H1 Measurements of F2, Fcc2

and Fbb2

Katja Kruger, H1 Collaboration, Kirchhoff Institut fur Physik, Uni Heidelberg

F2 Measurements at low Q2

Measurement of F cc2 and F bb

2

Experimental method

Results at medium and high Q2

Deep Inelastic Scattering

p

Wxp

γ

l'l

electron

proton

Q2

Neutral Current

cms energy√

s =√

(l + p)2

γ virtuality Q2 = −(l − l′)2

Bjorken variable x = Q2

2p·(l−l′)

inelasticity y ≈ Q2

xs

d2σdxdQ2 = 2πα2

x Q4 [(1 + (1 − y)2)F2(x, Q2) − y2FL(x, Q2)]

Accessible Phase Space

x

Q2 /

GeV

2

HERA Kine

matic l

imit

y =

1

Reson

ance

Reg

ion

W =

2 GeV

HERA Standard DIS

HERA Shifted Vertex

ZEUS BPT

Fixed Target Experiments

H1 Shifted Vertex ISR (prel.)

H1 QEDC 1997

10-1

1

10

10 2

10 3

10 4

10-6

10-5

10-4

10-3

10-2

10-1

1

medium-high Q2

• asymptotic freedom

• perturbative QCD

low Q2

• transition to soft

hadronic physics

• αs(Q2) becomes large

• phenomenological

models

The H1 Detector

pe

θe

Q2

LAr

BST

SpaCal

Q2 = 2EeE′e(1 + cos θe)

standard DIS in

LAr Calorimeter:

Q2 >∼ 100GeV2

SpaCal

2 <∼ Q2 <∼ 100GeV2

possibilities to reach lower Q2:

• extend to larger polar angles θe

• use events with lower initial electron energy Ee

F2 at low Q2: Experimental Techniques

Nominal IP

Shifted IP

70 cm BST

pe

SpaCal

Shifted Vertex Runs

larger θe

Initial State Radiation (ISR)

lower Ee

l

l′

k

qP

X

QED Compton (QEDC)

larger θe

Untagged ISR in Shifted Vertex Runs

ISR - γ

LAr

SpaCal

Hadrons

e’BST

• γ is undetected

• photoproduction background

rejected by BST

• reconstruction of initial electron

energy by E − pz:

2Ee = (E − pz)e′ + (E − pz)had

Untagged ISR in Shifted Vertex Runs: F2

H1

Co

lla

bo

rati

on

⇒ ISR extends shifted vertex measurement at low Q2 to higher x

difference between reduced cross section and F2 at low x allows FL measurement

Inelastic QED Compton Events

l

l′

k

qP

X

e + p → e + γ + X

Z

R

e (l’)

γ (k)

• smaller θ of the final state electron and photon

• larger θ of the intermediate electron ⇒ access to low Q2

• DIS background: – π0 fakes QEDC photon

– dominates at low x

Inelastic QED Compton Events: F2

0

0.1

0.2

0.3

0.4

10-5

10-4

10-3

10-2

10-1

1

0

0.25

0.5

0.75

1

10-5

10-4

10-3

10-2

10-1

1

0

0.5

1

10-5

10-4

10-3

10-2

10-1

1

x

F2

Q2 = 0.5 GeV

2

x

F2

Q2

= 2 GeV2

x

F2

Q2 = 7 GeV

2

E665

NMC

SLAC

H1 SV 2000 prel

H1 1999 prel

ZEUS BPT

H1 QEDC 1997

ALLM97

Fractal

⇒ high x: overlap with fixed target experiments, good agreement

F cc2

and F bb2

Measurement

Goal: measure structure function for heavy quarks

as inclusively as possible

⇒ use impact parameter of as many tracks as possible

two Q2 regions:

• high Q2: scattered electron in LAr: Q2 > 150GeV2

(Eur. Phys. J. C40 (2005) 349, hep-ex/0411046)

– high beauty fraction (∼ 3%)

– high pt of hadronic final state

• medium Q2: scattered electron in Spacal: 3.75 < Q2 < 60GeV2

experimentally much more difficult!

