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

3. What is DAFNE-2? Upgraded Dafne with 1 interaction region Energy (cm) (GeV)1.02<2.5 Peak luminosity > (cm -1 sec -2 )8 10 32 10 32 Total integrated luminosity (fb -1 )203 Start time~2011 Discussion on detector upgrade has started I will not discuss in this talk this issue!

4. MachinePhysics Program on REnergy rangeStarting date VEPP-2000L = 10 32 Scan+ISR(?) 0.4<  s<2 GeV >2007 BESIII L=10 33 @  (3770), ISR(?)2.4<  s<4.2 GeV >2007 CESR-c? 3<  s<5 GeV Working BabarISR Thr.<  s<10 GeV Working BelleISR (?) Thr.<  s<10 GeV Working Competitors (on R)

5. 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. 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) Disadvantages: High order process (radiative corrections must be kept under control at high precision) Requires a high suppression of FSR and  or  background Needs high integrated luminosity: for 2  at Dafne statistics is not problem, but it can be just at the limit for DAFNE-2 Big work from Karlsruhe/Katowice group (Kühn, Czyz) to provide generators for ISR processes (Phokhara) at 0.5% accuracy!

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

7. Topics on R in the region 2m  <  s<2.4 GeV Exclusive analysis: 2  channel (the biggest contribution to (g-2)  ): Threshold region: below 600 MeV poorly covered by data (error between 1 and 3%) Around the  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 with  2  spectral function from  Above  GeV: O(1-4%) from CMD-2        2   2     +  -  0  0, K + K -    , 3(  +  - , 2(  +  - )  0  0 ; accuracy in the range 5 to 20%, recently presented by BABAR Inclusive analysis: Old data, inconsistency between inclusive measurements and the sum of exclusive channels.

8. 2  spectrum 0.35<  s<.95 GeV 2 Discrepancy with tau data: KLOE and CMD-2 lower than  data at high M   Error on theoretical corrections (I.B., FSR) underestimated? New tau data available from B factories: 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… CMD-2 (‘04) and KLOE agree @ high M   disagreement btw KLOE and CMD-2/SND at  peak M  2 (GeV 2 ) interpolation of KLOE 60 data points from 0.35 to 0.95 GeV 2 +10% -10% s (GeV 2 ) +10% -10% hep-ex/0512071 Comparison of e + e - data

9. It contributes for 20% of a    a    m   eV  100  10 -10 This region is poorly covered by data; Different authors use different ranges for analytical expansion  data do not agree so well (F.J. ’01), also with e  e  data (NA7,1987) extrapolated in timelike. s (GeV 2 )  (nbarn) 2  threshold region

10.     nb, sqrt(s)=1003.71 MeV (from SND, PRD66 (2002) 032001)    nb    nb 65432106543210 10 10  (  a  ) stat  : stat. error on a  : [1.5-2.5]  10 -10 (300-100 pb -1 ) comparible with the expected syst.error (     ) syst ~ 2% from region < 0.35 GeV 2 KLOE Data at off peak (1 GeV) (started at mid of Dec. 05)

11. Impact of DAFNE-2 on the threshold region (     ) stat 1) total accuracy better than 3% in the region <0.35 GeV 2 ( ~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) bin width = 0.01 GeV 2 efficiency = 50% flat during the KLOE data taking campaign @  s = 1 GeV we can learn a lot

12. Issues in the region [1-2] GeV from Burkhardt & Pietrzyk, PRD72 (2005) 057501  s (GeV) R(s) 1) the most critical region for  had and the second relevant one for a  hlo 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    had 1.05-2GeV 40% of the total error

13. How DAFNE-2 can improve this region [1-2.4 GeV] 1.Energy Scan: 20 pb -1 per single point (2-3 days at 10 32 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) 2.ISR at 2.4 GeV: 2 fb -1 (1 year at 10 32 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?

