KLOE results on Hadronic cross section Graziano Venanzoni Laboratori Nazionali di Frascati (for the KLOE collaboration) Topical Workshop on (g-2) Glasgow, 25-26 Oct 2007

Outlook Motivation of s(e+e- ) at low energy Reminder: KLOE published results on |F and awith 2001 data (normalization to Bhabha) Update of |F and a with 2002 data, using two selection schemes (large and small angle) Work in progress: Extract |F via bin-by-bin normalisation to  Use data collected at 1 GeV Ccorreggere extract fpi …

a= (g-2)/2 =  aaaaa had and the muon anomaly Hadronic Cross Section & Muon-Anomaly Motivation: High Precision Test of the Standard Model  Anomalous magnetic moment of the muon  Fine structure constant at Z0-mass aQED (MZ) Hadronic Vacuum Polarization 2nd largest contribution, pQCD not applicable Error of hadronic contribution dominates total error of am! µ+ g* q Muon-Anomaly a= (g-2)/2 =  aaaaa theo QED had weak New physics Dispersion-Relation Channel  = s(e+ e ) gives >70% contribution to ahad! K(s) = analytic kernel-function, above typically 2…5 GeV, use pQCD Alternative: Spectral function from decay ( t  nt Hadrons) taking into account isospin breaking corrections amhad shad (s) M. Davier

(e+e-+-) with ISR: Since DANE runs at fixed energy (1020 MeV), we measure the cross section s(e+ e-  hadrons ) as a function of the hadronic c.m. energy M hadr by using ISR (”radiative return”): This method is a complementary approach to the standard energy scan. Rho - Resonanz dds 0.1 0.3 0.5 0.7 0.9 Mpp2 [GeV2] a.u. S. Binner, J.H. Kühn, K. Melnikov, Phys. Lett. B 459, 1999 Neglecting FSR effects: ´ = ) ( 2 s dM d M pp ppg H(s) 4mp2£ sp = M£ mf2 Mettere la seconda aprte come flash Radiator function H(s) Luminosity, acceptance (and other normalizations) enter only once ! Requires precise calculations of the radiator H  PHOKHARA MC NLO Generator (H. Czyż, A. Grzelińska, J.H. Kühn, G. Rodrigo, Eur. Phys. J. C 27, 2003) H. Czyz 0.1 0.3 0.5 0.7 0.9 Mpp2 [GeV2]

This talk is based on 240pb-1 DANE: A -Factory e+e- - collider with =m1.0195 GeV Integrated Luminosity Peak Luminosity Lpeak= 1.5 • 1032cm-2s-1 Total KLOE int. Luminosity: L dt ~ 2500 pb1 (2001 - 05) DEAR, This talk is based on 240pb-1 from 2002 data! 2006: Energy scan with 4 points around m-peak 220 pb-1 at = 1000 MeV

KLOE Detector sp/p = 0.4% (for 900 tracks) sxy  150 mm, sz  2 mm Drift chamber sp/p = 0.4% (for 900 tracks) sxy  150 mm, sz  2 mm Excellent momentum resolution

Excellent timing resolution KLOE Detector Electromagnetic Calorimeter sE/E = 5.7% / E(GeV) sT = 54 ps / E(GeV) 100 ps (Bunch length contribution subtracted from constant term) Excellent timing resolution

Extracting |F|2 from eve: a) Via absolute Normalisation to VLAB Luminosity (as in 2001 analysis): dsg(g)/dM2 is obtained by subtracting background from observed event spectrum, divide by selection efficiencies, and int. luminosity: 1) Obtain s from (ISR) - radiative cross section dsg(g)/dM2 via theoretical radiator function H(s): 2) Ccorreggere extract fpi … 3) Relation between |Fp|2 and the cross section s(e+e-  +-) b) Via bin-by-bin Normalisation to rad. Muon events (see later…)

Event Selection Pion tracks at large angles 50o< p <130o a) Photons at small angles  < 15o or  > 165o  Photon momentum from kinematics:   High statistics for ISR photons Very small contribution from FSR Reduced background contamination   

Event Selection Pion tracks at large angles 50o< p <130o a) Photons at small angles  < 15o or  > 165o  Photon momentum from kinematics:   High statistics for ISR photons Very small contribution from FSR Reduced background contamination   b) Photons at large angles 50o <  < 130o   Photon is explicitly measured in the detector! Threshold region accessible Increased contribution from FSR Contribution from f0(980)

