Perspectives on η η physics

Transcription

1 Perspectives on η η physics S. Giovannella (INFN LNF) F. Ambrosino (Università e Sezione INFN, Napoli)

2 xpected data sample Working hypothesis: 20 fb 1 of integrated luminosity (a factor 10 more w.r.t. the expected KLOE final data sample) φ = 3.3 µb R(φ ηγ) = ( ± )% N η (20 fb 1 ) σ φ = 3.3 µb BR(φ η γ) = (6.2 ± 0.7) 10 5 N η (20 fb 1 )

3 identification produced through φ ηγ Identified by the monochromatic recoil photon E recoil (η) = 363 MeV Very clean and tagged η sample φ ηγ π 0 π 0 π 0 γ φ ηγ π + π π 0 γ Eγ (MeV)

4 ain η decay channels Decay η γγ η π 0 π 0 π 0 BR (PDG04) ( ± 0.26 ) % ( ± 0.29 ) % η π + π π 0 ( 22.6 ± 0.4 ) % η π + π γ ( 4.68 ± 0.11 ) % ε ana (KLOE) 70% 45% 36.5% 46% N exp PDG fit needs to scale BRs of main η decay modes from 1.2 to 1.3 Main BRs known with O(%) precision. Further improvement requires a complete measurement of all main decay channels All these decays already KLOE By tagging the recoil photon, it is possible to overcome the normalization problem

5 ain η decay channels Decay η γγ η π 0 π 0 π 0 BR (PDG04) ( ± 0.26 ) % ( ± 0.29 ) % η π + π π 0 ( 22.6 ± 0.4 ) % η π + π γ ( 4.68 ± 0.11 ) % ε ana (KLOE) 70% 45% 36.5% 46% N exp PDG fit needs to scale BRs of main η decay modes from 1.2 to 1.3 Main BRs known with O(%) precision. Further improvement requires a complete measurement of all main decay channels All these decays already KLOE By tagging the recoil photon, it is possible to overcome the normalization problem Probably not not too too much to to say say on on main decay channels after the the analysis of of the the final KLOE data data sample (2.5 (2.5 fb fb 1 1 ))

6 π + π γ t the moment just poor experimental data from the 70 s. Dalit plot: left right asymmetry parameter. Shape of the E γ spectrum to test ChPT predictions Resonant contribution: 1. ρ production whit its subsequent decay to a pion pair (VDM) 2. existence of a small non-vdm contribution Anomalous contribution: box anomaly (similar to the classical triangle anomaly), responsible for η/η π + π γ decays predicted by PCAC and by the Wess-Zumino-Witten chiral lagrangian

7 π + π γ : box anomaly

8 π + π γ : Μ ππ spectrum nfortunately η π + π γ not sensitive to the box anomaly contribution

9 π + π KLOE Preliminary KLOE analysis looks promising First sample analyzed: 29 pb 1 of 2001 data Bhabha φ π + π π 0 Signal Analysis scheme: 1 vtx with 2 tracks 2 prompt neutral clusters Kin fit: P(χ 2 ) > < E γ recoil < MeV M miss (π + π ) > 160 MeV S/B ~ 460 M miss miss (MeV)

10 π 0 γγ nteresting from the theoretical point of view because the bigger ontribution comes from p 6 in χ PT π + p η + n (CERN, Brookhaven, GAMS, Crystal Ball) π + + d p + p + η (67) π + + p π + + p +η (67,69) Κ + p Λ + η (70 AGS) π + + n η + p (71) π + n π + n + η (80) φ ηγ (SND 01) Prel. KLOE measuremen

11 π 0 γγ : mass spectrum measurement A further improvement on BR is expected with 20 fb 1, but more interesting is the shape of the γγ mass spectrum E.Oset, J.R.Pelaez, L.Roca, PRD67 (2003) VMD-p 4 int. a 0 contr. very small Rescaling KLOE results: 3500 events expected at the end of the analysis p 4 VMD-tree

12 alitz decays he study of the e.m. structure of neutral mesons can be done hrough the η γl + l η γ γ l + l transition form factor f (q 2 ) arising in the vertex provides information n the meson structure Observable: l + l invariant mass F(q 2 ) calculations: (1) VMD (2) Quark triangle loop (3) ChPT

