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Anomalous Soft Photon Production in Multiple Hadron Processes

Anomalous Soft Photon Production in Multiple Hadron Processes. Vassili Perepelitsa ITEP, Moscow/IFIC, Valencia for WA83, WA91, WA102 and DELPHI Collaborations. Content. Introduction: The puzzle of anomalous soft photons Experiments with hadronic beams LEP, DELPHI observations:

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Anomalous Soft Photon Production in Multiple Hadron Processes

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  1. AnomalousSoftPhoton ProductioninMultipleHadronProcesses Vassili Perepelitsa ITEP, Moscow/IFIC, Valencia for WA83,WA91,WA102 and DELPHI Collaborations

  2. Content • Introduction: The puzzle of anomalous soft photons • Experiments with hadronic beams • LEP, DELPHI observations: experimental technique; the signal; cross-checks; • Striking behaviour of the signal • Discussion

  3. Content • Introduction: The puzzle of anomalous soft photons • Experiments with hadronic beams • LEP, DELPHI observations: experimental technique; the signal; cross-checks; • Striking behaviour of the signal • Discussion

  4. Theory:Bremsstrahlungfromexternallinesshoulddominate • SoftPhotons: having transverse momenta pT<< pT of typical transverse momenta of hadrons in HE interactions=300-400MeV/c • Lowtheorem/Gribovextension ⇝ ISR FSR Radiationfromcentralblob ⇝ ⇝ and Enhanced Suppressed 2 2 M ~ 1/[(p – k) – m ] = 1/2pk

  5. Bremsstrahlungcalculations where K and k denote photon four- and three-momenta, P are the four-momenta of all the charged particles participating in the reaction. ƞ = +1 for negative incoming and for positive outgoing particles, ƞ = -1 for positive incoming and negative outgoing particles, and the sum is extended over all the N + 2 charged particles involved. The last factor in the integrand is a differential hadron production ratio.

  6. CERNWA27:beginningthepuzzle(1983-1984) + • K p hadrons + gamma at 70 GeV/c BEBC Photons: -0.001<X <0.008, p <60 MeV/c After subtraction of photons coming from all known hadronic decays the residual signal was found to be similar in shape to the brems- strahlung, but bigger in size by a factor of about four = 4.0 ± 0.8 In such a way the effect of anomalous soft photons has F T Signal/Brems arrived

  7. CERNNA22andWA83:confirmationofthesignal • CERNNA22 (1990-1991), EHS Spectrometer πp hadrons + gamma at 250 GeV/c K p hadrons + gamma at 250 GeV/c p < 40 MeV/c = 6.9 ± 1.3 (pion beam) = 6.3 ± 1.6 (kaon beam) • CERNWA83 (1985-1992), Ω Spectrometer+El.Mag.Cal. πp hadrons + gamma at 280 GeV/c p < 10 MeV/c = 7.9 ± 1.6 + + T Signal/Brems Signal/Brems _ T Signal/Brems

  8. WA91experiment,π-p exposure, 280 GeV/c

  9. WA91eventexamples

  10. WA91 raw signal

  11. WA91 energy dependence dNɣ α — = A (—), E E =1 GeV dE E 0 0 Signalenergydependenceagreeswiththatofthebremsstrahlung

  12. WA91 results -3 -3 Signal/Brems

  13. WA102experiment, pp exposure, 450 GeV/c

  14. WA102 soft photon events

  15. WA102 pT and angular distributions

  16. WA102 results -3 -3 Signal/Brems

  17. Fixed target experiments + + + - -

  18. LEP, DELPHI observations • Signal discovery • Check-ups • Muon inner bremsstrahlung: control experiment • Signal dependence on the parent jet characteristics • Non-trivial behaviour with the jet neutral and total multiplicities

  19. LEP,DELPHIobservations • Signal discovery EPJC47(2006)273 • Check-ups • Muon inner bremsstrahlung: control experiment EPJC57 (2008) 499 • Signal dependence on the parent jet characteristics CERN-PH-EP/2009-14 • Non-trivial behaviour with the jet neutral and total multiplicities

  20. TheDELPHIdetector

  21. Typical hadronic event with soft ɣ + <— e , p=390MeV/c - e , p=100MeV/c —›

  22. High neutral flow soft ɣ Eɣ=630MeV —› Neutral jet energy=40GeV—›

  23. Signalobservation Signal/Brems Signal/Brems =3.4±0.2±0.6 =4.0±0.3±0.8

  24. DELPHI results -3 -3 Signal/Brems

  25. Check-ups Changinggenerator Testwithchargedparticles Difference/Signal = 1:7 Difference/Signal = 1:11

  26. Testwithneutralpions Twoconvertedphotons Converted + HPC photons Combined upper limit: RD/MC < 1.015 at 95% CL

  27. DELPHI dimuon event

  28. thesameevent, the photon region

  29. + _ Muon inner bremsstrahlung in μμ events of Z decays 0

  30. Deadcone of the muon bremsstrahlung Г = 432 Max at √3/Г 4 mrad 2 Max at 1/Г

  31. Dependences on jet characteristics Jet momentum Jet charged multiplicity SIMILARLY TO BREMSSTRAHLUNG

  32. Dependences on jet mass and hardness κj = Ejet sin θ/2 mjet = √ Ejet ― pjet 2 2 Θ is angle to the closest jet Similarly to bremsstrahlung

  33. Dependences on Nneu and Npar SURPRISE!

  34. Whataboutexplanation? • No theoretical explanation of the phenomenon still exists, in spite of the problem being under active investigation.

  35. Testing theoretical models StrongdependenceonNneusuggests: a) either the radiation comes from individual quarks and/or quark-antiquark pairs; b) or it comes, due to some collective effects, from a jet as a whole. Collective models fail experimental tests: no dependence on Mjet, neither on jet net charge (collective behaviour predicts Nnet dependence). Noncoherentmodels agree well with linear dependence on total particle multiplicity (the radiation ~ sum of quark charges squared) Modificationofnoncoherentapproach: consider quark-antiquark pairs as radiating (electromagnetic) dipoles: d = Ʃ q i r i 2 ---> but fail to explain stronger dependence on Nneu example: LUND string model of fragmentation; needs 2-order enhancement! 2 —› —› i=1

  36. Stringfragmentationmodel

  37. Listof(failed)models • String (Lund) model • Van-Hove/Lichard model (cold quark-gluon plasma, via processes qq->gɣ, qg->qɣ) • Collective model (Barshay’s pion condensate) • Armenian model (Unruh-Davies effect) • Nachtmann’s model (quark synchrotron radiation in the stochastic QCD vacuum) • Shuryak’s model (confinement forces) _

  38. Modelsstillalivebutunderdeveloped • Internal quark loop model (Simonov Yu.A.): based on nonperturbative QCD methods applied to the large size systems (contains a strong enhancement mechanism) • Gluon dominance model (Kokoulina E.S.) appeals to a new physics phenomenon: exitation of physical vacuum leading to thermal radiation with T ~ 30 MeV _

  39. Wong’s model(arXiv:1001.1691) Exploits longitudinal dominance and transversal confinement of fragmentation process in order to use the formalism of 2-dimensional QED (QED2) for calculation of anomalous soft photon yield associated with the meson production. Production of mesons in the model arises from the oscillations of colour charge densities of the quark vacuum in the flux tube when a quark and antiquark pull away from each other at high energies. Because a quark carries both a colour charge and an electric charge, the underlying dynamical motion of quarks will also generate electric charge oscillations which will lead to ASP production. _

  40. Is it a tail of New Physics?

  41. Is it a tail of NewPhysics?

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