zeus o u t l i n e · hall ouest (hera-b) hall est (hermes) rayonnement synchrotron hall sud (zeus)...

Heavy flavour production at HERA

Uri KarshonWeizmann Institute of Science, ISRAEL

On behalf of the H1 and ZEUS Collaborations

PHOTON-2015 Conference

Budker Institute of Nuclear Physics,

Novosibirsk, Russia

15-19 June, 2015

ZEUS

O U T L I N E

• Introduction and experimental set-up• Theory of heavy quark production• D∗± photoproduction at 3 center-of-mass energies• Charm fragmentation fractions in photoproduction• D± production in deep inelastic scattering• HERA charm data combination in DIS• Combination of D∗± differential cross sections in DIS• Beauty production in DIS• Summary

Introduction and experimental set-up

e+ (k')e+ (k)

proton (P)g (xgP)

γ* (q)c

c_

W2

e±(k) + p(P ) → e±(k′) + X ; s = (P + k)2

Photon virtuality: Q2 = −q2 = −(k − k‘)2

Bjorken x: x = Q2

2q·P ; Inelasticity: y =q·Pk·P

Q2 = sxy; W = γ∗p CM energy

Photoproduction (PHP): Q2 ≃ 0 GeV 2 (e± undetected)Deep Inelastic Scattering (DIS): Q2 > 1 or 5 GeV 2 (e± detected)

BGF: Dominant process for c,b production in DIS

Direct probe of gluon density in proton; Sensitivity to c,b quark masses

HERA

PETRA

DORIS

HASYLAB

DESY

Halle NORD (H1)Hall NORTH (H1)

Halle OST (HERMES)Hall EAST (HERMES)

Halle SÜD (ZEUS)Hall SOUTH (ZEUS)

Halle WEST (HERA-B)Hall WEST (HERA-B)

Elektronen / PositronenElectrons / Positrons

ProtonenProtons

SynchrotronstrahlungSynchrotron Radiation

Hall nord (H1)

Hall ouest (HERA-B)

Hall est (HERMES)

Rayonnement Synchrotron

Hall sud (ZEUS)

Electrons / Positons

Protons

HERA: unique e±p collider with E(e±, p) = 27.6, 820/920 GeV

2 main experiments: H1, ZEUS

2 run periods: HERA I, HERA II

1995-2000 2003-2007√

s 318 (300) 318 GeV

L 1.5 · 1031 7 · 1031 cm−2 s−1

Lint 126 373 pb−1

HERA II data taken ≈ half e+p and half e−pIn 2007 two short runs at lower p energies: Ep = 575 GeV; Ep = 460 GeV

Heavy Flavour production at HERA U. Karshon 2

Theory of heavy quark production

Several QCD NLO schemes for heavy quark (Q=c or b) production:

1)Massive scheme: Q2 ≈ m2Q Fixed flavour number scheme (FFNS)• 3 active flavours in proton; Q-quark not considered as parton in p• c or b produced perturbatively in hard scattering (see p.2)• Mass effects correctly included• Spoiled by large logs of Q2/m2Q, pt/mQ...

2)Massless scheme: Q2 >> m2QZero-mass variable flavour number scheme (ZM-VFNS)

• c or b treated as massless parton• Resummation of large logarithms of Q2/m2Q• ⇒ c or b density added as 4th flavour like the light quarks

At intermediate Q2 the 2 schemes should be merged

3) General-mass variable flavour number scheme (GM-VFNS)

• Equivalent to FFNS for Q2 ≤ m2Q and to ZM-VFNS for Q2 > m2Q• Interpolation in between (various schemes interpolate differently)• Used in parton density function (PDF) fits (useful at LHC)


D∗± photoproduction at 3 CM energies

Clear D∗± signals seen in M(K−π+π+s ) − M(K−π+) distributionsat 3 different CM energies:

√s = 318, 251, 225 GeV

in the kinematic region: 1.9 < pD∗

T < 20 GeV ; |ηD∗| < 1.6 ;

