IV Euridice Collaboration Meeting Marseille, 8-11 February 2006 Hadronic Cross Section measurement at DA  NE with the KLOE detector Hadronic Cross Section measurement at DA  NE with the KLOE detector Paolo Beltrame IEKP, Universität Karlsruhe For the KLOE collaboration

Outline Euridice Collaboration Meeting 8-11/2/2006 The Radiative Return method at DA  NE Status of the Large Angle analysis DA  NE run off-resonance Conclusion and outlook

Radiative return Euridice Collaboration Meeting 8-11/2/2006 DA  NE is designed for a fixed center-of-mass energy:  s = m  = 1.02 GeV New and completely complementary method: events with Initial State Radiation (ISR) S. Binner, J.H. Kühn, K. Melnikov, Phys.Lett. B459 (1999) 279 “Radiative Return” to  -resonance: e  e       for (2m  ) 2 < M  2 < s FF  ISR MC - Generator PHOKHARA = NLO J. Kühn, H. Czyż, G. Rodrigo Radiator-Function H(s) ISR H(s)

The KLOE detector at the DA  NE  -factory Magnetic Field of 0.52 T sense wires wires in total Track momentum resolution  p /p  0.4% (  > 45 ° ) Vertex resolution  xy  150  m,  z  2 mm Drift chamber Pb/Scint fibres 4880 PM Energy resolution  E /E = 5.7% /  E(GeV) Time resolution  T = 54 ps /  E(GeV)  50 ps Electromagnetic calorimeter Electromagnetic calorimeter Euridice Collaboration Meeting 8-11/2/2006

DA  NE statistics Euridice Collaboration Meeting 8-11/2/2006 In 2004 and 2005 run DA  NE has provided 2fb -1 of data Statistics used for the published analysis (Small angle analysis) Data for the analysis in preparation

KLOE result (140 pb -1 of 2001) Phys. Lett. B606 (2005) 12 KLOE result (140 pb -1 of 2001) Phys. Lett. B606 (2005) 12 KLOE: Small Angle analysis Euridice Collaboration Meeting 8-11/2/2006 Pion tracks: 50 o <    <130 o Photons:   165 o No photon tagging: SELECTION M  2 (GeV 2 ) MC: FSR /(ISR + FSR) (%) high statistics for ISR low relative FSR contribution suppressed       background threshold region not covered no kinematic closure of event PRO & CONTRA

KLOE result compared with CMD-2 Euridice Collaboration Meeting 8-11/2/2006  (e + e -  +  - ) result statistical error: negligible experimental systematic uncertainty: 0.9% theoretical systematic uncertainty: 0.9% Total systematic error: 1.3%  Dispersion integral evaluation KLOE: (375.6  0.8 stat  4.9 syst+theo ) CMD-2: (378.6  2.7 stat  2.3 syst+theo ) KLOE and CMD-2 in good agreement  Pion Form Factor comparison with result from CMD-2 experiment: KLOE and CMD-2 in fair agreement 1.3 % Error 0.9 % Error CMD-2 KLOE s (GeV 2 ) |F  (s)| 2 M  2 (GeV 2 ) a   ·10 10

Muon anomaly comparison Theory - Experiment Euridice Collaboration Meeting 8-11/2/2006 KLOE and CMD-2 results used to evaluate the hadronic contribution and therefore the muon anomaly a m ∙ a m ∙ DEHZ’03 [e+e- based] DEHZ’03 [ t based] a  ∙ DEHZ‘03 Experiment E821 Standard model prediction: CMD-2 and KLOE averaged in hadronic contribution DEHZ’04 [e + e - ] New Theory (SM) - Experiment a  exp - a  theo = ( 25.2 ± 9.2 ) · standard deviations difference ! New KLOE measurement Phys. Lett. B606 (2005) 12 New 4 th order QED calculation (Kinoshita, Nio) Phys. Rev. D70 (2004) New ‘Light-by-light’ calculation (Melnikov, Vainshtein) Phys. Rev. D70 (2004)

