R measurement at DAFNE-2

1. LNF-19-Jan-06 R measurement at DAFNE-2 G. Venanzoni LNF

2. What is DAFNE-2? • Upgraded Dafne with 1 interaction region • Discussion on detector upgrade has started I will not discuss in this talk this issue!

3. Competitors (on R)

4. Radiative Return vs Energy Scan Energy scan seems the natural way of measuring hadronic cross section. However experience at KLOE and BABAR have shown that the Radiative Return has to be considered a (working) complementary approach. • Disadvantages: • High order process (radiative corrections must be kept under control at high precision) • Requires a high suppression of FSR and f or  background • Needs high integrated luminosity: for 2p at Dafne statistics is not problem, but it can be just at the limit for DAFNE-2 • Advantages: • Data comes as a by-product of the standard program of the machine • Systematic errors from luminosity, acceptance, normalization, s,… enters only once • It allows fine tuning of the binning (expecially important in the resonances region) Big work from Karlsruhe/Katowicegroup (Kühn, Czyz) to provide generators for ISR processes (Phokhara) at 0.5% accuracy!

5. Region Covered by DAFNE-2 Status of R measurements (s <10 GeV):

6. Topics on R in the region 2mp<s<2.4 GeV • Exclusive analysis: • 2p channel (the biggest contribution to (g-2)m ): • Threshold region: below 600 MeV poorly covered by data (error between 1 and 3%) • Around the r peak: syst. error of 0.6% from CMD-2, 1.3% from SND, KLOE. Not perfect agreeement on the spectra between different experiments, and discrepancy with2p spectral function from t • Above 1 GeV: O(1-4%) from CMD-2 • p+p-p0 , 2p+2p-,p+ p-p0p0 , K+K-p+p-, 3(p+ p-), 2(p+ p-)p0p0; accuracyin the range 5 to 20%, recently presented by BABAR • Inclusive analysis: • Old data, inconsistency between inclusive measurements and the sum of exclusive channels.

7. +10% hep-ex/0512071 -10% +10% interpolation of KLOE 60 data points from 0.35 to 0.95 GeV2 -10% Mpp2 (GeV2) • CMD-2 (‘04) and KLOE agree @ high Mpp2 • disagreement btw KLOE and CMD-2/SND at r peak s (GeV2) • Discrepancy with tau data: • KLOE and CMD-2 lower than t data at high Mpp2 • Error on theoretical corrections (I.B., FSR) underestimated? • New tau data available from B factories: 2p spectrum 0.35<s<.95 GeV2 Comparison of e+e- data • Most likely this issue will continue (hopefully solved) in the next years • New data KLOE,BABAR, Belle(?), CMD-2, will hopefully bring the error <1%. However the path to reach few per-mill accuracy is still long…

8. 2p threshold region • It contributes for 20% of ampp : • ampp (2mp<E<600 MeV) = 100 10-10 • This region is poorly covered by data; • Different authors use different ranges for analytical expansion • t data do not agree so well (F.J. ’01), also with epepg data (NA7 ,1987) extrapolated in timelike. s (nbarn) s (GeV2)

9. 6 5 4 3 2 1 0 1010  (dam)stat KLOE Data at off peak (1 GeV)(started at mid of Dec. 05) sp+p-p0 = 329.8 nb sp+p-g = 4.4 nb • stat. error on a: [1.5-2.5]10-10 (300-100 pb-1) • comparible with the expected syst.error (dsppg/sppg )syst~ 2% from region < 0.35 GeV2 sp+p-p0 = 6 nb, sqrt(s)=1003.71 MeV (from SND, PRD66 (2002) 032001)

10. Impact of DAFNE-2 on the threshold region bin width = 0.01 GeV2 efficiency = 50% flat 1) total accuracy better than 3% in the region <0.35 GeV2 ( ~3 × 10-10)is a hard task for KLOE 2) This accuracy could be improved in the future, using ISR at DAFNE-2 (off-peak) (dsppg/sppg )stat during the KLOE data taking campaign @ s = 1 GeV we can learn a lot

11. Issues in the region [1-2] GeV from Burkhardt & Pietrzyk, PRD72 (2005) 057501 1) the most critical region for Dahad and the second relevant one for amhlo 2) significant difference btw inclusive and sums of exclusive measurements 3) most recent inclusive measurements from DC1 and ADONE (~ 1981!!) d2Dahad 1.05-2GeV 40% of the total error from Martin et al., EPJ,C19 (2001) 681 R(s) s (GeV)

12. How DAFNE-2 can improve this region [1-2.4 GeV] • Energy Scan: • 20 pb-1 per single point (2-3 days at 1032 cm-2 sec-1) • Allows inclusive measurement with high statistics • Needs a dedicate programme • Knowledge of s at with O(10-4) accuracy, using bhabha events (?) • (without resonant depolarization) • ISR at 2.4 GeV: • 2 fb-1 (1 year at 1032 cm-2 sec-1) • Compatible with other programs • Statistics can be an issue Competitors: VEPP-2000 (up to 2 GeV) Babar Belle (?) ISR at Tau/charm factories?

