Charm Jets In Photoproduction At ZEUS - UCL HEP Group · JHL 2 nd Year PhD T alk, UCL, 30 Sep. 2003...

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

JH

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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

JH

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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


sππK→±*D

> 3 GeVPt

±*D

1998-2000 Data



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

er

of

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


sππK→±*D

> 3 GeVPt±*D

1998-2000 Data



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


→ 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


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


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 <


(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 <


(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 <


• 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.

JH

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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


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.

JH

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Sep.2003

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



(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




• 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.

JH

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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


> 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


> 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.

JH

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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


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.

Charm Jets In Photoproduction At ZEUS - UCL HEP Group · JHL 2 nd Year PhD T alk, UCL, 30 Sep. 2003...

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Transcript of Charm Jets In Photoproduction At ZEUS - UCL HEP Group · JHL 2 nd Year PhD T alk, UCL, 30 Sep. 2003...