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Hadron multiplicity induced by top quark decays at the LHC

Hadron multiplicity induced by 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.

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Hadron multiplicity induced by top quark decays at the LHC

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  1. Hadron multiplicity inducedby top quark decays at the LHC R.Ryutin, IHEP, Protvino QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  2. Plan • Motivations and outlook • Basic model • Numerical estimations for the LHC • Experimental situation. • Summary QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  3. 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. QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  4. Multiplicity measurements in e+e- → t anti-t 2 t t t* t + - e+ t* t* γ*, Z* - - t t - • Advantages: • t-anti-t is a singlet state • t is heavy and have small life-time • Assumption: independent fragmentation • of on-shell t and anti-t: • analogous to e+e- =>W+W- , experimentally confirmed b 2 t* b e- - b* + t t* W W t t Test of QCD independent on fragmentation models! Main results do not depend on the exact form of QCD CALC. Phenom. parametrization normalized to real data (the mean hadron multiplicity in a virtual gluon with a fixed p²) local parton-hadron duality QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  5. Basic model [R. Ryutin, ArXiv: 1105.4776] gluon propagator p • p 2 h h 2 [ E. Leader, E. Predazzi, ArXiv: 1101.3425] QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  6. Multiplicity measurements in pp → X t anti-t Basic mechanism of t anti-t production at LHC (also with virtual(!) gluon) t 2 t* t* t + + + + + - t* - t = + + No pT(jet) cuts pT(t)>10 GeV, pT(g)>5 GeV pT(t)>30 GeV, pT(g)>10 GeV 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) 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 QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  7. Multiplicity measurements in pp → X t anti-b 2 2 t t q t t* W* t* + + + - - - - q' b* b* b - - b b • 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) No pT(jet) cuts pT(t)>30 GeV, pT(g)>15 GeV pT(t)>60 GeV, pT(g)>30 GeV QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  8. Multiplicity measurements in pp → X t q’ t 2 t* t + + + q‘ q‘* q‘ t • (b+q) may be nonsinglet=> pt(jet)>15-20 GeV to suppress interaction with beam remnants • cross-section is rather high at LHC (~250 pb at 14 TeV) b t* W* q‘* q q‘ No pT(jet) cuts pT(t)>30 GeV, pT(g)>15 GeV pT(t)>60 GeV, pT(g)>30 GeV fixed by the low energy data Looks the most interesting process for this measurement, since we have the possibility to estimate the multiplicity from beam remnants plus color reconnection effects and use it in other processes. QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  9. Multiplicity measurements in pp → X t W b t 2 + + + + + + + W = + • (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 GeV pT(t)>30 GeV, pT(g)>15 GeV QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  10. Experimental situation Example of complicated fragmentation picture in top anti-top events at the LHC Beam remnants Color interaction of beam remnants with Final State Radiation from top or bottom quarks. PDF t t* “hadrons from t decay” Result of t anti-t interaction - - t* t PDF QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  11. 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-tbarithe 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: direct test of QCD calculations independent on fragmentation models. to check independent fragmentation of heavy quarks. to check parton-parton-C.M.Energy dependence of hadron multiplicities. to estimate multiplicity from beam remnants plus from color reconnection effects in t-channel single top for further use in other processes 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 could extract number of tracks which are included into hadronic cluster from single t or t anti-t. QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

  12. Backup slides QFTHEP 2011, Sochi, Russia Top Physics R.Ryutin

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