at HERA ZEUS Collaboration

The azimuthal distribution of jets produced in the Breit frame in high-Q deep inelastic ep scattering has been studied with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb. The measured azimuthal distribution shows a structure that is well described by next-to-leading-order QCD predictions over the Q range considered, Q > 125 GeV. The ZEUS Collaboration S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida Argonne National Laboratory, Argonne, Illinois 60439-4815 n M.C.K. Mattingly Andrews University, Berrien Springs, Michigan 49104-0380 P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi University and INFN Bologna, Bologna, Italy e G. Aghuzumtsyan, D. Bartsch, I. Brock, S. Goers, H. Hartmann, E. Hilger, P. Irrgang, H.-P. Jakob, A. Kappes, U.F. Katz, O. Kind, E. Paul, J. Rautenberg, R. Renner, H. Schnurbusch, A. Stifutkin, J. Tandler, K.C. Voss, M. Wang, A. Weber Physikalisches Institut der Universität Bonn, Bonn, Germany b D.S. Bailey, N.H. Brook, J.E. Cole, B. Foster, G.P. Heath, H.F. Heath, S. Robins, E. Rodrigues, J. Scott, R.J. Tapper, M. Wing H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom m M. Capua, A. Mastroberardino, M. Schioppa, G. Susinno Calabria University, Physics Department and INFN, Cosenza, Italy e J.Y. Kim, Y.K. Kim, J.H. Lee, I.T. Lim, M.Y. Pac Chonnam National University, Kwangju, Korea g A. Caldwell, M. Helbich, X. Liu, B. Mellado, Y. Ning, S. Paganis, Z. Ren, W.B. Schmidke, F. Sciulli Nevis Laboratories, Columbia University, Irvington on Hudson, New York 10027 o J. Chwastowski, A. Eskreys, J. Figiel, K. Olkiewicz, P. Stopa, L. Zawiejski Institute of Nuclear Physics, Cracow, Poland i L. Adamczyk, T. Bo ld, I. Grabowska-Bo ld, D. Kisielewska, A.M. Kowal, M. Kowal, T. Kowalski, M. Przybycień, L. Suszycki, D. Szuba, J. Szuba Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy, Cracow, Poland p A. Kotański, W. S lomiński Department of Physics, Jagellonian University, Cracow, Poland

l Aviv University
Tel AvivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

D Lontkovskyi 
Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and University of Amsterdam
AmsterdamNetherlands

O Yu Lukina 
Physics Department
Ohio State University
43210ColumbusOhioUSA

P Lużniak 
J Maeda 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

S Magill 
Argonne National Laboratory
60439-4815ArgonneIllinoisUSA

III Moscow Engineering Physics Institute
MoscowRussia

Dipartimento di Fisica
Università 'La Sapienza' and INFNRomeItaly

Department of Physics
University of Tokyo
TokyoJapan

Department of Physics
Tokyo Metropolitan University
TokyoJapan

Università di Torino
INFN
TorinoItaly

I Makarenko 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J Malka 
Department of Physics
University of Wisconsin
53706MadisonWisconsinUSA

R Mankel 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Margotti 
INFN Bologna
BolognaItaly B

Faculty of Physics and Applied Computer Science
AGH-University of Science and Technology
CracowPoland

G Marini 
The Henryk Niewodniczanski Institute of Nuclear Physics
Polish Academy o

Sci-ences
Cra
owPoland

Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J F Martin 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Mastroberardino 
Physics Department and INFN
Calabria University
CosenzaItaly B

T Matsumoto 
Department of Physics and Astronomy
University of Glasgow
GlasgowUnited Kingdom

