Search for contact interactions, large extra dimensions and finite quark radius in ep collisions at HERA
 S. Chekanov
 M. Derrick
 D. Krakauer
 J.H. Loizides
 S. Magill
 S. Miglioranzi
 B. Musgrave
 J. Repond
 R. Yoshida
 M.C.K. Mattingly
 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
 A. Montanari
 R. Nania
 F. Palmonari
 A. Pesci
 G. Sartorelli
 A. Zichichi
 G. Aghuzumtsyan
 D. Bartsch
 I. Brock
 S. Goers
 H. Hartmann
 E. Hilger
 P. Irrgang
 H.P. Jakob
 O. Kind
 U. Meyer
 E. Paul
 J. Rautenberg
 R. Renner
 A. Stifutkin
 J. Tandler
 K.C. Voss
 M. Wang
 A. Weber
 D.S. Bailey
 N.H. Brook
 J.E. Cole
 G.P. Heath
 T. Namsoo
 S. Robins
 M. Wing
 M. Capua
 A. Mastroberardino
 M. Schioppa
 G. Susinno

 J.Y. Kim
 Y.K. Kim
 J.H. Lee
 I.T. Lim
 M.Y. Pac

 A. Caldwell
 M. Helbich

 X. Liu
 B. Mellado
 Y. Ning
 S. Paganis
 Z. Ren
 W.B. Schmidke
 F. Sciulli
 J. Chwastowski
 A. Eskreys
 J. Figiel
 A. Galas
 K. Olkiewicz
 P. Stopa
 L. Zawiejski
 L. Adamczyk
 T. Bołd
 I. GrabowskaBołd
 D. Kisielewska
 A.M. Kowal
 M. Kowal
 T. Kowalski
 M. Przybycień
 L. Suszycki
 D. Szuba
 J. Szuba
 A. Kotański
 W. Słomiński
 V. Adler
 U. Behrens
 I. Bloch
 K. Borras
 V. Chiochia
 D. Dannheim
 G. Drews
 J. Fourletova
 U. Fricke
 A. Geiser
 P. Göttlicher
 O. Gutsche
 T. Haas
 W. Hain
 S. Hillert
 B. Kahle
 U. Kötz
 H. Kowalski
 G. Kramberger
 H. Labes
 D. Lelas
 H. Lim
 B. Löhr
 R. Mankel
 I.A. MelzerPellmann
 C.N. Nguyen
 D. Notz
 A.E. NuncioQuiroz
 A. Polini
 A. Raval
 L. Rurua
 U. Schneekloth
 U. Stösslein
 R. Wichmann
 G. Wolf
 C. Youngman
 W. Zeuner
 S. Schlenstedt
 G. Barbagli
 E. Gallo
 C. Genta
 P.G. Pelfer
 A. Bamberger
 A. Benen
 F. Karstens
 D. Dobur
 N.N. Vlasov
 M. Bell
 P.J. Bussey
 A.T. Doyle
 J. Ferrando
 J. Hamilton
 S. Hanlon
 D.H. Saxon
 I.O. Skillicorn
 I. Gialas
 T. Carli
 T. Gosau
 U. Holm
 N. Krumnack
 E. Lohrmann
 M. Milite
 H. Salehi
 P. Schleper
 S. Stonjek
 K. Wichmann
 K. Wick
 A. Ziegler
 Ar. Ziegler
 C. CollinsTooth
 C. Foudas
 R. Gonçalo
 K.R. Long
 A.D. Tapper
 P. Cloth
 D. Filges
 M. Kataoka
 K. Nagano
 K. Tokushuku
 S. Yamada
 Y. Yamazaki
 A.N. Barakbaev
 E.G. Boos
 N.S. Pokrovskiy
 B.O. Zhautykov
 D. Son
 K. Piotrzkowski
 F. Barreiro
 C. Glasman
 O. González
 L. Labarga
 J. del Peso
 E. Tassi
 J. Terrón
 M. Vázquez
 M. Zambrana
 M. Barbi
 F. Corriveau
 S. Gliga

 J. Lainesse
 S. Padhi
 D.G. Stairs
 R. Walsh
 T. Tsurugai
 A. Antonov
 P. Danilov