Published result, 2001 data Published KLOE Result: Acceptance 0.3% Trigger Tracking Vertex Reconstruction filter 0.6% Particle ID 0.1% Trackmass cut 0.2% Background Unfolding effects Total experimental Error 0.9% Luminosity ( LA Bhabhas ) Vacuum polarization FSR corrections Radiator function 0.5% Total theoretical Error 0.9% TOTAL ERROR 1.3% Acceptance 0.3% Trigger Tracking Vertex Reconstruction filter 0.6% Particle ID 0.1% Trackmass cut 0.2% Background Unfolding effects Total experimental Error 0.9% Phys. Lett. B606 (2005) 12 s ( e+e-  p+p- ) nb KLOE 2001 Data 140pb-1 Statistical error negligible (1.5 Million events) Phys. Lett. B606 (2005) 12 app(0.35-0.95 GeV2) = (388.7  0.8stat4.9syst) · 10-10

C. M. Calame et al., Nucl. Phys. B758 (2006) 227 2002 data: improvements wrt 2001 Larger data set allows for more refined evaluation of systematic errors associated with selection efficiencies; evaluate all contributions again 2002 data less effected by pile-up events from machine background additional online software trigger level introduced to recover cosmic veto inefficiency in 2002 (that gave an inefficiency of up to 30% in 2001) Improved offline-event filter reduces its systematic uncertainty to <0.1%, was the largest contribution (0.6%!) to the error in published result Trigger issue in 2001 data resolved (see below) New event generator BABAYAGA@NLO - theoretical error of Bhabha effective cross section decreases from 0.5% to 0.1% - Bhabha cross section lowered by 0.7%; therefore pion form factor decreases by 0.7% C. M. Calame et al., Nucl. Phys. B758 (2006) 227

Trigger 2001 update Impact of update on trigger correction on 2001 cross section: KLOE 2001 TRG updated KLOE 2001 published KLOE 2001 TRG updated KLOE 2001 published Changes published value on app by 0.4%

Small angle analysis 2002  Preliminary r-w Interference Statistics: 242pb-1 of 2002-data 3.4 Million Events qMiss<150 or qMiss>1650  r-w Interference M2 (GeV2) M2 (GeV2)

Small Angle Analysis Experimental challenge: Fight background from  ,ee  , , reduced by means of kinematical cuts in (trackmass), and likelihood function signal region Normalization to integrated luminosity, which is obtained from large-angle- Bhabha events (clean exp. selection) mp Background from LO-FSR negligible (reduced by acceptance cuts: small qg), NLO-FSR not reduced and not a background, efficiency has to be known mm mr2 Surviving background evaluated by MC and subtracted LO-FSR NLO-FSR

Background: ppp events only fitted below 0.6 GeV2 Main backgrounds estimated from MC shapes fitted to data distribution in MTrk (ppg/mmg, ppp, eeg) Data S MC g , eeg Data S MC g eeg 0.42< M2 < 0.44 GeV2 0.68< M2 < 0.7 GeV2 MTrk [MeV] MTrk [MeV] Bhabha contamination small ppp events only fitted below 0.6 GeV2 ppp-peak is cut by event streaming and elliptical Cut in MTrk Excellent agreement on TRK mass spectrum Between data and MC

Luminosity: Quoted theor. accuracy: 0.1% At KLOE, Luminosity is measured using „Large angle Bhabha“ events (55o<qe<125o) KLOE is its own Luminosity Monitor! F. Ambrosino et al. (the KLOE Coll.) Eur.Phys.J.C47:589-596,2006 The luminosity is given by the number of Bhabha events divided for an effective cross section obtained by folding the theory with the detector simulation. Generator used for Bhabha cross section: BABAYAGA (Pavia group): seff = (428.00.3stat) nb C. M. Calame et al., Nucl. Phys. B758 (2006) 227 Systematics on Luminosity Theory 0.10 % Acceptance 0.25 % Background (ppg) 0.08 % Tracking+Clustering Energy Calibration 0.13 % Knowledge of s run-by-run TOTAL 0.10 % theo  0.32% exp = 0.34 % New version of generator (BABAYAGA@NLO) gives 0.7% decrease in cross section compared to previous version Quoted theor. accuracy: 0.1%