Comparison among e + e - experiments Euridice Collaboration Meeting 8-11/2/2006 CMD-2 and KLOE agree at high M 2  disagreement between KLOE and CMD-2/SND around the  peak  /  KLOE - 1 interpolation of 60 KLOE data points from 0.35 to 0.95 GeV 2 M  2 (GeV 2 ) In summer 2005 SND has released preliminary results for the Pion Form Factor in the energy range MeV with a systematic error of 1.3% on  peak and higher at low  s (hep-ex/ )

Euridice Collaboration Meeting 8-11/2/2006  KLOE Large Angle analysis  KLOE Small Angle analysis with 2002 data  new e + e - data from CMD-2, SND, BaBar, Belle Looking forward to Looking for…

KLOE: Large Angle analysis Euridice Collaboration Meeting 8-11/2/2006         the threshold region is accessible the ISR photon is detected (4-momentum constraints) large       background contamination lower signal statistics large FSR contributions irreducible background from  decays PRO & CONTRA Pion tracks: 50 o <    <130 o Photons: at least one with 50 o <   <130 o and E  > 50 MeV SELECTION

The Large Angle analysis step 1 Euridice Collaboration Meeting 8-11/2/ Acceptance Pion tracks: 50 o <    <130 o Photons: at least one with 50 o <   <130 o and E  > 50 MeV  large       background contamination       MC      MC M 2  (GeV 2 ) 2. Kinematic fit Kinematic fit with       background hypothesis Two tracks in 40  <   < 140  At least two “prompt” photons, one of them with E  > 40 MeV and 40  <   < 140   4-momenta conservation  M inv (  ) = m   Negligible inefficiency for the  signal and rejects ca. 40% of       data 22 Cut  33 The Large Angle analysis steps 1 & 2

Data       MC (140 pb -1 ) Normalization by integrated luminosity The Large Angle analysis step 3 Euridice Collaboration Meeting 8-11/2/ Trackmass M trk charged particle (x  ) mass with the hypothesis of  x  x         – MC      – MC      – MC M trk (MeV) M  2 (GeV 2 ) Selecting       background events only by means of the kinematic fit (after angular cut):  2  <20 (MeV) M trk Inclusive in M  2 Very good agreement Data –  MC

The Large Angle analysis step 3 Euridice Collaboration Meeting 8-11/2/ Trackmass 0.25<M  2 <0.3 GeV <M  2 <0.4 GeV <M  2 <0.6 GeV 2 M  2 <0.2 GeV <M  2 <0.7 GeV 2 M trk (MeV) M trk Selecting      events by means of the kinematic fit (  2  >500) and without any other cuts but the angular (acceptance) cut Very good agreement Data –  MC Data      MC (800 pb -1 ) Normalization by integrated luminosity

The Large Angle analysis step 4 Euridice Collaboration Meeting 8-11/2/  angle Solid angle between the missing momentum and the detected photon momentum M  2 <0.2 GeV 2  (  ) 0.2<M  2 <0.4 GeV 2  (  )      MC       MC  cut function       MC      MC  (  ) M  2 (GeV 2 ) Relying on the good Data – MC agreement for  and  events, possible to study a cut based on the distribution of  as a function of M  2.    

Background after all the selection cuts Euridice Collaboration Meeting 8-11/2/2006 After      selection cuts mentioned before Data   ee  M  2 (GeV 2 ) Using the 2001 Data (144 pb -1 ) statistics is an issue at low masses. We will use 2002 Data for final result (~300 pb -1 ) High efficiency for  at the end of the analysis, even at low M 2  still high about 80% Background: - ee  negligible -  under control with fitting procedure -  small amount, but to reduce the statistical error more statistics is needed: new MC production already done

