Initial State Radiation and Inclusive Hadron Production at BABAR

1
Initial State Radiation and Inclusive Hadron
Production at BABAR

• Fabio Anulli
• University of Perugia, INFN Laboratori
  Nazionali di Frascati

On behalf of the BABAR Collaboration

• Outline
• ISR studies in BABAR
• hadron spectroscopy
• measurement of R shad/smm in the energy
  region 1-4 GeV
• lineshape for J/y ?mm Gtot and 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
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Initial State Radiation motivations
ISR studies at the ?(4S) can yield the same
observables as the low energy ee- experiments

• precise measurements of ee- cross sections at
  low c.m. energy
• hadron spectroscopy for 1 lt ?s lt 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 lt s

1/ s2
main contribution from low energy region
3
R measurement work in progress

• CMD-2 and KLOE recently measured s(ee- ? pp-)
  at 1 level
• very few data with large errors for ?s gt 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 gt 1
  GeV

highest uncertainties for aem from energy
region 1 lt ?s lt 5 GeV

• perspectives on R measurements by BABAR
• comparable accuracy w.r.t. CMD-2 and KLOE for ?s
  lt 1 GeV
• few accuracy for 1 lt ?s lt 3 GeV

relative contributions to the error on aem by
energy range
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ISR studies program in BABAR

• Many analysis in progress
• pp- pion form factor
• pp- pp-
• pp- ?0 ?0 r resonance recurrences
• pp- h
• pp- ?0 w resonance recurrences
• 5?,7?
• 6?
  structures between 1 and 3 GeV
• KK-pp, KK-KK-
• KK- , KSKL kaon form factor
• KK- h, f h f resonance recurrences
• K0K ?
• f p0 4-quark state?
• p p proton form factor
• The ratio R will be measured from the sum of
  cross sections of all exclusive channels
• J/y and y(2s) production via ISR

Shown here
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ISR cross section
ISR Cross Section ( Born approximation for sf )
f can be a hadronic state or mm-
f
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
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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)
GeV/c2
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ee- ? g p p- p p-

• ISR photon 4 charged hadrons
• 1C fit in 4p hypothesis

topology
70000 events

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

BABAR Preliminary
preliminary evaluation of amhadr (?s lt 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
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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

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Mass substructures in K K- p p-
f
BABAR preliminary
no MC generators available yet
events not in K bands
r
no evidence so far for expected f f0 events
no evidence of r in the f band (C-parity
conservation)
events in f band
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J/y production in ee- ? g m m-

• for a narrow state such as the J/y

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

• J/y cross section (i.e. number of selected
  events) proportional to

use the PDG values of to get

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

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Results on GJ/y?ee- and GJ/y

• BABAR measurement

• combine with PDG values

Accepted for publication Phys. Rev. D Rapid
Comm.

• improved measurements w.r.t. PDG values

comparison of GJ/y measurements with previous
results
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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 ee- events at ?s 10.54
  GeV
• so far, have studied p, K, p/p and h
• measurements also done at ?(4S)

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p, K, p/p spectra
BABAR Preliminary
cross sections

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

p

• given
• - excellent particle-ID system
• - tracking, photon, PID efficiencies
• calibrated from data
• BABAR can reach few precision level

K

• 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

p/p
Scaled momentum xp 2pcm/Ecm
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p, K, p/p spectra
cross sections scaling
BABAR Preliminary
pions
protons

• 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
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p, K, p/p test QCD
Gaussian fit to cross section distributions

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

p
peak position x from symmetric gaussian fits
K
BABAR Preliminary

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

while it is observed xp ? xK
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p, K, p/p test QCD
peak position vs Ecm

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

• p
• K
• p/p

x peak position
BABAR

• total number of particles produced per event
  extrapolated using fit to ds/d? distribution

s (GeV2)
continuum (BABAR ?s 10.54 GeV)
PR D 31, 2161
Z. Phys C62, 371
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Conclusions

• lots of hadron physics at BABAR !

• ISR has been proven to be an effective tools to
  study low energy ee- processes
• very rich program in the energy range ?s lt 4
  GeV
• precise ee- 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

• inclusive spectra of p, K, p/p and h have been
  measured, with competitive precision
• produced both in ee- 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)

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BACKUP SLIDES
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The BABAR Detector
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Study of ee- ? pp-

• 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 ee-, mm- and
  KK-

hard work! less than 1 systematic errors needed
for (g-2)m hope to have results soon
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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 ?? mass 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.