 B.A. Dolgoshein
 D. Gladkov
 V. Sosnovtsev
 S. Suchkov
 R.K. Dementiev
 P.F. Ermolov
 Yu.A. Golubkov
 I.I. Katkov
 L.A. Khein
 I.A. Korzhavina
 V.A. Kuzmin
 B.B. Levchenko
 O.Yu. Lukina
 A.S. Proskuryakov
 L.M. Shcheglova
 S.A. Zotkin
 N. Coppola
 S. Grijpink
 E. Koffeman
 P. Kooijman
 E. Maddox
 A. Pellegrino
 S. Schagen
 H. Tiecke
 J.J. Velthuis
 L. Wiggers
 E. de Wolf

 N. Brümmer
 B. Bylsma
 L.S. Durkin
 T.Y. Ling
 A.M. CooperSarkar
 A. Cottrell
 R.C.E. Devenish
 B. Foster
 G. Grzelak
 C. Gwenlan
 S. Patel
 P.B. Straub
 R. Walczak
 A. Bertolin
 R. Brugnera
 R. Carlin
 F. Dal Corso
 S. Dusini
 A. Garfagnini
 S. Limentani
 A. Longhin
 A. Parenti
 M. Posocco
 L. Stanco
 M. Turcato
 E.A. Heaphy
 F. Metlica
 B.Y. Oh
 J.J. Whitmore
 Y. Iga
 G. D'Agostini
 G. Marini
 A. Nigro
 C. Cormack
 J.C. Hart
 N.A. McCubbin
 C. Heusch
 I.H. Park
 N. Pavel
 H. Abramowicz
 A. Gabareen
 S. Kananov
 A. Kreisel
 A. Levy
 M. Kuze
 T. Fusayasu
 S. Kagawa
 T. Kohno
 T. Tawara
 T. Yamashita
 R. Hamatsu
 T. Hirose
 M. Inuzuka
 H. Kaji
 S. Kitamura
 K. Matsuzawa
 M.I. Ferrero
 V. Monaco
 R. Sacchi
 A. Solano
 M. Arneodo
 M. Ruspa
 T. Koop
 J.F. Martin
 A. Mirea
 J.M. Butterworth
 R. HallWilton
 T.W. Jones
 M.S. Lightwood
 M.R. Sutton
 C. TargettAdams
 J. Ciborowski
 R. Ciesielski
 P. Łużniak
 R.J. Nowak
 J.M. Pawlak
 J. Sztuk
 T. Tymieniecka
 A. Ukleja
 J. Ukleja
 A.F. Żarnecki
 M. Adamus
 P. Plucinski
 Y. Eisenberg
 L.K. Gladilin
 D. Hochman
 U. Karshon
 M. Riveline
 D. Kçira
 S. Lammers
 L. Li
 D.D. Reeder
 M. Rosin
 A.A. Savin
 W.H. Smith
 A. Deshpande
 S. Dhawan
 S. Bhadra
 C.D. Catterall
 S. Fourletov
 G. Hartner
 S. Menary
 M. Soares
 J. Standage
ABSTRACT A search for physics beyond the Standard Model has been performed with highQ2 neutral current deep inelastic scattering events recorded with the ZEUS detector at HERA. Two data sets, e+p→e+X and e−p→e−X, with respective integrated luminosities of 112 pb−1 and 16 pb−1, were analyzed. The data reach Q2 values as high as 40 000 GeV2. No significant deviations from Standard Model predictions were observed. Limits were derived on the effective mass scale in eeqq contact interactions, the ratio of leptoquark mass to the Yukawa coupling for heavy leptoquark models and the mass scale parameter in models with large extra dimensions. The limit on the quark charge radius, in the classical form factor approximation, is 0.85×10−16 cm.