High Energy Nuclear Physics Group
Imperial College London
LondonUnited Kingdom

Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridS ain

Physics and Astronomy Department
University College London
LondonUnited Kingdom

M C K Mattingly 
Andrews University
49104-0380Berrien SpringsMichiganUSA

III Moscow Engineering Physics Institute
MoscowRussia

Department of Physics
University of Oxford
OxfordUnited Kingdom

Dipartimento di Fisica
Università 'La Sapienza' and INFNRomeItaly

Department of Physics
University of Tokyo
TokyoJapan

Department of Physics
Tokyo Metropolitan University
TokyoJapan

Università di Torino
INFN
TorinoItaly

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

I.-A Melzer-Pellmann 
S Miglioranzi 
The Henryk Niewodniczanski Ins itute of Nuclear Physics
Polish Academy of Sci-ences
CracowPoland

F Mo- Hamad Idris 
V Monaco 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Montanari 
Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of Ministry of E ucation and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv University
Tel AvivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle P

sics
Weizmann Instit
te
RehovotIsrael

J D Morris 
H.H. Wills Physics Laboratory
University of Bristol
BristolUnited Kingdom

University and INFN Florence
FlorenceItaly

Fakultät für Physik
Universität Freiburg i.Br
Freiburg i.BrGermany

Department of Physics
Pennsylvania State University
16802University ParkPennsylvaniaUSA

F Polytechnic University
SagamiharaJapan

Rutherford Appleton Laboratory
Chilton, DidcotOxonUnited Kingdom

Università del Piemonte Orientale
Novara

INF TorinoItaly

Department of Physics
University of Toronto
M5S 1A7TorontoOntarioCanada

B Musgrave 
Argonne National Laboratory
60439-4815ArgonneIllinoisUSA

Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridSpain

K Nagano 
T Namsoo 
Department of Physics
University of Wisconsin
53706MadisonWisconsinUSA

R Nania 
INFN Bologna
BolognaItaly B Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of Ministry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv University
Tel AvivIsrae Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

D Nicholass 
Argonne National Laboratory
60439-4815ArgonneIllinoisUSA

Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Nigro 
Y Ning 
U Noor 
Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Pa ticle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of Ministry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev N tional University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv University
Tel AvivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

D Notz 
Department of Physics
University of Wisconsin
53706MadisonWisconsinUSA

R J Nowak 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A E Nuncio-Quiroz 
Physikalisches Institut
Universi

t Bonn
BonnGermany C

Un
versity and INFN Florence
FlorenceItaly

Fakultät für Physik
Universität Freiburg i.Br
Freiburg i.BrGermany

Department of Physics
Pennsylvania State University
16802University ParkPennsylvaniaUSA

F Polytechnic University
SagamiharaJapan

Rutherford Appleton Laboratory
Chilton, DidcotOxonUnited Kingdom

Università del Piemonte Orientale
Novara

INFN
TorinoItaly

Department of Physics
University of Toronto
M5S 1A7TorontoOntarioCanada

B Y Oh 
Institute of Nuclear Physics
Moscow State University
MoscowRussia

N Okazaki 
Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridSpain

K Oliver 
Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridSpain

K Olkiewicz 
Yu Onishchuk 
Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and University of Amsterdam
AmsterdamNetherlands

O Ota 
Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridSpain

K Papageorgiu 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Parenti 
E Paul 
Physikalisches Institut
Universität Bonn
BonnGermany C

Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

Physics and Astronomy Department
University College London
LondonUnited Kingdom

J M Pawlak 
University and INFN Florence
FlorenceItaly

Fakultät für Physik
Universität Freiburg i.Br
Freiburg i.BrGermany

Department of Physics
Pennsylvania State University
16802Uni ersity ParkPennsylvaniaUSA

F Polytechnic University
SagamiharaJapan

Rutherford Appleton Laboratory
Chilton, DidcotOxonUnited Kingdom

Università del Piemonte Orientale
Novara

INFN
TorinoItaly

Department of Physics
University of Toronto
M5S 1A7TorontoOntarioCanada

B Pawlik 
Faculty of Physics and Applied Computer Science
AGH-University of Science and Technology
CracowPoland