13. Energy scan

14. Impact of DAFNE-2 on inclusive measurement 20 pb-1 1) the most recent inclusive measurements are from MEA and B antiB, with total integrated luminosity of 200 nb-1 (on hour of data taking at 1032 cm-2 sec-1).10% stat.+ 15% syst. errors 2) With 20 pb-1 per energy point, stat. errors on d(Dahad)/Dahad  O(5%); systematic error will be reduced as well 4) a precise comparison exclusive vs. inclusive can be carried out Lint (nb-1) • MEA, 14 points, Lett. Nuovo Cim.30 (1981) 65 • B antiB, 19 points, Phys.Lett.B91 (1980) 155 s (GeV)

15. Impact of DAFNE-2 on the range [1-2] GeV (4p) BaBar, with the published Lint per point BaBar, with 10  (the present Lint ) DAFNE-2, with 20 pb-1 per point • comparison among the present BaBar analysis, an (O(1 ab-1)) BaBar update, • and Lint = 20 pb-1 per energy point • @ DAFNE-2, in the impact on d(Dahad) /Dahad: • 2p+2p- : O(2%) |O(0.7%)|O(0.5%) statistical dshad / shad (%) s (GeV)

16. Impact of DAFNE-2 on the range [1-2] GeV (2K2p) comparison among the present BaBar analysis, an (O(1 ab-1)) BaBar update, and Lint = 20 pb-1 per energy point @ DAFNE-2, in the impact on d(Dahad) /Dahad : p- p+K- K+: O(15%) |O(5%)|O(3%) BaBar, with the published Lint per point BaBar, with 10  (the present Lint ) DAFNE-2, with 20 pb-1 per point statistical dshad / shad (%) s (GeV)

17. Impact of DAFNE-2 on the range [1-2] GeV (3p) BaBar, with the published Lint per point BaBar, with 10  (the present Lint ) DAFNE2, with 20 pb-1 per point comparison among the present BaBar analysis, an (O(1 ab-1)) BaBar update, and Lint = 20 pb-1 per energy point @ DAFNE-2, in the impact on d(Dahad) /Dahad : p- p+ p0: O(9%) |O(3%)|O(1%) statistical dshad / shad (%) s (GeV)

18. Radiative Return @ 2.4 GeV ISR differential luminosity • q0is the minimum polar angle of ISR photon. In the following, we will assume to tag the photon, withq0=20o. • eis the overall efficiency, we will use 10%. • m is the invariant mass of the hadronic system (p+p-, p+p- p0, 2 p0p+p-, 2 p+2p-, …) • x is 2Eg/s, s= e+e- c.m. energy • L0 is the total integrated luminosity

19. ISR Luminosity for different c.m. energies • We integrated dL/dm for 25 MeV bin sizes. 2fb-1 @ s=1.02 GeV [nb-1/25MeV] 2fb-1 @ s=2.4 GeV 1pb-1 89fb-1 @ s=10.6 GeV 2fb-1 @ 2.4 GeV 89fb-1 @ 10.6 GeV 1 GeV GeV

20. Impact of DAFNE-2 on the range [1-2] GeV (3p) using ISR @ 2.4 GeV BaBar, with the published Lint per point BaBar, with 10  (the present Lint ) DAFNE-2, with 2 fb-1 @ 2.4 GeV comparison among the present BaBar analysis, an (O(1 ab-1)) BaBar update, and Lint = 2 fb-1 at 2.4 GeVper energy point @ DAFNE-2, in the impact on d(Dahad) /Dahad : p- p+ p0: O(9%) |O(3%)|O(8%) statistical dshad / shad (%) On the other channels the improvement can be larger s (GeV)

21. ISR @ 2.4 GeV vs scan • Assuming to tag the ISR g, 2fb-1@ 2.4 GeV, translates in a luminosity for single point in the range [100 nb-1 - few pb-1] which would correspond to [few hours - a day] of data taking with a scan @1032 cm-2 sec-1 . • 2fb-1 @ 2.4 GeV is statistically competitive with current results from B factories (90 fb-1). The much higher ISR probability of photon emission at lower s, compensates for the lower luminosity. However we should keep in mind that the planned luminosity of B factories is 1000 fb-1. • In any case different systematics, background, etc… ISR @ 2.4 GeV vs B-factories