 Wang D, Pan K, Subedi R, Deng X, Ahmed Z, Allada K, Aniol KA, Armstrong DS, Arrington J, Bellini V, [......], Suleiman R, Sulkosky V, Sutera CM, Tobias WA, Urciuoli GM, Waidyawansa B, Wojtsekhowski B, Ye L, Zhao B, Zheng X[Show abstract] [Hide abstract]
ABSTRACT: Symmetry permeates nature and is fundamental to all laws of physics. One example is parity (mirror) symmetry, which implies that flipping left and right does not change the laws of physics. Laws for electromagnetism, gravity and the subatomic strong force respect parity symmetry, but the subatomic weak force does not. Historically, parity violation in electron scattering has been important in establishing (and now testing) the standard model of particle physics. One particular set of quantities accessible through measurements of parityviolating electron scattering are the effective weak couplings C2q, sensitive to the quarks' chirality preference when participating in the weak force, which have been measured directly only once in the past 40 years. Here we report a measurement of the parityviolating asymmetry in electronquark scattering, which yields a determination of 2C2u  C2d (where u and d denote up and down quarks, respectively) with a precision increased by a factor of five relative to the earlier result. These results provide evidence with greater than 95 per cent confidence that the C2q couplings are nonzero, as predicted by the electroweak theory. They lead to constraints on new parityviolating interactions beyond the standard model, particularly those due to quark chirality. Whereas contemporary particle physics research is focused on highenergy colliders such as the Large Hadron Collider, our results provide specific chirality information on electroweak theory that is difficult to obtain at high energies. Our measurement is relatively free of ambiguity in its interpretation, and opens the door to even more precise measurements in the future.Nature 02/2014; · 42.35 Impact Factor  SourceAvailable from: Riccardo C. Storti
Conference Paper: The Natural Philosophy of Fundamental Particles
[Show abstract] [Hide abstract]
ABSTRACT: Theoretical estimates and correlations, based upon the ElectroGraviMagnetics (EGM) Photon radiation method, are presented for the RootMeanSquare (RMS) charge radius and massenergy of many well established subatomic particles. The EGM method is a set of engineering equations and techniques derived from the purely mathematical construct known as Buckingham's "Π" (Pi) Theory. The estimates and correlations coincide to astonishing precision with experimental data presented by the Particle Data Group (PDG), CDF, D0, L3, SELEX and ZEUS Collaborations. Our tabulated results clearly demonstrate a possible natural harmonic pattern representing all fundamental subatomic particles. In addition, our method predicts the possible existence of several other subatomic particles not contained within the Standard Model (SM). The accuracy and simplicity of our computational estimates demonstrate that EGM is a useful tool to gain insight into the domain of subatomic particles.Proc. SPIE 6664, The Nature of Light: What Are Photons?, 66640J (August 31, 2007);, San Diego, California, USA; 08/2007  SourceAvailable from: arxiv.org[Show abstract] [Hide abstract]
ABSTRACT: Recent results for direct searches for physics beyond the Standard Model are reviewed. The results include Tevatron II data up to 1.2 fb1 and HERA results up to 350 pb1. Searches for Supersymmetry, for compositeness and for large extra dimensions are presented. The excess of events with an isolated lepton and high missing transverse momentum at HERA is discussed.International Journal of Modern Physics A 01/2012; 22(30). · 1.09 Impact Factor
Page 1
arXiv:hepex/0401009v2 2 Apr 2004
DESY–03–218
December 2003
Search for contact interactions, large extra
dimensions and finite quark radius in ep
collisions at HERA
ZEUS Collaboration
Abstract
A search for physics beyond the Standard Model has been performed with high
Q2neutral current deep inelastic scattering events recorded with the ZEUS de
tector at HERA. Two data sets, e+p → e+X and e−p → e−X, with respective
integrated luminosities of 112pb−1and 16pb−1, were analyzed. The data reach
Q2values as high as 40000GeV2. No significant deviations from Standard Model
predictions were observed. Limits were derived on the effective mass scale in
eeqq contact interactions, the ratio of leptoquark mass to the Yukawa coupling
for heavy leptoquark models and the mass scale parameter in models with large
extra dimensions. The limit on the quark charge radius, in the classical form
factor approximation, is 0.85 · 10−16cm.
Page 2
The ZEUS Collaboration
S. Chekanov, M. Derrick, D. Krakauer, J.H. Loizides1, S. Magill, S. Miglioranzi1, B. Mus
grave, J. Repond, R. Yoshida
Argonne National Laboratory, Argonne, Illinois 604394815, USAn
M.C.K. Mattingly
Andrews University, Berrien Springs, Michigan 491040380, USA
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, A. Montanari, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli,
