initial state radiation and inclusive hadron production at b a b ar fabio anulli university of...
TRANSCRIPT
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
XXXIXth Rencontres de Moriond - March 28th-April 4th 2004 QCD and Hadronic Interactions at High Energy
Outline ISR studies in BABAR
hadron spectroscopy
measurement of R = had/ in the energy region ~1-4 GeV
lineshape for J/→totandee measurement
inclusive hadron production studies K, ±, p/p, production at s = 10.54 GeV and at (4S)
test of QCD, hadronization models, scaling
conclusions and perspectives
Fabio Anulli 2 April 1, 2004
24
22
3
m
had
s
sKsRds
ma
)()()(
precise measurements of eecross 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:
Initial State Radiation: motivations
)(
)()(
s
ssR
ee
hadronsee
ISR studies at the (4S) can yield the same observables as the low energy eeexperiments
Hadronic Vacuum Polarization
q
q
main contribution from low energy region
weakhadQEDSM aaaga )( 2
hadtoplepQED s
;)(
)(
1
0
~ 1s2
Mf2 < s
Fabio Anulli 3 April 1, 2004
R measurement: work in progress
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 em by energy range
CMD-2 and KLOE recently measured (ee→ at ~1% level very few data with large errors for s > 1.4 GeV
R ~ 10-15%data from different experiments and different systematics
ahad and em will benefit of precise hadronic cross
section measurements also at energies > 1 GeV
highest uncertainties for em from energy region 1 < s < 5 GeV
Fabio Anulli 4 April 1, 2004
ISR studies program in BABAR Many analysis in progress: pion form factor 0 0 resonance recurrences 0 resonance recurrences 5,7 6 structures between 1 and 3 GeV K+K-K+K-K+K-
K+K- , KSKL kaon form factor
K+K- , resonance recurrences K0K 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/andsproduction via ISR
Shown here
Fabio Anulli 5 April 1, 2004
ISR cross sectionISR Cross Section ISR Cross Section ( Born approximation for ( Born approximation for f f ))
)(),(),(
xsxsWdx
xsdf 1
2112
2 2xx
m
s
xxsW
e
ln),(
s
Ex
*2
cross section for final state cross section for final state ff (normalized to (normalized to final state) final state)
energy in c.m. of the radiated photon
“radiator function at lowest order”
)( invMdL
)'()(
)())('( s
dN
dNxss
eefradf
radff
1
11
detection efficiencies
corrections forfinal state radiation
“effective c.m. energy squared”
ISR equivalent luminosity
f can be a hadronic state or
photon tagging acceptance at BABAR: 10 -15%
f
Fabio Anulli 6 April 1, 2004
ISR equivalent luminosity experimentally measured from
topology: “hard” + 2 charged tracks + ID ee
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)
BABAR 89.3 fb-1
equivalent ee luminosityL : 0.7 3.6 pb-1/0.1GeV M 1 4 GeV
a 1C kinematics fit (E and p conservation) improve the mass resolution (J~ 16 MeV/c2 before fit)
~ 8 MeV/c2
J/ massafter fit
)()(
)()(
inveerad
invinv M
MdNMdL
1
GeV/c2
Fabio Anulli 7 April 1, 2004
ee →
BABAR 89.3 fb-1
even
ts/0
.025
GeV
4 invariant mass distribution
data
ISR bkgd
non-ISR bkgd
very competitive statistical uncertainties
estimated total systematic error:5% (1 < s < 3 GeV )
no point-to-point normalization problemBABAR is the only experiment which covers whole energy range
ISR photon + 4 charged hadrons 1C fit in 4 hypothesis
topology
preliminary evaluation of ahadr (s < 1.8 GeV):
101013064095124 )...(][ exp,
radLOhadra
101023087021144 )...(][ exp,
radLOhadra
using BABAR data
all previous data10
2 1040096035124 )...(][ exp,
SULOhadra 03
Davier, Edelman, Höcker, Zang Eur. Phys. J. C31 (2003) 503
Davier (2003) hep-ex/0312063
BABARPreliminary
~70000 events
Fabio Anulli 8 April 1, 2004
)()( KKeeKee 2 and 2 ) KKee( ) KKKKee(
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
first measurement ever
Fabio Anulli 9 April 1, 2004
Mass substructures in
no evidence of in the band(C-parity conservation)
no evidence so far for “expected” f0 events
events not in K* bands
no MC generators available yet
BABAR preliminaryK*
events in band
Fabio Anulli 10 April 1, 2004
BABAR 89.3 fb-1
J/ production in ee →
for a narrow state such as the J/:
s
mxxsW
sm
Bs ee
J
2
00 112
),,()(
W(s,x) can be calculated with < 1% accuracy
J/ cross section (i.e. number of selected events) proportional to :
BBB eetotee
use the PDG values of to get BBee , totee and
J/ obtained from the ratio of events from J/ peak to continuum
compute the product:
007000803300 ... Bee
Fabio Anulli 11 April 1, 2004
Results on J/→ee and J/
BABAR measurement
keV007000803300 ... Bee
combine with PDG values:
)%..(
)%..(
100885
100935
B
Bee
keV44794
keV200615
..