Physics Department
Ohio State University
43210ColumbusOhioUSA

P G Pelfer 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Pellegr

o 
W Perlanski 
Dep
rtment of Physics
Jagellonian University
CracowPoland

Deutsches Elektronen-Synchrotron DESY
HamburgGermany

Deutsches Elektronen-Synchrotron DESY
INFN Florence
Zeuthen, FlorenceGermany, Italy

H Perrey 
Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridSpain

K Piotrzkowski 
Physics Department
Ohio State University
43210ColumbusO ioUSA

P Plucinski 
Institute of Nuclear Physics
Moscow State University
MoscowRussia

N S Pokrovskiy 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Polini 
INFN Bologna
BolognaItaly B

Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A S Proskuryakov 
Physics and Astronomy Department
University College London
LondonUnited Kingdom

M Przybycień 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Raval 
Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of inistry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv Uni

rsity
Tel AvivIsrael

Institute of Experiment
l Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

D D Reeder 
University and INFN Florence
FlorenceItaly

Fakultät für Physik
Universität Freiburg i.Br
Freiburg i.BrGermany

Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Insti ute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of Ministry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National U iversity
DaeguSouth Ko-rea

Department of Physics
Pennsylvania State University
16802University ParkPennsylvaniaUSA

F Polytechnic University
SagamiharaJapan

Rutherford Appleton Laboratory
Chilton, DidcotOxonUnited Kingdom

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv University
Tel AvivIsrael

Università del Piemonte Orientale
Novara

INFN
TorinoItaly

Department of Physics
University of Toronto
M5S 1A7TorontoOntarioCanada

Institute of Experimental Physics
Warsaw Universit WarsawPoland

Institute for Nuclear Studies
Wars n Institute
RehovotIsrael

B Reisert 
Z Ren 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J Repond 
Argonne National Laboratory
60439-4815ArgonneIllinoisUSA

Y D Ri 
Department of Engi eering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGerma y

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of Ministry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Department of Physics
University of Oxford
OxfordUnited King om

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv University
Tel AvivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

Department of Physics
York Univers ty
M3J 1P3 M IVOntarioCanada

agA Robertson 
Physics Depar ment
Ohio State University
43210ColumbusOhioUSA

P Roloff 
E R n 
III Moscow Engineering Physics Institute
MoscowRussia

Dipartimento di Fisica
Università 'La Sapienza' and INFNRomeItaly

Department of Physics
University of Tokyo
TokyoJapan

Department of Physics
Tokyo Metropolitan University
TokyoJapan

Università di Torino
INFN
TorinoItaly

I Rubinsky 
Physics and Astronomy Department
University College London
LondonUnited Kingdom

M Ruspa 
Department of Physics
University of Wisconsin
53706MadisonWisconsinUSA

R Sacchi 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOnta

oCanada

A Salii 
U Samson 
Phys
kalisches Institut
Universität Bonn
BonnGermany C

Faculty of Physics and Applied Computer Science
AGH-University of Science and Technology
CracowPoland

G Sartorelli 
University and INFN Bologna
BolognaItaly B

Department of Physics
University of Oxford
Oxford nited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A A Savin 
Department of Physics
Jagellon an University
CracowPoland

Deutsches Elektronen-Synchrotron DESY
HamburgGermany

Deutsches Elektronen-Synchrotron DESY
INFN Florence
Zeuthen, FlorenceGermany, Italy

Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Technology of Ministry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Department of Physics
University of Oxford
OxfordUnited Kingdom

Raymond and Beverly Sackler Faculty of xact Sciences
School of hysics
Tel Aviv University
Tel AvivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPol nd

Department of Particle hysics
Weizmann Institute
RehovotIsrael

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

D H Saxon 
Physics and Astronomy Department
University College London
LondonUnited Kingdom