A. Zichichi
University and INFN Bologna, Bologna, Italye
G. Aghuzumtsyan, D. Bartsch, I. Brock, S. Goers, H. Hartmann, E. Hilger, P. Irrgang, H.
P. Jakob, O. Kind, U. Meyer, E. Paul2, J. Rautenberg, R. Renner, A. Stifutkin, J. Tandler,
K.C. Voss, M. Wang, A. Weber3
Physikalisches Institut der Universit¨ at Bonn, Bonn, Germanyb
D.S. Bailey4, N.H. Brook, J.E. Cole, G.P. Heath, T. Namsoo, S. Robins, M. Wing
H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdomm
M. Capua, A. Mastroberardino, M. Schioppa, G. Susinno
Calabria University, Physics Department and INFN, Cosenza, Italye
J.Y. Kim, Y.K. Kim, J.H. Lee, I.T. Lim, M.Y. Pac5
Chonnam National University, Kwangju, Koreag
A. Caldwell6, 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 10027o
J. Chwastowski, A. Eskreys, J. Figiel, A. Galas, K. Olkiewicz, P. Stopa, L. Zawiejski
Institute of Nuclear Physics, Cracow, Polandi
L. Adamczyk, T. Bo? ld, I. GrabowskaBo? ld7, D. Kisielewska, A.M. Kowal, M. Kowal,
T. Kowalski, M. Przybycie´ n, L. Suszycki, D. Szuba, J. Szuba8
Faculty of Physics and Nuclear Techniques, AGHUniversity of Science and Technology,
Cracow, Polandp
A. Kota´ nski9, W. S? lomi´ nski
Department of Physics, Jagellonian University, Cracow, Poland
I
Page 3
V. Adler, U. Behrens, I. Bloch, K. Borras, V. Chiochia, D. Dannheim, G. Drews, J. Fourletova,
U. Fricke, A. Geiser, P. G¨ ottlicher10, O. Gutsche, T. Haas, W. Hain, S. Hillert11, B. Kahle,
U. K¨ otz, H. Kowalski12, G. Kramberger, H. Labes, D. Lelas, H. Lim, B. L¨ ohr, R. Mankel,
I.A. MelzerPellmann, C.N. Nguyen, D. Notz, A.E. NuncioQuiroz, A. Polini, A. Raval,
L. Rurua, U. Schneekloth, U. St¨ osslein, R. Wichmann13, G. Wolf, C. Youngman, W. Zeuner
Deutsches ElektronenSynchrotron DESY, Hamburg, Germany
S. Schlenstedt
DESY Zeuthen, Zeuthen, Germany
G. Barbagli, E. Gallo, C. Genta, P. G. Pelfer
University and INFN, Florence, Italye
A. Bamberger, A. Benen, F. Karstens, D. Dobur, N.N. Vlasov
Fakult¨ at f¨ ur Physik der Universit¨ at Freiburg i.Br., Freiburg i.Br., Germanyb
M. Bell, P.J. Bussey, A.T. Doyle, J. Ferrando, J. Hamilton, S. Hanlon, D.H. Saxon,
I.O. Skillicorn
Department of Physics and Astronomy, University of Glasgow, Glasgow, United King
domm
I. Gialas
Department of Engineering in Management and Finance, Univ. of Aegean, Greece
T. Carli, T. Gosau, U. Holm, N. Krumnack, E. Lohrmann, M. Milite, H. Salehi, P. Schleper,
S. Stonjek11, K. Wichmann, K. Wick, A. Ziegler, Ar. Ziegler
Hamburg University, Institute of Exp. Physics, Hamburg, Germanyb
C. CollinsTooth, C. Foudas, R. Gon¸ calo14, K.R. Long, A.D. Tapper
Imperial College London, High Energy Nuclear Physics Group, London, United King
domm
P. Cloth, D. Filges
Forschungszentrum J¨ ulich, Institut f¨ ur Kernphysik, J¨ ulich, Germany
M. Kataoka15, K. Nagano, K. Tokushuku16, S. Yamada, Y. Yamazaki
Institute of Particle and Nuclear Studies, KEK, Tsukuba, Japanf
A.N. Barakbaev, E.G. Boos, N.S. Pokrovskiy, B.O. Zhautykov
Institute of Physics and Technology of Ministry of Education and Science of Kazakhstan,
Almaty, Kazakhstan
D. Son
Kyungpook National University, Center for High Energy Physics, Daegu, South Koreag
II
Page 4
K. Piotrzkowski
Institut de Physique Nucl´ eaire, Universit´ e Catholique de Louvain, LouvainlaNeuve, Bel
gium
F. Barreiro, C. Glasman17, O. Gonz´ alez, L. Labarga, J. del Peso, E. Tassi, J. Terr´ on,
M. V´ azquez, M. Zambrana
Departamento de F´ ısica Te´ orica, Universidad Aut´ onoma de Madrid, Madrid, Spainl
M. Barbi, F. Corriveau, S. Gliga, J. Lainesse, S. Padhi, D.G. Stairs, R. Walsh
Department of Physics, McGill University, Montr´ eal, Qu´ ebec, Canada H3A 2T8a
T. Tsurugai
Meiji Gakuin University, Faculty of General Education, Yokohama, Japanf
A. Antonov, P. Danilov, B.A. Dolgoshein, D. Gladkov, V. Sosnovtsev, S. Suchkov
Moscow Engineering Physics Institute, Moscow, Russiaj