Irreducible background Euridice Collaboration Meeting 8-11/2/2006 By means of kinematic constraints       is a reducible background… … but FSR events as  and   f 0     all of them with  final state are not! At low M  2 ISR and FSR are not the only contributions to the mass spectrum and to the charge asymmetry, model dependence for the additional contributions Three processes of the same family: their amplitudes interfere     ffff         includes also:  FSR f0f0 

Charge asymmetry Euridice Collaboration Meeting 8-11/2/2006 MC: FSR /(ISR + FSR) M  2 (GeV 2 ) 50% 30% 10% FSR-NLO FSR-LO After angular cuts FSR-LO FSR-NLO hep-ex/ Forward-backward asymmetry Test of scalar QED model for FSR Another tool to understand the f 0 : Off  resonance peak Data MC: ISR + FSR + f 0 (980) (Kaon Loop)

The Off peak’s goals Euridice Collaboration Meeting 8-11/2/2006  Study of the structure of the scalar meson f 0  Benefit from run at  s = 1 GeV to make a “       background free” measurement  At  s = M     nb    nb  s = M        MC      MC  At  s= MeV    nb (from SND, PRD66 (2002) )  s = 1 GeV       MC      MC

Off peak data taking Euridice Collaboration Meeting 8-11/2/2006 Our statistics goal:  More than 200 pb -1 of off-resonance data collected What we are doing:   scan and long run at  s = 1.00 GeV started in December 2005 will last until 31 March 2006 How are we going:  Integrated luminosity at 1 GeV up today greater than 150 pb -1  … Maybe we can arrive at 300 pb -1 … or we can take more scan points run number  s ( MeV )   s = 1023  s = 1030  s = 1018  s = 1010  s = 1000

Conclusion Euridice Collaboration Meeting 8-11/2/2006  Measurement at Small photon polar angles published (untagged measurement) - low background contribution - analysis of 2002 data in preparation - we plan normalization with radiative muon pairs  Measurement at Large photon angles in preparation - cross check of published results - completely different systematic errors -       background reduced by means of selection cuts - measurement of charge asymmetry to test FSR model dependence  Irreducible background from  f       and (maybe)      (which is model dependent) THEORY INPUT NEEDED!  DA  NE is taking data off-resonance at  s = 1.00 GeV in order to allow for a background-free measurement of the Hadronic Cross Section

The Off slides Euricice Collaboration Meeting 8-11/2/2006

The radiative return (off slides) Euricice Collaboration Meeting 8-11/2/2006  Rho - Resonanz    Resonanz M   [GeV 2 ] Non-radiative cross section a.u. Rho - Resonanz Radiator- function H(s) M   [GeV 2 ] MC- generator PHOKHARA J. Kühn, H. Czyż, G. Rodrigo Theoretical radiator-function a.u. Rho - Resonanz    )( 2 2 s dM d M      H(s) M   [GeV 2 ] Radiative cross section a.u.

 e  e       (off slides) Euricice Collaboration Meeting 8-11/2/2006 Acceptance0.3% Trigger0.3% Tracking0.3% Vertex0.3% Reconstruction filter0.6% Particle ID0.1% Trackmass cut0.2% Background0.3% Unfolding effects0.2% Total experimental Error 0.9% Luminosity0.6% Vacuum polarization0.2% FSR corrections0.3% Radiator function0.5% Total theoretical Error 0.9% TOTAL ERROR 1.3%  ( e + e -      ) ( nb ) M pp 2 (GeV 2 ) KLOE 2001 Data 140pb -1 Acceptance0.3% Trigger *0.3% Tracking0.3% Vertex0.3% Reconstruction Filter *0.6% Particle ID0.1% Trackmass Cut0.2% Background0.3% Unfolding Effects0.2% Total experimental error 0.9% Luminosity *0.6% Vacuum Polarization0.2% FSR Corrections0.3% Radiator Function0.5% Total theoretical error 0.9% *Goal 2002 data: Error < 1%

