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2 photon physics @ BaBar

Trigger Workshop CalTech – 2 nd Dec 2004. 2 photon physics @ BaBar. Jamie Boyd. Introduction. PEP-II is a: B-Factory / Charm Factory / Tau Factory Also a 2 Photon Physics Factory Little 2 Photon analysis done to date with BaBar data though

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2 photon physics @ BaBar

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  1. Trigger Workshop CalTech – 2nd Dec 2004 2 photon physics @ BaBar Jamie Boyd

  2. Introduction • PEP-II is a: • B-Factory / Charm Factory / Tau Factory • Also a 2 Photon Physics Factory • Little 2 Photon analysis done to date with BaBar data though • Trigger and Filter very important for 2 photon physics as • Low multiplicity final states • Low energy/mass final states Jamie Boyd

  3. Overview • This is a very short talk with 2 aims • Try to show that there is interesting 2 photon physics that can be done at BaBar • We need to think about this physics when making trigger/filter decisions • Will show simple MC study results for • 2 photon -> 2 charged tracks (tagged & untagged) • 2 photon -> 2pi0’s (tagged & untagged) Jamie Boyd

  4. Motivation • BaBar has orders of magnitudes more stats than most of the old experiments where many 2 photon measurements were made – AND has better detector • BUT trigger/filters and detector not optimised for this type of physics • QCD studies • Distinguish between different QCD models – test pQCD • Resonance structure • Can study resonance parameters and partial widths • Glueball / Exotic particle hunting • Glueballs shouldn’t couple to photons (much) Jamie Boyd

  5. γγ -> 2 tracks - Efficiency pi+ pi- MC (not near threshold – see next slide) Skim inefficiency all from BGF Jamie Boyd

  6. γγ -> 2 tracks – L1 Data Eff 2 Track data (Etot<8GeV, Ntrack = 2, Sum of Pt <0.2, track mass set to Kaon mass ) Pt ~ sqrt((W/2)2 - mK2)sin θ Turn on different in MC and data (only data shown I'm afraid) Other L1 lines 2M&A+ and 2BM&2M contribute to the efficiency but probably have similar Pt turn on Jamie Boyd W(GeV)

  7. γγ -> 2 tracks - BGFTwoProngFilter Can we edit this or write a new one with better efficiency? Put a total Energy cut on to kill BhaBha’s? Jamie Boyd

  8. Tagged 2 tracks Tagged pi+pi- MC where all 3 tracks are reconstructed Jamie Boyd W(GeV)

  9. γγ->π0π0 All 4 gammas reconstructed L3 eff low for W<1.8 GeV BGFAN eff lowish after that Can we do pi0 making in L3? & in BGFAN? Jamie Boyd W(GeV)

  10. γγ->π0π0 tagged All 4 gammas and tagged electron reconstructed Presence of tag track improves L3 eff but now we don’t pass any BGFilter! Jamie Boyd W(GeV)

  11. MC versus Data • These plots made using MC • Very important that MC models L1 / L3 efficiencies well (even at low Pt, low energy etc..) • We know that the Pt turn on for PTD isnt well modelled in current setup (hopefully will be better for ZPD) • Will have to carry out dedicated trg studies using the data for L1/L3 versus Pt (tracks) / E (neutrals) • For tagged decays the MC/Data comparison for L1/L3/BGF maybe worse for very backwards tracks (the tag)? Jamie Boyd

  12. Summary • There is lots of good 2 photon physics that should be done at BaBar • For data already taken • L1 efficiency generally OK • L3 ok except for all neutral mode • Can we improve 2 prong & AllNeutral BGFilter • For new data • Can we make L3 more efficient for pi0pi0 • When improving L1&L3 trigger algorithms can we think about 2photon physics Jamie Boyd

  13. QCD stuff… • R = Γ(γγ->π+π-) / Γ(γγ->π0π0) predicted to be very different by different QCD models (pQCD versus ‘handbag model’) • γγ->p+p- spectra (as function of W) can also distinguish between models (di-quark / pQCD) • Angular distributions for γγ-> h+h- can be predicted by pQCD • For tagged decays you can look at how the cross-section scales with Q2 which is predicted by pQCD (eg. for γγ->π+π-) Jamie Boyd

  14. Meson Spectroscopy • Look at ηC, ηC(2S), a0(980), f0(980), f0(1370), f2(1270),a2(1320),f2’(1525),f2(1720), χc0, χc2 …. • Measure mass, width (Γ) and partial width (Γγγ) • This can test QCD models (eg. Ratio Γ/ Γγγ well predicted for ηC => can measure αS) • Can also use these resonance's produced by 2photon collisions to study the decay process eg. Gautier is looking at the ηC -> KKπ Dalitz plot • For untagged can observe any C=+1 J=0,2 • For tagged can also see J=1 (Yangs theorem) Jamie Boyd

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