R.K. Dementiev, P.F. Ermolov, Yu.A. Golubkov18, I.I. Katkov, L.A. Khein, I.A. Korzhav
ina, V.A. Kuzmin, B.B. Levchenko19, O.Yu. Lukina, A.S. Proskuryakov, L.M. Shcheglova,
S.A. Zotkin
Moscow State University, Institute of Nuclear Physics, Moscow, Russiak
N. Coppola, S. Grijpink, E. Koffeman, P. Kooijman, E. Maddox, A. Pellegrino, S. Schagen,
H. Tiecke, J.J. Velthuis, L. Wiggers, E. de Wolf
NIKHEF and University of Amsterdam, Amsterdam, Netherlandsh
N. Br¨ ummer, B. Bylsma, L.S. Durkin, T.Y. Ling
Physics Department, Ohio State University, Columbus, Ohio 43210n
A.M. CooperSarkar, A. Cottrell, R.C.E. Devenish, B. Foster, G. Grzelak, C. Gwenlan20,
S. Patel, P.B. Straub, R. Walczak
Department of Physics, University of Oxford, Oxford United Kingdomm
A. Bertolin, R. Brugnera, R. Carlin, F. Dal Corso, S. Dusini, A. Garfagnini, S. Limentani,
A. Longhin, A. Parenti, M. Posocco, L. Stanco, M. Turcato
Dipartimento di Fisica dell’ Universit` a and INFN, Padova, Italye
E.A. Heaphy, F. Metlica, B.Y. Oh, J.J. Whitmore21
Department of Physics, Pennsylvania State University, University Park, Pennsylvania
16802o
Y. Iga
Polytechnic University, Sagamihara, Japanf
G. D’Agostini, G. Marini, A. Nigro
Dipartimento di Fisica, Universit` a ’La Sapienza’ and INFN, Rome, Italye
III
Page 5
C. Cormack22, J.C. Hart, N.A. McCubbin
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, United Kingdomm
C. Heusch
University of California, Santa Cruz, California 95064, USAn
I.H. Park
Department of Physics, Ewha Womans University, Seoul, Korea
N. Pavel
Fachbereich Physik der Universit¨ atGesamthochschule Siegen, Germany
H. Abramowicz, A. Gabareen, S. Kananov, A. Kreisel, A. Levy
Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics, TelAviv
University, TelAviv, Israeld
M. Kuze
Department of Physics, Tokyo Institute of Technology, Tokyo, Japanf
T. Fusayasu, S. Kagawa, T. Kohno, T. Tawara, T. Yamashita
Department of Physics, University of Tokyo, Tokyo, Japanf
R. Hamatsu, T. Hirose2, M. Inuzuka, H. Kaji, S. Kitamura23, K. Matsuzawa
Tokyo Metropolitan University, Department of Physics, Tokyo, Japanf
M.I. Ferrero, V. Monaco, R. Sacchi, A. Solano
Universit` a di Torino and INFN, Torino, Italye
M. Arneodo, M. Ruspa
Universit` a del Piemonte Orientale, Novara, and INFN, Torino, Italye
T. Koop, J.F. Martin, A. Mirea
Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7a
J.M. Butterworth24, R. HallWilton, T.W. Jones, M.S. Lightwood, M.R. Sutton4, C. Targett
Adams
Physics and Astronomy Department, University College London, London, United King
domm
J. Ciborowski25, R. Ciesielski26, P. ? Lu˙ zniak27, R.J. Nowak, J.M. Pawlak, J. Sztuk28,
T. Tymieniecka29, A. Ukleja29, J. Ukleja30, A.F.˙Zarnecki
Warsaw University, Institute of Experimental Physics, Warsaw, Polandq
M. Adamus, P. Plucinski
Institute for Nuclear Studies, Warsaw, Polandq
Y. Eisenberg, L.K. Gladilin31, D. Hochman, U. Karshon M. Riveline
Department of Particle Physics, Weizmann Institute, Rehovot, Israelc
IV
Page 6
D. K¸ cira, S. Lammers, L. Li, D.D. Reeder, M. Rosin, A.A. Savin, W.H. Smith
Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USAn
A. Deshpande, S. Dhawan
Department of Physics, Yale University, New Haven, Connecticut 065208121, USAn
S. Bhadra, C.D. Catterall, S. Fourletov, G. Hartner, S. Menary, M. Soares, J. Standage
Department of Physics, York University, Ontario, Canada M3J 1P3a
V
Page 7
1also affiliated with University College London, London, UK
2retired
3selfemployed
4PPARC Advanced fellow
5now at Dongshin University, Naju, Korea
6now at MaxPlanckInstitut f¨ ur Physik, M¨ unchen,Germany
7partly supported by Polish Ministry of Scientific Research and Information Technology,
grant no. 2P03B 122 25
8partly supp. by the Israel Sci. Found. and Min. of Sci., and Polish Min. of Scient.
