hadron multiplicity induced by top quark decays at the lhc

Hadron multiplicity inducedby top quark decays at the LHC

R.Ryutin, IHEP, Protvino

QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

Plan


• Motivations and outlook• Basic model• Numerical estimations for the LHC• Experimental situation.• Summary

Bibliography


[1] A.V. Kisselev and V.A. Petrov, “Multiple hadron production in e+e- annihilation induced by heavy primary quarks: New analysis”, Phys. Part. Nucl. 39 (2008) 798.[2] A.V. Kisselev and V.A. Petrov, “Hadron multiplicity in e+e- events induced by top quark pair at the ILC energy”, PMC Phys. A 2 (2008) 3.[3] A.V. Kisselev and V.A. Petrov, “Hadron multiplicities in e+e- annihilation with heavy primary quarks”, Eur. Phys. J. C 50 (2007) 21.[4] A.V. Kisselev and V.A. Petrov, “On hadron multiplicities in e+e- events induced by massive quarks”, Z. Phys. C 66 (1995) 453.

Multiplicity measurements in e+e- → t anti-t


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(the mean hadron multiplicity in a virtual gluon with a fixed p²)

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Advantages:- t-anti-t is a singlet state- t is heavy and have small life-timeAssumption: independent fragmentation of on-shell t and anti-t: analogous to e+e- =>W+W- , experimentally confirmed

QCD CALC.

Phenom. parametrizationnormalized to real data

Test of QCD independent onfragmentation models! Main results do not dependon the exact form of

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Basic model


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Multiplicity measurements in pp → X t anti-t


Basic mechanism of t anti-t production at LHC (also with virtual(!) gluon)

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MOTIVATIONS: - to check directly (independent on fragmentation model!) QCD predictions for multiplicities in jets, especially induced by a virtual gluon ( is normalized to the real data!), - to check model independent fragmentation of t anti-t,- to check (visible!) parton-parton-C.M.Energy dependence of

)( 2kN g

t*

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++

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Here t-anti-t may be a nonsinglet state, but interaction with beam remnants can be suppressed if we take pT(jet)>15-20 GeV

Cross-section is high (~900 pb at 14 TeV)

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No pT(jet) cutspT(t)>10 GeV, pT(g)>5 GeVpT(t)>30 GeV, pT(g)>10 GeV

Multiplicity measurements in pp → X t anti-b


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- similar to e+e-, W* is a color singlet => color reconnection with beam remnants is small

but cross-section is small(~10 pb at 14 TeV)

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Multiplicity measurements in pp → X t q’


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cross-section is rather high at LHC (~250 pb at 14 TeV)

fixed by the low energy data

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Looks the most interesting process for thismeasurement, since we havethe possibility to estimate the multiplicity from beamremnants plus color reconnection effects and use itin other processes.


Multiplicity measurements in pp → X t W


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- (b+g) may be nonsinglet => pt(jet)>15-20 GeV to suppress interaction with beam remnants

intermediate cross-section at LHC (~50 pb at 14 TeV) No pT(jet) cuts

pT(t)>10 GeV, pT(g)>5 GeVpT(t)>30 GeV, pT(g)>15 GeV

Experimental situation


t*

t*-

t

t-

Color interaction of beam remnants withFinal State Radiation from top or bottomquarks.

Example of complicated fragmentation picture in top anti-top events at the LHC

PDF

PDF

Beam remnants

“hadrons from t decay”

Result of t anti-t interaction

Summary


It is proposed to extract average charged multiplicity of hadrons in "t-induced-jets" in single-top and t anti-t events. This work is based on ideas of [1-4], where authors have calculated charge hadron multiplicities for t-tbar production in e+e- annihilation. The basic argument for calculations is the independent fragmentation of tops. In e+e- it was experimentally proved for e+e-=>W+W- (for t-tbar ithe situation is similar).At LHC the experimental situation is more difficult, since jet partons can interact with beam remnants, but: a) in s-channel single top the situation is similar to e+e- (W* is a color singlet), b) in other processes we can take jets with high pt, and such interaction will be suppressed.- Numbers nb, nW, nt, nq are fixed and energy independent (calculated by data fitting at low energies).- Numbers are calculated in QCD, where are independent on fragmentation model and fixed by data fitting at low energies (Local Parton-Hadron Duality).Motivations:a) direct test of QCD calculations independent on fragmentation models.b) to check independent fragmentation of heavy quarks.c) to check parton-parton-C.M.Energy dependence of hadron multiplicities.d) to estimate multiplicity from beam remnants plus from color reconnection effects in t-channel single

top for further use in other processese) we can calculate also the difference to cancel effects of color reconnection and

beam remnants Final task: to extract number of tracks in jets which are produced in top quark decay.Comments: to estimate efficiencies etc. we can use any MC generator for top production. To suppress (estimate) dependence on a fragmentation model we can use several different models (generators: PYTHIA, HERWIG and so on). At the same time with the top-mass reconstruction procedure (in hadronic mode) we couldextract number of tracks which are included into hadronic cluster from single t or t anti-t.

gMN gN

qQQq NNN

Backup slides


15 30 5 10 0 0

),( ),-( min,min, GeVjetgkGeVjetqp

hadronictt

leptonicthadronict ,

leptonictt

hadron multiplicity induced by top quark decays at the lhc

Documents

e e t

e e events

e e annihilation

case t antit

shell t

physics r

singlet state t

mean hadron multiplicity