M Schioppa 
Physics Department and INFN
Calabria Univ

m

J Schwartz 
III Moscow En
s Institute
MoscowRussia

Dipartimento di Fisica
Università 'La Sapienza' and INFNRomeItaly

Department of Physics
University of Tokyo
TokyoJapan

Department of Physics
Tokyo Metropolitan University
TokyoJapan

Università di Torino
INFN
TorinoItaly

F Sciulli 
The Henryk Niewodniczanski Institute of Nuclear Physics
Polish Academy of Sci-ences
CracowPoland

Department of Physics
McGill University
H3A 2T8MontréalQuébecCanada

Faculty of General Education
M Meiji Gakuin University
YokohamaJapan

Physics and Astronomy Department
University College London
LondonUnited Kingdom

L M Shcheglova 
Department of Physics
University of Wisconsin
53706MadisonWisconsinUSA

R Shehzadi 
Phys kalisches Institut
Universität Bonn
BonnGermany C

S Sh mizu 
III Moscow Engineering Physics Institute
MoscowRus ia

Dipartimento di Fisica
Università 'La Sapienza' and INFNRomeItaly

Department of Physics
University of Tokyo
TokyoJapan

Department of Physics
Tokyo Metropolitan University
TokyoJapan

Università di Torino
INFN
TorinoItaly

I Singh 
Depa III Moscow Engineering Physics Institute
MoscowRussia

Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and University of Amsterdam
Amsterdam etherlands

Dipartimento di Fisica
Università 'La Sap enza' and INFNRomeItaly

Department of Physics
University of Tokyo
TokyoJapan

Department of Physics
Tokyo Metropolitan University
Tokyo apan

Università di Torino
INFN
TorinoItaly

I O Skillicorn 
W S Lomiński 
Department of Physics
Jagellonian University
CracowPoland

Deutsches Elektronen-Synchrotron DESY
HamburgGermany

Deutsches Elektronen-Synchrotron DESY
INFN Florence
Zeuthen, FlorenceGermany, Italy

W H Smith 
V Sola 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Solano 
Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Insti demy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Raymond and Beverly Sackler Faculty of Exa Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

D Son 
V Sosnovtsev 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Spiridonov 
Department of Physics
Jagellonian University
CracowPoland

Deutsches Elektronen-Sy chrotron DESY
HamburgGermany

Deutsches Elektronen-Synchrotron DESY
INFN Florence
Zeuthen, FlorenceGermany, Italy

H St

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Department of Physics
McGi
H3A 2T8MontréalQuébecCanada

Faculty of General Education
M Meiji Gakuin University
YokohamaJapan

L Stanco 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Stern 
Physics Department
Ohio State University
43210ColumbusOhioUSA

T P Stewart 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Stifutkin 
Physics Department
Ohio State University
43210ColumbusOhioUSA

P Stopa 
S Suchkov 
Faculty of Physics and Applied Computer Science
AGH-University of Science and Technology
CracowPoland

G Susinno 
Physics Department and INFN
Calabria University
CosenzaItaly B

Department of Physics
McGill University
H3A 2T8MontréalQuébecCanada

Faculty of General Education
M Meiji Gakuin University
YokohamaJapan

L Suszycki 
Institut de Physique N cléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J Sztuk 
Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of Ministry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Raymond and Beverly Sackler Faculty of Exact Sciences

hool of Physics
Tel Aviv Unive
vivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

D Szuba 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J Szuba 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A D Tapper 
Department of Engineering in Management and Finance
Univ. of the Aegean
ChiosGreece

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institute of Physics and Technology of Ministry of Education and Science of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv University
Tel AvivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

E Tassi 
Physics Department and INFN
Calabria University
CosenzaItaly B

Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J Terrón 
T Theedt 
Department of Physics

agellonian University
CracowPoland

Deutsc
es Elektronen-Synchrotron DESY
HamburgGermany

Deutsches Elektronen-Synchrotron DESY
INFN F Tiecke 
Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridSpain

K Tokushuku 
Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and University of Amsterdam
AmsterdamNetherlands