22. Different event topology btw 2.4 and 10.6 GeV: 2p+2p-channel s=2.4 GeV Eg min(qg,p) s=10.6 GeV BABAR • At 10.6 GeV: • Hard photon: Eg* = 3-5.3 GeV at s’ = 0-7 GeV. Þ No fakes from beam-gas processes. • Hadronic system collimated by recoil. • Harder spectrumÞ better detection efficiency. GeV degrees Ep • At 2.4 GeV: • Hard photon: Eg* < 1.1 GeV. • Distribution of particles and photon “uniform” distributed GeV degrees

23. Conclusions • F. J. aks for shad at 1% up to the . L. Roberts will also be happy! • Tough task! However big activities around the world: • pp region: 1.3% of syst. err. from KLOE/SND; 0.6% from CDM-2. Not perfect agreement among data, needs additional clarification. New data from KLOE and B-factories will help. 2p threshold also very important: KLOE off-peak data will help. • [1.02-2.4] GeV energy range: the most important for Dahad; DAFNE-2 could give a relevant contribution (expecially with a scan). Other competitive experiment are running (B-Factories) or are expected to taka data in few years (VEPP-2000, BESIII with ISR(?)). All these efforts are very welcome (almost mandatory): 1% accuracy needs confirmation from different experiments! • Region above 2.4 GeV: ISR at B-factories, scan at t/charm factory (BES-III).

24. spares

25. Detector requirements: a wishlist • Momentum measurement: charged particles selection, kinematic fitting and/or identification of the several processes require good momentum resolution, furthermore, with a scan R-measurement, luminosity and s need good accuracy (e.g. in KLOE dL/L ~ 0.3% and ds ~ 50 keV, with Bhabha events), a good dE/dx resolution should not be neglected for good p±/K± separation (see V. Patera’s talk) • Electromagnetic calorimetry: it is crucial for good measurements of time, direction and energy of the g’s from p0, h (e.g. a completely neutral inclusive R measurement), for efficient trigger criteria and for e/p particle identification • Vertex detector: in the multitrack channels, a vertex detector is really helpful, matching similar requirements of the interferometry in the semileptonic channels (see A. Di Domenico’s talk)

26. Conclusions and perspectives • in the future years the impact of amhlo and Dahad is conditioned to different factors • KLOE and VEPP-2M are successfully covering the pp region, waiting for B factories results; • despite of KLOE, VEPP-2M and BaBar results there is still room for improving the R measurement in the future • DAFNE2 can give major contributions mostly on the threshold region and in the [1.02-2] GeV energy range

27. Conclusions • A scan at Dafne-2 will allow to improve • Statistical error expected at the level of 5-10% for single point (in ISR case). Systematics and background are different. • A scan @1032 cm-2 sec-1 for single point gives higher statistics then B-factories even at 1000fb-1. However for am or aem . what really matters is also the systematics.

28. Conclusions -II • Crucial point: • Time schedule of the data above phi in D2 (2015?) • Keep in mind: • Scan: • Better than B-factories. However also VEPP-2000 will enter in the game in few fears from now (2008?), with a scan up to 2 GeV at 1032 cm-2 sec-1. • ISR: • Compatible with other D2 programs at 2.4 GeV (NN,gg physics, etc…). It doesn’t required a dedicated program. However statistically limited, compared with full luminosity B-factories.Systematics are different. • In any case keep in mind that for precision physics the more data you have the better it is. And systematics are different!

29. Different topology btw 2.4 and 10.6 GeV: p+p-p0gchannel s=2.4 GeV Eg min(qg,p) s=10.6 GeV BABAR • At 10.6 GeV: • Hard photon: Eg* = 3-5.3 GeV at s’ = 0-7 GeV. Þ No fakes from beam-gas processes. • Hadronic system collimated by recoil. • Harder spectrumÞ better detection efficiency. GeV degrees Ep • At 2.4 GeV: • Hard photon: Eg* < 1.1 GeV. • Distribution of particles and photon more symmetric in polar angle. GeV degrees

30. Event Yeld with 1fb-1@ 2.4 GeV p+p-p0g 2p+2p-g 20o<qg<160o e=10% N/fb-1/25MeV Above 1 GeV Statistical error for single point at 5-10% level. However what matters for am or aem is the systematic error (which must be kept below 5%). GeV GeV p+p-2p0g m+m-g GeV GeV

31. ppg/mmg with 1fb-1@ 2.4 GeV: inclusive measurement N/25MeV m+m-g qg<20o m+m-g qg>20o e=10% p+p-g qg<20o GeV

32. ′ ′ ′ KLOE impact with 2 fb-1 only ISR at the NLO for both processes 50o < qp, qg < 130o ,Eg > 50 MeV, bin = 0.01 GeV2 L = 2 fb-1 , e = 50% flat in s′, in both channels ds/ds′ (nb/GeV2) ppg mmg s’ (GeV2) s’ (GeV2)