14. Energy scan

15. Impact of DAFNE-2 on inclusive measurement  s (GeV) L int (nb -1 ) o MEA, 14 points, Lett. Nuovo Cim.30 (1981) 65 B antiB, 19 points, Phys.Lett.B91 (1980) 155 B antiB, 19 points, Phys.Lett.B91 (1980) 155 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 10 32 cm -2 sec-1).10% stat.+ 15% syst. errors 2) With 20 pb -1 per energy point, stat. errors on  had  had  O(5%); systematic error will be reduced as well 4) a precise comparison exclusive vs. inclusive can be carried out

16. Impact of DAFNE-2 on the range [1-2] GeV (4  ) statistical  had  had   s (GeV) BaBar, with the published L int per point BaBar, with 10  (the present L int ) DAFNE-2, with 20 pb -1 per point comparison among the present BaBar analysis, an (O(1 ab -1 )) BaBar update, and L int = 20 pb -1 per energy point @ DAFNE-2, in the impact on  had  had :         : O(2%) | O(0.7%) | O(0.5%)

17. Impact of DAFNE-2 on the range [1-2] GeV (2K2  ) statistical  had  had   s (GeV) comparison among the present BaBar analysis, an (O(1 ab -1 )) BaBar update, and L int = 20 pb -1 per energy point @ DAFNE- 2, in the impact on  had  had :                 : O(15%) | O(5%) | O(3%) BaBar, with the published L int per point BaBar, with 10  (the present L int ) DAFNE-2, with 20 pb -1 per point

18. Impact of DAFNE-2 on the range [1-2] GeV (3  ) statistical  had  had   s (GeV) BaBar, with the published L int per point BaBar, with 10  (the present L int ) DAFNE2, with 20 pb -1 per point comparison among the present BaBar analysis, an (O(1 ab -1 )) BaBar update, and L int = 20 pb -1 per energy point @ DAFNE-2, in the impact on  had  had :             : O(9%) | O(3%) | O(1%)

19. Radiative Return @ 2.4 GeV   is the minimum polar angle of ISR photon. In the following, we will assume to tag the photon, with    20 o.  is the overall efficiency, we will use 10%. -m is the invariant mass of the hadronic system (    ,                …  -x is 2E  /  s,  s= e + e - c.m. energy -L 0 is the total integrated luminosity ISR differential luminosity

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

21. Impact of DAFNE-2 on the range [1-2] GeV (3  ) using ISR @ 2.4 GeV statistical  had  had   s (GeV) BaBar, with the published L int per point BaBar, with 10  (the present L int ) DAFNE-2, with 2 fb -1 @ 2.4 GeV comparison among the present BaBar analysis, an (O(1 ab -1 )) BaBar update, and L int = 2 fb -1 at 2.4 GeVper energy point @ DAFNE-2, in the impact on  had  had :             : O(9%) | O(3%) | O(8%) On the other channels the improvement can be larger

22. ISR @ 2.4 GeV vs scan -Assuming to tag the ISR , 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 @10 32 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

23. Different event topology btw 2.4 and 10.6 GeV: 2  + 2  -  channel EE  s=2.4 GeV  s=10.6 GeV min    degrees GeV EE At 10.6 GeV: Hard photon: E  * = 3-5.3 GeV at  s’ = 0-7 GeV.  No fakes from beam-gas processes. Hadronic system collimated by recoil. Harder spectrum  better detection efficiency. BABAR At 2.4 GeV: Hard photon: E  * < 1.1 GeV. Distribution of particles and photon “uniform” distributed

24.  F. J. aks for  had at 1% up to the . L. Roberts will also be happy! Conclusions  Tough task! However big activities around the world:   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. 2  threshold also very important: KLOE off-peak data will help.  [1.02-2.4] GeV energy range: the most important for  had ; 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  /charm factory (BES-III).

25. spares

26. 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  L/L ~ 0.3% and  s ~ 50 keV, with Bhabha events), a good dE/dx resolution should not be neglected for good     separation (see V. Patera’s talk)  Electromagnetic calorimetry: it is crucial for good measurements of time, direction and energy of the  ’s from  ,  (e.g. a completely neutral inclusive R measurement), for efficient trigger criteria and for e/  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)

27.  in the future years the impact of a  hlo and  had is conditioned to different factors  KLOE and VEPP-2M are successfully covering the  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 Conclusions and perspectives

28. 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 @10 32 cm -2 sec -1 for single point gives higher statistics then B-factories even at 1000fb -1. However for a  or  em. what really matters is also the systematics.

29. 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 10 32 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!

