initial state radiation and inclusive hadron production at b a b ar
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Initial State Radiation and Inclusive Hadron Production at B A B AR. Fabio Anulli University of Perugia, INFN – Laboratori Nazionali di Frascati. On behalf of the B A B AR Collaboration. Outline ISR studies in B A B AR hadron spectroscopy

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initial state radiation and inclusive hadron production at b a b ar

Initial State Radiation and Inclusive Hadron Production atBABAR

Fabio Anulli

University of Perugia, INFN – Laboratori Nazionali di Frascati

On behalf of the BABARCollaboration


  • ISR studies in BABAR
    • hadron spectroscopy
    • measurement of R = shad/smmin the energy region ~1-4 GeV
    • lineshape for J/y →mm Gtotand Gee measurement
  • inclusive hadron production studies
    • K±, p±, p/p, h production at s = 10.54 GeV and at (4S)
    • test of QCD, hadronization models, scaling
  • conclusions and perspectives

XXXIXth Rencontres de Moriond - March 28th-April 4th 2004

QCD and Hadronic Interactions at High Energy

initial state radiation motivations





HadronicVacuum Polarization

Initial State Radiation: motivations

ISR studies at the(4S) can yield the same observables as the low energye+e-experiments

  • precise measurements of e+e- cross sections at low c.m. energy
  • hadron spectroscopy for 1 < s < 4 GeV
  • measurement of the ratio
  • R(s) allow the calculation of hadronic contribution to

Anomalous magnetic moment of the muon

Running Fine Structure Constant at Z0-mass

by means of dispersion integrals:

Mf2 < s

~ 1/ s2

main contribution from low energy region

Fabio Anulli

r measurement work in progress
R measurement: work in progress
  • CMD-2and KLOE recently measured s(e+e- → p+p-) at ~1% level
  • very few data with large errors for s > 1.4 GeV
    • DR ~ 10-15%
  • data from different experiments and different systematics
  • amhad and Daem will benefit of precise hadronic cross section measurements also at energies > 1 GeV

highest uncertainties for aem from energy region 1 < s < 5 GeV

perspectives on R measurements by BABAR:

  • comparable accuracy w.r.t. CMD-2 and KLOE for s < 1 GeV
  • few % accuracy for 1 < s < 3 GeV

relative contributions to the error on aem by energy range

Fabio Anulli

isr studies program in babar
ISR studies program in BABAR
  • Many analysis in progress:
  • p+p- pion form factor
  • p+p- p+p-
  • p+p- 0 0 r resonance recurrences
  • p+p- h
  • p+p- 0 w resonance recurrences
  • 5,7
  • 6 structures between 1 and 3 GeV
  • K+K-p+p, K+K-K+K-
  • K+K- , KSKLkaon form factor
  • K+K- h, f hfresonance recurrences
  • K0K 
  • f p04-quark state?
  • p p proton form factor
  • The ratio R will be measured from the sum of cross sections of all exclusive channels
  • J/yandy(2s) production via ISR

Shown here

Fabio Anulli

isr cross section
“effective c.m.

energy squared”

corrections for

final state radiation

detection efficiencies

ISR cross section

ISR Cross Section

( Born approximation for sf )

f can be a hadronic state orm+m-


energy in c.m. of the radiated photon

“radiator function at lowest order”

photon tagging acceptance

at BABAR: 10 -15%

cross section for final state f (normalized to mmg final state)

ISR equivalent luminosity

Fabio Anulli

isr equivalent luminosity
BABAR 89.3 fb-1

equivalent e+e- luminosity

L : 0.7  3.6 pb-1/0.1GeV

Mmm : 1  4 GeV

ISR equivalent luminosity
  • experimentally measured from
  • topology: “hard” g + 2 charged tracks + m-ID
  • statistically very competitive sample
  • uniform data all-over the energy range

limits of ISR techniques:

  • resolution on invariant mass:

(limits the width of the narrowest

resonances which can be measured)

J/y mass

after fit

s ~ 8 MeV/c2

a 1C kinematics fit (E and p conservation) improve the mass resolution (sJ/y~ 16 MeV/c2 before fit)

Fabio Anulli


e e g p p p p
4p invariant mass distribution

events/0.025 GeV


ISR bkgd

non-ISR bkgd

e+e-→ g + p+ p- p+ p-
  • ISR photon + 4 charged hadrons
  • 1C fit in 4p hypothesis


~70000 events

  • very competitive statistical uncertainties
  • estimated total systematic error:
    • 5% (1 < s < 3 GeV )
  • no point-to-point normalization problem
  • BABAR is the only experiment which covers whole energy range



preliminary evaluation of amhadr (s < 1.8 GeV):

BABAR 89.3 fb-1

using BABAR data

Davier (2003) hep-ex/0312063

all previous data

Davier, Edelman, Höcker, Zang Eur. Phys. J. C31 (2003) 503

Fabio Anulli

first measurement ever
  • K-ID required for 1 or 2 tracks
  • systematic errors dominate
    • acceptance corrections
    • K-ID calibration
  • K-ID required for 3 or 4 tracks
  • systematic errors dominate
    • acceptance corrections
    • K-ID calibration

