alberto lusianimoriond.in2p3.fr/qcd/2013/tuesdayafternoon/lusiani.pdfa. lusiani (infn & sns,...

Inclusive hadron production at B factories

Alberto LusianiINFN and Scuola Normale Superiore

Pisa

Rencontres de Moriond, QCD and High Energy Interactions

La Thuile, March 9-16, 2013

A. Lusiani (INFN & SNS, Pisa) Inclusive hadron production at B factories

Results on inclusive hadron production fragmentation functions

� experimental hadron multiplicities in e+e− → qq events

Fh(z, Q2) =1σtot

dσ(e+e− → hX)dz

[z =Eh√s/2

]

� theory hadron multiplicities

Fh(z, Q2) =∑

i

Ci(z,αs) ⊗ Dhi (z, Q2) where f (z) ⊗ g(z) =

∫ 1

z

dyy

f (y)g

(zy

)

◮ index i for initial partons (quarks, antiquarks, gluons) (in this case from e+e− → qq)

◮ Ci(z,αs) (coefficient functions) describe parton content of the process, known at NNLO

◮ Dhi

(z, Q2) fragmentation functions

� Q2 evolution calculable in perturbative QCD: DGLAP (Dokshitzer-Gribov-Lipatov-Altarelli-Parisi)

� fragmentation functions depend also on the parton and hadron spins

◮ spin-independent FF: unpolarized hadron multiplicities

◮ spin-dependent FF: polarized hadron multiplicities azymuthal asymmetries

� experiments measure differential hadron multiplicities

� fragmentation functions are determined from global fits on hadron multiplicities data

Rencontres de Moriond, QCD and High Energy Interactions, La Thuile, March 9-16, 2013 1


High precision results on unpolarized light hadron fragmentation functions

� inclusive charged pion, charged kaon and proton production in BABAR, preliminary, new

◮ updated preliminary results, BABAR internal review in final stage for paper submission

� charged pion and kaon Multiplicities in e+e− annihilations at Belle, preliminary

◮ arXiv:1210.2137 [nucl-ex], DIS2012 proceedings

Results on polarized light hadron fragmentation functions

� Collins Asymmetries in inclusive hadron-pair production, BABAR, preliminary

◮ arXiv:1211.5293 [hep-ex], ICHEP 2012 proceedings

� Azimuthal Asymmetries in Inclusive Production of Hadron Pairs, Belle

◮ PRD 78, 032011 (2008), Erratum PRD D 86, 039905(E) (2012)

� Transverse Polarization Asymmetries of Charged Pion Pairs, Belle, PRL 107, 072004 (2011)

◮ interference fragmentation functions



Interest of inclusive hadron production results from B -factories

� unpolarized hadron multiplicities measurements

◮ improve global fits for quark-gluon fragmentation functions

improve access to flavor structure of the nucleon in semi-inclusive DIS and pp experiments

� polarized hadron multiplicities asymmetries measurements:

◮ first time direct measurement of Collins and “interference fragmentation functions” effects

access to transversity distribution functions of the nucleon



Unpolarized fragmentation functions results



Belle inclusive pion and kaon spectra, preliminary

� arXiv:1210.2137 [nucl-ex], DIS2012 proceedings

� motivation: improve precision on hadronic fragmentation functions from low energy e+e−

◮ in particular improve knowledge of gluon fragmentation functions

� sample: ∼220·106 e+e− annihilations at 10.52 GeV (below the Υ(4S))

� special care on PID

◮ invert 5 × 5 id / mis-id matrix

◮ calibrate id / mis-id probabilities on data control samples

� corrections for :

◮ backgrounds (e.g. tau)

◮ kinematic smearing, decay-in-flight, detector interaction/shower particles detector

◮ tracking efficiencies and selection acceptance

◮ initial state radiation



Pion and kaon multiplicities at Belle, preliminary

Systematic uncertainties:

� z ∼ 0.6 1% for pions, 2% for kaons

� z ∼ 0.9 14% for pions, 50% for kaons



Pion multiplicities, comparison with existing data, Belle preliminary

(plots from M.Leitgab, Fragmentation 2012)

selected data from e+e− collisionsrelative uncertainties



Kaon multiplicities, comparison with existing data, Belle preliminary

(plots from M.Leitgab, Fragmentation 2012)

selected data from e+e− collisionsrelative uncertainties



Pion, kaon and proton multiplicities at BABAR, preliminary, new

� update on previous Moriond 2004 prelim. results, still prelim. but paper is to be submitted soon

� samples:

◮ 0.91 fb−1 e+e− annihilations at 10.54 GeV (below the Υ(4S))

◮ 3.6 fb−1 e+e− annihilations at Υ(4S) peak for checks and calibrations

� precision dominated by systematics, achieved few % uncertainties up to large values of z

◮ data control samples used to calibrate particle id / mis-id probabilities

◮ data control samples used to improve MC-based backgrounds subtraction

◮ control reconstruction effects comparing & combining 6 samples at different θLAB

� results are consistent with Belle




comparison with ARGUS

0

10

20

30

40

(1/N

evt)

dnπ/

dxp

BaBar (10.54 GeV)ARGUS (9.98 GeV)

0

1

2

3

4

(1/N

evt)

dnK/d

x p

BaBarARGUS

0 0.1 0.2 0.3 0.4 0.5 0.6Scaled Momentum

0

0.5

1

(1/N

evt)

dnp/

dxp

BaBarARGUS

π±

K±

pp

comparison with UCLA, JETSET, HERWIG

10-5

10-4

10-3

10-2

10-1

100

101

(1/N

evts

) dn

/dx p

π±

K± (x0.5)

0 0.2 0.4 0.6 0.8 1Scaled Momentum, xp

p/p (x0.25)UCLAJETSETHERWIG

BaBarPrompt




Modified Leading Logarithm Approximation (MLLA) with Local Parton-Hadron Duality (LPHD) ansatz predicts

hadron multiplicities approx. Gaussian on ξ=− ln(xp)

plots show BABAR data compared to the MLLA predictions

0

0.5

1.0

1.5

2.0

2.5

3.0

(1/N

evt)

dnπ/

dξ

π± (stat.)

Syst. errorsGaussian FitDistorted

BaBarprompt

Gaussian Fit

1 2 3ξ=− ln(xp )

0

0

0.1

0.2

0.3

0.4

0.5(1

/Nev

t) dn

K/d

ξ K±

1 2 3ξ=− ln(xp )

0

0 1 2 30

0.02

0.04

0.06

0.08

0.10

(1/N

evt)

dnp/

dξ p/p

1 2 3ξ=− ln(xp )



Polarized fragmentation functions results



Polarized fragmentation functions: Collins term

� Dhq↑

(z, P2h⊥) = Dh

1,q(z, P2hT ) + H⊥h

1,q(z, P2hT )

(̂k × PhT ) · Sq

zMh� polarized term ∝ (̂k × PhT ) · Sq ∝ sin φ

Collins effect

Polarized fragmentation functions: interference fragmen tation function

� hadron pair multiplicity influenced by partons polarization

� polarized term ∝ (̂k × RT ) · Sq ∝ sin φ

interference fragmentation function effect



Collins asymmetries in e+e− → qq → π+π−X

� entangled primary qq transverse spin components induce

azymuthal asymmetries on hadron pair multiplicities, ∝ cos (φ1 + φ2)

� double ratio method: measure ratio of unlike-sign vs. like sign (UL) or vs. all (UC)

remove reconstruction acceptance effects



Collins Asymmetries vs. z1, z2 from Belle

� PRD 78 032011 (2008)

� erratum PRD 86, 039905(E) (2012)

◮ thrust smearing corrections applied

� sample: 547 fb−1 e+e− annihilations

at the Υ(4S) and 60 MeV below

� Collins asymmetries ,

◮ azimuthal cos(φ1 + φ2) modulations A12

of the normalized yield ratios of unlike-

sign pion pairs over like-sign pion pairs

AUL (triangles), and of unlike-sign pion

pairs over any charged pion pairs AUC

(squares) as a function of the fractional

energy z2 for 4 different bins of z1, from

top left to bottom right

◮ systematics shown as bands

(large correlations between bins)