13 Dalitz decays alitz and double Dalitz decay can be easily reached with 20 fb 1 Decay η e + e γ η µ + µ γ η e + e e + e η π + π e + e BR (PDG04) ( 6.0 ± 0.8 ) 10 3 ( 3.1 ± 0.4 ) 10 4 < ( ) 10 4 Bckgs: φ π + π π 0 η π + π γ 60,000 produced ll these measurements can be significantly improved and a first bservation of e + e e + e can be achieved ( theoretical expectations: R(η e + e e + e ) = [PR 98 (1955) 1355] )

14 π + π e + e : test of CP violation beyond CKM Standard model: source of CP violation is a single phase in CKM mixing matrix describing quark flavor changing weak interaction couplings Test CP simmetry in flavour conserving process, where Standard Model predictions are vanishingly small TEST OF NEW PHYSICS BEHOND THE STANDARD MODEL

15 CP violation in KL π+π e+e 15

16 CP violation in η π+π e+e 16

17 η e + e / µ + µ Decay η e + e η µ + µ BR (PDG04) < ( 5.8 ± 0.8 ) 10 6 Prediction large improvement on U.L. expected from the statistical oint of view for η e + e owever large background from e + e e + e (γ) expected. Kinematic fit imposing η mass. Study of angular and momentum distributions of the decay products

18 C, P, CP, LF violating η decays lready measured with KLOE 2001/2002 data: Decay η π + π η γγγ BR (KLOE) < < Violation P, CP C pper limits on π + π /γγγ, background limited, will improve with (L NEW /L OLD ) ther decays: Decay BR (PDG04) Violation η π 0 π 0 η π 0 π 0 π 0 π 0 < < P, CP P, CP φ Sγ Too much bckg: φ K S K η π 0 e + e η π 0 µ + µ η µ + e, µ e + < < < C C LF π + π π 0 bckg to be removed Similar search of φ ηγ with η µ + µ

19 Competitors: Crystall MAMI σ E /E = 2%/ 4 E(GeV) σ θ = 2 3 degrees 30M η AGS (BNL) [π (720 MeV/c)p nη] 30M η MAMI (MAINZ) in 2004, 300 hours run [γ( MeV)p pη] MAMI upgrade in progress: next run E γ up to 1.5 GeV 300M η expected + η sample

20 Competitors: COSY CsI calorimeter Plastic scintillator barrel Mini drift chamber Forward detector Production mechanism: pp ppη(η ) Expected rate : 2500 η/s 30 η /s Expected start-up: January 2007

21 η decays N η (20 fb 1 ) DAFNE2 is an η factory! But beware: WASA@ COSY claims η /day. Decay η π + π η η π + π γ η π 0 π 0 η η ωγ η γγ η main BRs known with an error of 3 10% BR (PDG04) ( 44.3 ± 1.5 ) % ( 29.5 ± 1.0 ) % ( 20.0 ± 1.2 ) % ( 3.03 ± 0.31 ) % ( 2.12 ± 0.14 ) % We can probably improve the situation on the less frequent decay by measuring ratio of BRs (sth KLOE/DAFNE) For the others, we need tagged measurement of all the decay chain Hard, but this could reduce the systematic error in the measurem of R= BR(φ η γ)/br(φ ηγ) which dominates already its error

22 η γγ BR currently known at 7%. BR is the main uncertainty in the extraction of the η full width events produced. With 10 % efficiency can improve BR accuracy to about 4%. But hard from the exp. point of view (QED bkg Γγγ is already known to 3% thus no improvement for η η mixing parameters. not a big issue.

23 η ηππ : Dalitz plot analysis Interesting to study scalar mesons (no tree contributions from VMD) Sensitive to σ(600) (PRD 60, ) Expect evts in Dalitz plot with realistic efficiency.

24 η π + π π 0 : first observation? Interesting, because is sensitive to isospin violating part of strong agrangian, and proportional to m d -m u Currently only upper 5% (!) Expected at O(10-3 ) i.e evts produced With realistic efficiency can expect to measure some % level

25 η π + π γ : asymmetry and spectrum Interesting, because γ energy spectrum is sensitive to the box nomaly term of the WZW chiral Lagrangian Asymmetry related to possible C violation in strong interactions Difficult background from ρπ ( but we know we can deal with it easonably for the η ) More than 1 million events produced

26 Other η decays With an expected BR of the Dalitz decay could be observed with rder 10% accuracy or less (transition form factor, light by light cattering etc.) 4π decays could possibly be observed but we could not find heoretical prediction for that. Reasonably one could slightly improve limits on C, CP violating ecays down to 10-4 level.