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Evaluation of a m pp between 0.35 and 0.95 GeV 2 with data from the KLOE detector. Stefan E. M üller Laboratori Nazionali di Frascati. (f or the KLOE collaboration). 2007 Europhysics Conference on High Energy Physics Manchester, 19-25 July 2007. Dispersion integral :. .

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Stefan E. M üller Laboratori Nazionali di Frascati

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Stefan e m ller laboratori nazionali di frascati

Evaluation of ampp between 0.35 and 0.95 GeV2 with data from the KLOE detector

Stefan E. Müller

Laboratori Nazionali di Frascati

(for the KLOE collaboration)

2007 Europhysics Conference on High Energy Physics

Manchester, 19-25 July 2007


Stefan e m ller laboratori nazionali di frascati

Dispersion integral:

ahadr can be expressed in terms of

(e+e- hadrons) by the use of a

dispersion integral:

  • Ecut is the threshold energy above which pQCD is applicable

  • s is the c.m.-energy squared of the hadronic system

  • K(s) is a monotonous function that goes with 1/s,

  • enhancing low energy contributionsofhadr(s)


Stefan e m ller laboratori nazionali di frascati

(e+e-+-) with ISR:

Mhadr

ds(e+ e- hadrons +g)

dMhadr

=s(e+ e- hadrons) H(Mhadr)

Particle factories have the opportunity to measure the cross section

s(e+ e- hadrons) as a function of the hadronic c.m. energy M hadr by using

the radiative return:

This method is a complementary approach to the standard energy scan.

Neglecting FSR effects:

Requires precise calculations of the radiator H

 EVA + PHOKHARA MC Generator

(S. Binner, J.H. Kühn, K. Melnikov, Phys. Lett. B 459, 1999)

(H. Czyż, A. Grzelińska, J.H. Kühn, G. Rodrigo, Eur. Phys. J. C 27, 2003)


Stefan e m ller laboratori nazionali di frascati

DANE: A -Factory

e+e--collider with =m1.0195 GeV

Integrated Luminosity

Peak Luminosity Lpeak= 1.4 • 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

  • 225pb-1 at = 1000 MeV


Stefan e m ller laboratori nazionali di frascati

KLOE Detector

Driftchamber

sp/p = 0.4% (for 900 tracks)

sxy 150mm, sz 2 mm

Excellent momentum

resolution


Stefan e m ller laboratori nazionali di frascati

KLOE Detector

sE/E = 5.7% /E(GeV)

sT= 54 ps /E(GeV)  50 ps

(Bunch length contribution subtracted from constant term)

Excellent timing resolution

Electromagnetic Calorimeter


Stefan e m ller laboratori nazionali di frascati

Event Selection

Pion tracks at large angles

50o< p <130o

a) Photons at small angles

< 15oor > 165o

 No photon detection!

  • High statistics for ISR photons

  • Very small contribution from FSR

  • Reduced background contamination


Stefan e m ller laboratori nazionali di frascati

Event Selection

Pion tracks at large angles

50o< p <130o

a) Photons at small angles

< 15oor > 165o

 No photon detection!

  • High statistics for ISR photons

  • Very small contribution from FSR

  • Reduced background contamination

b) Photons at large angles

50o<  < 130o

  • Photon is observed in the

    detector!

  • Threshold region accessible

  • Increased contribution from FSR

  • Contribution from

  • f0(980)


Stefan e m ller laboratori nazionali di frascati

Event selection

MTrk (MeV)

220

200

p+p-p0

180

p+p-g(g) signal

region

160

140

120

m+m-g(g)region

(+ e+e-g(g)

100

80

0.4

1.0

0.5

0.6

0.7

0.8

0.9

0.3

Mpp2(GeV2)

  • Experimental challenge: Fight

  • background from

    • 

    • ee ee(g)

    • ee (),

  • separated by means of kinematical

  • cuts in trackmass MTrk

  • (defined by 4-momentum conservation

  • under the hypothesis of 2 tracks with

  • equal mass and one photon)

  • and Missing Mass Mmiss

    (defined by 4-momentum conservation

    under the hypothesis of e+e-+-x

    To further clean the samples from radiative Bhabha events, a particle ID estimator for each charged track based on Calorimeter Information and Time-of-Flight is used.


