GeV with ee-anti-k alg., s=133GeV
OPAL DP(prel.) N-jet events E>6GeV with ee-anti-k alg., s=177GeV
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
T
1.4
Njets=2 E>6.0GeV
1.2
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
Fraction
1.2
Fraction
T
Njets=2 E>6.0GeV
1.4
Njets=2 E>6.0GeV
1.2
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
0
0.2
0.4
0.6
0.8
1
1.2
0
0.2
R
0.4
0.6
0.8
1
1.2
0.2
0.4
0.6
0.8
R
1
1.2
R
OPAL DP(prel.) N-jet events E>6GeV with ee-anti-k alg., s=197GeV
T
Fraction
Fraction
T
1.4
1.4
Njets=2 E>6.0GeV
1.2
Njets=3 E>6.0GeV
1
Njets=4 E>6.0GeV
Monotonic dependence on R.
0.8
The choice can be done in a wide
range.
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1
1.2
R
18 / 34
Predictions with Pythia8, Herwig++2.7 and Sherpa2.2,
SISCone with R = 0.7
Many generators were tuned to LEP data. How do these describe
the data? We consider:
Pythia8 with LEP-I tuning;
Default Herwig++2.7;
Default SHERPA2.2 (AHADIC++).
19 / 34
Predictions with Pythia8, Herwig++2.7 and Sherpa2.2,
SISCone with R = 0.7
Fraction
Fraction
Njets=2
1
Njets=3
Njets=4
0.8
Njets=3
Njets=4
0.8
Njets=2 herwig++
0.6
Njets=2
1
Njets=2 herwig++
Njets=3 herwig++
Njets=3 herwig++
Njets=4 herwig++
Njets=4 herwig++
0.6
Njets=2 pythia8
Njets=2 pythia8
Njets=3 pythia8
0.2
Njets=2 sherpa
Njets=2 sherpa
Njets=3 sherpa
Njets=3 sherpa
0.2
0
20
30
40
Njets=4
Njets=2 herwig++
Njets=3 herwig++
Njets=4 herwig++
0.6
Njets=2 pythia8
50
Njets=2 sherpa
Njets=3 sherpa
0.2
Njets=4 sherpa
Njets=4 sherpa
0
0
Ecut,GeV
Njets=4 pythia8
0.4
0
10
Njets=3
0.8
Njets=3 pythia8
Njets=4 pythia8
0.4
Njets=4 sherpa
0
Njets=2
1
Njets=3 pythia8
Njets=4 pythia8
0.4
OPAL DP(prel.) SISCone R=0.7, s=177GeV
Fraction
OPAL DP(prel.) SISCone R=0.7, s=133GeV
OPAL DP(prel.) SISCone R=0.7, s=91GeV
10
20
30
40
50
0
10
20
30
Ecut,GeV
40
50
Ecut,GeV
Fraction
OPAL DP(prel.) SISCone R=0.7, s=197GeV
Njets=2
1
Njets=3
Njets=4
0.8
Njets=2 herwig++
Njets=3 herwig++
Njets=4 herwig++
0.6
Njets=2 pythia8
Good description of data.
√
The best one is for s = 91 GeV.
Njets=3 pythia8
Njets=4 pythia8
0.4
Njets=2 sherpa
Njets=3 sherpa
0.2
The solid lines are data, the dashed and doted are MC. The uncertainties
Njets=4 sherpa
are statistical only. Full uncertainties are in the backup.
