Colour-Octet-Annihilation in Leading Neutral Systems of Gluon Jetswqcd/2007/Mandl.pdf · 2008. 2....

Colour-Octet-Annihilation in Leading Neutral Systems of Gluon Jets Franz MandlQCD@Work 2007

Brigitte Buschbeck, Franz Mandl

QCD@Work 2007 Colour-Octet-Annihilation in Leading Neutral Systems of Gluon JetsFranz Mandl

Colour-Octet-Annihilation in LeadingNeutral Systems of Gluon Jets


1 Introduction• Quark jets are described well by the LUND-STRING model

(chain-like, charged ordered particle production);

• Gluon-jets are less known: JETSET/ARIADNE regard the Gluon-jetas a „kink“ in the Lund-String;

• Exists the process of the direct neutralisation of the octet field byan other Gluon by creating a 2-Gluon system ?

• Do Glueballs exist ? Predicted by QCD !

H. Fritsch and P. Minkowski, Nuovo Cimento 30A (1975)

I. Montvay, Phys. Lett. B84 (1979) 331,

C. Peterson and T.F. Walsh, Phys. Lett. B91 (1980) 455,

*)H. Spiesberger and P.M. Zerwas, Phys. Lett. B481 (2000) 236,

*)P. Minkowski and W. Ochs, Phys. Lett. B485 (2000) 139.

*) Investigate the „Gluon-corner“ in 3-jet Events!


another gluon


2


(Suppresssion by Sudakov form factor)


Colour-Octet-Annihilation in Leading Neutral Systems of Gluon Jets Franz MandlQCD@Work 2007QCD@Work 2007 Colour-Octet-Annihilation in Leading Neutral Systems of Gluon JetsFranz Mandl

3


4. Analysis4.1 The sum of charges in theleading system with a rapiditygap (sample1)

SQ = ∑qi


4.2 The dependence onthe size of therapidity gap

Subtract the offset(due to the Bose-Einstein correlations)


Estimation of the effect for pure gluon jets

At small rapidities: Gluon jets emit more particles per unit than quark

Estimate: Gluon purity (Δy)

• Directly from MC Fraction of gluon jets reduced with increased Δy Purity of gluon jet sample obtained directly from MC for each Δy

• From reduction rate 3 samples i defined: (q=udsc, b, g) fi(Δy) …… reduction rate for sample i at Δy determine: (Δy) of pure q, b, g jets F = A F’ matrix A: represents the q, b, g purities at Δy = 0 (from MC) F’ = A-1F

Apply to 2 data sets (untagged and tagged jets)

!

fi

'



5. Mass spectra

• Where in the mass spectra is the excess of neutral systems located ?

• Are the Mass spectra in enriched Gluon jets different from those in quark jets ?

a) M (= Minv) with charged particles (p>0.2GeV/c) only,

b) M with charged (p>0.2) and neutrals (mainly γ’s), E>0.5 GeV)


a) Massspectrawith onlychargedparticles

f0(980)?


All charged

Green: 2 charged

Red: ≥ 4 charged

Minv

Nr. of Jetsat Δy=1.5

Explanation of the 2-peak structure


b) Mass spectra includingcharged and neutrals


The DELPHI collaboration has investigated the leading systems of gluon and quark jets,defined by a rapidity gap, in e+e- reactions at an energy of 91.2 GeV.

One observes for (enriched) gluon jets a higher rate of neutral leading systems thanpredicted by string models (JETSET, ARIADNE).

At a rapidity gap of 1.5 and in pure gluon jets, this excess has been estimated to beabout 10% with a significance of 3.6σ.

It is expected to be of the order of 0.5% in pure gluon jets without any charge or gapselection

On contrary, quark jets do not show any excess.

Invariant mass spectra, which include charged and neutral particles show clearly, thatthe excess is concentrated at low Minv ≤ 2 GeV/c2.

