Experimental considerations about  physics at DA  NE2 F. Anulli, D. Babusci, G. Pancheri Laboratori Nazionali di Frascati  Physics window at DA  NE2 and yield estimate for the main processes (using W.W. approximation)  A feasibility study for  physics at DA  NE was performed ~12 years ago * :  Review of the main results obtained  The tagging system proposed for DA  NE  Very preliminary studies on higher energy option (E b =1.2 GeV)  Conclusions * For reference see: - F. Anulli et al., “Two Photon Interaction Measurements with the KLOE Small Angle Tagging System”, LNF-95/007, “The Second DAFNE Handbook” (1995) - G. Alexander et al., “Two-Photon Capabilities of KLOE at DAFNE”, Il Nuovo Cimento, 107 A, (1994)

Frascati, 19/01/06F. Anulli - INFN road map2  luminosity function  E b =510 MeV : very limited phase-space available for W  500 MeV/c 2 Only the low mass region can be effectively exploited:    →   at threshold (polarizabilities)   →      challenging, especially if tagging is needed)  E b =1200 MeV : much more favorable conditions  f 0 (980), a 0 (980)  ÷  →     can be effectively studied

Frascati, 19/01/06F. Anulli - INFN road map3 Main characteristics Da  ne 510 MeVDa  ne 1200 MeV PEP/PETRA E b (GeV)0.51 = 10 3 m e 1.2 = 2.4 ·10 3 m e 15 = 3 ·10 4 m e ~ m e /E b ~ 1 mrad~ 0.5 mrad~10 -5 rad W  (MeV/c 2 ) W   s ~ 0.3~ 0.6~ 0.125~ 0.25~ 0.01 x = E  /E b ~ 0.3~ 0.6~ 0.125~ 0.25~ 0.01 y = E e /E b ~ 0.7~ 0.4~ 0.9~ Q 2 ~ E b E e  e Gev 2  e Gev 2  e Gev 2  e Gev 2  e Gev 2  e 2  Q 2 small  “quasi-real”  interactions   system axis close to that of e  e   Relatively wide angular distribution:  ~50% of e ± scattered at  > 10 mrad  ~15% of e ± scattered at  > 100 mrad

Frascati, 19/01/06F. Anulli - INFN road map4 Example: e  e   e  e      Electron scattering angle (rad) Electron Energy (MeV) X = E  /E beam  invariant mass (MeV/c 2 ) 510 MeV 1200 MeV

Frascati, 19/01/06F. Anulli - INFN road map5 A closer look at E b =510 MeV operation point channelTotal Production (L = 10 fb -1 ) e  e  → e  e    4 × 10 6 e  e  → e  e   1 × 10 6 e  e  → e  e      2 × 10 6 e  e  → e  e      2 × 10 4 Background from  decays Estimated yields  Additional sizable backgrounds from non  decays, like ISR and continuum processes  Kinematics cut would bring a rejection factor <100 (mainly from P T of the hadronic system )  hopeless w/o tagging at the  peak  above the peak, tagging would unambiguously select  events W(  P T  scale factor 10 4 to be applied!  decay mode Escaped particle EventsBkgd to: K S (      K L KLKL ~ 10 9  K S (      K L KLKL ~2×10 9         ~ 10 9  ~ 10 8     ~5×10 8 

Frascati, 19/01/06F. Anulli - INFN road map6 Electron tagging  Electrons emitted preferentially at small angles  Most of them depart from the main beam orbit after several meters  However, they behave differently w.r.t. the nominal beam when going through magnets, because of lower energy  A tagging system can be conceived only taking into account the constraints imposed by the design of the machine lattice  Interaction with accelerator group to optimize acceptance in specific regions  Careful evaluation of machine backgrounds (mainly radiative Bhabha events) - Collect scattered electrons bent by the Split Field Magnet - SAT located at ~8.5m from the IP - Beam pipe shaped to allow electrons to escape - Quads and sextupoles with large horizontal aperture IP ~5m Small angle Tagging (SAT) system proposed for Da  ne (1994) SAT 0 <  e < ~20 mrad 250 < E e < 450 MeV E beam = 510 MeV B Z = 0.17 T

Frascati, 19/01/06F. Anulli - INFN road map7 What events would be collected at the SAT - Simulation uses DAFNE old machine layout. - Consider free space after SFM. - SAT location 1.5m downstream the SFM exiting edge Radial displacement w.r.t. beam pipe axis x(m ) E(MeV) vs x(m ) E(MeV) Energy of electrons collected at the SAT beam pipe E beam = 510 MeV beam pipe beam SAT scattered e  x

Frascati, 19/01/06F. Anulli - INFN road map8 What events would be collected at the SAT - Bz of SFM increased to account for higher energy. - SAT location 1.5m downstream the SFM exiting edge E beam = 1200 MeV x(m ) E(MeV) E(MeV) vs x(m ) Radial displacement w.r.t. beam pipe axis Energy of electrons collected at the SAT beam pipe

Frascati, 19/01/06F. Anulli - INFN road map9 W  vs Tagging Scheme  Tagging at very small angles introduce a cut on the minimun energy for tagged electrons  cut on the maximum photon energy  cut on the high side of the invariant mass spectrum, especially for double small angle tag  problems if working at  peak, need to add a relatively large-angle tagging

Frascati, 19/01/06F. Anulli - INFN road map10 Conclusions   physics can be successfully exploited at the energy range covered by DAFNE2 (1 <  s < 2.4 GeV), with some advice: It is not clear that the much higher hadronic background can be fully suppressed with kinematic cuts A tagging system would clean up the selected samples  E b = 510 MeV Very few channels available Precise measurements of radiative   and  widths, and  cross section at threshold If working at  peak, tagging is necessary, reducing the available phase space  study of the  (400÷600) over the full width looks problematic.  E b = 1200 MeV Very interesting physics program. M  up to 1 GeV/c 2 can be reached, giving access to  f 0, a 0, It should also allow a precise study of the  →     channel Single tagging would not cut the invariant mass spectrum Small yield reduction, but possible full background suppression