H1 Measurements of and b 2 - TevatronH1 Measurements of F2, Fcc 2 and Fb b 2 Katja Kr uger, H1...
Transcript of H1 Measurements of and b 2 - TevatronH1 Measurements of F2, Fcc 2 and Fb b 2 Katja Kr uger, H1...
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