colour reconnection in w w

OPAL Thursday Meeting, 21-Oct-2004

Nige Watson 1

Colour Reconnection in WColour Reconnection in WWWColour Reconnection in WColour Reconnection in WWW

“Particle Flow” CR analysis used by ADLO

Basis for combination by LEP WG L published -1.5yr, D ~end 2004, A

perhaps not? O -> Ed. Board (tomorrow)

Outline Particle flow method Particle flow distributions in data Quantitative measures Inclusive multiplicity (Miriam Watson) Systematics Summary


Nige Watson 2

Colour Reconnection in WColour Reconnection in WWWColour Reconnection in WColour Reconnection in WWW

WWqqqq, default selection

W-j-j association,WWJPLH

4 planes defined by jet axes

from 4-c fit

Most energetic jet jet 1; jet 2 from same W

Choose jets 3, 4 to minimise angles: (j2-j3)+ (j4-j3)

Particles projected onto 4 planes

Interested in particles “between” jets

True for >1 plane? Assign to closest in angle

Highest energy jet

j1 j2

j4 j3

W2

W1


Nige Watson 4

All data 189-206 GeVAll data 189-206 GeVAll data 189-206 GeVAll data 189-206 GeV

Normalised particle density no-CR models (upper) Sk CR models (lower)

(to be added, with reduced data sample, 189/200/206)

Correlations between bins

Compare intra-W with inter-W


Nige Watson 5

Ratio intra-W/inter-W particle density: Rflow

no-CR models (upper)

CR models (lower)

Most sensitivity outside jet cores

Particle FlowParticle FlowParticle FlowParticle Flow


Nige Watson 6

Quantitative measureQuantitative measureQuantitative measureQuantitative measure

Quantify using ratio of sums, RN Inverted since PN448 for ADLO consistency

bin-bin correlations important, integrate event-by-event Range of integral must avoid jet-cores

D assign error as variance in MC subsets, AL use empirical correlation matrix from MC, O calculate error.

8.0

2.0 RR

8.0

2.0 RR

regionsW -interdχdχd1

regionsW -intradχdχd1

nN

nN

R

event

eventN


Nige Watson 10

Inclusive MultiplicityInclusive MultiplicityInclusive MultiplicityInclusive Multiplicity

First OPAL analyses used inclusive measurements (Nch, xp, etc.)

Main measure used by theorists in all CR papers

From all data, 189-206GeV

n4q: 38.76 +- 0.13 +- 0.27

nqqlv: 19.39 +- 0.11 +- 0.09

=-0.04 +- 0.25 +- 0.02

nqq: 19.39 +- 0.06 +- 0.11

206 GeV206 GeV


Nige Watson 11

Inclusive MultiplicityInclusive MultiplicityInclusive MultiplicityInclusive Multiplicity

Taus not used due to poorly defined tails in distribution

206 GeV206 GeV

qq onlyqq only


Nige Watson 12

EEcmcm evolution of evolution of multiplicitiesmultiplicities

EEcmcm evolution of evolution of multiplicitiesmultiplicities

Measure <Nch> for 4q, qqlv, difference

Points are fully corrected data (stat. errs. shown)

Curves hadron level predictions

Data show No significant Ecm

dep. No diff. 4q/qqlv

Average to giveW->qq multiplicity

4q4q qqlvqqlv

4q-2*qqlv

4q-2*qqlv


Nige Watson 13

Summary of systematicsSummary of systematicsSummary of systematicsSummary of systematics Harmonise systematics in the two analyses as appropriate

Average of all s made, assuming Flat energy dependence Energy dependence correctly described by Koralw and Jetset

This case, average to 199.52 GeV and compare with full set CR models

WW Hadronisation Model differences between {Jt,Hw,Ar, Jt/}

RN – model differences Multiplicity, unfold JT as if background free data, all models

BEC, {intra-W — no-BE}

Background subtraction Z qq, vary production cross-section 5% qqqq, 20%

qqlv Z qq Hadronisation model, max. effect from default to

kk2f+{Py,Hw,Ar} and Py+Py ZZ, vary production cross-section 11% (ZZ PR) 4-f modelling: use KandY in place of Koralw/grc4f for

non-WW-like 4f (+correct WW by -2.5%)


Nige Watson 14

Summary of systematicsSummary of systematicsSummary of systematicsSummary of systematics

Detector effects Variation of track quality cuts in data/MC

Unfolding method Compare direct multiplicity method with (main) xp

measurement

Energy dependence Difference between Jetset parametrisation and s indep.

Cross-check or RN with qqlv events


Nige Watson 15

qqlv events for particle qqlv events for particle flowflow

qqlv events for particle qqlv events for particle flowflow

Normalised particle density, using qqlv events no-CR models

Data at s~200 GeV

Compare intra-W with inter-W regions

inter interintra

intra


Nige Watson 16

Summary of particle flow Summary of particle flow systematicssystematics

Summary of particle flow Summary of particle flow systematicssystematics


Nige Watson 17

Summary of multiplicity Summary of multiplicity systematicssystematics

Summary of multiplicity Summary of multiplicity systematicssystematics


Nige Watson 18

Summary of data, CR sensitivitySummary of data, CR sensitivitySummary of data, CR sensitivitySummary of data, CR sensitivity

Predicted stat. sensitivity

Assumes CR models as at 199.5 GeV

Extreme scenario of SKI excluded

Most models completely compatible with data Herwig the least favoured of non-CR models


Nige Watson 19


Nige Watson 20

Compare average RN with SKI

Best agreement for 34% events reconnected

Scan of reconnection probability in SKIScan of reconnection probability in SKIScan of reconnection probability in SKIScan of reconnection probability in SKI

Better to scan in % reconnected

than model parameter kI:

reconnected fraction asymptotic with kI

% CR


Nige Watson 21

SummarySummarySummarySummary Updated analysis using 189—208 GeV data

Data (just) exclude extreme case SKI Data and models with/without CR compatible Now use 2 phase Ar1 model which we implemented for qqlv

Data most consistent with SKI when 34% events reconnected Limits weaker than previously due to detector corrections May be changed during (by) editorial process

We find enhanced sensitivity (~x2) with Ar2/Ar1-2-phase model

Inclusive multiplicity analysis included (Miriam)

Editorial board waiting…

colour reconnection in w w

Documents

cr papersfrom

intraw regions

binscompare intraw

wwparticle flow cr analysis

jet axes

corrected data

c fitmost energetic

itplot of result data