The observed excess, its increase with gap-size and gluon purity is in agreement withexpectations, if the hitherto unobserved but predicted process of octet neutralization ofthe gluon field takes place in nature;

Its concentration at low invariant mass could be a signal of gluonic states, predicted byQCD.

Summary


GLUEBALLS ?

Experimental:

search since several tenth of years!

p-pbar reactions at rest,

central high energy hadronproduction,

J/Ψ radiative decay

π π scatteringcontroversial interpretations! Is it a broad object,interfering with known qqbar resonances with the samequantum nambers?

Excess of neutral systems is concentrated in the low masspart ⇒ Gluonic states ⇒ GLUEBALLS ?


GLUEBALLS ?

Excess of neutral systems is concentrated in the lowmass part ⇒ Gluonic states ⇒ GLUEBALLS ?

Theoretically:

lattice calculations predict the lightest Glueball inthe scalar channel with JPC = 0++ at about 1600Mev/c2.

QCD sum rules predict also a possible gluonic statenear 1 Gev/c2.

Alternatively it could be also a very broad object.


Results from LatticeCalculationsSee E. Klempt,

PSI ZUOZ Summer School.Phenomenology of Gauge

Intertactions, 13.-19. 8. 2000,hep-ex/0101031


E. Klempt, PSI Zuoz Summer School, Phenomenology of GaugeInteractions, 2000, arXiv: hep-ex/0101031 v1, Jan.2001

GLUEBALLS ?

P. Minkowski and W. Ochs, Proc. of the Ringberg Workshop on New Trends in HERA,Sept. 2003, arXiv: hep-ph/0401167, 22.Jan. 2004


•The experimental detection of Glueballs which arean early prediction of QCD is of primary interest.

•The present study gives evidence for the existenceof octet neutralization of the gluon field and thepossibility that new information on gluonic systemscan be obtained from the comparative study of theleading particle systems in quark and gluon jets.

•This is especially important for future studies withmuch better statistics at LHC where gluon jets willbe produced frequently.


SPARES


J.W. Gary,

Recent results in jetphysics,

Int. Symp. on MultiparticleDynamics,

Krakow, Sept. 2003


Strategy: compare measured 3-jet events with the LUND-STRING Model (JETSET/ARIADNE)


4.3 The dependence on the Gluon purity


Make a rough estimate of the amount of excess in allpure Gluon jets (without charge (SQ) or gap-selection)

1. At SQ=0, but without gap-selection: Rg(0) ≈ R‘g(1.5)∗fg(1.5), fg(1.5)=0.11

Rg(0) ≈ 0.011

extending this to Δy=1.0 : 1-2% excess in systems with SQ=0 and Δy=0

2. All Gluon jets without a charge (SQ) selection or gap-selection: Pg ≈ Rg(0) ∗Pg(0,0), Pg(0,0) = 0.26

Pg ≈ 0.015 ∗0.26 = 0.04

Result: A possible octet neutralisation occurs with aprobability of about 1/2 %.


Mass spectra with charged only, actionof polar jet-angle cut

No polar angle cut Polar angle cut at 50 deg.


Δy=1.0

Δy=1.5


6. Studies with the detector response matrix

• All comparisons are done on detector level• Systematic shifts of mass spectra with neutrals expected: Due to

the loss of neutrals ( mainly γ‘s ), the measured spectra are shiftedto lower mass values by 0.3-0.5 GeV/c2

• Study with the detector response matrix with the SVD (SingularValue Decomposition) Approach

A.Höcker and V. Kartvelishvili, “The SVD Approach to Data Unfolding“,MC-TH-95/15, LAL-95/55, arch-ive/9509307, August 1995


The detector response matrix


“The red dragon”


GLUEBALLS ?

P. Minkowski and W. Ochs, Proc. of the Ringberg Workshop on NewTrends in HERA, Sept. 2003, arXiv: hep-ph/0401167, 22.Jan. 2004

Colour-Octet-Annihilation in Leading Neutral Systems of Gluon Jetswqcd/2007/Mandl.pdf · 2008. 2....

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