-0.05

0

0.05

0.1

0.15

0.2

-0.05

0

0.05

0.1

0.15

0.2

0.2 0.4 0.6 0.8

A12

0.2<z1<0.3

AUL

AUC

0.3<z1<0.5

z2

A12

0.5<z1<0.7

z2

0.7<z1<1

0.2 0.4 0.6 0.8



Collins Asymmetries vs. z1, z2 from BABAR, prelim. (ICHEP 2012, arXiv:1211.5293 [hep-ex])

� sample: 468 fb−1 e+e− annihilations at the Υ(4S)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

12

A

-210

-110

12,ULA

12,UCA

z1=[0.15-0.2]

2z0.2 0.4 0.6 0.8

12

A

-210

-110

z1=[0.4-0.5] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-210

-110

z1=[0.2-0.3]

2z

0.2 0.4 0.6 0.8

-210

-110

z1=[0.5-0.7] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-210

-110

z1=[0.3-0.4]

2z

0.2 0.4 0.6 0.8

-210

-110

z1=[0.7-0.9]



Collins Asymmetries vs. pt 1, pt 2 from BABAR, prelim. (ICHEP 2012, arXiv:1211.5293 [hep-ex])

� sample: 468 fb−1 e+e− annihilations at the Υ(4S)

0 0.2 0.4 0.6 0.8 1

12A

0

0.05

12,ULA

12,UCA

=[0.-0.25]t1

p

(GeV/c)t2

p0 0.2 0.4 0.6 0.8 1

12A

0

0.05

=[0.5-0.75]t1

p 0 0.2 0.4 0.6 0.8 1

=[0.25-0.5]t1

p

(GeV/c)t2

p0 0.2 0.4 0.6 0.8 1

=[>0.75]t1

p



Collins Asymmetries: BABAR vs. Belle new

� BABAR: 0.15 < z < 0.9

� Belle 0.2 < z < 1

� 10+1 symmetrized z1, z2 bins

� courtesy of I.Garzia

Belle data after erratum paper

bin)

2,z

1(z

0 1 2 3 4 5 6 7 8 9 10 11

12UL

A

0

0.1

0.2

0.3

0.4

0.5BaBar

Belle

bin)

2,z

1(z

0 1 2 3 4 5 6 7 8 9 10 11

12UC

A

0

0.05

0.1

0.15BaBar

Belle



Interference fragmentation function asymmetries in Belle

� PRL 107, 072004 (2011) “Transverse Polarization Asymmetries of Charged Pion Pairs”

� sample: 672 fb−1 e+e− annihilations at the Υ(4S) and 60 MeV below

� measure cos(φ1 + φ2) modulations a12 of normalized yield of charged pion pairs in opposite hemispheres

� a12 = a12(z1, z2, m1, m2)

◮ zi fractional energies of pion pairs

◮ mi invariant masses of pion pairs



Belle IFF asymmetries as function of z2 for 9 bins of z1

< 0.42 2

0.35 < z < 0.35 2

0.28 < z

12

a

-0.14-0.12

-0.1-0.08-0.06-0.04-0.02

00.020.04

< 0.28 2

0.20 < z

< 0.65 2

0.57 < z < 0.57 2

0.50 < z

12

a

-0.14-0.12

-0.1-0.08-0.06-0.04-0.02

00.020.04

< 0.50 2

0.42 < z

1z0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

< 1.00 2

0.82 < z

1z0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

< 0.82 2

0.72 < z

1z0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

12

a

-0.14-0.12

-0.1-0.08-0.06-0.04-0.02

00.020.04

< 0.72 2

0.65 < z

filled areas represent the systematic uncertainties



Belle IFF asymmetries as function of invariant mass m2 for 8 different bins of m1