O Tomalak 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J Tomaszewska 
T Tsurugai 
Physics and Astronomy Department
University College London
LondonUnited Kingdom rtment of Physics and Astronomy
University of Glasgow
GlasgowUnited Kingdom

High Energy Nuclear Physics Group
Imperial College London
LondonUnite Kingdom

C Uribe-Estrada 
Physics and Astronomy Department
University College London
LondonUnited Kingdom

M Vázquez 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Verbytskyi 
Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and University of Amsterdam
AmsterdamNetherlands

O Viazlo 
Institute of Nuclear Physics
Moscow State University
MoscowRussia

N N Vlasov 
Institute of Nuclear Physics
Moscow State University
MoscowRussia

Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and University of Amsterdam
AmsterdamNetherlands

O Volynets 
Department of Physics
University of Wisconsin
53706MadisonWisconsinUSA

R Walczak 
Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
Yo

University
M3J 1P3 M IVO
tarioCanada

W A T Wan Abdullah 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J J Whitmore 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

J Whyte 
Institut de Physique Nucléaire
Université Catholique de Louvain
Louvain-la-NeuveBelgium

Department of Physics
McGill University
H3A 2T8MontréalQuébecCanada

Faculty of General Education
M Meiji Gakuin University
YokohamaJapan

L Wiggers 
Physics and Astronomy Department
University College London
LondonUnited Kingdom M Wing 
Physics and Astronomy Department
Un versity College London
LondonUnited Kingdom

M Wlasenko 
Physikalisches Institut
Universität Bonn
BonnGermany C

Facu ty of Physics and Applied Computer Science
AGH-University o Science and Technology
CracowPoland

G Wolf 
Department of Physics
Jagellonian University
CracowPoland

D utsches Elektronen-Synchrotron DESY
HamburgGermany

Deutsches Elektronen-Synchrotron DESY
INFN Florence
Zeuthen, FlorenceGermany, Italy

H Wol e 
Departamento de Física Teórica
Universidad Autónoma de Madrid
MadridSpain

K Wrona 
Faculty of Physics and Applied Computer Science
AGH-University of Science and Technology
CracowPoland

Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Ph sics
York University
M3J 1P3 M IVOntarioCanada

A G Yagüe -Molina 
S Yamada 
Y Yamazaki 
Department of Physics
University of Wisconsin
53706MadisonWisconsinUSA

R Yoshida 
Argonne National Laboratory
60439-4815ArgonneIllinoisUSA

Department of Physics and Astronomy
University of Glasgow
GlasgowUnited Kingdom

High Energy Nuclear Physics Group
Imperial College London
L ndonUnited Kingdom

C Youngman 
The Henryk Niewodniczanski Institute of Nuclear Physics
Polish Academy of Sci-ences
CracowPoland

Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A F Żarnecki 
Department of Physics
McGill University
H3A 2T8MontréalQuébecCanada

Faculty of General Education
M Meiji Gakuin University
YokohamaJapan

L Zawiejski 
Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and University of Amsterdam
AmsterdamNetherlands

O Zenaiev 
W Zeuner 
University and INFN Florence
FlorenceItaly

Fakultät für Physik
Universität Freiburg i Br
Freiburg i.BrGermany

Max-Planck-Institut für Physik
MünchenGermany

NIKHEF and Unive sity of Amsterdam
AmsterdamNetherlands

Department of Physics Pennsylvania State University
16802University ParkPennsylvaniaUSA

F Polytechnic University
SagamiharaJapan

Rutherford Appleton Laboratory
Chilton, DidcotOxonUnited Kingdom

Università del Piemonte Orientale
Novara

INFN
TorinoItaly

Department of Physics
University of Toronto
M5S 1A7TorontoOntarioCanada

B O Zhautykov 
Institute o Nuclear Physics
Moscow State University
MoscowRussia

N Zhmak 
C Zhou 
Department of Physics and Astronomy
University of Glasgow
GlasgowUnited Kingdom