33. 2 3 (+,) 4 > 4 (+KK) 1.8 - 3.7 3.7 - 5 (+J/, ) 5 - 12 (+) 12 -  < 1.8 GeV Hadronic regions: contributions and errors based on estimates from Davier et al., EPJ,C27 (2003) 497 ahad: 8% [2mp - 0.5 GeV] 54% [0.6 - 1.0 GeV] 10% [rest < 1.8 GeV] had(MZ):  2[had]:  2[ahad]: 8% [2mp - 0.5 GeV] 34% [0.6 - 1.0 GeV] 31% [rest < 1.8 GeV]

34. Contribution to Da(5)had from F. Jegerlehner

35. Comparison of different evaluations of Da(5)had

36. 2 3 (+,) 4 > 4 (+KK) 1.8 - 3.7 3.7 - 5 (+J/, ) 5 - 12 (+) 12 -  < 1.8 GeV 2p contrib. ahad 8% [2mp - 0.5 GeV] 54% [0.6 - 1.0 GeV] 10% [Rest<1.8 GeV] r 2p contrib. dahad 8% [2mp - 0.5 GeV] 34% [0.6 - 1.0 GeV] 31% [Rest< 1.8 GeV] r > 1GeV Hadronic contributions to amhad Calculations based on Davier, Eidelman, Höcker, Zhang ahad <1.8 GeV 2[ahad] <1.8 GeV 1% e+e- data only!

37. Burkhardt & Pietrzyk 2001 Contributions toDahad magnitude errors Including KLOE results, a preliminary analysis of B.& P. found a value of Da(5)(mZ2) which confirms their 2001 estimate: Da(5)(mZ2) =0.02761±0.00036

38. the MC code Phokhara with full NLO ISR corrections [Kühn et al., EPJ,C24 (2002) 71] Current activities: ISR events standard way (energy scan): measuring se+ e-  hadrons(s) by varying e beam energy alternative approach: given a fixed s, by studying Initial State Radiation events H= radiation function qmin= emitted g min. ang. ISR vs. SCAN • cleaner topology: minor impact from FSR corrections and the H function • the resolution is that of s rather than that of Mhad • an inclusive R measurement can be performed with smaller systematic uncertainty wrt ISR experiments • uncertainties related to the beam energy and the luminosity are the same for each Mhad2 value • it may be performed in parallel with other measurement programs • the ideal solution for interference region (e.g. r-w), and the only way for the 2mp threshold

40. Impact of DAFNE-2 on the range [1-2] GeV (4p) using ISR @ 2.4 GeV BaBar, with the published Lint per point BaBar, with 10  (the present Lint ) DAFNE-2, with 2 fb-1 @ 2.4 GeV comparison among the present BaBar analysis, an (O(1 ab-1)) BaBar update, and Lint = 2 fb-1 at 2.4 GeVper energy point @ DAFNE-2, in the impact on d(Dahad) /Dahad : 2p+2p- : O(2.5%) |O(0.8%)|O(1%) statistical dshad / shad (%) s (GeV)

41. Impact of DAFNE-2 on the range [1-2] GeV (2K2p) using ISR @ 2.4 GeV BaBar, with the published Lint per point BaBar, with 10  (the present Lint ) DAFNE-2, with 2 fb-1 @ 2.4 GeV comparison among the present BaBar analysis, an (O(1 ab-1)) BaBar update, and Lint = 2 fb-1 at 2.4 GeVper energy point @ DAFNE-2, in the impact on d(Dahad) /Dahad : p- p+K- K+: O(15%) |O(5%)|O(5%) statistical dshad / shad (%) s (GeV)

42. e+ e-p+p-p0g Babar @89 fb-1 N/25MeV Results obtained with Phokhara 5, NLO ISR D2@2fb-1 GeV We have assumed a 10% eff. in both cases. 2fb-1@ 2.4 GeV 89fb-1@ 10.6 GeV Number of events for Babar consistent with publication (hep-ex/0408078) GeV

43. Issues in the region [1-2] GeV from Burkhardt & Pietrzyk, PRD72 (2005) 057501 1) the most critical region for Dahad and the second relevant one for amhlo 2) significant difference btw inclusive and sums of exclusive measurements 3) most recent inclusive measurements from DC1 and ADONE (~ 1981!!) from Martin et al., EPJ,C19 (2001) 681 R(s) s (GeV)

44. ISR Luminosity for different c.o.m. energies • We integrated dL/dm for 25 MeV bin sizes. L0 = 1 fb-1 [nb-1/25MeV] 1fb-1 @ s=1.02 GeV 1fb-1 @ s=2.4 GeV ISR L @ 2.4 GeV ISR L @ 10.6 GeV 1fb-1 @ s=10.6 GeV GeV GeV