2002 Data chance and challenge (off slides) Euricice Collaboration Meeting 8-11/2/2006 global systematic error < 1% The goal is to achieve a global systematic error < 1% instead of the present 1.3% Experimental systematic ( Trigger, Vertex, Reconstruction Filter) Theoretical systematic  the challenge for 2002 data: normalizing to     ,  in the limit of neglecting FSR effects ′ ′ ′ In addition: 2 fb -1 of total data statistics

10 10  (  a  ) stat Statistics and error (off slides) Euricice Collaboration Meeting 8-11/2/2006 Absolute contribution (in ) to the statistical Error on a  had,  as function of integrated Luminosity from different energy regions: Statistical error is fully dominated by energy region <0.35 GeV 2  Absolute contribution to a  ca · ( pb -1 ) Systematic error of 2% gives ca. 2· from region below 0.35 GeV 2 (ca. 100 · contribution to a  )

Euricice Collaboration Meeting 8-11/2/2006 New generator: Phokhara5 (off slides) New MC generator Phokhara5 with some differences with respect to Phokhara3 (last version inserted in GEANFI) 1 st news: more channels e + e -   +  -  e + e -   +  -  (also f 0 models added) e + e -   +  -        +  -  +  -  e + e -  pp   nn  e + e -  K + K -   K 0 K 0  e + e -   +  -    } new in Phokhara5 2 nd news: more photons Comparison for the      channel Initial state vertex correction to FSR added in Phokhara4 (now also soft ISR+hard FSR is possible, before ISR photon 1 had to be hard)  2-3 % different in cross section for inclusive measurement  Less than 1 ‰ for Small Angle cuts (0º<  miss <15º)

Theoreticians now “officially” included Gounaris-Sakurai parametrization (in addition to Kühn-Santamaria) For GS-parametrization, the contribution from ,  ’,  ’’ are evaluated using a BW GS. Theory part is evaluated only up to n=1000… 3 rd news: more parametrizations Phokhara5 vs. Phokhara3 for      (off slides) Higher BW contribution have a non-negligible effect on the spectrum … “If you have infinite sums, everything can happen” (H. Czyz) higher BW on higher BW off (off-on)/on M  2 (GeV 2 ) Two parametrizations for the Pion Form Factor: Kühn-Santamaria and Gounaris-Sakurai Euricice Collaboration Meeting 8-11/2/2006

Acc Phok5 Acc Phok3 M  2 (GeV 2 ) Phok5/Phok3 - 1 Phokhara5 vs. Phokhara3 for      (off slides) Acc = (dN/dM    SA cuts)  (dN/dM    Incl.)  SA cuts: 50º<   <130º, 0º<  miss <15º a) ISR+FSR, FSR-NLO off Agreement between Phok5 and Phok3 b) ISR+FSR, FSR-NLO on Disagreement between Phok5 and Phok3! Phok5/Phok3 - 1 Acc Phok5 Acc Phok3 M  2 (GeV 2 ) a) However, what enters in the analysis is the acceptance as a function of M  2, not the one in M  2 The actual change will most likely influence only the bins at very high M    Phokhara5  generator (  flagged as ISR or FSR) is under construction b) Euricice Collaboration Meeting 8-11/2/2006

Charge asymmetry (off slides) Euricice Collaboration Meeting 8-11/2/2006  +  - system: A(ISR)  C-odd A(FSR), A(f 0 )  C-even  an asymmetry is expected in the variable: Using the f 0 amplitude from Kaon Loop fit, good agreement data-MC also at low masses Q (MeV) What about  s = 1 GeV? FSR  F  (  s)   f 0 zoom data  MC: ISR+FSR  MC: ISR+FSR + f 0 (Kaon Loop) Kaon Loop fit The  is coupled to the scalar through a loop of charged kaon for each scalar meson three free parameter: the mass, the coupling to K + K - and to the    

Off peak (off slides) Euricice Collaboration Meeting 8-11/2/2006 Good agreement with on peak data Marginal with the off peak ones kaon-loop amplitude 2002 scan (~ 5pb -1 ) on-peak data