High Energy Nuclear Physics Group
Imperial College London
LondonUnited Kingdom

Department of Physics
University of Oxford
OxfordUnited Kingdom

Department of Physics
York University
M3J 1P3 M IVOntarioCanada

A Zichichi 
University and INFN Bologna
BolognaItaly B

Physics and Astronomy Department
University College London
LondonUnited Kingdom

M Zolko 
Departm nt of Engineering in Management and Finance
Univ. of the Aegean
ChiosGree e

Institute of Exp. Physics
Hamburg University
HamburgGermany

Institute of Particle and Nuclear Studies
KEK
TsukubaJapan

I Institu e of Physics and Technology of Ministry of Education and Scie ce of Kaza-khstan
AlmatyKazakhstan

Institute for Nuclear Research
National Academy of Sciences
and Kiev National University
KievUkraine

Center for High Energy Physics
Kyungpook National University
DaeguSouth Ko-rea

Raymond and Beverly Sackler Faculty of Exact Sciences
School of Physics
Tel Aviv Universi y
Tel AvivIsrael

Institute of Experimental Physics
Warsaw University
WarsawPoland

Institute for Nuclear Studies
WarsawPoland

Department of Particle Physics
Weizmann Institute
RehovotIsrael

D S Zotkin 
Z Zulkapli 
Ii 
Jabatan Fizik 
Universiti Malaya 
Kuala Lumpur 
Padova, Italy BInfn Padova 
University and INFN Florence
FlorenceItaly

Fakultät für Physik
Universität Freiburg i.Br
Freiburg i.BrGermany

Department of Physics
Pennsylvania State University 6802University ParkPennsylvaniaUSA

F Polytechnic University
SagamiharaJapan

Rutherford Appleton Laboratory
Chilton, DidcotOxonUnited Kingdom

Università del Piemonte Orientale
Novara

INFN
TorinoItaly

Department of Physics
University of Toronto
M5S 1A7TorontoOntarioCanada


Nevis Laboratories
Columbi University
10027Irvington on HudsonNew YorkUSA


Dipartimento di Fisica dell' Universi à and INFN
PadovaItaly


Department of Physics
Tokyo Institute of Technology
TokyoJapan

Measurement of D + and Λ + c production in deep in

astic sc
ttering at HERA
June 20108D79559BD11BE7E1ED1BAC187BD5057AarXiv:1007.1945v2[hep-ex]
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 120 pb −1 .The h dronic decay channels D + → K 0 S π + , Λ + c → pK 0 S and Λ + c → Λπ + , and their charge conjugates, were reconstructed.The presence of a neutral strange hadron in the final state reduces the combinatorial background and extends the measured sen

tivity into the low
transverse momentum region.The kinematic range is 0GeV 2 and 0.02 < y < on of D + mesons are compared to next-to-leading-order QCD predictions.The fraction of c quarks hadronising into Λ + c baryons is extracted.

h now at Rockefeller Universit , New York, NY 10065, USA i now at DESY group FS-CFEL-1 j now at Institute of High Energy Physics, Beijing, China k now at DESY group FEB, Hamburg, Germany l also at Moscow State University, Russia m now at University of Liverpool, United Kingdom n on leave of absence at CERN, Geneva, Switzerland o now at CERN, Geneva, Switzerland p now at Goldman Sachs, London, UK q also at In titute of Theoretical and Experimental Physics, Moscow, Russia r also at INP, Cracow, Poland s also at FPACS, AGH-UST, Cracow, Poland t partially supported by Warsaw University, Poland u partially supported by Moscow State University, Russia v also affiliated with DESY, Germany w now at Japan Synchrotron Radiation Research Institute (JASRI), Hyogo, Japan x also at University of Tokyo, Japan y now at Kobe University, Japan z supported by DESY, Germany † deceased aa STFC Advanced Fellow ab nee Korcsak-Gorzo ac This material was based on work supported by the National Science Foundation, while working at the Foundation.ad also

