Gamma-Gamma Physics and Transition Form Factors with KLOE/KLOE-2

Transcription

1 Gamma-Gamma Physics and Transition Form Factors with KLOE/KLOE- on behalf of the KLOE- Collaboration PhiPsi 017 June 6-9, 017 Mainz, Germany

2 DAΦNE (Double Annular Φ Factory for Nice Experiments) + - e e collider s = MΦ = MeV interaction regions e+ e- separated rings bunches spaced by.7 ns KLOE data taking campaign ended in 006 ~.5 fb-1 ~ 60 pb-1 off-peak DAΦNE upgrade (008): new interaction scheme Large beam crossing angle crab waist sextupoles Drift Chamber Low-mass gas mixture 90% Helium + 10% isobutane δp / p < 0.4% (θ >45 ) σxy = 150 μm ; σz = mm 158 cells v Stereo geometry 4m diameter, 3.3m long Calorimeter 98% coverage full solid angle σe/e = 5.7% / E(GeV ) σt = 57 ps / E(GeV ) 140 ps Barrel + end-caps: Pb/scintillating fiber read out by 4880 PMTs Magnetic field B = 0.5 T

3 KLOE- Upgrade KLOE- new data taking campaign started on November 014 It will collect more than 5 fb-1 up to March 018 New detectors fully operative Tagging system LET & HET e+e--taggers for γγ-physics CCALT & QCALT new calorimeters CCALT for low angle γ s (down to 10º) Quadrupole coverage for KL decays Inner Tracker 4 layers of C-GEM better vertex reconstruction and track parameters LET HET 11 m from IP CCALT QCALT IT 3

4 KLOE- Upgrade IT CCALT HET 11 m from IP LET QCALT 4

5 High Energy Tagger (HET) HET stations located approximately at 11m from IP after bending dipoles Strong energy-trajectory correlation Scintillating hodoscope + PMTs σt = 550(1)ps Scattered e± of E > 400 MeV escape beam pipe after first bending dipole of DAΦNE spectrometer fast feedback on machine operation Rates dominated by single arm Bhabha s Blue measurement Red expectation Tdiff between stations RHET ~ Rtrig(αL + βi) 5

6 Physics with KLOE- KLOE- has started a new data campaign in November 014 All KLOE- detectors operational It will collect more than 5 fb-1 till the end of March 018 DAΦNE luminosity: peak =.x103 & daily delivered >10 pb-1 6

7 γγ Physics with KLOE KLOE- Program: Eur. Phys. J C68 (010) 619 Photon coupling to S and P mesons meson quark structure X = η, π0 Γ(X γγ) at ~ 1% TFF F (q, q ) xγ*γ* 1 Input for the light-by-light contribution to (g-) of muon X = π0π0 f0(500) KLOE data no e± tagging off-peak data 7

8 γ*γ* Data sample s = 1.0 GeV Sample of 40 pb-1 No taggers Main background from e+e- ηγ with lost γ Selection: η π+π-π0 events with two tracks and two prompt protons η π0π0π0 events with no tracks and 6 prompt protons -D fit in the (Mmiss, p) Combining both channels σ(e+e- e+e-η) = (3.7 ± 1.3 ± 0.7) pb Γ(η γγ) = (50 ± 0 ± 13) ev KLOE - JHEP01(013)119 8

9 γ*γ* KLOE- 0 chiral anomaly Precision measurement of Γ(π0 γγ) L = 5 fb-1 KLOE- aims to measure down to δγ(π0 γγ) 1% Measurement with taggers HET-HET coincidence + γ s in EMC σ (e+e- e+e-π0) 0.8 nb TOT Γth(π0 γγ) = (8.09±0.11) ev ==> 1.4% uncertainty Γexp(π0 γγ) = (7.8 ± 0.14(stat) ± 0.1(syst)) ev ==>.8% uncertainty (PrimEx JLAB) PRD79(009) PRL106(011)

10 γ*γ* KLOE- 0 First measurement of π0 γ*γ TFF Fπ0 γ*γ (q,0) in the space-like region q < 0.1 GeV γ s in EMC + HET Lepton detection in DCH/EMC q < 0.1 GeV Lepton detection in HET q 0 Impact in the precision of the a μlbyl;π0 L = 5 fb-1 ==> 6% uncert. at each point Uncertainty in the single π0 contribution to the HLbL can be reduced by a factor of ~ Fπ0 γ*γ KLOE- - EPJC7(01)1917 Fπ0 γ*γ (0) KLOE simul. Err. Bars corresponding to a stat of 5 fb-1 CELLO CLEO LMD+V model 10

