Download presentation

Presentation is loading. Please wait.

1
Multijets in e+e- annihilations Hasko Stenzel

2
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 2 Outline Jet rates and algorithms energy evolution measurements of α s 4-jet analyses color factors measurements of α s quark mass effects Multijet event shapes NP-analysis out-of-plane momentum non-global variables beyond 4-jets mostly perturbative QCD !

3
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 3 Jet algorithms Jet definition based on a pair-wise track metric JADE algorithm Durham/k t algorithm Cambridge ordering parameter

4
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 4 Jet rates Corrections applied for: background subtraction (LEPII) ISR/FSR QED corrections acceptance/efficiency detector resolution Corrected distributions represent the hadron level. Hadronisation corrections are applied to perturbative predictions (e.g. for fits). Hadr. corrections Exp. uncertainties Detector corrections Hadronisation uncertainty claimed ~2% at LEPI < 1 % at LEPII

5
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 5 Energy dependence of jet observables As in the case of event-shape Variables, jet rates, mean jet multiplicities and differential jet rates are evolving with energy through the running of α s. 3-jet fraction mean jet multiplicity

6
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 6 Measurements of α s from jet observables Observables derived from jet rates: differential two jet rate mean jet multiplicity mean jet multiplicity differential 2-jet rate Fits to the data with perturbative prediction O(α s 2 )+ NNLA, LogR matching (mostly in the 3-jet region)

7
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 7 Results from an OPAL analysis Observables derived from jet rates: differential two jet rate mean jet multiplicity Cambridge and Durham Measurements at LEPI and LEPII Observableα s (91.2)Δ stat Δ exp Δ pert Δ had Δ tot D2CD2C 0.1147±0.0004±0.0017±0.0030±0.0026±0.0043 D2DD2D 0.1199±0.0004±0.0025±0.0037±0.0017±0.0048 0.1254±0.0005±0.0013±0.0037±0.0033±0.0051 0.1272±0.0004±0.0006±0.0034±0.0039±0.0052

8
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 8 4-jet observables 4-jet observables have been used extensively to determine QCD color factors α s (fixing color factors to QCD) using NLO calculations O(α s 3 )+ NNLA L3

9
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 9 QCD color factors in parton splitting 2 2 2 CFCF CACA nfTRnfTR QCD : SU(3) C F =4/3, C A =3, T R =1/2

10
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 10 Color factors from 4-jets Leading order diagrams for 4-jet production

11
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 11 Observables in 4-jet system Bengtsson-Zerwas-Angle: angle between (p 1 x p 2 ) and (p 3 x p 4 ), ie. angle between planes P1 and P2 spanned by the two high and the two low energetic jets P2 P1 p1p1 p2p2 p3p3 p4p4 Angles between the 4 jets, e.g. Complete set of observables: + R 4 (y cut ) + y 23

12
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 12 NLO fits to angular variables and jet rates Including NLLA resummation

13
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 13 Results of simultaneous fit to α s and color factors α s (M Z )CACA CFCF ALEPH0.119±0.006±0.0262.93±0.14±0.581.35±0.07±0.26 OPAL0.120±0.011±0.0203.02±0.25±0.491.34±0.13±0.22 QCD34/3

14
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 14 Determination of α s from 4-jet observables (fixing color factors to QCD) OPAL recently analysed 4-jet rate D-parameter T minor at LEPI and LEPII

15
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 15 OPAL results on α s from 4-jet observables OPAL resultsα s (M Z ) ± Δ stat.Δ exp.Δ had.Δ scale.Δ mass R 4 (Durham)0.1182 ± 0.00030.00150.00110.00120.0013NLO+NLLA D-parameter0.1047 ± 0.00140.00370.00610.0052-NLO x µ =1 T minor 0.1318 ± 0.00160.00560.00230.0111-NLO x µ =1 The uncertainty for α s from 4-jet observables is reduced wrt 3-jet case:

16
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 16 ALEPH/DELPHI results on α s from R 4 α s (M Z ) ± Δ stat.Δ sys.Data set OPAL0.1182 ± 0.00030.002691-209NLO+NLLA ALEPH0.1170 ± 0.00010.002291NLO+NLLA DELPHI0.1175 ± 0.00050.0030LEPINLO x µ opt DELPHILogarithmic slope = 1.14 ± 0.3689-209QCD: 1.27 ± 0.10 DELPHI tested the energy dependence of α s from 4-jets at E=150 GeV:

17
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 17 Testing b-quark mass effects in the 4-jet rate Cambridge y cut =0.0085Δ sys. R 4 bl 0.898 ± 0.0140.014 m b (MZ)3.56 ± 0.330.43 MbMb 4.61 ± 0.410.54 DELPHI analysed flavour tagged 4-jet ratios: in order to extract the b-quark mass: preliminary result:

18
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 18 non-perturbative analysis of 4-jet observables L3α s (M z )α 0 (2 GeV) D-parameter 0.1046 ± 0.0078 ± 0.0096 0.682 ± 0.094 ± 0.018 all combined 0.1126 ± 0.0045 ± 0.0039 0.478 ± 0.054 ± 0.024 L3 analysis of mean value of D-parameter Results:

19
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 19 other 4-jet observables BnBn narrow jet broadening MlMl light jet mass T minor Thrust Minor, AKA K out OOblateness, T M -T m y 34 4-jet resolution parameter … measured at LEPI & LEPII but not analysed in the scope of power corrections …

20
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 20 out-of-plane momentum for near-to-planar configurations … with different y cuts …

21
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 21 non-global variables … sensitive to local radiation in restricted phase space regions: single jet mass and single jet broadening

22
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 22 beyond 4-jets 5- and more jet rates, y ij multijet resolution parameters

23
13.01.2006 FRIF workshop e+e- multi-jets H.Stenzel 23 Conclusion Multijet observables (mostly 4-jets) have given access to precision measurements of α s color factors test of quark mass effects many variables have been measured D-parameter, T minor, Oblateness, y 34 out-of-plane momenta non-global variables few of them have been analysed for power corrections D-parameter The potential of ≥5-jet configurations is to be explored.

Similar presentations

© 2020 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google