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Exploring Low Mass Scalars: Challenges and Opportunities in Hadron Physics

This presentation discusses the complex landscape of low mass scalar states below 2 GeV, highlighting the difficulty in their production and analysis. Key features include inverted spectra and a controversial extra f0 state, suggesting significant space for exotic states. The sigma pole is present but not a Breit-Wigner resonance, manifested as mass distribution bumps. We examine strong couplings of f0(980) and a0(980) to kaons and issues with isospin violations, drawing on recent advances from BES3. The need for further experimental insights into the nature of hadrons, particularly scalar states, is emphasized.

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Exploring Low Mass Scalars: Challenges and Opportunities in Hadron Physics

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  1. Low Mass Scalars - Experimental C.Bini Sapienza Università and INFN Roma 22 June 2012

  2. A richstructureofstatesbelow2GeV hard to produce and toanalyze. Twointerestingfeatures in the twomultiplets:  inverted spectra  one extra f0 state (I=0) (even if strongly controversial) Muchspaceforexotics: 4q + gluonium

  3. Fewclearpoints: • The sigma pole isthere, but IT IS NOT a BW (aspointed out severaltimesbyD.Bugg). Itmanifestsitselfas a bump in mass distributions or Dalitzplots, tipically people needittofit data, but “handlewith care”; • f0(980) and a0(980) are stronglycoupledtoKaons, hencehave a large s-quark contentin theirwavefunctions • (KLOE and NovosibirskfSg results); • Problemswithisospin (violationsobserved (seeJ/ygppp) talk byB.Liu; • ggisapparentlynot conclusive (evenifinterestingworks are there, seePennington), butprobably more insightisneeded on this.

  4. BES3 is in the frontlineforthisphysics (J/ydecays): poorstatisticsis no more a problem

  5. Notonlyimprovementofstatistics, butalsoof detector performance BES3 BES2 Strong reductionof background due toimprovement in gdetection.

  6. BES presented at thisconference a detailedstudyof the ppamplitude in J/ygp0p0 with PWA (covariant tensor formalism) (B.Liu). f0(980) and f0(1370) belowsignificance limits

  7. BES presented MC testsof MIPWA and conclude:

  8. “a nightmare for experiment and a paradise for theory!” (S.Eidelman) Conclusionfromanexperimentalistpointofview: not a nightmarebut a sortof “frustration”: so beautiful and high quality data and not a firmconclusionfromthem. Are “newexperimental data badlyneeded” ? Bottomline: the nature ofhadrons (and of scalar hadrons in particular) isintrinsicallycomplicated, out ofour full understanding at leastnow. A realstepforward in interpretationisbadlyneeded.

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