Res. and Inform. Techn., grant no.2P03B12625
9supported by the Polish State Committee for Scientific Research, grant no. 2 P03B
09322
10now at DESY group FEB
11now at Univ. of Oxford, Oxford/UK
12on leave of absence at Columbia Univ., Nevis Labs., N.Y., US A
13now at DESY group MPY
14now at Royal Holoway University of London, London, UK
15also at Nara Women’s University, Nara, Japan
16also at University of Tokyo, Tokyo, Japan
17Ram´ on y Cajal Fellow
18now at HERAB
19partly supported by the Russian Foundation for Basic Research, grant 020281023
20PPARC Postdoctoral Research Fellow
21on leave of absence at The National Science Foundation, Arlington, VA, USA
22now at Univ. of London, Queen Mary College, London, UK
23present address: Tokyo Metropolitan University of Health Sciences, Tokyo 1168551,
Japan
24also at University of Hamburg, Alexander von Humboldt Fellow
25also at ? L´ od´ z University, Poland
26supported by the Polish State Committee for Scientific Research, grant no. 2 P03B
07222
27? L´ od´ z University, Poland
28? L´ od´ z University, Poland, supported by the KBN grant 2P03B12925
29supported by German Federal Ministry for Education and Research (BMBF), POL
01/043
30supported by the KBN grant 2P03B12725
31on leave from MSU, partly supported by University of Wisconsin via the U.S.Israel BSF
VI
Page 8
a
supported by the Natural Sciences and Engineering Research Council of
Canada (NSERC)
supported by the German Federal Ministry for Education and Research
(BMBF), under contract numbers HZ1GUA 2, HZ1GUB 0, HZ1PDA 5,
HZ1VFA 5
supported by the MINERVA Gesellschaft f¨ ur Forschung GmbH, the Israel
Science Foundation, the U.S.Israel Binational Science Foundation and the
Benozyio Center for High Energy Physics
supported by the GermanIsraeli Foundation and the Israel Science Foundation
supported by the Italian National Institute for Nuclear Physics (INFN)
supported by the Japanese Ministry of Education, Culture, Sports, Science
and Technology (MEXT) and its grants for Scientific Research
supported by the Korean Ministry of Education and Korea Science and Engi
neering Foundation
supported by the Netherlands Foundation for Research on Matter (FOM)
supported by the Polish State Committee for Scientific Research, grant no.
620/E77/SPB/DESY/P03/DZ 117/20032005
partially supported by the German Federal Ministry for Education and Re
search (BMBF)
partly supported by the Russian Ministry of Industry, Science and Technology
through its grant for Scientific Research on High Energy Physics
supported by the Spanish Ministry of Education and Science through funds
provided by CICYT
supported by the Particle Physics and Astronomy Research Council, UK
supported by the US Department of Energy
supported by the US National Science Foundation
supported by the Polish State Committee for Scientific Research, grant no.
112/E356/SPUB/DESY/P03/DZ 116/20032005,2 P03B 13922
supported by the Polish State Committee for Scientific Research, grant no.
115/E343/SPUBM/DESY/P03/DZ 121/20012002, 2 P03B 07022
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
VII
Page 9
1 Introduction
The HERA ep collider has extended the kinematic range of deep inelastic scattering
(DIS) measurements by two orders of magnitude in Q2, the negative square of the four
momentum transfer, compared to fixedtarget experiments. At values of Q2of about
4 × 104GeV2, the eq interaction, where q is a constituent quark of the proton, is probed
at distances of ∼ 10−16cm. Measurements in this domain allow searches for new physics
processes with characteristic mass scales in the TeV range. New interactions between e
and q involving mass scales above the centerofmass energy can modify the cross sec
tion at high Q2via virtual effects, resulting in observable deviations from the Standard
Model (SM) predictions. Many such interactions, such as processes mediated by heavy
leptoquarks, can be modelled as fourfermion contact interactions. The SM predictions
for ep scattering in the Q2domain of this study result from the evolution of accurate mea
surements of the proton structure functions made at lower Q2. In this paper, a common
method is applied to search for fourfermion interactions, for graviton exchange in models
with large extra dimensions, and for a finite charge radius of the quark.
In an analysis of 199497 e+p data [1], the ZEUS Collaboration set limits on the effective
mass scale for several parityconserving compositeness models. Results presented here
are based on approximately 130pb−1of e+p and e−p data collected by ZEUS in the years
19942000. Since this publication also includes the early ZEUS data, the results presented
here supersede those of the earlier publication [1].