..
tot
ee
improved measurements w.r.t. PDG values
keV587
keV370265
tot
ee
..
comparison of J measurements with previous results
Accepted for publication:Phys. Rev. D – Rapid Comm.
Fabio Anulli 12 April 1, 2004
BABAR can provide precise measurements of inclusive spectra in e+eevents at s = 10.54 GeVso far, have studiedK, p/p and measurements also done at (4S)
Inclusive hadronic spectra at s ~ 10 GeVHadronization:
not yet understood quantitativelydescribed by several modelsmany recent high-energy resultsimproved low-energy measurements would be usefulrecently 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
Fabio Anulli 13 April 1, 2004
K, p/p spectracross sections
GeV s BABAR 5410.
given: - excellent particle-ID system - tracking, photon, PID efficiencies calibrated from data BABAR can reach few % precision level
data samples used in these analysis:- 0.9 fb-1 off-resonance- 3.6 fb-1 on-resonance
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 cmcmp Epx /2
Scaled momentum xp = 2pcm/Ecm
p/p
BABARPreliminary
Fabio Anulli 14 April 1, 2004
K, p/p spectra
pions
cross sections scaling
GeV s BABAR 5410.
Hadronization should be scale invariant except for “small” effects of hadron masses, running of S ,…
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 data; reproduced by models NOT seen in p/p data! Wrong model
predictions observed violations in K, data, also smaller
than in models
GeV s BABAR 5410.
protons
important experimental input for tuning fragmentation models
BABARPreliminary
Fabio Anulli 15 April 1, 2004
K, p/p : test QCD
In the Modified Leading Logarithmic Approximation (MLLA ), distributions versus ξ = -ln(xp) should be Gaussian near the peak.
Gaussian fit to cross section distributions
π+ 2.36 ± 0.01
K+ 1.64 ± 0.01
p 1.61 ± 0.01
1.44 ± 0.02
peak position from symmetric gaussian fits
GeV 5410.s
QCD prediction is that falls monotonically with increasing particle mass.
while it is observed *p *K
p/p
BABARPreliminary
Fabio Anulli 16 April 1, 2004
K, p/p : test QCD
s (GeV2)
p
eak
posi
tionAll data are consistent with the
expected logarithm dependence with the center-of-mass energy
but, different slopes, protons data above kaons…
peak position vs Ecm
total number of particles produced per event extrapolated using fit to dσ/dξ distribution
BABAR ARGUS CLEO JETSET UCLA
π+ 6.40 ± 0.17 6.38 ± 0.12 8.3 ± 0.4 6.22 6.44
K+ 0.910 ± 0.018 0.888 ± 0.030 1.3 ± 0.2 0.934 1.01
p/p 0.235 ± 0.012 0.271 ± 0.018 0.40 ± 0.06 0.336 0.217
0.276±0.002±0.017 0.19±0.04 ±0.04 --- 0.410
continuum (BABAR : s = 10.54 GeV)
BABAR
p/p
PR D 31, 2161Z. Phys C62, 371
Fabio Anulli 17 April 1, 2004
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 < 4 GeV
precise eecross section measurements will improve the accuracy on the hadronic contribution to (g-2) and QED(MZ)
many interesting results in hadron spectroscopy expected
precise measurements ee and tot for J/ to be published
inclusive spectra of K, p/p and have been measured, with competitive precision produced both in eeannihilation 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 18 April 1, 2004
BACKUP SLIDES
Fabio Anulli 19 April 1, 2004
The BABAR Detector
Fabio Anulli 20 April 1, 2004
Study ofee→
topology: “hard” + 2 charged tracks + NO -ID
2)(sF
N
N
ratio (bin-by-bin) cancels:luminosity
radiative corrections
efficiencies: photon, trigger, tracking
relatively large background from ee and
hard work! less than 1% systematic errors needed for (g-2) hope to have results soon
Fabio Anulli 21 April 1, 2004
→ spectrumsimilar analysis to measure inclusive production of in continuum and in (4S) decays
35.5 fb-1 on-resonance data
3.8 fb-1 off-resonance data
use dominant decay →
fit the γγ 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 momentumclear scaling violation.
GeV 5410.s