Q2 < 1 GeV2 ; 0.167 < y < 0.802

JHEP 10 (2014) 003

HER: L = 144 pb−1 MER: L = 6.3 pb−1 LER: L = 13.4 pb−1

) (GeV)π)-M(KsππM(K0.14 0.145 0.15 0.155 0.16 0.165 0.17

Ent

ries

0

1000

2000

3000

4000

5000

6000

ZEUS

sπ π K →D* = 318 GeV)s (-1ZEUS 144 pb

Wrong-sign combinations

Signal region

Background fit (correct-sign)

Background fit (wrong-sign)

ZEUS

) (GeV)π)-M(KsππM(K0.14 0.145 0.15 0.155 0.16 0.165 0.17

Ent

ries

0

20

40

60

80

100

120

140

160

180

200

220

240ZEUS

sπ π K →D* = 251 GeV)s (-1ZEUS 6.3 pb


Signal region



ZEUS

) (GeV)π)-M(KsππM(K0.14 0.145 0.15 0.155 0.16 0.165 0.17

Ent

ries

0

50

100

150

200

250

300

350

400

ZEUS

sπ π K →D* = 225 GeV)s (-1ZEUS 13.4 pb


Signal region



ZEUS

N(D∗) = 12256 ± 191 N(D∗) = 417 ± 37 N(D∗) = 859 ± 49

Background estimated by fitting simultaneously correct- and wrong-sign

distributions in the range ∆M < 0.168 GeV


D∗± photoproduction at 3 CM energies

Visible D∗ PHP cross sections obtained from: σvis(D∗) =Ndata(D∗)A·BR·L

BR = B(D∗ → D0π) · B(D0 → Kπ) = 0.0263; A = acceptanceRatio of visible cross sections: Rσ =

σiσHER

; i = HER, MER, LER

yields higher precision of E-dependence of cross section

since some syst. uncertainties in data and theory cancel

Data compared to FFNS NLO predictions:

(GeV)s240 260 280 300 320

σR

0

0.2

0.4

0.6

0.8

1

1.2ZEUS

0.167 < y < 0.802 < 20 GeV D*

T1.9 < p

| < 1.6D*η|

2 < 1 GeV2Q

=〉W〈136 GeV 152 GeV

192 GeV

D* X→ZEUS ep

NLO QCD

Total syst. uncertainty ≈ 5% in datafew % in theory

< W > = mean W from generated MC

MER/LER cross sections similar

HER cross section higher

Cross sections increase with increasing ep CM energy

This increase is predicted by NLO QCD


Charm fragmentation fractions in PHP

Fragmentation fractions of c-quarks into charm hadrons:

Probability of c quark to hadronise into a given charm hadron

f(c → charm hadron) = σ(charm hadron)/σ(total charm production)

• Needed to go from partonic QCD to hadronic cross sections• No QCD predictions; crucial to compare pQCD with measurements• Are they the same for c-quarks produced in e+e−, ep, pp collisions ?• Test fragmentation universality by measuring all of them

Measurements performed in PHP regime: Q2 < 1 GeV2

Charm hadrons reconstructed in the range:

pT > 3.8 GeV, |η| < 1.6, 130 < W < 300 GeV

Charm hadrons measured: D0 → K−π+, D+ → K−π+π+D∗+ → D0π+s → K−π+π+sD+s → φπ+, Λ+c → K−pπ+

σtot = σeq(D0) + σeq(D+) + σ(D+s ) + 1.14 σ(Λ

+c )

Full HERA II data: 372 pb−1 JHEP 09 (2013) 058


Charm fragmentation fractions in PHP

Silicon-strip detector used for charm vertices

⇒ Clear charm hadron signals for all channals

Cha

rm fr

agm

enta

tion

frac

tions

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

pγ

ZEUSHERA II

pγ

ZEUSHERA I

ep DIS

ZEUSHERA I

ep DIS

H1

-e+e

)0 D→f (c )+ D→f (c )+ D*→f (c

)s D→f (c )cΛ →f (c

Charm fragmentation fractions:

Results (left column) in good

agreement with previous results:

ZEUS PHP, ZEUS DIS, H1 DIS, e−e−

Precision of charm f.f. competitive with combined e+e− LEP results

Fragmentation fractions of c-quarks independent of production

Support hypothesis of universality of heavy-quark fragmentation

Universality supported also by new LHC pp data (ALICE + LHCb)


D± production in DIS

)2 (GeV2Q10 210 310

)2 (

nb/G

eV2

/dQ

σd

-410

-310

-210

-110

1-1 354 pb+ZEUS D

-1 133.6 pb+ZEUS DHVQDIS

ZEUS

y 0.1 0.2 0.3 0.4 0.5 0.6 0.7

/dy

(nb)

σd

0

2

4

6

8

10

12

14

16

18

20

-1 354 pb+ZEUS D

HVQDIS

ZEUS

) (GeV)ππM(K1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1

Com

bina

tions

/ 10

MeV

0

500

1000

1500

2000

2500

3000

3500

4000

4500

ZEUS

-1 354 pb+ZEUS D

+ backgroundmodGauss

) (GeV)+(DT

p2 3 4 5 6 7 8 9 10

) (n

b/G

eV)

+(D

T/d

pσd

-210

-110

1

-1 354 pb+ZEUS D-1 133.6 pb+ZEUS D

HVQDIS

ZEUS

) +(Dη-1.5 -1 -0.5 0 0.5 1 1.5

) (n

b)+

(Dη/dσd

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

-1 354 pb+ZEUS D-1 133.6 pb+ZEUS D

HVQDIS

ZEUS

Full HERA II data: 354 pb−1

JHEP 05 (2013) 023

Clean D+ signal

N(D+) = 8356 ± 198

D+ differential cross sections

w.r.t Q2, y, pT (D+), η(D+)

in kinematic region

5 < Q2 < 1000 GeV2,

1.5 < pT (D+) < 15 GeV,

|η(D+)| < 1.6,0.02 < y < 0.7

NLO QCD predictions based on FFNS describe data well

up to Q2 ≈ 1000 GeV2

Similar agreement for double differential cross sections

dσ/dy for different Q2 ranges


D± production in DIS

0

0.2

0.4

0

0.2

0.4

10-4

10-3

10-2

0

0.2

0.4

10-4

10-3

10-2

ZEUS

F2 c

c

Q2 = 6.5 GeV2 Q2 = 20.4 GeV2

Q2 = 35 GeV2 Q2 = 60 GeV2

xQ2 = 200 GeV2

x

ZEUS D+ 354 pb -1

ZEUS D* 81.9 pb -1

HERAPDF1.5

ZEUS-S PDF

Charm contribution to proton structure function:

Express double differential cross section as:

d2σcc̄

dxdQ2= 2πα

2

xQ4[(1 + (1 − y)2)F cc̄2 − y2F cc̄L ]

F cc̄2 , Fcc̄L are charm contributions to

proton structure functions F2 and FL

dσ/dy for different Q2 bins used

to extract F cc̄2 at reference points

xi, Q2i for each bin i using

F cc̄2,meas(xi, Q2i ) = σi,meas

F cc̄2,theo(xi,Q2i )

σi,theo

F2,theo and σi,theo calculated at NLO in FFNS with HVQDIS program

D± results compared to previous ZEUS D∗ results and to predictions of GM-VFNS

based on HERAPDF1.5 parton densities and of FFNS based on ZEUS-S PDF

HERAPDF1.5 uses HERA ep data to provide NLO predictions

compatible with other PDF groups

The NLO calculations describe new precise data wellHeavy Flavour production at HERA U. Karshon 9

HERA charm data combination in DIS

Combined 9 data sets of D∗, D+, D0, µ and liftime tag data

with 155 H1 and ZEUS cross section measurements

from various HERA I and HERA II analyses EPJ C73 (2013) 2311

Charm reduced cross section, σcc̄red, obtained in kinematic range:

2.5 < Q2 < 2000 GeV2; 3 · 10−5 < x < 5 · 10−2d2σcc̄

dxdQ2= 2πα

2

xQ4[(1 + (1 − y)2)σcc̄red]

Q2=18 GeV2

HERA

H1 and ZEUS

H1 VTX

H1 D* HERA-II

H1 D* HERA-I

ZEUS c → µ X

ZEUS D* 98-00

ZEUS D* 96-97

ZEUS D0

ZEUS D+

x

σ red cc_

10-3 10-20

0.2

0.4

0.6 Reduced cross sections σcc̄red

as function of x for fixed Q2 values:

Example for Q2 = 18 GeV2

Combined results - filled circles

Correlated systematics fully taken into account

Combined results uncertainty ≈ factor 2better than each most precise data set

in the combination



How well does the mixed massive-massless scheme GM-VFNS work?

Reduced cross sections σcc̄red as function of x for fixed Q2 values

-4 -3 -20

0.2

2=2.5 GeV2Q

-4 -3 -20

0.2

2= 5 GeV2Q

-4 -3 -20

0.2

2= 7 GeV2Q

-4 -3 -20

0.52=12 GeV2Q

-4 -3 -20

0.52=18 GeV2Q

-4 -3 -20

0.52=32 GeV2Q

-30

0.52=60 GeV2Q

-30

0.52=120 GeV2Q

-30

0.52=200 GeV2Q

-4 -3 -20

0.52=350 GeV2Q

-4 -3 -20

0.52=650 GeV2Q

-4 -3 -20

0.52=2000 GeV2Q

redc

c σ

0

0.2

0

0.5

0

0.5

0

0.5

-410 -310 -210 -410 -310 -210x

-410 -310 -210

HERA HERAPDF1.5

H1 and ZEUS Combined inclusive DIS data (HERA I+II)

compared to NLO predictions based

on HERAPDF1.5 extracted in

RT standard scheme

Lines are predictions with Mc = 1.4 GeV

Mc = effective (not physical)

mass parameter in GM-VFNS

Large theory uncertainty

dominated by Mc variation

Within uncertainties NLO GM-VFNS

describe data well



Combined NLO analysis with σcc̄red and inclusive DIS cross sections

in kinematic range: W > 15 GeV, x < 0.65, Q2 > 3.5 GeV2

For each HFL scheme, PDF fits performed with 1.2 < Mc < 1.8 GeV

χ2 values vs. Mc from PDF

fits for various HFL schemes

VFNS predictions for σcc̄red with

Mc = 1.4 GeV (up) and Mc = Moptc (down)

[GeV] cM1.2 1.4 1.6 1.8

) c (

M2 χ

600

650

700

750

RT standardRT optimisedACOT-full

χS-ACOT-ZM-VFNS

optC M

H1 and ZEUS

Charm + HERA-I inclusive

Minimal χ2 values observed for

each scheme at different Moptc

Data described much better

with Moptc than with fixed Mc

Predictions of all schemes are

very similar for Q2 ≥ 5 GeV2Heavy Flavour production at HERA U. Karshon 12


Implications on NLO predictions for W, Z production at LHC

W +, W −, Z0 cross section predictions for LHC at√

s = 7 TeV

Calculated for each scheme for 1.2 < Mc < 1.8 GeV in 0.1 GeV steps

[GeV]cM1.2 1.4 1.6 1.8

[nb]

+Wσ

54

56

58

60

62

64

optC M

RT standard RT optimised

ACOT-fullχ S-ACOT-

ZM-VFNS

= 7 TeVs


H1 and ZEUS

[GeV]cM1.2 1.4 1.6 1.8

[nb]

-Wσ

38

40

42

44

optC M


ACOT-fullχ S-ACOT-

ZM-VFNS

= 7 TeVs


H1 and ZEUS

[GeV]cM1.2 1.4 1.6 1.8

[nb]

Zσ

27

28

29

30

31

32optC M


ACOT-fullχ S-ACOT-

ZM-VFNS

= 7 TeVs


H1 and ZEUS

All cross sections rise monotonically with Mc

Significant spread of ≈ 6% between predictions for any fixed McReduces to ≈ 1.4 − 2% when taking Moptc for each scheme