⇒ details and plots in the following for medium Q2 analysis

F cc2

and F bb2

: Experimental Method

Study the signed impact parameter in the rϕ plane for all tracks with

precise masurement from Central Silicon Tracker (CST)

δ

α > π/2 δ = − δα < π/2 δ = + δ

δ

1. Vertex Jet

αα

1. Vertex

Jet

Track Trackrϕ plane

• sign determination needs a reference axis approximating the ori-

ginal quark direction

events with decays of long-lived

heavy flavour particles will have

large positive impact parameters

w.r.t. the primary vertex

light flavour primary decays will

have small negative and posi-

tive impact parameters due to

resolution effects

The H1 Central Silicon Tracker

• 2 cylindrical layers of double-sided

silicon strip detectors surrounding

the beam pipe

• radii 5.7 cm and 9.7cm

• angular coverage: 30◦ < θ < 150◦

• hit resolution: 12µm in rϕ,

25µm in z

• impact parameter resolution (for

central tracks with CST hits in

both layers):

33µm⊕ 90µm

pT[GeV]

• hit efficieny: 97% for rϕ hits

Determination of Reference Axis: Jets vs. HFS

two possible methods to determine the reference axis:

• jet axis of the highest pT jet

• four-vector of the Hadronic Final State:

ϕref.axis approximated by opposite ϕ to electron

jet measurement much more precise than HFS

⇒ jet cuts as low as possible to have high jet fraction

• inclusive kT algorithm in the lab frame

• pT > 4GeV

• 15◦ < θ < 155◦

low jet fraction at low Q2 due to small pT of hadrons

Impact Parameter and Significance

• tracks matched to reference axis within ∆ϕref.axis < π/2

• for matched tracks, plot impact parameter δ in rϕ plane

cut |δ| < 0.1cm to remove e.g. K0s

• significance of each track given by Si = δ/σδ

/ cmδ-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

Tra

cks

310

410

510

610 H1 Preliminary

Total MC

uds

c

b

/ cmδ-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

Tra

cks

310

410

510

610

Si-20 -15 -10 -5 0 5 10 15 20

Eve

nts

1

10

210

310

410

510

610H1 Preliminary

Total MC

uds

c

b

Si-20 -15 -10 -5 0 5 10 15 20

Eve

nts

1

10

210

310

410

510

610

Impact Parameter Significance

Significance Distributions

at medium Q2 beauty fraction is smaller than at high Q2

⇒ need 3 distributions to separate b, c, and uds (2 at high Q2)

1S-10 -5 0 5 10

Eve

nts

210

310

410

510

610H1 PreliminaryTotal MCudsc

b

1S-10 -5 0 5 10

Eve

nts

210

310

410

510

610

S1

2S-10 -5 0 5 10

Eve

nts

1

10

210

310

410

510H1 PreliminaryTotal MCudsc

b

2S-10 -5 0 5 10

Eve

nts

1

10

210

310

410

510

S2

3S-8 -6 -4 -2 0 2 4 6 8

Eve

nts

1

10

210

310

410

H1 PreliminaryTotal MCudsc

b

3S-8 -6 -4 -2 0 2 4 6 8

Eve

nts

1

10

210

310

410 S3

• S1 signif. of highest significance track

• S2 signif. of 2nd highest significance track with same sign as S1

• S3 signif. of 3rd highest significance track with same sign as S1

and S2

’Negatively Subtracted’ Significance Distributions

subtract bins at negative Si from the corresponding positive bin

⇒ reduce sensitivity to resolution effects

1S0 2 4 6 8 10 12 14

) 1 )

- n

( -S

1 n

( S

210

310

410

H1 Preliminary

Total MC

uds

c

b

S1

2S0 2 4 6 8 10

) 2 )

- n

( -S

2 n

( S

1

10

210

310

410

H1 Preliminary

Total MC

uds

c

b

S2

3S0 1 2 3 4 5 6 7 8

) 3 )

- n

( -S

3 n

( S

-110

1

10

210

310

410 H1 Preliminary

Total MC

uds

c

b

S3

for each x − Q2 bin fit simultanously the subtracted Si distributi-

ons and the total number of inclusive events before the CST track

selection with 3 parameters:

• Pc scale factor for charm MC (RAPGAP) Pc = 1.34 ± 0.06

• Pb scale factor for beauty MC (RAPGAP) Pb = 1.43 ± 0.17

• Pl scale factor for light quark MC (DJANGO) Pl = 1.16 ± 0.01

Extraction of Cross Section Fractions, F cc2

and F bb2

• reduced charm cross section σcc:

σcc(x, Q2) = σ(x, Q2) PcNMCgenc

PcNMCgenc +PbN

MCgenb +PlN

MCgenl

σ(x, Q2) taken from the inclusive H1 measurement

• charm cross section fraction:

fcc = σcc/σ

• charm structure function F cc2 :

σcc = F cc2 − y2

1+(1−y)2F cc

L

F ccL estimated from the NLO QCD expectation

Charm Structure Function F cc2

• results consistent with H1 and

ZEUS D∗ measurements

• consistent with pQCD predic-

tions

• highest Q2 F cc2 measurement

for H1

theory curves:

MRST04 - Variable FNS

CTEQ6HQ - Variable FNS

CCFM - Massive BGF

H1 PRELIMINARY

0

0.2

0.4

0.6

10 -4 10 -3 10 -2 x

Q2= 3.5 GeV2

x

F 2cc_

H1 Preliminary

H1 Data (High Q2)

H1 D✽

ZEUS D✽

0

0.2

0.4

0.6

10 -4 10 -3 10 -2 x

Q2= 12 GeV2

0

0.2

0.4

0.6

10 -4 10 -3 10 -2 x

Q2= 25 GeV2

0

0.2

0.4

0.6

10 -4 10 -3 10 -2 x

Q2= 60 GeV2

MRST04

CTEQ6HQ

CCFM

0

0.2

0.4

0.6

10-4

10-3

10-2

x

Q2= 200 GeV2

0

0.2

0.4

0.6

10-4

10-3

10-2

x

Q2= 650 GeV2

Beauty Structure Function F bb2

• first F bb2 measurement

• lowest Q2 point consistent

with zero

• consistent with pQCD predic-

tions

• MRST04 preferred by data

theory curves:

MRST04 - Variable FNS

CTEQ6HQ - Variable FNS

CCFM - Massive BGF

H1 PRELIMINARY

0

0.005

0.01

0.015

0.02

10 -4 10 -3 10 -2 x

F 2bb_

Q2= 3.5 GeV2

H1 Preliminary

H1 Data (High Q2)

MRST04

CTEQ6HQ

CCFM

0

0.005

0.01

0.015

0.02

10 -4 10 -3 10 -2 x

Q2= 12 GeV2

0

0.01

0.02

0.03

10 -4 10 -3 10 -2 x

Q2= 25 GeV2

0

0.01

0.02

0.03

10 -4 10 -3 10 -2 x

Q2= 60 GeV2

0

0.02

0.04

0.06

10-4

10-3

10-2

x

Q2= 200 GeV2

0

0.02

0.04

0.06

10-4

10-3

10-2

x

Q2= 650 GeV2

x

F cc2

and F bb2

vs. Q2

H1 PRELIMINARY

10-2

10-1

1

10

10 2

10 3

1 10 102

103

x=0.0002 (x 45)

x=0.0005 (x 44)

x=0.002 (x 43)

x=0.005 (x 42)

x=0.013 (x 41)

x=0.032 (x 40)

H1 Preliminary

H1 Data (High Q2)

H1 D✽

ZEUS D✽

MRST04

CTEQ6HQ

CCFM

Q2 /GeV2

F 2cc_

H1 PRELIMINARY

10-3

10-2

10-1

1

10

10 2

10 3

10 102

103

x=0.0002 (x 85)x=0.0002 (x 85)x=0.0002 (x 85)x=0.0002 (x 85)x=0.0002 (x 85)x=0.0002 (x 85)

x=0.0005 (x 84)

x=0.002 (x 83)

x=0.005 (x 82)

x=0.013 (x 81)

x=0.032 (x 80)

Q2 /GeV2

F 2bb_

H1 Preliminary

H1 Data (High Q2)

MRST04

CTEQ6HQ

CCFM

Cross Section Fractions fcc and fbb

• fqq = σqq/σ

• c and b fractions increase

with Q2

• c fraction up to ∼ 30%

b fraction up to ∼ 3%

theory curves:

MRST04 - Variable FNS

H1 PRELIMINARY

10-3

10-2

10-1

10 -4 10 -3 10 -2 x

f qq_

Q2= 3.5 GeV2

H1 Preliminary

f cc_

f bb_

10-3

10-2

10-1

10 -4 10 -3 10 -2 x

Q2= 12 GeV2

10-3

10-2

10-1

10 -4 10 -3 10 -2 x

Q2= 25 GeV2

10-3

10-2

10-1

10 -4 10 -3 10 -2 x

Q2= 60 GeV2

MRST04 f cc_

MRST04 f bb_

10-3

10-2

10-1

10-4

10-3

10-2

x

Q2= 200 GeV2

10-3

10-2

10-1

10-4

10-3

10-2

x

Q2= 650 GeV2

H1 Data (High Q2)

f cc_

f bb_

Summary

• phase space for F2 measurements at low Q2 extended by special

techniques like untagged ISR in shifted vertex runs and inelastic

QEDC scattering

• inclusive measurement of F cc2 and F bb

2 at medium and high Q2

using impact parameter method

– first measurement of F bb2

– measurements well described by pQCD