Radiative corrections Radiator-Function H(s) (ISR): Fp=1 s (ppg) with Fp=1 [nb] ISR-Process calculated at NLO-level PHOKHARA generator (Czyż, Kühn et.al) Precision: 0.5% H(s) Radiative Corrections: i) Bare Cross Section divide by Vacuum Polarisation  from F. Jegerlehner: http://www-com.physik.hu-berlin.de/~fjeger/ ii) FSR - Corrections Cross section spp must be incl. for FSR FSR corrections have to be taken into account in the efficiency eval. (small angle acceptance, MTrk) and in the passage M2 Net effect of FSR is ca. 0.8%: FSR contr. (sQED)

Correcting for FSR energy: Go from M2  M2g* The presence of FSR results in a shift of the measured quantity M2towards lower values: M2g* M2 g* [GeV2] Use special version of PHOKHARA which allows to determine whether photon comes from initial or final state  build matrix which relates pp to g* . MonteCarlo ISR only:  = M2 FSR photon present:  = M2g(FSR) pp [GeV2]

Small angle result from 2002 data: Preliminary Systematic errors on ampp: Offline Filter negligible Background 0.3% Trackmass/Miss. Mass 0.2% (prelim) p/e-ID Vertex 0.5% Tracking 0.4% Trigger 0.2% Acceptance () Mpp2 Mg* (FSR corr.) 0.3% (prelim) Software Trigger 0.1 % Luminosity 0.3% Acceptance (Miss) 0.1% Radiator H 0.5% Vacuum polarization negligible STotal = 1.1%

Comparison 2001-2002: (updated)

Evaluating ampp with small angle Dispersion integral for 2p-channel in energy interval 0.35 <Mpp2<0.95 GeV2 2001 published result (Phys. Lett. B606 (2005) 12): app(0.35-0.95GeV2) = (388.7  0.8stat4.9syst) · 10-10 Applying update for trigger eff. and change in Bhabha-cross section used for luminosity evaluation: app(0.35-0.95GeV2) = (384.4  0.8stat4.9syst) · 10-10 2002 preliminary: app(0.35-0.95GeV2) = (386.3  0.6stat3.9syst) · 10-10

Large angle analysis: Preliminary FSR f0 rp important cross check with small angle analysis threshold region is accessible photon is explicitly required (allows 4-momentum constraints) lower statistics for signal FSR not negligible large   p+p-p0 background irreducible bkg. from f decays 240 pb-1 2002 Data Nr. of events / 0.01 GeV2 Mpp2 [GeV2] Threshold region non-trivial due to irreducible FSR-effects, to be computed from MC using phenomenological models (interference effects unknown) f f0 g p  important! f, r p g  small! f r p g & & FSR f0 rp

Apply specific selection cuts: Large angle analysis (cont‘d): Apply specific selection cuts: Preliminary Exploit kinematic closure of the event  Cut on angle  btw. ISR-photon and missing momentum Kinematic fit in p+p-p0 hypothesis using 4-momentum and p0-mass as constraints FSR contribution added back to cross section (estimated from PHOKHARA generator) 2002 Data L = 240 pb-1 p+ p- W g LA stat.+syst. error Error on LA dominated by syst. uncertainty on f0 contr. Reducible background from p+p-p0 and µ+µ-g well simulated by MC Mpp2 [GeV2] Model dependence of irreducible background from f f0g p+p-g is the dominating uncertainty. Computed using different models for f0-decay and input from dedicated KLOE f f0g analyses (with f0 decaying to charged and neutral pions).

(60% (=3.110-10) of systematical error due to f0-uncertainty) Comparison SA-LA 2002: Preliminary   (sLA-sSA)/sSA Range of comparison LA stat.+syst. error Range of comparison app between 0.5 - 0.85 GeV2: Small angle: app(0.50-0.85GeV2) = (255.4  0.4stat  2.5syst) · 10-10 Large angle: app(0.50-0.85GeV2) = (252.5  0.6stat  5.1syst) · 10-10 (60% (=3.110-10) of systematical error due to f0-uncertainty)