2 < 0.62 GeV/c2 < m20.50 GeV/c2 < 0.50 GeV/c2 < m20.40 GeV/c

12

a

-0.16-0.14-0.12

-0.1-0.08-0.06-0.04-0.02

00.02

2 < 0.40 GeV/c2 < m20.25 GeV/c

]2 [GeV/c1m0.4 0.6 0.8 1 1.2 1.4 1.6

2 < 1.10 GeV/c2 < m20.90 GeV/c2 < 0.90 GeV/c2 < m20.77 GeV/c

12

a

-0.16-0.14-0.12

-0.1-0.08-0.06-0.04-0.02

00.02

2 < 0.77 GeV/c2 < m20.62 GeV/c

]2 [GeV/c1m0.4 0.6 0.8 1 1.2 1.4 1.6

2 < 2.00 GeV/c2 < m21.50 GeV/c

]2 [GeV/c1m0.4 0.6 0.8 1 1.2 1.4 1.6

12

a

-0.16-0.14-0.12

-0.1-0.08-0.06-0.04-0.02

00.02

2 < 1.50 GeV/c2 < m21.10 GeV/c

filled areas represent the systematic uncertainties



Conclusions

� B-factories provided:

◮ more complete and precise light quark unpolarized fragmentation functions

◮ first direct extraction of spin-dependent fragmentation asymmetries



Extra backup slides



Fragmentation function extraction from data

� In LO: FF Dih describes probability for a parton i to fragment into a hadron h

� FF at different energy scales relatable by DGLAP evolution equations

� FFs Dih can be extracted from e+e- data in pQCD analysis:

¦

��

�

{o�

gqqi

his

NLOi

cmshh

QzDzC

s

Ez

dz

hXeedQzN

,,

2QCD NLO

hadtot

2

),(),(

2

)1),(

D

VV

measured: hadron multiplicity

extracted: FFs Simultaneous pQCD fit for several

q

q � e-

e+

h

hqD

),( 2QzN h



B-factories

� e+e− annihilations at the Υ(4S), high luminosity

� general purpose detectors

� select hadronic jet-like events that are well contained in the detector

� clean events, accurate simulation (except Bhabhas)

� subtract well simulated tau pair background

� systematic-limited measurements, exploit statistics to reduce systematics



Careful particle identification

p( e -> �)

p ( e -> K)

p ( e -> p)

p ( µ -> �)

p ( µ -> K)

p ( µ -> p)

p ( p -> e )

p ( p -> K )

� Particle misidentification expected to be largest uncertainty:

particle identification probabilities p ( i -> j ):

probability that particle of species i PID-selected as particle of species j.

^ ~

N i = P -1 N j : correction through inversion of matrix.

^ ~ N j = P N i

¸¸¸¸¸¸

¹

·

¨¨¨¨¨¨

©

§

p

K

e

x

N

N

N

N

N

N S

P&

[P]ij = p( e -> µ) p( � -> µ )

p ( � -> � )

p ( � -> K )

p ( � -> p )

p( K -> µ )

p ( K -> � )

p ( K -> K )

p ( K -> p )

p ( p -> µ )

p ( p -> � )

p ( p -> p )

p ( µ -> µ)

p( e -> e) p( � -> e ) p( K -> e ) p( µ -> e)

Physical particle

Belle PID likelihood information from: Drift Chamber (dE/dx), Cherenkov, ToF, Calorimeter, Muon Detector

�

Reconstructed particle p ( � -> e )

p ( � -> µ )

p ( � -> ��)

p ( � -> K )

p ( � -> p )

e

µ

�

K

p



Particle identification performance measured on data contr ol samples

� Experimental data based extraction of PID probabilities by decay sample study

e.g. D* D0

�+slow

K-

�+fast

a) Kinematically reconstruct D* b) extract PID probability from invariant mass plots

------------- p( K- -> � - ) =

p ( K- -> �- ) §��± 0.004

mD* -mD° for K- tracks with plab in [1.4; 1.6] GeV/c,

cos�lab in [0.02; 0.21]

mD* -mD° for K- tracks with plab in [1.4; 1.6] GeV/c, cos�lab in [0.02; 0.21],

reconstructed as �



Similar preliminary results from BABAR shown in Moriond QCD 2004 by F.Anulli

π± , �± ��

�� =

��

��

��

�� !�"��

��#��

��$%��&��

��'(��&��

��#��

��#��√��%&�)�*��#��#�� +�=

,��#��

π±

Κ ±

��

��

��


alberto lusianimoriond.in2p3.fr/qcd/2013/tuesdayafternoon/lusiani.pdfa. lusiani (infn & sns,...

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