Combined charm data vs. ABM FFNS prediction: Uses instead

of pole mass the running mass definition in MS scheme

0

0.2

0

0.5

0

0.5

0

0.5

σ red cc_

H1 and ZEUSQ2=2.5 GeV2 Q2=5 GeV2 Q2=7 GeV2

Q2=12 GeV2 Q2=18 GeV2 Q2=32 GeV2

Q2=60 GeV2 Q2=120 GeV2 Q2=200 GeV2

Q2=350 GeV2

10-4 10-3 10-2

Q2=650 GeV2

10-4 10-3 10-2

Q2=2000 GeV2

HERA

ABM09NNLO MS

ABM09NLO MS

10-4 10-3 10-2

x

Data well described in full kinematic region

Similar NLO/NNLO predictions

Less sensitivity to higher order corrections)

mc(mc) extraction in MS scheme:

Same minimisation procedure as for VFNS

) [GeV]c

(mcm1 1.2 1.4 1.6

2 χ

620

640

660

680

700

FF (ABM)

H1 and ZEUS


0.05 GeV±)=1.26 c

(mcm

mc(mc) = 1.26 ± 0.05exp. ± 0.03mod.±0.02param. ± 0.02αs GeV

Uncertainties are experimental,

model, parametrisation and αs

Consistent with PDG: 1.275 ± 0.025 GeV



Measurement of running mc

[GeV]µ1 10

) [G

eV]

c(m c

m

0.8

1

1.2

1.4

1.6

1.8

2

H1 and ZEUS preliminary

HERA (prel.)PDG with uncertainty

[GeV]µ1 10

) [G

eV]

µ( cm

0.4

0.6

0.8

1

1.2

1.4

1.6

H1 and ZEUS preliminary

HERA (prel.)

PDG with evolved uncertainty

Extract mc(mc) separately for

6 different kinematic ranges in

µ =√

< Q2 > +4mc(mc)2

< Q2 > is the logarithmic average Q2

of the subset

Red points at scale mc and bands are

PDG average

mc(mc) translated to mc(µ) by:

mc(µ) = mc(mc)(αs(µ)

π )β−10

(αs(mc)

π )β−10

β0 = 9/4 for Nf = 3

Data consistent with expected QCD running

First measurement of mc(µ) from combined

HERA charm reduced cross section data

Important consistency check, similar to running mb at LEP

EPJ C55 (2008) 525


Combination of D∗± differential cross sections in DIS

Combined H1+ZEUS D∗+ visible differential cross sections w.r.t pD∗

T , ηD∗

hep-ex 1503.06042; JHEP to be published

(D

*) (

nb/G

eV)

T/d

pσd

-410

-310

-210

-110

1

(D*) (GeV)T

p2 3 4 5 6 7 8 9 10 20

ratio

to H

ER

A

0.8

1

1.2

2 < 1000 GeV25 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

p(D*)| < 1.5η|

HERAH1ZEUS

X H1 and ZEUS± eD*→ ep

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

(D

*) (

nb)

η/dσd

0

1

2

2 < 1000 GeV25 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

p(D*)| < 1.5η|

HERAH1ZEUS


Correlations in systematic uncertainties fully taken into account

Impressive reduction of uncertainties in the combined results

Precision of combined data ≈ 5% in large fraction of phase spaceSimilar results and precision obtained for dσ/dQ2 and dσ/dy



Differential cross sections compared to NLO predictions: HVQDIS

HVQDIS setup for ep → cc̄X → D∗X uses some arbitrary variable definitione.g. µr = µf =

√

Q2 + 4m2c ; mpolec = 1.5 GeV

Try to change parameters such that normalisation and shapes of all

differential cross sections describe the data well

Found this to happen with µr = 0.5√

Q2 + 4m2c ; mpolec = 1.4 GeV

and with some softening of the fragmantation function used

(Kartvelishvili et al.)