Max Planck Institute, Munich, Germany, Alexander
von Humboldt Research Award ae now at Nihon Institute of Medical Science, Japan af now at SunMelx Co. Ltd., Tokyo, Japan ag now at Osaka Univ rsity, Osaka, Japan ah now at University of Bonn, Germany ai also at Lódź University, Poland aj member of L Introduction

Heavy-quark production in ep interactions in deep inelastic scattering (DIS) is dominated by the Boson Gluon Fusion (BGF) process.Heavy-quark production provides a two-fold test of perturbative quantum chromodynamics (pQCD); a study of the BGF process and the higher-order corrections to it, and an independent check of the validity of the gluon density in the proton extracted from the inclusive DIS data.Of the tw is strongly suppressed due to its smaller electric charge and larger mass.

The production of charm via the identification of D and D * mesons in DIS has been extensively studied at HERA in the kinematic range 1 < Q 2 < 1000 GeV 2 , p T (D, D * ) > 1.5 GeV [1][2][3][4][5][6][7][8], where Q 2 is th ron vertex and p T is the transverse momentum.The results are co by the ZEUS collaboration in the photoproduction regime [9].The obtained fragmentation fraction is larger than but consistent within uncertainties with the average from e + e − collisions [10].

In this paper, a charm quark in the final state was identified by the presence of a charmed hadron.The π + .These decay channels were chosen since the presence of a neutral strange hadron in the final state significantly reduces the combinatorial background.Measurements of D + and Λ + c cross sections provide information ab studies, in this analysis the kinematic region of the measurement is extended to very low transverse momenta of the produced charmed hadrons.No explicit cut on the transverse m

enta of the
econstructed charmed hadrons was applied.This is particularly relevant at low Q 2 , where charm quarks are predominantly produced with low transverse momentum.In addition, Λ + c production was studied for the first time at HERA in DIS.From a comparison of the D + and Λ + c cross sections, the fragmentation fraction f (c → Λ + c ) is extracted.


Experimental set-up

The analysis was performed with data taken from 1996 to 2000 corresponding to a luminosity of 120.4 ± 2.4 pb −1 .The sample consists of 38.6 pb −1 of e + p data collected at a 1 The charge conjugated modes are implied throughout this paper.

centre-of-mass energy of 300 GeV and of 65.1 pb −1 collected at 318 GeV, plus 16.7 pb −1 of e − p data collected at 318 GeV. 2 detailed description of the ZEUS detector can

found else
here [11].A brief outline of the components most relevant for this analysis is given below.

Charged particles were tracked in the central tracking detector (CTD) [12], which operated in a magnetic field of 1.43 T provided by a thin superconducting coil.The CTD consisted of 72 cylindrical drift chamber layers, organised in 9 superlayers covering the polar-angle3 region 15 • < θ < 164 • .The transverse-momentum resolution for full-length tracks was σ(p T )/p T = 0.0058p T ⊕ 0.0065 ⊕ 0.0014 rated hits.The measured dE/dx values were corrected by normalising to the measured average dE/dx for tracks around the region of minimum ionisation for pions with momentum p satisfying 0.3 < p < 0.4 GeV.Henceforth, dE/dx is quoted in units of minimum ionising particles (mips).

The high-resolution uranium-scintillator calorimeter (CAL) [14] consisted of three parts: the forward (FCAL), the barrel (BCAL) and the rear (RCAL) calorimeters.Each part was subdivided transversely into towers and longitudinally into one electromagnetic section (EMC) and either one (in RCAL) or two (in BCAL and FCAL) hadronic sections (HAC).The smallest subdivision of the calorimeter is called a cell.The CAL energy resolutions, as measured under test-beam conditions, are σ(E)/E = 0.18/ √ E for electrons and σ(E)/E = 0.35/ √ E for hadrons, with E in GeV.

The position of the scattered electron at the CAL was deter