0
0
10
20
30
40
50
Ecut,GeV
20 / 34
Predictions with Pythia8, Herwig++2.7 and Sherpa2.2,
anti-kT with R = 0.7
OPAL DP(prel.) ee-anti-k R=0.7, s=91GeV
OPAL DP(prel.) ee-anti-k R=0.7, s=133GeV
Njets=3
Njets=4
Njets=3
Njets=4
0.8
Njets=2 herwig++
0.6
Njets=2
1
Njets=2 herwig++
Njets=3 herwig++
Njets=3 herwig++
Njets=4 herwig++
Njets=4 herwig++
0.6
Njets=2 pythia8
Njets=2 pythia8
Njets=3 pythia8
0.2
Njets=2 sherpa
Njets=2 sherpa
Njets=3 sherpa
Njets=3 sherpa
0.2
0
20
30
40
Njets=4
Njets=2 herwig++
Njets=3 herwig++
Njets=4 herwig++
0.6
Njets=2 pythia8
50
Njets=2 sherpa
Njets=3 sherpa
0.2
Njets=4 sherpa
Njets=4 sherpa
0
0
Ecut,GeV
Njets=4 pythia8
0.4
0
10
Njets=3
0.8
Njets=3 pythia8
Njets=4 pythia8
0.4
Njets=4 sherpa
0
Njets=2
1
Njets=3 pythia8
Njets=4 pythia8
0.4
T
Fraction
Fraction
Fraction
Njets=2
0.8
OPAL DP(prel.) ee-anti-k R=0.7, s=177GeV
T
T
1
10
20
30
40
50
0
10
20
30
Ecut,GeV
40
50
Ecut,GeV
OPAL DP(prel.) ee-anti-k R=0.7, s=197GeV
Fraction
T
Njets=2
1
Njets=3
Njets=4
0.8
Njets=2 herwig++
Njets=3 herwig++
Njets=4 herwig++
0.6
Njets=2 pythia8
Good description of data.
√
The best one is for s = 91 GeV.
Njets=3 pythia8
Njets=4 pythia8
0.4
Njets=2 sherpa
Njets=3 sherpa
0.2
The solid lines are data, the dashed and doted are MC. The uncertainties
Njets=4 sherpa
are statistical only. Full uncertainties are in the backup.
0
0
10
20
30
40
50
Ecut,GeV
21 / 34
Hadronization corrections with Pythia8, Herwig++2.7 and
Sherpa2.2
How large and stable are the hadronisation corrections? We
consider:
Pythia8 with LEP-I tuning;
Default Herwig++2.7;
Default SHERPA2.2 (AHADIC++).
22 / 34
Hadronisation correction, anti-kT with R = 0.7
OPAL DP(prel.) ee-anti-k R=0.7, s=91GeV
OPAL DP(prel.) ee-anti-k R=0.7, s=133GeV
Njets=3 KK2f
Njets=4 KK2f
1.8
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Njets=2 KK2f
2
Njets=3 KK2f
Njets=4 KK2f
1.8
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Njets=2 pythia8
1.4
Njets=3 pythia8
Njets=2 sherpa
1.4
Njets=3 pythia8
Njets=4 sherpa
0.8
Njets=2 sherpa
1.2
0.1
0.2
0.3
0.4
0.5
Njets=4 KK2f
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Njets=2 pythia8
1.4
Njets=3 pythia8
Njets=4 pythia8
Njets=2 sherpa
1.2
Njets=3 sherpa
Njets=4 sherpa
1
0.8
0
Njets=3 KK2f
1.8
Njets=4 pythia8
Njets=3 sherpa
1
Njets=2 KK2f
2
Njets=2 pythia8
Njets=4 pythia8
1.2
T
Hadr. correction
2
Hadr. correction
Hadr. correction
Njets=2 KK2f
OPAL DP(prel.) ee-anti-k R=0.7, s=177GeV
T
T
Njets=3 sherpa
Njets=4 sherpa
1
0.8
0
0.1
0.2
0.3
Ecut/Evis
0.4
0.5
0
0.1
0.2
0.3
Ecut/Evis
0.4
0.5
Ecut/Evis
OPAL DP(prel.) ee-anti-k R=0.7, s=197GeV
Hadr. correction
T
Njets=2 KK2f
2
Njets=3 KK2f
Njets=4 KK2f
1.8
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Njets=2 pythia8
1.4
Njets=3 pythia8
Njets=4 pythia8
Njets=2 sherpa
1.2
Corrections:
Larger for 3 and 4-jet events.
Larger for lower energies.
Smaller for tuned MC.