30. At 10.6 GeV: Hard photon: E  * = 3-5.3 GeV at  s’ = 0-7 GeV.  No fakes from beam-gas processes. Hadronic system collimated by recoil. Harder spectrum  better detection efficiency. Different topology btw 2.4 and 10.6 GeV:  +  -  0  channel EE  s=2.4 GeV  s=10.6 GeV min    degrees GeV EE BABAR At 2.4 GeV: Hard photon: E  * < 1.1 GeV. Distribution of particles and photon more symmetric in polar angle.

31. Event Yeld with 1fb -1 @ 2.4 GeV GeV N/fb -1 /25MeV +-0+-0 + 2  -  +-20+-20 +-+- 20 o <   <160 o  =10% Above 1 GeV Statistical error for single point at 5-10% level. However what matters for a  or  em is the systematic error (which must be kept below 5%).

32.  with 1fb -1 @ 2.4 GeV: inclusive measurement GeV N/25MeV  +  -       =10%  +  -       +  -     

33. KLOE impact with 2 fb -1   s’ (GeV 2 ) d  /ds′ (nb/GeV 2 ) s’ (GeV 2 ) ′ ′ ′ only ISR at the NLO for both processes           E   MeV, bin = 0.01 GeV 2 L = 2 fb -1,  = 50% flat in s′, in both channels

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

35. Contribution to   had from F. Jegerlehner

36. Comparison of different evaluations of   had   had MethodRef 0.0280  0.00065 data<12 GeVS.Eidelman F.Jegerlehner ’95 0.02777  0.00017 data<1.8 GeVJ.H.Kuhen, M.Steinhauser ’98 0.02763  0.00016 data<1.8GeVM.Davier, A.Höcker ’98 0.027730  0.000148 Euclidean>2.5 GeVF.Jegerlehener ’99 0.027426  0.000190 scaled data, pQCD 2.8-3.7, 5-  A.D.Martin et al. ’00 0.027896  0.000391 data<12 GeV (new data CMD2 & BES) F.Jegerlehner ’01 0.02761  0.00036 data<12 GeV (new data CMD2 & BES) H.Burkhardt,B.Pietrzyk ’01 ( ’05) 0.00007 (0.00005)  up to J/  up to  )

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

38. magnitudeerrors Burkhardt & Pietrzyk 2001 Contributions to  had Including KLOE results, a preliminary analysis of B.& P. found a value of  (5) (m Z 2 ) which confirms their 2001 estimate:  (5) (m Z 2 ) =0.02761±0.00036

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

41. Impact of DAFNE-2 on the range [1-2] GeV (4  ) using ISR @ 2.4 GeV statistical  had  had   s (GeV) BaBar, with the published L int per point BaBar, with 10  (the present L int ) DAFNE-2, with 2 fb -1 @ 2.4 GeV comparison among the present BaBar analysis, an (O(1 ab -1 )) BaBar update, and L int = 2 fb -1 at 2.4 GeVper energy point @ DAFNE-2, in the impact on  had  had :         : O(2.5%) | O(0.8%) | O(1%)

42. Impact of DAFNE-2 on the range [1-2] GeV (2K2  ) using ISR @ 2.4 GeV statistical  had  had   s (GeV) BaBar, with the published L int per point BaBar, with 10  (the present L int ) DAFNE-2, with 2 fb -1 @ 2.4 GeV comparison among the present BaBar analysis, an (O(1 ab -1 )) BaBar update, and L int = 2 fb -1 at 2.4 GeVper energy point @ DAFNE-2, in the impact on  had  had :                 : O(15%) | O(5%) | O(5%)

43. e + e -   +  -  0  Babar @89 fb -1 D2@2fb -1 2fb -1 @ 2.4 GeV 89fb -1 @ 10.6 GeV N/25MeV We have assumed a 10% eff. in both cases. Results obtained with Phokhara 5, NLO ISR Number of events for Babar consistent with publication (hep-ex/0408078) GeV

44. Issues in the region [1-2] GeV from Burkhardt & Pietrzyk, PRD72 (2005) 057501  s (GeV) R(s) 1) the most critical region for  had and the second relevant one for a  hlo 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

45. ISR Luminosity for different c.o.m. energies -We integrated dL/dm for 25 MeV bin sizes. L 0 = 1 fb -1 1fb -1 @  s=1.02 GeV 1fb -1 @  s=2.4 GeV 1fb -1 @  s=10.6 GeV [nb -1 /25MeV] ISR L @ 2.4 GeV ISR L @ 10.6 GeV GeV