2 Standard Model cross section
The differential SM cross section for neutral current (NC) ep scattering, e±p → e±X, can
be expressed in terms of the kinematic variables Q2, x and y, which are defined by the
fourmomenta of the incoming electron1(k), the incoming proton (P), and the scattered
electron (k′) as Q2= −q2= −(k − k′)2, x = Q2/(2q · P), and y = (q · P)/(k · P). For
unpolarized beams, the leadingorder electroweak cross sections can be expressed as
d2σNC(e±p)
dxdQ2
(x,Q2) =
2πα2
xQ4
??1 + (1 − y)2?FNC
2
∓?1 − (1 − y)2?xFNC
3
?
,(1)
where α is the electromagnetic coupling constant. The contribution of the longitudinal
structure function, FL(x,Q2), is negligible at high Q2and is not taken into account in
this analysis. At leading order (LO) in QCD, the structure functions FNC
2
and xFNC
3
are
1Unless otherwise specified, ‘electron’ refers to both positron and electron.
1
Page 10
given by
FNC
2
(x,Q2) =
?
?
q=u,d,s,c,b
Aq(Q2)
?xq(x,Q2) + xq(x,Q2)?
?xq(x,Q2) − xq(x,Q2)?
,
xFNC
3
(x,Q2) =
q=u,d,s,c,b
Bq(Q2)
,
where q(x,Q2) and q(x,Q2) are the parton densities for quarks and antiquarks. The
functions Aqand Bqare defined as
Aq(Q2) =1
2
?(VL
(VL
q)2+ (VR
q)2+ (AL
q)2+ (AR
q)2?
,
Bq(Q2) =
q)(AL
q) − (VR
q)(AR
q) ,
where the coefficient functions VL,R
q
and AL,R
q
are given by:
Vi
Ai
q= Qq− (ve± ae)vqχZ,
q=− (ve± ae)aqχZ,
vf= T3
f− 2sin2θWQf,
af= T3
f,
χZ=
1
4sin2θWcos2θW
Q2
Q2+ M2
Z
.
(2)
In Eq. (2), the superscript i denotes the left (L) or right (R) helicity projection of the
lepton field; the plus (minus) sign in the definitions of Vi
i = L(R). The coefficients vfand afare the SM vector and axialvector coupling constants
of an electron (f = e) or quark (f = q); Qfand T3
component of the weak isospin; MZand θW are the mass of the Z0and the electroweak
mixing angle, respectively.
qand Ai
qis appropriate for
fdenote the fermion charge and third
3Models for new physics
3.1General contact interactions
Fourfermion contact interactions (CI) represent an effective theory, which describes low
energy effects due to physics at much higher energy scales. Such models would describe
the effects of heavy leptoquarks, additional heavy weak bosons, and electron or quark
compositeness. The CI approach is not renormalizable and is only valid in the low
energy limit. As strong limits have already been placed on scalar and tensor contact
2
Page 11
interactions [2], only vector currents are considered here. They can be represented by
additional terms in the Standard Model Lagrangian, viz:
LCI
=
?
i,j=L,R
q=u,d,s,c,b
ηeq
ij(¯ eiγµei)(¯ qjγµqj) ,(3)
where the sum runs over electron and quark helicities and quark flavors. The couplings
ηeq
(Eq. (3)) results in the following modification of the functions Vi
ijdescribe the helicity and flavor structure of contact interactions. The CI Lagrangian
qand Ai
qof Eq. (2):
Vi
q= Qq− (ve± ae)vqχZ+Q2
− (ve± ae)aqχZ+Q2
2α(ηeq
iL+ ηeq
iR) ,
Ai
q=
2α(ηeq
iL− ηeq
iR) .
It was assumed that all uptype quarks have the same contactinteraction couplings, and
a similar assumption was made for downtype quarks2:
ηeu
ij
ηed
ij
= ηec
= ηes
ij
= ηet
= ηeb
ij,
ijij,
leading to eight independent couplings, ηeq
setting limits in an eightdimensional space, a set of representative scenarios was analyzed.
Each scenario is defined by a set of eight coefficients, ǫeq
±1 or zero, and the compositeness scale Λ. The couplings are then defined by
ij, with q = u,d. Due to the impracticality of
ij, each of which may take the values
ηeq
ij
= ǫeq
ij
4π
Λ2.
Note that models that differ in the overall sign of the coefficients ǫeq
of the interference with the SM.
ijare distinct because
In this paper, different chiral structures of CI are considered, as listed in Table 1. Models
listed in the lower part of the table were previously considered in the published analysis
of 199497 e+p data [1]. They fulfill the relation
ηeq
LL+ ηeq
LR− ηeq
RL− ηeq
RR
= 0 ,
which was imposed to conserve parity, and thereby complement strong limits from atomic
parity violation (APV) results [3,4]. Since a later APV analysis [5] indicated possible
2The results depend very weakly on this assumption since heavy quarks make only a very small con
tribution to highQ2cross sections. In most cases, the same massscale limits were obtained for CI
scenarios where only firstgeneration quarks are considered. The largest difference between the ob
tained massscale limits is about 2%.