Njets=3 sherpa
Njets=4 sherpa
1
0.8
The solid lines are old MC, the dashed and doted are new MC.
0
0.1
0.2
0.3
0.4
0.5
Ecut/Evis
23 / 34
Hadronisation correction, SISCone with R = 0.7
2
Njets=3 KK2f
Njets=4 KK2f
1.8
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Hadr. correction
Hadr. correction
Njets=2 KK2f
Njets=2 KK2f
2
Njets=3 KK2f
Njets=4 KK2f
1.8
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Njets=2 pythia8
1.4
Njets=3 pythia8
Njets=2 sherpa
1.4
Njets=3 pythia8
Njets=4 sherpa
0.8
Njets=2 sherpa
1.2
0.1
0.2
0.3
0.4
0.5
Njets=4 sherpa
1
Hadr. correction
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Njets=2 pythia8
1.4
Njets=3 pythia8
Njets=4 pythia8
Njets=2 sherpa
1.2
Njets=3 sherpa
Njets=4 sherpa
1
0.8
0
0.1
0.2
0.3
Ecut/Evis
OPAL DP(prel.) SISCone R=0.7, s=197GeV
Njets=4 KK2f
Njets=3 sherpa
0.8
0
Njets=3 KK2f
1.8
Njets=4 pythia8
Njets=3 sherpa
1
Njets=2 KK2f
2
Njets=2 pythia8
Njets=4 pythia8
1.2
OPAL DP(prel.) SISCone R=0.7, s=177GeV
Hadr. correction
OPAL DP(prel.) SISCone R=0.7, s=133GeV
OPAL DP(prel.) SISCone R=0.7, s=91GeV
0.4
0.5
0
0.1
0.2
0.3
Ecut/Evis
0.4
0.5
Ecut/Evis
Corrections:
Njets=2 KK2f
2
Njets=3 KK2f
Njets=4 KK2f
1.8
Larger for 3 and 4-jet events.
Njets=2 herwig++
Njets=3 herwig++
1.6
Njets=4 herwig++
Larger for lower energies.
Njets=2 pythia8
1.4
Njets=3 pythia8
Njets=4 pythia8
Smaller for tuned MC.
Njets=2 sherpa
1.2
Njets=3 sherpa
Njets=4 sherpa
1
Smaller than for anti-kT .
0.8
0
0.1
0.2
0.3
0.4
0.5
Ecut/Evis
The solid lines are old MC, the dashed and doted are new MC.
24 / 34
Conclusions
Presented measurements of distributions of jet rate fractions
with anti-kT and SISCone algorithms at LEP.
The old and new (Pythia8, SHERPA2.2, Herwig++2.7)
Monte Carlo describes the data well.
Studied hadronisation corrections to the presented quantities
with different hadronisation models.
The mesurements can be used for the precise αs
determination.
25 / 34
Backup slides
26 / 34
Access policy
The OPAL data is analysed in “Data Preservation“ mode. It
implies some specific features:
Absence of regular collaboration structure: groups,
spokesperson, administration.
Absence of dedicated manpower, support and infrastructure.
Still, if the data is available it can be used!
27 / 34
Systematics
The systematic uncertainties are estimated with the strategy used
in the previous analyses.
In brief the following sources were considered:
s reconstruction;
Selection procedure;
Hadronisation model;
Background modelling.
28 / 34
data/MC
1.05
1.04
1.03
1.02
1.01
1
0.99
0.98
0.97
0.96
0.95
data/MC
1.05
1.04
1.03
1.02
1.01
1
0.99
0.98
0.97
0.96
0.95
data/MC
Jet energy scale
(a)
OPAL
Jet energy scale
1.3
(b)
Jet energy resolution
1.25
1.2
1.15
1.1
1.05
1
0.95
0
0.2
0.4
0.6
0.8
1
cosθ
(c)
Jet energy scale linearity
20
30
40
50
0.9
0
0.2
0.4
0
0.6
0.8
Z 2-jet
Corrected
Z0 3-jet
Corrected
Z/γ high energy
Corrected
60
70
80
90
1
cosθ
OPAL Coll.,
“Measurement of the
mass and width of
the W boson,” EPJC
45 (2006) 307.
