Charm Jets In Photoproduction At ZEUS John Loizides UCL/ANL 2 nd year PhD Talk, 30 September 2003 ZEUS e (Ee = 27.5 GeV) p (Ep = 820/920 GeV) s = 300/318 GeV HERA
Charm Jets In Photoproduction At ZEUS
John LoizidesUCL/ANL
2nd year PhD Talk, 30 September 2003
ZEUS e (Ee = 27.5 GeV) p (Ep = 820/920 GeV)
s = 300/318 GeV
HERA
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1.1
Introduction
The HERA collider provides a unique laboratory for the
study of Heavy Flavour Physics
• Charm Jets can be used to test pQCD
→ Parton Dynamics of the Hard Scatter
→ Probe the photon and proton structure
• Study of the non perturbative part of QCD
→ Fragmentation, Hadronisation
By studying charm production using Jets, the uncertainty from the
fragmentation from the c-quark into D∗ meson can be reduced.
• Jets are as close as you can get to reconstructing the
parton dynamics of the event, as quarks and gluons cannot be directly
observered.
• Heavy Flavour production is still an unresolved part
of QCD, and requires further theoretical understanding
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1.2
Kinematics of Lepton-Proton Scattering at HERA
HERA collides 27.5 GeV leptons with 820 (920) GeV protons
→ √s = 300 (318) GeV
• Negative four-momentum transfer squared:
Q2 = −q2 = −(k − k′)2 = sxy
• Photon Proton Center-of-Mass Energy:
W2 = (P + q)2
• Bjorken scaling variable:
x ≡ Q2
2p.q
• Inelasticity:
y ≡ p.qp.k
≡ W2
s
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1.3
Photoproduction at HERA
• In Photoproduction the electron is
lost down the beam pipe.
• Photoproduction is defined as Q2 < 1 GeV2
The main contributing processes to Heavy
Flavour production (Leading Order) :
(a) BGF (Boson Gluon Fusion)
’Direct Process’ point like photon(γ).
The other processes have a ’Resolved-γ’
(b) is Hadron like,(c) c-Excitation &
q-Propagator,(d) g-Propagator.
• pQCD (Next-to-Leading-Order) calculations
should give a better description of the data.
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1.4
Pseudorapidity & Jet Energy loss
HAC1
CENTRAL TRACKING
FORWARD
TRACKING
SOLENOID
HAC1HAC2
1.5 m .9 m
RCAL
EM
C
HAC
1 H
AC2
FCAL
EM
C
BCAL EMC
3.3 m
η=0.0
27.5 GeVpositrons
920 GeVprotons
η=3.0
η=1.1 η
η=-2.7
=-0.74
BCAL RCALFCAL
jetsη-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
jetsη-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
det je
tT
/ Eha
d jet
TE
0.98
1
1.02
1.04
1.06
1.08
1.1
1.12
Jetsη Jet Energy Before Corrections Vs Jetsη Jet Energy Before Corrections Vs
Pseudorapidity (η) is defined as:
η = −ln(tanθ2)
To reconstruct jets, a combination of Tracking
and Calorimeter information are used
(energy flow algorithm).
Jets loose the most amount of energy
in the super-crack regions of the Calorimeter.
and from interactions with dead material.
→ Jet energies corrected for.
The C++ Kt Algorithm is used with
massless objects.
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1.5
D∗± Photoproduction at HERA Overview
ZEUS
0
2
4
6
8
10
12
14
-1 0 1
η(D*)
dσ
/dη
(n
b)
ZEUS (prel.) 98-001.9 < pT(D*) < 3.25 GeV
a)
0
0.5
1
1.5
2
2.5
3
3.5
-1 0 1
η(D*)
dσ
/dη
(n
b)
3.25 < pT(D*) < 5 GeVb)
0
0.2
0.4
0.6
0.8
1
-1 0 1
η(D*)d
σ/d
η (
nb
)
5 < pT(D*) < 8 GeV c)
NLO QCD
0
0.05
0.1
0.15
0.2
0.25
0.3
-1 0 1
η(D*)
dσ
/dη
(n
b)
8 < pT(D*) < 20 GeV d)
FONLL
• Charm is tagged at ZEUS most efficiently with
the reconstruction of a D∗ meson,in the
decay channel D∗± → K∓ π± π±s .
• The plot shows the differential cross-section
dσ/dη,for inclusive D∗± photoproduction
These data are compared with NLO
calculations (upper and lower bounds
show NLO uncertainties).
• These data are not described by the NLO
predictions. Charm with the addition
requirement of a jet could help understanding
and reduce theoretical uncertinties.
Another hard scale is included reducing the
dependence of non-perturbative parts.
