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Graziano Venanzoni Laboratori Nazionali di Frascati

KLOE results on Hadronic cross section. Graziano Venanzoni Laboratori Nazionali di Frascati. (f or the KLOE collaboration). Topical Workshop on (g-2)  Glasgow, 25-26 Oct 2007. Outlook. Motivation of s (e + e -      ) at low energy

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Graziano Venanzoni Laboratori Nazionali di Frascati

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  1. 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

  2. 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

  3. had and the muon anomaly HadronicVacuum Polarization g* q µ+ µ+ q 2nd largest contribution, pQCDnot applicable Error of hadronic contribution dominates total error of am! Dispersion-Relation Channel  = s(e+ e) gives >70% contribution to ahad! shad (s) amhad Alternative: Spectral function from decay ( t  nt Hadrons) taking into account isospin breaking corrections • K(s) = analytic kernel-function, • above typically 2…5 GeV, use pQCD 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) a= (g-2)/2 =  Muon-Anomaly weak QED theo New physics had aaaaa M. Davier

  4. (e+e-+-) with ISR: Rho - Resonanz a.u. dds 0.1 0.7 0.5 0.9 0.3 Mpp2 [GeV2] s d ppg H(s) = s ´ 2 M ( s ) pp pp 2 dM pp 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. S. Binner, J.H. Kühn, K. Melnikov, Phys. Lett. B 459, 1999 Neglecting FSR effects: 4mp2£ sp = M£ mf2 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 0.7 0.5 0.9 0.1 0.3 Mpp2 [GeV2]

  5. 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

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

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

  8. 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) Relation between |Fp|2 and the cross section s(e+e- +-) 3) b) Via bin-by-bin Normalisation to rad. Muon events (see later…)

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

  10. Event Selection     Pion tracks at large angles 50o< p <130o a) Photons at small angles < 15oor > 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)

  11. Published result, 2001 data Published KLOE Result: 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

  12. 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 recovercosmic 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

  13. 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%

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

  15. 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

  16. Background: 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

  17. Luminosity: 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 New version of generator (BABAYAGA@NLO) gives 0.7% decrease in cross section compared to previous version Quoted theor. accuracy: 0.1%

  18. Radiative corrections Fp=1 s (ppg) with Fp=1 [nb] H(s) Radiator-Function H(s) (ISR): • ISR-Process calculated at NLO-level • PHOKHARAgenerator (Czyż, Kühn et.al) • Precision: 0.5% 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)

  19. 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 ppto g* . MonteCarlo  = M2 ISR only: FSR photon present:  = M2g(FSR) pp [GeV2]

  20. Small angle result from 2002 data: Preliminary Systematic errors on ampp: STotal= 1.1%

  21. Comparison 2001-2002: (updated)

  22. Evaluating amppwith small angle Dispersion integralfor2p-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

  23. Large angle analysis: p g f, r p g f p p f g f0 r p p  small!  important! Preliminary • 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-p0background • 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) & & f0 FSR rp

  24. Large angle analysis (cont‘d): p+ g p- W Apply specific selection cuts: Preliminary • Exploit kinematic closure of the event •  Cut on angle btw. ISR-photon and missing momentum • Kinematic fit inp+p-p0hypothesis using 4-momentum andp0-mass as constraints • FSR contribution added back to • cross section (estimated from PHOKHARA • generator) 2002 Data L = 240 pb-1 LA stat.+syst. error Error on LA dominated by syst. uncertainty on f0 contr. • Reducible background fromp+p-p0 • andµ+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 f0decaying to charged and neutral pions).

  25. 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)

  26. Asymmetry: In case of non-vanishing FSR contribution, the interference term between ISR and FSR is odd under exchangep+ 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

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

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

  29. 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

  30. Outlook: • 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…

  31. Extracting |F|2 from norm. to  (exact only in the absence of FSR) Some Effects cancel out in the ratio: needs to select µµgevents with similar precision asppg x 0.3% In presence of FSR: Corr. due to FSR „Observed“ cross sections

  32. p-m separation: ppg mmg No man‘s land MTrk[MeV] Data   p-m separation is achieved in the analysis by a rigid cut in MTrk: 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 • Data -- MC • NN >0.7 for mmg • NN <0.2 for ppg

  33. 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

  34. DAFNE Off-peak data: s ( MeV ) s = 1030 s = 1023 Preliminary F s = 1018 s = 1010 s = 1000 Data 2006 off-peak Tagged photons Run-Nr MC Phokhara • 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 • 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)

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

  36. Backup slides

  37. Relative difference btw. e+e- Data and t-spectral function from ALEPH • KLOE published • CMD-2 published • SND hep-ex/0605013 ••• CMD-2 prel. ALEPH t-data Plot from I. Logashenko using non-published data from CMD-2 and SND! Reminder: Comparison with e+e- - and t - Data Relative difference btw. published KLOE (2001) and CMD-2, SND 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 • aµhadfrom all recent e+e- experiments agree now within 0.5s • Waiting for new results from KLOE (this talk), Babar, and t data (Belle)

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