100
Ejet (GeV)
29 / 34
Generators reminder
KK2f :
Ultimate precision for e + e − → ff ;
Used version 4.13, CPC 130 (2000) 260;
Last version 4.22, PRD 88 (2013) no.11, 114022.
grc4f :
Background from e + e − → 4fermions;
Takes into account all contributions.
KoralW :
Monte Carlo for e + e − → ff ;
See also TAUOLA, PHOTOS and KoralZ.
30 / 34
Numerical results for some energies
First uncertainty is statistic the second is systematic
31 / 34
Results for
R = 0.7
√
s = 91 GeV, anti-kT first, SISCone second;
Ecut , GeV
Njets = 2
Njets = 3
Njets = 4
2.00
+0.0089
0.4288+0.0011
−0.0011 −0.0089
+0.0012 +0.0011
0.3370−0.0012
−0.0011
+0.0053
0.1681+0.0014
−0.0014 −0.0053
+0.0024
0.7929+0.0007
−0.0007 −0.0024
+0.0013 +0.0074
0.1914−0.0013
−0.0074
+0.0012
0.0167+0.0015
−0.0015 −0.0012
6.00
10.00
14.00
18.00
22.00
25.50
29.00
+0.0066
0.6909+0.0008
−0.0008 −0.0066
+0.0026
0.8653+0.0005
−0.0005 −0.0026
+0.0031
0.9224+0.0004
−0.0004 −0.0031
+0.0104
0.9631+0.0003
−0.0003 −0.0104
+0.0164
0.9548+0.0003
−0.0003 −0.0164
+0.0217
0.9018+0.0005
−0.0005 −0.0217
+0.0013 +0.0068
0.2599−0.0013
−0.0068
+0.0014 +0.0044
0.1313−0.0014
−0.0044
+0.0014 +0.0025
0.0756−0.0014
−0.0025
+0.0015 +0.0018
0.0265−0.0015
−0.0018
+0.0015 +0.0002
0.0032−0.0015
−0.0002
+0.0000 +0.0000
0.0000−0.0000
−0.0000
+0.0030
0.0466+0.0015
−0.0015 −0.0030
+0.0004
0.0044+0.0015
−0.0015 −0.0004
+0.0000
0.0004+0.0015
−0.0015 −0.0000
+0.0000
0.0000+0.0000
−0.0000 −0.0000
+0.0000
0.0000+0.0000
−0.0000 −0.0000
+0.0000
0.0000+0.0000
−0.0000 −0.0000
Ecut , GeV
Njets = 2
Njets = 3
Njets = 4
2.00
+0.0105
0.5251+0.0010
−0.0010 −0.0105
+0.0012 +0.0035
0.3213−0.0012
−0.0035
+0.0005
0.1143+0.0014
−0.0014 −0.0005
+0.0024
0.8115+0.0006
−0.0006 −0.0024
+0.0014 +0.0061
0.1723−0.0014
−0.0061
+0.0011
0.0152+0.0015
−0.0015 −0.0011
6.00
10.00
14.00
18.00
22.00
25.50
29.00
+0.0062
0.7158+0.0008
−0.0008 −0.0062
+0.0030
0.8761+0.0005
−0.0005 −0.0030
+0.0026
0.9270+0.0004
−0.0004 −0.0026
+0.0095
0.9610+0.0003
−0.0003 −0.0095
+0.0159
0.9580+0.0003
−0.0003 −0.0159
+0.0208
0.9111+0.0004
−0.0004 −0.0208
+0.0013 +0.0063
0.2394−0.0013
−0.0063
+0.0014 +0.0035
0.1187−0.0014
−0.0035
+0.0014 +0.0027
0.0689−0.0014
−0.0027
+0.0015 +0.0021
0.0268−0.0015
−0.0021
+0.0015 +0.0002
