R at CLEO Surik Mehrabyan University of Puerto Rico at Mayaguez on behalf of CLEO collaboration Heavy Quarkonium 2006 June BNL

Transcription

1 R at CLEO Surik Mehrabyan University of Puerto Rico at Mayaguez on behalf of CLEO collaboration Heavy Quarkonium 2006 June BNL

2 Overview The ratio of lowest order cross section for hadrons and µ-pair can be represented theoretically as -It is proportional to the # of quark colors. On the other hand, Standard Model (SM) parameters such as, running coupling constants, and, the anomalous magnetic momentum of muon, depend on R through hadronic vacuum polarization and dispersion integral, respectively. A precise measurement of R can help narrow uncertainties for both parameters.

3 Overview (cont.) CLEO has done one of the precise measurement of R = GeV Phys. Rev. D57:1350 (1998). CLEO ongoing GeV 7 energy GeV 12 energy points.

4 CLEOIII - (Energy points) Energy point Luminocity GeV pb The plot from Davier and Höcker : hep-ph/ Our preliminary results at low energy points are in agreement with Crystal Ball results.

5 CLEOIII cross section the way that we are measuring hadronic cross section. - is the contribution from known lower energy resonances. - is the sum of combined soft and virtual photon parts, which depends on only hadronic event detection efficiency when Initial State Radiation (ISR) is turned off, and hard photon part ( the details in a Radiative Correction page). This approach of hadronic cross section calculation is used by Berends and Kleiss (Nucl. Phys. B178, 141 (1981)).

6 CLEOIII hadronic events selection The following selection criteria has been used to suppress background. Zvertex <0.06 m beam-gas/wall. (z-component of event vertex) Evis/2Ebeam>0.5 - two-photon, beam-gas/wall (Visible energy of event) PzMiss/Evis/2Ebeam <0.3 - two-photon, QED. (z-component of missing momentum) FW2 < 0.9 QED. (Ration of Fox-Wolfram moments) CC/2Ebeam < 0.9 Bhabha events. (Charged tracks Calorimeter energy) Multiplicity > 3 - two-photon, QED. (# of charge tracks) nominal cut Distribution of charged tracks calorimeter energy over 2Ebeam (CC) when all other cuts have been applied.

7 CLEOIII background suppression The net-charge distribution after hadronic event selection cuts. The hadronic event selection cuts suppress background very well, however, the main background, which stays after the cuts, comes from tau-pairs. The level of tau-pair background is about 4% for all energy points.

8 CLEOIII Radiative correction Differential efficiencies have been used to calculates radiative correction for hard photon integral. summary of final corrections E nergy point [GeV]

9 CLEOIII resonances A beam particle emits a photon and loses its energy before the interaction. When it then annihilates it can create a quarkonium resonances. When the resonance decays to hadrons it increases hadronic cross section. The radiated kernel is Energy point GeV Di-electron width of Upsilon(1S, 2S, 3S), J/Psi, and Psi(2S) resonances have been taken from CLEO publications: Phys.Rev.Lett.96:092003, 2006, Phys.Rev.D71:111103, 2005, and Phys.Rev.Lett.96:082004, The others have been taken from PDG-2004.

10 CLEOIII multiplicity correction There is a generator level discrepancy and we decided to correct continuum multiplicity distribution because data and MC do not match. i represents the bin which has multiplicity i. Energy point Multiplicity system. GeV % The difference between corrected and uncorrected R values has been assigned as a systematic error associated with multiplicity.

11 CLEOIII systematic error (cont.) Visible energy distribution for GeV. The tail shows the two-photon background. nominal cut Less than 0.5% of two-photon interactions survive hadronic selection cuts, according to toy MC. We are not subtracting two-photon background, instead of it, we are assigning it to our systematic error by varying visible energy cut by 20% and taking the difference as a systematic error.

12 CLEOIII systematic errors The preliminary systematic errors [%] E nergy P oint [GeV] L uminos ity T rigger R adiative Correction Multiplicity Correction Event Selection T otal

13 CLEOIII systematic errors The preliminary systematic errors [%] E n er gy P oin t [GeV] L u min os ity T r igger R adiative Cor r ection Mu ltiplicity Cor r ection E vent S election T otal

14 CLEO-c Energy points The measurements of R between GeV have been used to obtain. This is a dedicated scan to determine the running energy that will maximize the Ds yield. There are 12 energy point which are shown on the plots by green and blue triangles. The minimum luminosity is at GeV (1500 nb-1), and the maximum luminosity is at 4.26 GeV (13000 nb-1).

15 CLEO-c charm mesons separations The plot shows the CLEO-c ability to separate different charm states. The variables that have been used are: the charm meson beam-constrained mass,, and the energy difference between the beam and charm meson

16 CLEO-c charm cross section The plot shows the scan result for maximum Ds yield.

17 CLEO-c charm cross section Three different methods have been used to determine charm cross section. Exclusive method: both charm mesons are observed. Inclusive method: one charm meson is observed. Hadron-Counting method: the hadrons are used: Discrepancy between Inclusive and exclusive methods is due to the multi-body background : The hadron-counting technique was used by CLEO to determine Psi(3770) hadronic cross section : Phys. Rev. Lett.96:092002,2006

18 CLEO-c Results is obtained after fitting PDG continuum cross section between 3.2 and 3.72 GeV (slide 13), using the 1/s functional form. is obtained after dividing charm cross section (inclusive method) to the µ-pair Born cross section.

19 In summary CLEOIII: R measurement at seven energy points: GeV Preliminary systematic uncertainties are in the order of 2%. Background is well understood. Corrections and efficiencies are almost final. CLEO-c: R measurement at twelve energy points: GeV preliminary results agree with PDG. work on systematic uncertainties. Both analysis are progressing.

20 Backup slides:

21 CLEOIII Radiative and Efficiency correction The observed hadronic cross section at s can be written as sum of The effective soft and virtual part of observed cross section can be determined as with The hard photon contribution is actually an integral over all radiated energies.

22 CLEOIII Rad.Cor. (cont.) The hard photon contribution is actually an integral over all radiated energies where and Thus total efficiency and radiative correction read The integration starts from 0 because we moved 1- t*ln(kmin) term from soft to hard part, the Kmin is implemented by Bonneau and Martin to separate spectrum of soft and hard radiated photons.

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