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1.6
Event and Trigger Selection
CTD
CTD
CAL
CAL
SLTCTD
FLT
SLT
FLT
Accept/Reject
OtherComponents
Front End
5 5 µ µ
Accept/Reject
CTD ...
Event Builder
Third Level Trigger
cpu cpu cpu cpu cpu cpu
Offline Tape
CALFront End
CAL ...
OtherComponents
s P
ipel
ine
s P
ipel
ine
Rate: 100 Hz
Rate: 500Hz
Rate: 10 Hz
Rate: 10 MHz
Eve
nt B
uffe
r
Eve
nt B
uffe
r
Global
Trigger
Trigger
GlobalSecond Level
First Level
• ZEUS has a three level trigger system.
• Photoproduction selection:
No electron candidate, |Zvertex| < 50 cm
130 < WJB < 280 GeV
• D∗± selection:
PT,πs > 0.12 GeV , PT,πK > 0.4 GeV, |ηtrack| < 1.75
PT,D∗ > 3.0 GeV , |ηD∗| < 1.5
1.80 < m(D0) < 1.92 GeV
0.143 < ∆ M (M(D∗) − M(D0)) < 0.148 GeV
• Jet Selection one or more
ET,jet > 6 GeV,|ηjet| < 2.4
• Luminosity used: 1998-2000 Data → 82pb−1
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1.7
D∗± → K∓ π± π±s Fitting
Normal Gaussian: ∼ exp(−0.5.x2) where x = x − aσ
Modified Gaussian: ∼ exp(−0.5.x(1 + 1
1 + 0.5.x)) where, x = |x − a
σ|
))0
)-M(D*
m (M(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Nu
mb
er
of
Even
ts
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200Entries= 52671
/ndf=2.650392χ
0.00001 GeV±Mean=0.14546
0.0000168 GeV±Width=0.00077
114± Candidates= 6182 ±*# D
sππK→±*D
> 3 GeVPt
±*D
1998-2000 Data
Wrong Charge Background
145± Candidates (W.C. Subtraction) =6044 ±*# D
With Jets ’Normal’ Gaussian Fit±*1998-2000 Data D
))0
)-M(D*
m (M(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Nu
mb
er
of
Even
ts
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200Entries= 52671
/ndf=1.546922χ
0.00001 GeV±Mean=0.14546
0.0000026 GeV±Width=0.00070
95± Candidates= 5888 ±*# D
sππK→±*D
> 3 GeVPt
±*D
1998-2000 Data
Wrong Charge Background
145± Candidates (W.C. Subtraction) =6044 ±*# D
With Jets ’Modified’ Gaussian Fit±*1998-2000 Data D
→ ’Modified’ Gaussian gives a better fit; ’Modified’ Gaussian will be
used for all fits.
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1.8
D∗± → K∓ π± π± Wrong Charge Subtratction Method
))0
)-M(D*
m (M(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Numb
er of
Eve
nts
0
200
400
600
800
1000
1200
1400
1600
1800
2000
A B
With Jets±*1998-2000 Data D
))0
)-M(D*
m (M(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Numb
er of
Eve
nts
0
100
200
300
400
500
600
700
800
C D
With Jets Wrong Charge Background±*1998-2000 Data D
Wrong charge background subtraction method:
Number of Events = N(A) − N(C).N(B)N(D)
Error =
√
(N(A) + N(C).N(B).N(C) + N(B) + N(C).
N(B)N(D)
N(D)2)
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1.9
D∗± → K∓ π± π±s & Jets
))0m (M(D*)-M(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Nu
mb
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Even
ts
0
200
400
600
800
1000
1200
1400
1600
1800
With Jets ’Modified’ Gaussian Fit±1998-2000 Data D*
Entries= 35854
/ndf=0.298302χ
0.00002 GeV±Mean=0.14546
0.0000159 GeV±Width=0.00059
112± Candidates= 5233 ±*# D
sππK→±*D
> 3 GeVPt±*D
1998-2000 Data
Wrong Charge Background
120± Candidates (W.C. Subtraction) =4975 ±*# D
Mass (GeV)1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2
Nu
mb
er
of
Even
ts
0
200
400
600
800
1000
1200
With Jets01998-2000 Data D
Entries= 41279
/ndf=0.474402χ 0.00053 GeV±Mean=1.86276 0.00067 GeV±Width=0.01938
180± Candidates= 5417 0# D
πK→0D
> 3 GeVPt
±*D
1998-2000 Data
Wrong Charge Background
→ Plentiful data to be able to make some differential distibutions.
