Initial State Radiation and Inclusive Hadron Production at B A B AR Fabio Anulli University of...

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


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


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


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


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


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


)()( 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


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


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


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.


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


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


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


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


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


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)


BACKUP SLIDES


The BABAR Detector


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


→ 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

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