All other parameters left at default values

The value of mpolec = 1.4 GeV was also found to describe better

the data in the study of σcc̄red (p.14)

”NLO QCD customised” shown as red dots in the following plots

This is NOT a prediction, but may hint at which direction theory can be improved



HERA D∗+ differential cross sections w.r.t pD∗

T , ηD∗, Q2, y vs. theory (HVQDIS)

Negligible theoretical uncertainties in data points, since no extrapolation

(D

*) (

nb/G

eV)

T/d

pσd

-410

-310

-210

-110

1

(D*) (GeV)T

p2 3 4 5 6 7 8 9 10 20

ratio

to H

ER

A

0.6

0.8

1

1.2

HERA-IINLO QCDNLO QCD customised

± D*→NLO QCD b

2 < 1000 GeV25 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

p(D*)| < 1.5η|


(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

(D

*) (

nb)

η/dσd

0

1

2


± D*→NLO QCD b

2 < 1000 GeV25 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

p(D*)| < 1.5η|


)2 (

nb/G

eV2

/dQ

σd

-510

-410

-310

-210

-110

1

)2 (GeV2Q10 210 310

ratio

to H

ER

A

0.6

0.8

1

1.2

1.4


± D*→NLO QCD b

2 < 1000 GeV25 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

p(D*)| < 1.5η|


y0.1 0.2 0.3 0.4 0.5 0.6 0.7

/dy

(nb)

σd

0

10

20


± D*→NLO QCD b

2 < 1000 GeV25 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

p(D*)| < 1.5η|


Combined data reach

precision of ≈ 5%

NLO describe data

within large uncertainties

(≈ 10 − 30%)

NLO customised describe

data very well

NNLO calculations and

improved fragmentation

models may help

Similar conclusions for

D∗ double-differential

cross sections in Q2, y


Beauty production in DIS

(GeV)jetTE

5 10 15 20 25 30 35 40

Ent

ries

1

10

210

310

(GeV)jetTE

5 10 15 20 25 30 35 40

Ent

ries

1

10

210

310

jetη-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

Ent

ries

0

100

200

300

400

500

jetη-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

Ent

ries

0

100

200

300

400

500

)2/GeV2(Q10

log0.5 1 1.5 2 2.5 3

Ent

ries

0

50

100

150

)2/GeV2(Q10

log0.5 1 1.5 2 2.5 3

Ent

ries

0

50

100

150

x10

log-4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1

Ent

ries

0

100

200

300

x10

log-4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1

Ent

ries

0

100

200

300

ZEUS < 6 GeV, |S|>8vtx2 < m

-1ZEUS 354 pbMonte CarloLFCharmBeauty

)2 (GeV2Q10 210 310

)2 (

pb /

GeV

2 /

dQσd

-210

-110

1

10

210

-1ZEUS 354 pbhad C×HVQDIS+ZEUS-S

had C×HVQDIS+ABKM Rapgap x 1.49

ZEUS

e jet X→X b e b→ep

)2 (GeV2Q10 210 310D

ata

/ HV

QD

IS

0.5

1

1.5

2

′ ′ ′

x

-410 -310 -210 -110

/ dx

(pb

)σd

310

410

510

610

710-1ZEUS 354 pb

had C×HVQDIS+ZEUS-S had C×HVQDIS+ABKM

Rapgap x 1.49

ZEUS

e jet X→X b e b→ep

x

-410 -310 -210 -110Dat

a / H

VQ

DIS

0.5

1

1.5

2

′ ′ ′

JHEP 09 (2014) 127

Beauty cross section at HERA

much smaller than charm

With a micro-vertex detector at HERA II,

lifetime information can be used

EjetT , ηjet, Q2, x distributions of sec. vertices

for b-enriched sample with 2 < mvtx < 6 GeV

and |S| = |d/δd| > 8 d=decay length

Differential cross sections for

inclusive jet production in b-events

as function of Q2 and x

Good description of the data by the

NLO FFNS HVQDIS prediction



)2 (GeV2Q10 210 310

+ 0

.03

ib

b 2F

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22 -1ZEUS vtx 354 pb-1ZEUS e 363 pb-1 114 pbµZEUS