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1.10
D∗+, D∗− & Jets
))0m (M(D*)-M(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Nu
mb
er
of
Even
ts
0
200
400
600
800
1000
With Jets Modified Gaussian Fit+1998-2000 Data D*
Entries= 20144
/ndf=0.296232χ 0.00002 GeV±Mean=0.14545
0.0000176 GeV±Width=0.00049
74± Candidates= 2618 +*# D
sππK→+*D
> 3 GeVPt+*D
1998-2000 Data
Wrong Charge Background
89± Candidates (W.C. Subtraction) =2410 +*# D
))0m (M(D*)-M(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Nu
mb
er
of
Even
ts
0
100
200
300
400
500
600
700
800
900
With Jets Modified Gaussian Fit-1998-2000 Data D*
Entries= 19958
/ndf=0.211612χ 0.00003 GeV±Mean=0.14547
0.0000312 GeV±Width=0.00074
94± Candidates= 2772 -*# D
sππK→-*D
> 3 GeVPt-*D
1998-2000 Data
Wrong Charge Background
88± Candidates (W.C. Subtraction) =2592 -*# D
→ D∗+ & D∗− widths are different. This is due to the CTD
reconstruction difference of positive and negative tracks at lower Pt.
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1.11
D∗± Photoproduction Inclusive jet cross sections
dσ/dEjett
(GeV)jetEt10 15 20 25 30 35 40
(n
b /
GeV
)je
t/d
Et
σd
10-3
10-2
10-1
11998-2000 Data
HERWIG
Pythia
NLO FMNR
< 1.5jetη-1.5 <
jett / dEσInclusive jet cross sections d
(GeV)jetEt10 15 20 25 30 35 40
(n
b /
GeV
)je
t/d
Et
σd
10-3
10-2
10-1
1998-2000 Data
HERWIG
Pythia
NLO FMNR
< -0.5jetη-1.5 <
jett / dEσInclusive jet cross sections d
(GeV)jetEt10 15 20 25 30 35 40
(n
b /
GeV
)je
t/d
Et
σd
10-3
10-2
10-1
1
1998-2000 Data
HERWIG
Pythia
NLO FMNR
< 0.5jetη-0.5 <
jett / dEσInclusive jet cross sections d
(GeV)jetEt10 15 20 25 30 35 40
(n
b /
GeV
)je
t/d
Et
σd
10-4
10-3
10-2
10-1
1998-2000 Data
HERWIG
Pythia
NLO FMNR
< 1.5jetη0.5 <
jett / dEσInclusive jet cross sections d
• Kinematic region:
Q2 < 1 GeV2, 130 < WJB < 280 GeV,
PT,D∗ > 3.0 GeV, |ηD∗| < 1.5
• The plot shows all jets within
|ηjet| < 1.5 &, Ejett > 6 for the whole
ηjet range,backwards,central & forward
regions.
• These data are compared to LO & NLO.
Mass of the charm is fixed to 1.5 GeV,light
flavours are massless.
• Poor description by both Herwig(LO),
Pythia(LO) & FMNR(NLO)
• Discrepency seems to be large when
requiring a jet.
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1.12
D∗± and non-D∗± jet cross sections dσ/dEjett
D*
Jet
(GeV)jetEt10 15 20 25 30 35 40
(n
b /
GeV
)je
tt
/dE
σd
10-2
10-1
1
jett / dEσMatched D* Inclusive jet cross sections d
1998-2000 DataHERWIGPYTHIANLO FMNR
jett / dEσMatched D* Inclusive jet cross sections d
(GeV)jetEt10 15 20 25 30 35 40
(n
b /
GeV
)je
tt
/dE
σd10
-2
10-1
1
jett / dEσUN-Matched D* Inclusive jet cross sections d
1998-2000 DataHERWIGPYTHIANLO FMNR
jett / dEσUN-Matched D* Inclusive jet cross sections d
D∗± selected by ∆R cut:
∆R =√
(Φjet − ΦD∗)2 + (ηjet − ηD∗)2
Matched Jets ∆R < 0.6, Measurements
have jets & D∗ associated according to
the Kt algorithm
Kinematic region:
Q2 < 1 GeV2, 130 < WJB < 280 GeV,
PT,D∗ > 3.0 GeV, |ηD∗| < 1.5
|ηjet| < 2.4 &,Ejett > 6 GeV
These data are corrected back to true jets
clustered with the D∗
Poor description by FMNR(NLO), Herwig(LO)
& Pythia(LO), underestimated these data
by a factor 2-3, shape is good.
