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R Measurement at charm resonant region. Haiming HU BES Collaboration. Charm 2007 Cornell University Ithaca, NY. US. What is R value. Definition .

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## R Measurement at charm resonant region

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**R Measurement at charm resonant region**Haiming HU BES Collaboration Charm 2007 Cornell University Ithaca, NY. US**What is R value**Definition i.e.R value is the inclusive hadronic cross section in e+e collision and through single photon annihilation, and normalized by Born cross section of + The measured R value, Rexp, contains the contributions from the continuous and resonant states. In theory, they may be written as:**R value in experiment**R value is measured by : observed number of hadronic events; : number of background events; : integrated luminosity; : acceptance for hadronic events; : trigger efficiency; : initial state radiative correction factor. • In which, each quantity is obtained by • Data analysis • Theoretical calculations • Monte Carlo simulations**The original R value from BES**• In 1998 & 1999, scan data were taken between 2-5 GeV with BES • the energy steps in 3.7– 4.6 GeV are 10 20 MeV • the statistic errors are about 2~3 % • the systematic errors are about 5~8 % • the results published in Phys. Rev. Lett. 84 (2000)594, and 88 (2002)101802 In the calculation of ISR factor (1+), the values of resonant parameters in PDG2000 were used**Higher charmonia**The 4 heavy charmonia with J PC = 1ˉˉare Their properties of production and decays are characterized by the Breit-Wigner amplitude and resonant parameters: • Nominal mass M • total width tot • electronic width ee • phase angle According to Eichten’s model, there are following decay channels**K.K.Seth’s results**K.K.Seth fit the resonant parameters of (4040), (4160) and (4415) based on the R values measured by CB and BES (hep-ex/0405007) Conclusion: CB and BES measurements are in excellent agreement**Summary of the previous fitting**Some works have measured the resonant parameters of the higher chamonia. The methods of these works may be summarized as: • Fit the published R values • Did not consider the phase angle of the Breit-Wigner amplitude • Neglected the interference effects • Assumed the total width is energy independent Fitting Experimental quantity Theoretical quantity Resonant parameters**Problems in Fitting**If we inspect the previous fittings, the following questions should be reviewed Physical • Breit-Wigner amplitude with or not? • energy dependence of total width? • form of the continuous charm BG? • interference among the 4? • Definition of 2in fitting • target function A: fitting true R value • target function B: fitting R-like value All of these physical problems and fitting schemes will influence the values of the resonant parameters**Problem in physics**• Breit-Winger amplitude Without phase-angle : with phase-angle: or • Interference the interferential summation of the amplitude for same decay channel the non-interferential summation for the different decay channels resonant cross section expressed by the form of R value**Problem in model**The continuous background • Non-resonant charm backgrounds near threshold ① Polynomial of degree 2 (experiential) C0 , C1, C2 are free parameters ② DASP form (phenomenological) Ak (k=1,…,6) are free parameters. Inclusive data can not give enough information to determine the correct ratios among Ak**Problem in model**• Energy dependence of hadronic width ① Potential well model in quantum mechanics , ② Effective interaction theory (EIT) Hamiltonian Inclusive data can not give enough information to determine the correct ratios among GPP, GVP,GVV. Hadronic width: Total width:**Fitting procedures**The values of the resonant parameters will influence (1+) and then Rexp value, so themeasurement of R value and the determination of the resonant parameters should bedone in iterative way and in same procedure with the MINUIT. But no one did so before. Initialization raw data, parameters Follow chart for fitting: 2 (Rexp , Rthe) No convergence ? Yes Output Rexp , M , tot , ee , **Fitting schemes**Two experimental quantities: R value or R-like value Scheme A: fitting true R value Scheme B: fitting R-like value Errors are not constant in iterative fitting, but they can not correctly update in fitting Errors are independent of fitting, and they keep constant in iterative fitting It is noticed that the errors of the experimental quantities will affect the convergence condition and then the fitting results. Therefore the correct input of the error is important. Errors in scheme B are correct.**Uncertainty in fitting**We have some different models and experiential expressions, but none of them is “correct”, they are only approximations. For this reason, we have tried all possible combinations, and the results are not the same, but they are consistent considering the errors. We will show the results which is obtained based on the original data taken in 1999 and a reasonable combination of models and target function of fitting. • The reasonable combination is • Breit-Wigner :relativistic form with phase angle • energy-dependence of had:potential model in quantum mechanics • continuous charm background: polynomial of degree 2 • interference:considered • target function of 2:scheme B**The new results**Fig.1**The new results**The comparison of the updated R value and the old results in Phys. Rev. Lett. 88 (2002)101802 The differences of R values are due to the updated resonant parametersandinitial state radiative correction factor (1+obs)**scheme dependence**Phase angle and =0 scheme A and scheme B total width energy dependence in QM and polynomial of degree 2 for charm BG Interference are different for or Fig.2 Scheme A It is noticed that the peak of (4040) in scheme A is clearer than in scheme B.But scheme A is incorrect !!! Fig.3 Fig.1 Scheme B Scheme A**model dependence**• Energy dependence for total width: QM and EIT • Breit-Wigner with non-zero phase angle • Polynomial of degree 2 for the charmed continuous BG • target function B for 2 Fig.1 Fig.4 Energy dependence of total width in quantum mechanics Energy-dependence of total width in effective interaction theory**Summary**• The R values and the resonant parameters are related closely, they should be measured in the same program in the iterative method; • The interferential effect is important in the determination of the shape of the resonant structure; • The extracted values of the resonant parameters are theory and model dependent; • The values of the resonant parameters are also fitting function or scheme dependent.**Prospects**• Theorists should make more reliable calculations on the energy-dependence of the total width and the continuous charm background. • It is hopeful to make more detailed scan and collect large sample between 3.7 4.6 GeVwith the future BESIII, so that one may determine the fine shape of the resonant structure and hadronic widths of the 4 higher charmonia. • PDG may set up a standard fitting procedure in order to avoid the uncertainty of the fitting among the different experiments.**Comparisons**T.Barnes’s paper Phys. Rev. D72, (2005)504026, hep-ph/0505002v3 studied the experimental and theoretical (nonrelativistic potential model and Godfrey-Isgur relativistic potential model) status of higher chamonia, the values about hadronic and total widths are listed below BES new value 25.6±6.3 BES new value 88.9±12.4**Comparison**BES new value 78.8±16.1 BES new fitting:(4159)(4195)**Comparison**BES new value 80.4±24.7**Upper limit of electronic width of Y(4260)**Scanned resonant structure of the higher charmonia by BES BABAR discovered Y(4260) ! Based on the published R value measured at BES, the upper limit of the electronic width of Y(4260) was estimated: ee < 580 eV/c2 at 90% CL See the detail descriptions in Phys. Lett.B640, (2006)182-187

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