-1+vtx 126 pbµZEUS -1H1 vtx 246 pb

HERAPDF 1.5

ABKM NNLO

MSTW08 NLO

MSTW08 NNLO

CTEQ6.6 NLO

JR09

x=0.032 i=0

x=0.013 i=1

x=0.005 i=2

x=0.002 i=3

x=0.0013 i=4

x=0.0005 i=5

x=0.0002 i=6

x=0.00013 i=7

-30

0.005

0.01

0.015

0.02

-30

0.005

0.01

0.015

0.02

-30

0.005

0.01

0.015

0.02

-30

0.02

0.04

-30

0.02

0.04

-30

0.02

0.04

-30

0.01

0.02

0.03

x -410 -310 -210

x -410 -310 -210

x -410 -310 -210

bb rσ

0

0.005

0.01

0.015

0.02

0

0.02

0.04

0

0.01

0.02

0.03-1ZEUS 354 pb

=4.07 GeV (best fit)b

QCD fit, m

=3.93 GeVb

QCD fit, m

=4.21 GeVb

QCD fit, m

ZEUS2 = 6.5 GeV2Q 2 = 12 GeV2Q 2 = 25 GeV2Q

2 = 30 GeV2Q 2 = 80 GeV2Q 2 = 160 GeV2Q

2 = 600 GeV2Q

Left: Structure function F bb̄2 as function of Q2 for fixed x values in good agreement

with FFNS and GM-VFNS NLO and NNLO predictions

Right: Reduced b cross section σbb̄r as function of x for fixed Q2 values used

to determine b-quark mass in a QCD fit as done for the c-quark mass

Lines are results with mb = 4.07 (best fit), 3.93 and 4.21 GeV

Sensitivity to mb comes mostly from low Q2



) (GeV)b

(mbm3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5

2 χ

586

588

590

592

594

596

598

600ZEUS

Inclusive DIS + beauty QCD fit

mb(mb) = 4.07 ± 0.14(fit)+0.01−0.07(mod.)+0.05−0.00(param.)+0.08−0.05(theo.) GeVPDG: 4.18 ± 0.03 GeV from lattice QCD + time-like processes

Extraction of mb(mb) from NLO FFNS fit

using MS scheme

Uncertainties are from fit, model,

PDF parametrisation and theory

mb(mb) translated, as for mc(mc),

to mb(µ) with µ = 2mb and compared

to PDG and LEP results

Mass running is consistent with QCD


Summary• H1 and ZEUS still providing new charm(ing) and beauty(full) results

with full HERA data ⇒ tighter constraints on QCD• σ(D∗) in PHP vs. ep CM energy measured for the first time at HERA.

The D∗ cross sections increase with√

s as predicted by NLO QCD

• New precise charm fragmentation fractions measurements in PHP competitivewith e+e− collisions; support fragmentation universality

• New DIS charm measurements and HERA charm data combinationprovide constraints on PDFs and on QCD heavy quark calculations

• Most HERA DIS charm data were combined:Consistent data sets extracted using different methods; reduced uncertainties

Data are well described by FFNS and GM-VFNS QCD predictions

Optimal Mc parameter for different VFNS improves predictions of σW,Z at LHC

Running charm mass in MS FFNS: mc(mc) = 1.26± 0.06 GeV agree with PDGFirst measurement of the charm-mass running at HERA

• Combination of D∗ visible cross sections:Negligible theory uncertainties (no extrapolation)

Challenge to theory and fragmentation models

• New precise b-jet measurement + lifetime tag in DIS using secondary vertices:Data well described by NLO QCD

b mass measured in MS scheme: mb(mb) = 4.07 ± 0.17 GeV agree with PDGb mass running consistent with QCD


zeus o u t l i n e · hall ouest (hera-b) hall est (hermes) rayonnement synchrotron hall sud (zeus)...

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