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1.13
D∗± Photoproduction Inclusive jet cross sections
dσ/dηjet
(GeV)jetη-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
(n
b /
GeV
)je
tη
/dσd
0
0.5
1
1.5
2
2.5
3
jetη / dσInclusive jet cross sections d
1998-2000 DataHERWIGPYTHIANLO FMNR
jetη / dσInclusive jet cross sections d
(GeV)jetη-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
(n
b /
GeV
)je
tη
/dσd
00.20.40.60.8
11.21.4
jetη / dσInclusive jet cross sections d
1998-2000 DataHERWIGPYTHIANLO FMNR
jetη / dσInclusive jet cross sections d
• Kinematic cuts:
Q2 < 1 GeV2, 130 < WJB < 280GeV,
PT,D∗ > 3.0 GeV, |ηD∗| < 1.5, |ηjet| < 2.4
• The top plot shows dσ/dηjet ,Ejett > 6GeV
The bottom plot shows dσ/dηjet, Ejett > 8GeV
• These data are compared to FMNR NLO.
Mass of the charm is fixed to 1.5 GeV,light
flavours are massless.
• Poor description by FMNR(NLO), Herwig(LO)
& Pythia(LO) in all regions of ηjet.
Shape is good but normalisation is wrong.
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1.14
D∗± and non-D∗± jet cross sections dσ/dηjet
D*
Jet
jetη-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
(n
b /
GeV
)je
tη
/dσd
00.20.40.60.8
11.21.41.61.8
> 6jett E
jetη / dσD* Inclusive jet cross sections d
1998-2000 DataHERWIGPYTHIANLO FMNR
> 6jett E
jetη / dσD* Inclusive jet cross sections d
jetη-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
(n
b /
GeV
)je
tη
/dσd
0
0.2
0.4
0.6
0.8
1
1.2 > 6jet
t Ejet
η / dσNon-D* Inclusive jet cross sections d
1998-2000 DataHERWIGPYTHIANLO FMNR
> 6jett E
jetη / dσNon-D* Inclusive jet cross sections d
D∗± selected by ∆R cut:
∆R =√
(Φjet − ΦD∗)2 + (ηjet − ηD∗)2
Matched Jets ∆R < 0.6, Measurements
have jets & D∗ associated according to
the Kt algorithm
Kinematic region:
Q2 < 1 GeV2, 130 < WJB < 280 GeV,
PT,D∗ > 3.0 GeV, |ηD∗| < 1.5
|ηjet| < 2.4 &,Ejett > 6 GeV
These data are corrected back to true jets
clustered with the D∗
Poor description by FMNR(NLO), Herwig(LO)
& Pythia(LO), underestimated these data
by a factor 2-3, shape is good.
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1.15
Possible Extension To The Analysis
0.02
0.04
0.06
0.08
0.1
0 0.5 1 1.5 2 2.5 3
c quark Q0=1.0 GeV
u quark Q0=1.0 GeV
c quark Q0=0.6 GeV
u quark Q0=0.6 GeV
Dead Cone region
Θq (rad)
(1/N
tot) d
N/d
Θq
))0m (m(D*)-m(D∆0.135 0.14 0.145 0.15 0.155 0.16 0.165 0.17
Nu
mb
er
of
Even
ts0
20
40
60
80
100
120
140
With Three Jets ET >6,ET >5,ET>5 Modified Gaussian Fit±*1998-2000 Data D
Entries= 4723
/ndf=0.342142χ 0.00008 GeV±Mean=0.14536
0.0000866 GeV±Width=0.00055
34± Candidates= 274 +*# D
sππK→+*D
> 3 GeVPt
+*D
1998-2000 Data
Wrong Charge Background
41± Candidates (W.C. Subtraction) = 275 +*# D
Measure 3 jet events to study the effect of
the dead cone, cos(θ) =∑n
jet=1
~PD∗ · ~Pjet
|PD∗| · |Pjet| .
Kinematic region:
Q2 < 1 GeV2, 130 < WJB < 280 GeV,
PT,D∗ > 3.0 GeV, |ηD∗| < 1.5
|ηjet| < 2.4 &,Ejet1t > 6 GeV,
Ejet2t > 5 GeV, E
jet3t > 5 GeV
The Angular distribution of gluon radiation differs
from light quarks and charm quarks.
→ measurment of charm mass.
S.V. Chekanov, Phys. Lett. B484(2000) 51-57
Yu.L. Dokshitzer, V.A Khose, S.I. Troyan,
J. Phys. G 17 (1991) 1481, 1602
275 events for 3 jets with charm.
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1.16
Summary and Outlook
• HERA has produced a wealth of charm jet data in photoproduction
• These data have been analysed & compared to LO & NLO
pQCD predictions.
→ There are still big differences between these theories & data.
→ Differences bigger in charm & jets then in inclusive charm production.
• Parton dynamics of charm physics need more understanding at HERA.
pQCD is not able to reproduce cross sections in fundamental
quantities such as Et and η, normalisation off shape approximately o.k.
• Work in progress, systematic errors need to be calculated, more
Monte Carlo Models to be compared.
→ new theoretical developments, and NNLO calculations needed!
• Experimental precision and coverage of data is now good,
& can only get better with HERA II and the use of the MVD.