0.0035−0.0015
−0.0002
+0.0000 +0.0000
0.0000−0.0000
−0.0000
+0.0015
0.0397+0.0015
−0.0015 −0.0015
+0.0004
0.0042+0.0015
−0.0015 −0.0004
+0.0001
0.0004+0.0015
−0.0015 −0.0001
+0.0000
0.0000+0.0000
−0.0000 −0.0000
+0.0000
0.0000+0.0000
−0.0000 −0.0000
+0.0000
0.0000+0.0000
−0.0000 −0.0000
32 / 34
Results for
R = 0.7
√
s = 196 GeV, anti-kT first, SISCone second;
Ecut , GeV
Njets = 2
Njets = 3
Njets = 4
2.00
+0.0156
0.3368+0.0254
−0.0254 −0.0142
+0.0256 +0.0111
0.3302−0.0256
−0.0085
+0.0104
0.2285+0.0274
−0.0274 −0.0129
+0.0135
0.6569+0.0183
−0.0183 −0.0054
+0.0265 +0.0059
0.2818−0.0265
−0.0201
+0.0094
0.0517+0.0304
−0.0304 −0.0115
6.00
10.00
14.00
18.00
22.00
25.50
29.00
+0.0134
0.5626+0.0207
−0.0207 −0.0092
+0.0143
0.7256+0.0164
−0.0164 −0.0085
+0.0142
0.7675+0.0151
−0.0151 −0.0113
+0.0113
0.8136+0.0135
−0.0135 −0.0104
+0.0190
0.8285+0.0129
−0.0129 −0.0171
+0.0283
0.8382+0.0126
−0.0126 −0.0281
+0.0256 +0.0105
0.3298−0.0256
−0.0141
+0.0273 +0.0078
0.2357−0.0273
−0.0195
+0.0279 +0.0085
0.2040−0.0279
−0.0216
+0.0285 +0.0071
0.1690−0.0285
−0.0153
+0.0286 +0.0109
0.1598−0.0286
−0.0190
+0.0288 +0.0174
0.1497−0.0288
−0.0185
+0.0130
0.0978+0.0297
−0.0297 −0.0118
+0.0068
0.0276+0.0308
−0.0308 −0.0237
+0.0234
0.0038+0.0312
−0.0312 −0.0248
+0.0134
0.0108+0.0314
−0.0314 −0.0211
+0.0234
0.0246+0.0316
−0.0316 −0.0227
+0.0124
0.0148+0.0315
−0.0315 −0.0167
Ecut , GeV
Njets = 2
Njets = 3
Njets = 4
2.00
+0.0087
0.4112+0.0240
−0.0240 −0.0038
+0.0250 +0.0134
0.3605−0.0250
−0.0118
+0.0139
0.1705+0.0285
−0.0285 −0.0168
+0.0151
0.6841+0.0176
−0.0176 −0.0087
+0.0268 +0.0183
0.2637−0.0268
−0.0199
+0.0181
0.0459+0.0305
−0.0305 −0.0194
6.00
10.00
14.00
18.00
22.00
25.50
29.00
+0.0175
0.5920+0.0200
−0.0200 −0.0137
+0.0177
0.7346+0.0161
−0.0161 −0.0125
+0.0137
0.7883+0.0144
−0.0144 −0.0110
+0.0157
0.8240+0.0131
−0.0131 −0.0120
+0.0179
0.8420+0.0124
−0.0124 −0.0141
+0.0277
0.8559+0.0119
−0.0119 −0.0264
+0.0260 +0.0162
0.3088−0.0260
−0.0163
+0.0274 +0.0120
0.2293−0.0274
−0.0168
+0.0282 +0.0086
0.1859−0.0282
−0.0138
+0.0285 +0.0091
0.1651−0.0285
−0.0191
+0.0287 +0.0100
0.1531−0.0287
−0.0193
+0.0291 +0.0128
0.1323−0.0291
−0.0205
+0.0086
0.0879+0.0298
−0.0298 −0.0092
+0.0320
0.0495+0.0305
−0.0305 −0.0364
+0.0356