    Stefan e m ller laboratori nazionali di frascati

    Published result with 2001 data

    Published KLOE Result:

    Improvements/updates with respect to 2001:

    Phys. Lett. B606 (2005) 12

    s (e+e- p+p- ) nb

    30% cosmic veto inefficiency

    recovered in 2002 by introducing additional software trigger level

    KLOE

    2001 Data

    140pb-1

    Improved offline-event filter reduces its systematic uncertainty to <0.1%

    New generator [email protected] - theoretical error of Bhabha reference cross section goes from 0.5% to 0.1% - Bhabha cross section value is lowered by 0.7%

    Trigger efficiency correction had to be updated due to a doublecounting of

    efficiencies.

    Mpp2 (GeV2)

    app(0.35-0.95 GeV2) =

    (388.7  0.8stat4.9syst) · 10-10


    Stefan e m ller laboratori nazionali di frascati

    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%


    Stefan e m ller laboratori nazionali di frascati

    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)


    Stefan e m ller laboratori nazionali di frascati

    Luminosity:

    At KLOE, Luminosity is measured using „Large angle Bhabha“ events (55o<qe<125o)

    KLOE is its own Luminosity Monitor!

    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 gives 0.7% decrease in cross section

    compared to previous version

    Quoted accuracy:

    0.1%


    Stefan e m ller laboratori nazionali di frascati

    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)


    Stefan e m ller laboratori nazionali di frascati

    Small angle result from 2002 data:

    Preliminary!!!

    Systematic errors on ampp:

    STotal= 1.1%


    Stefan e m ller laboratori nazionali di frascati

    Comparison 2001-2002:

    (updated)


    Stefan e m ller laboratori nazionali di frascati

    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


    Stefan e m ller laboratori nazionali di frascati

    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 detected

      (4-momentum constraints)

    • lower signal statistics

    • FSR not negligible anymore

    • 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 estimated from MC using phenomenological models (interference effects unknown)

    &

    &

    f0

    FSR

    rp


    Stefan e m ller laboratori nazionali di frascati

    Large angle analysis (cont‘d):

    p+

    g

    p-

    W

    Apply dedicated 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. Estimated

    • using different models for f0-decay and input from dedicated KLOE f f0g analyses (with f0decaying to charged

    • and neutral pions).


    Stefan e m ller laboratori nazionali di frascati

    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% of systematical error due to f0-uncertainty)


    Stefan e m ller laboratori nazionali di frascati

    ampp Summary:

    Summary of the small angle results:

    Preliminary!!!

    Jegerlehner (hep-ph/0703125):

    Using new KLOE result would increase difference from 3.2s to 3.4s


    Stefan e m ller laboratori nazionali di frascati

    ampp Summary:

    Comparison withamppfrom CMD2 and SND in the range 0.630-0.958 GeV :

    Phys. Lett. B648 (2007) 28

    Preliminary!!!


    Stefan e m ller laboratori nazionali di frascati

    Conclusions:

    • We have obtained 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 has been used to obtain 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 results on app from the CMD2 and SND experiments at VEPP-2M in Novosibirsk


    Stefan e m ller laboratori nazionali di frascati

    Outlook:

    • Refine the small angle analysis by unfolding for detector resolution, evaluating further possible backgrounds, etc.

    • Continue evaluation of resonance contributions in the large angle analysis

    • Measure the pion form factor via bin-by-bin ratios of pions over muons (Normalization to muons instead of absolute normalization with Bhabhas)

    • Obtain pion form factor from data taken at= 1000 MeV

      (outside the f resonance)

      • suppression of background from f-decays

      • determination of f0-parameters


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