11 Meson Transition Form Factors V P γ* P l+ l Test on the theoretical description of meson structure TFF(q ) where q = m coupling of meson to virtual photons l+llight-by-light contribution to aμ Used to determine upper limit in dark forces searches Vector Meson Dominance (VMD) TFF described as F(q) = 1/(1 q/λ) VMD predictions discrepancy for ω l+ l- π0 Models developed to explain discrepancy 11

12 Meson Transition Form Factors 0 + Φ π e e Lint = 1.7 fb-1 and ~ 9500 signal events selected Main background contributions: radiative bhabha scattering and Φ π0 γ with photon conversion Overall efficiency 15% KLOE - Phys.Lett. B757 (016)

13 Meson Transition Form Factors 0 + Φ π e e KLOE - Phys.Lett. B757 (016) Branching Ratio measurement (a) (b) 5 BR(Φ π e e)=(1.35± ) x 10 (c) JETP Lett 75 (00) 449 PLB 503(001)37-44 Transition Form Factor Slope b π, Φ =(.0±0.11)GeV 0 KLOE data factor of 3.6 better accuracy KLOE data (black points) (a) Chiral theory: S. Ivashyn, Prob. Atomic Sci. Technol. 01N1 (01) 179 (b) Dispersive analysis: S. P. Schneider, B. Kubis, F. Niecknig Phys. Rev. D 86 (01) and I. Danilkin, et al. Phys. Rev. D 91 (015) (c) VMD: L. G. Landsberg Phys. Rept. 18 (1985)

14 Meson Transition Form Factors + Φ ηe e Lint = 1.7 fb-1 and ~ signal events selected with η 3π0 Background contribution ( ~ 3% ) dominated by Φ KSKL π+ π- 3π0 and Φ η γ Analysis efficiency ~ 15% Bin to bin background subtraction ~ 9600 event candidates e+ KLOE - Phys.Lett. B74 (015) 1-6 η ψ* e- 14

15 Meson Transition Form Factors + Φ ηe e KLOE - Phys.Lett. B74 (015) b η, Φ =(1.8± ) GeV VMD: ~1 GeV- (Phys. Rev.C 61 (000) 03506) SND: (3.8 ± 1.8) GeV- (PLB 504 (001) 75) KLOE result precision factor of 5 better Blue: fit result Red:C. Terschlusen and S. Leopold, Phys. Lett. B 691 (010) Pink: VMD expectation 4 BR(Φ ηe e)=(1.075±0.007±0.038) x 10 VMD: ~1.1 x 10-4 (Phys. Rev.C 61 (000) 03506) SND: (1.19 ± 0.31) x 10-4 (PLB 504 (001) 75) CMD-: (1.14 ± 0.16) x 10-4 (PLB 501 (001) 191) 15

16 Summary KLOE has delivered the most precise measurement of the two-photon width of the η meson by using off-peak data With the KLOE- taggers and luminosity we can measure the π0 width with 1% accuracy By using the HET of KLOE- also the TFF of π0 γ*γ with a quasi-real photon and a real one can be measured, covering a totally unexplored region of q Large data sample of light mesons available at KLOE provides important results on decay dynamics and transition form factor, together with limits on new physics, giving the most precise measurements for TFF for the reactions Φ η e+ e- and Φ π0 e+ ekloe- presently acquired ~ 4fb-1 with the aim of collecting more than 5 fb-1 by the end on March

17 Backup slides 17

18 γγ Physics with KLOE- KLOE-: Eur. Phys. J C68 (010) 619 Photon coupling to S and P mesons meson quark structure X = η, π0 Γ(X γγ) at ~ 1% TFF F (q, q ) xγ*γ* 1 Input for the light-by-light contribution to (g-) of muon X = π0π0 f0(600) KLOE measurement at s = 1 GeV KLOE- e-taggers for high and low energy rejection of background from Φ Close kinematics Better statistical accuracy 4γ invariant mass distribution 18