Fabio Anulli

mass substructures in k k p p
K* Mass substructures in K+ K- p+ p-


BABAR preliminary

no MC generators

available yet

events not in

K* bands


no evidence so far for “expected”f f0 events

no evidence of rin the f band

(C-parity conservation)

events in f band

Fabio Anulli

j y production in e e g m m
BABAR 89.3 fb-1J/y production in e+e-→ g m+ m-

W(s,x0) can be calculated with < 1% accuracy

  • for a narrow state such as the J/y:
  • J/ycross section (i.e. number of selected events) proportional to :

use the PDG values of to get

  • sJ/Y obtained from the ratio of m+m- events from J/Y peak to continuum
  • compute the product:

Fabio Anulli

results on g j y e e and g j y
Results on GJ/y→e+e- and GJ/y
  • combine with PDG values:
  • BABAR measurement

Accepted for publication:

Phys. Rev. D – Rapid Comm.

  • improved measurements w.r.t. PDG values

comparison of GJ/ymeasurements with previous results

Fabio Anulli

inclusive hadronic spectra at s 10 gev
Inclusive hadronic spectra at s ~ 10 GeV
  • Hadronization:
    • not yet understood quantitatively
    • described by several models
    • many recent high-energy results
    • improved low-energy measurements would be useful
    • recently little theoretical progress

check consistency with fragmentation models

test scaling predictions

test QCD predictions

data at (4S) will contribute to the understanding of B decays

BABAR can provide precise measurements of inclusive spectra in e+e- events at s = 10.54 GeV

so far, have studied p±, K±, p/p and h

measurements also done at(4S)

Fabio Anulli

p k p p spectra
p±, K±, p/p spectra



cross sections

  • data samples used in these analysis:
  • 0.9 fb-1 off-resonance
  • 3.6 fb-1 on-resonance

  • given:
  • - excellent particle-IDsystem
  • - tracking, photon, PID efficiencies
  • calibrated from data
  • BABAR can reach few % precision level

BABAR cover the full kinematics range

precision comparable to that from measurements at s = 91 GeV

test cross section scaling properties up to very high values of


Scaled momentum xp = 2pcm/Ecm

Fabio Anulli

p k p p spectra1
p±, K±, p/p spectra

cross sections scaling





Hadronization should be scale invariant except for “small” effects of hadron masses, running of aS ,…

scaling violations at low xp, due to masses are well known and modeled adequately (here JETSET is shown for comparison)

  • expect substantial scaling violations at high xp
    • seen clearly in p data; reproduced by models
    • NOT seen in p/p data! Wrong model predictions
    • observed violations in K, h data, also smaller than in models

important experimental input for tuning fragmentation models

Fabio Anulli

p k p p test qcd
p/pp±, K±, p/p : test QCD

Gaussian fit to cross section distributions

  • In the Modified Leading Logarithmic Approximation (MLLA ), distributions versus ξ = -ln(xp) should be Gaussian near the peak.

peak position x* from symmetric gaussian fits



  • QCD prediction is that x* falls monotonically with increasing particle mass.

while it is observed x*p x*K

Fabio Anulli

p k p p test qcd1
p±, K±, p/p : test QCD

peak position vsEcm

  • All data are consistent with the expected logarithm dependence with the center-of-mass energy
  • but, different slopes, protons data above kaons…
  • p/p

x* peak position

  • total number of particles produced per event extrapolated using fit to dσ/dξ distribution


s (GeV2)

continuum (BABAR : s = 10.54 GeV)

Z. Phys C62, 371

PR D 31, 2161

Fabio Anulli

  • ISR has been proven to be an effective tools to study low energy e+e- processes
    • very rich program in the energy range s < 4 GeV
    • precise e+e- cross section measurements will improve the accuracy on the hadronic contribution to (g-2)m and aQED(MZ)
    • many interesting results in hadron spectroscopy expected
    • precise measurements Gee and Gtot for J/Y to be published
  • lots of hadron physics at BABAR !
  • inclusive spectra of p±, K±, p/p and h have been measured, with competitive precision
    • produced both in e+e- annihilation and (4S) events
    • test of predictions of QCD, models of jet fragmentation and B hadron decays
    • clear discrepancies between models and data for protons (also for kaons and etas)

Fabio Anulli

backup slides

Fabio Anulli

the b a b ar detector
The BABAR Detector

Fabio Anulli

study of e e p p
Study ofe+e-→ p+p-
  • topology: “hard” g + 2 charged tracks + NO m-ID
  • ratio (bin-by-bin) cancels:
    • luminosity
    • radiative corrections
    • efficiencies: photon, trigger, tracking
  • relatively large background from e+e-, m+m-andK+K-

hard work! less than 1% systematic errors needed for (g-2)m

hope to have results soon

Fabio Anulli

h gg spectrum
h → gg spectrum
  • similar analysis to measure inclusive production of h in continuum and in (4S) decays
    • 35.5 fb-1 on-resonance data
    • 3.8 fb-1 off-resonance data
  • use dominant decay h → gg
  • fit the γγmass with an asymmetric function for the signal.
  • selection slightly different on- and off-peak
  • very good agreement with JETSET at high xp
  • overestimation by JETSET at low momentum
  • clear scaling violation.

Fabio Anulli