Asymmetry: In case of non-vanishing FSR contribution, the interference term between ISR and FSR is odd under exchange p+  p- .This gives rise to a non-vanishing forward-backward asymmetry: Binner, Kühn, Melnikov, Phys. Lett. B 459, 1999 KLOE  Data MC [ISR + FSR] MC* [ISR+FSR+f0(980)]  check the validity of the FSR model (Phokhara uses sQED, i.e. pointlike pions) radiative decays of the  into scalar mesons decaying to + - contribute to the charge asymmetry Czyz, Grzelinska, Kühn, hep-ph/0412239 *G. Pancheri et. al., arXiv:0706.3027 Possibility to study the properties of scalar mesons with charge asymmetry

ampp KLOE summary: Preliminary Jegerlehner (hep-ph/0703125): Using the new KLOE result increases difference from 3.2s to 3.4s

ampp Summary: Preliminary Comparison with ampp from CMD2 and SND in the range 0.630-0.958 GeV : Phys. Lett. B648 (2007) 28 Preliminary

Conclusions: KLOE has extracted app in the range between 0.35 - 0.95 GeV2 using cross section data obtained via the radiative return with photon emission at small angles. The preliminary result from 2002 data agrees with the updated result from the published KLOE analysis based on 2001 data Data from an independent and complementary KLOE measurement (Large angle analysis) of the 2p-cross section yelds app in the range between 0.5 - 0.85 GeV2 All three KLOE results are in good agreement KLOE results also agree with recent app results from the CMD2 and SND experiments at VEPP-2M in Novosibirsk

Outlook: See next slides… Refine the small angle analysis by unfolding for detector resolution, to release the  cross section table Continue evaluation of resonance contributions in the large angle analysis to decrease model dependence from f0(980) contribution Measure the pion form factor via bin-by-bin ratio of pions over muons (Normalization to radiative muon pairs) Obtain pion form factor from data taken at s = 1000 MeV (off-peak data) See next slides…

Extracting |F|2 from norm. to  (exact only in the absence of FSR) Some Effects cancel out in the ratio: Luminosity ( LA Bhabhas ) 0.6% Vacuum polarization 0.2% FSR corrections 0.3% Radiator function 0.5% Total theoretical Error 0.9% needs to select µµg events with similar precision as ppg x 0.3% In presence of FSR: Corr. due to FSR „Observed“ cross sections

p-m separation: p-m separation is achieved in the analysis by a rigid cut in MTrk: Data   ppg No man‘s land mmg MTrk[MeV] mmg MTrk< 115 MeV ppg MTrk> 130 MeV Additional tool used in evaluation of efficiencies: p-m ID by means of a Neural Network (NN): ppg mmg NN >0.7 for mmg NN <0.2 for ppg Data -- MC

Spectra after SMA selection: The spectra of selected events for the small angle analysis from 242.62 pb-1 of data taken in 2002: Pions 3.42 Mio events Muons 0.87 Mio. events

Forward-Backward-Asymmetry DAFNE Off-peak data: Run-Nr s ( MeV ) F s = 1023 s = 1030 s = 1018 s = 1010 s = 1000 It allows to extract |F|2 down to thresh. in a background-free enviroment 220 pb-1, competitive with VEPP-2M at threshold Study model-dependence of f0(980) (in connection with on-peak data) Forward-Backward-Asymmetry MC Phokhara Data 2006 off-peak Tagged photons Preliminary Run at √s=1000 MeV between Dec. 2005 and March 2006  220 pb-1 on tape Energy scan around -peak  4 scan points, 10 pb-1 each Mpp2 (GeV2)

http://www.lnf.infn.it/conference/phipsi08/ phipsi08@lnf.infn.it

Backup slides

Reminder: Comparison with e+e- - and t - Data Relative difference btw. published KLOE (2001) and CMD-2, SND Plot from I. Logashenko using non-published data from CMD-2 and SND! KLOE published SND hep-ex/0605013 CMD-2 published CMD-2 prel. ALEPH t-data • ••• Relative difference btw. e+e- Data and t-spectral function from ALEPH s / sKLOE - 1 interpolation of 60 KLOE data points from 0.35 to 0.95 GeV2 s [GeV2] s [GeV] KLOE confirmed the CMD-2 discrepancy with tau data and “...invalidates the use of t-data until a better understanding of the discrepancies is achieved” (A. Höcker ICHEP-04) Some disagreement btw. KLOE and SND/CMD-2 seen at low and high masses aµhad from all recent e+e- experiments agree now within 0.5s Waiting for new results from KLOE (this talk), Babar, and t data (Belle)