0.0427+0.0306
−0.0306 −0.0565
+0.0082
0.0009+0.0312
−0.0312 −0.0165
+0.0367
0.0287+0.0317
−0.0317 −0.0295
+0.0181
0.0171+0.0315
−0.0315 −0.0233
33 / 34
Results for
R = 0.7
√
s = 207 GeV, anti-kT first, SISCone second;
Ecut , GeV
Njets = 2
Njets = 3
Njets = 4
2.00
+0.0040
0.3252+0.0209
−0.0209 −0.0041
+0.0204 +0.0056
0.3578−0.0204
−0.0089
+0.0143
0.2089+0.0226
−0.0226 −0.0086
+0.0114
0.6478+0.0151
−0.0151 −0.0115
+0.0216 +0.0084
0.2777−0.0216
−0.0093
+0.0087
0.0650+0.0246
−0.0246 −0.0085
6.00
10.00
14.00
18.00
22.00
25.50
29.00
+0.0055
0.5643+0.0168
−0.0168 −0.0056
+0.0140
0.7065+0.0138
−0.0138 −0.0143
+0.0133
0.7490+0.0127
−0.0127 −0.0138
+0.0176
0.7843+0.0118
−0.0118 −0.0177
+0.0278
0.7999+0.0114
−0.0114 −0.0277
+0.0387
0.8137+0.0110
−0.0110 −0.0386
+0.0210 +0.0059
0.3158−0.0210
−0.0087
+0.0222 +0.0104
0.2391−0.0222
−0.0109
+0.0226 +0.0085
0.2097−0.0226
−0.0080
+0.0229 +0.0129
0.1886−0.0229
−0.0129
+0.0231 +0.0169
0.1721−0.0231
−0.0172
+0.0235 +0.0113
0.1493−0.0235
−0.0115
+0.0150
0.1071+0.0240
−0.0240 −0.0083
+0.0124
0.0477+0.0248
−0.0248 −0.0101
+0.0129
0.0254+0.0251
−0.0251 −0.0146
+0.0286
0.0075+0.0255
−0.0255 −0.0327
+0.0180
0.0240+0.0257
−0.0257 −0.0258
+0.0108
0.0134+0.0256
−0.0256 −0.0130
Ecut , GeV
Njets = 2
Njets = 3
Njets = 4
2.00
+0.0060
0.4005+0.0197
−0.0197 −0.0062
+0.0202 +0.0164
0.3687−0.0202
−0.0178
+0.0102
0.1725+0.0231
−0.0231 −0.0036
+0.0068
0.6784+0.0144
−0.0144 −0.0069
+0.0217 +0.0090
0.2702−0.0217
−0.0101
+0.0171
0.0371+0.0250
−0.0250 −0.0168
6.00
10.00
14.00
18.00
22.00
25.50
29.00
+0.0050
0.5903+0.0163
−0.0163 −0.0054
+0.0078
0.7320+0.0132
−0.0132 −0.0080
+0.0156
0.7674+0.0123
−0.0123 −0.0159
+0.0145
0.8008+0.0114
−0.0114 −0.0145
+0.0242
0.8188+0.0108
−0.0108 −0.0242
+0.0321
0.8371+0.0103
−0.0103 −0.0321
+0.0211 +0.0089
0.3122−0.0211
−0.0103
+0.0223 +0.0089
0.2348−0.0223
−0.0089
+0.0227 +0.0111
0.2034−0.0227
−0.0099
+0.0231 +0.0078
0.1772−0.0231
−0.0066
+0.0233 +0.0151
0.1590−0.0233
−0.0150
+0.0237 +0.0107
0.1287−0.0237
−0.0094
+0.0120
0.0832+0.0244
−0.0244 −0.0119
+0.0238
0.0072+0.0253
−0.0253 −0.0188
+0.0221
0.0026+0.0255
−0.0255 −0.0267
+0.0177
0.0043+0.0255
−0.0255 −0.0389
+0.0218
0.0162+0.0256
−0.0256 −0.0234
+0.0137
0.0097+0.0256
−0.0256 −0.0138
34 / 34