3
Page 12
deviations from SM predictions, models that violate parity, listed in the upper part of
Table 1, have also been incorporated in the analysis. The reported 2.3σ deviation [5]
from the SM was later reduced to around 1σ, after reevaluation of some of the theoretical
corrections [6,7].
3.2Leptoquarks
Leptoquarks (LQ) appear in certain extensions of the SM that connect leptons and quarks;
they carry both lepton and baryon numbers and have spin 0 or 1. According to the general
classification proposed by Buchm¨ uller, R¨ uckl and Wyler [8], there are 14 possible LQ
states: seven scalar and seven vector3. In the limit of heavy LQs (MLQ≫√s), the effect
of s and tchannel LQ exchange is equivalent to a vectortype eeqq contact interaction4.
The effective contactinteraction couplings, ηeq
of the leptoquark Yukawa coupling, λLQ, to the leptoquark mass, MLQ:
ij, are proportional to the square of the ratio
ηeq
ij
= aeq
ij
?λLQ
MLQ
?2
,
where the coefficients aeq
for scalar leptoquarks. Only firstgeneration leptoquarks are considered in this analysis,
q = u,d. The coupling structure for different leptoquark species is shown in Table 2.
Leptoquark models SL
supersymmetric theories with broken Rparity.
ijdepend on the LQ species [11] and are twice as large for vector as
0and˜SL
1/2correspond to the squark states˜dRand ˜ uL, in minimal
3.3Large extra dimensions
ArkaniHamed, Dimopoulos and Dvali [12–14] have proposed a model to solve the hierar
chy problem, assuming that spacetime has 4 + n dimensions. Particles, including strong
and electroweak bosons, are confined to four dimensions, but gravity can propagate into
the extra dimensions. The extra n spatial dimensions are compactified with a radius R.
The Planck scale, MP ∼ 1019GeV, in 4 dimensions is an effective scale arising from the
fundamental Planck scale MDin D = 4 + n dimensions. The two scales are related by:
M2
P
∼ RnM2+n
D
.
For extra dimensions with R ∼ 1mm for n = 2, the scale MD can be of the order of
TeV. At high energies, the strengths of the gravitational and electroweak interactions can
3Leptoquark states are named according to the socalled Aachen notation [9].
4For the invariant mass range accessible at HERA,√s ∼ 300GeV, heavy LQ approximation is applicable
for MLQ> 400GeV. For ZEUS limits covering LQ masses below 400GeV see [10].
4
Page 13
then become comparable. After summing the effects of graviton excitations in the extra
dimensions, the gravitonexchange contribution to eq → eq scattering can be described
as a contact interaction with an effective coupling strength of [15,16]
ηG =
λ
M4
S
,
where MS is an ultraviolet cutoff scale, expected to be of the order of MD, and the
coupling λ is of order unity. Since the sign of λ is not known a priori, both values λ = ±1
are considered in this analysis. However, due to additional energyscale dependence,
reflecting the number of accessible graviton excitations, these contact interactions are not
equivalent to the vector contact interactions of Eq. (3). To describe the effects of graviton
exchange, terms arising from pure graviton exchange (G), gravitonphoton interference
(γG) and gravitonZ (ZG) interference have to be added to the SM eq → eq scattering
cross section [17]:
dσ(e±q → e±q)
dˆt
=
dσSM
dˆt
πλ2
32M8
+dσG
dˆt
+dσγG
dˆt
+dσZG
dˆt
,
dσG
dˆt
dσγG
dˆt
dσZG
dˆt
=
S
1
ˆ s2
αQq
ˆ s2
?32ˆ u4+ 64ˆ u3ˆt + 42ˆ u2ˆt2+ 10ˆ uˆt3+ˆt4?,
(2ˆ u +ˆt)3
ˆt
α
ˆ s2sin22θW
ˆt − M2
= ∓πλ
2M4
πλ
2M4
S
,
=
S
?
±vevq(2ˆ u +ˆt)3
Z
− aeaq
ˆt(6ˆ u2+ 6ˆ uˆt +ˆt2)
ˆt − M2
Z
?
,
where ˆ s,ˆt and ˆ u, withˆt = −Q2, are the Mandelstam variables, while the other coefficients
are given in Eq. (2). The corresponding cross sections for e±¯ q scattering are obtained by
changing the sign of Qqand vqparameters.
Graviton exchange also contributes to electrongluon scattering, eg → eg, which is not
present at leading order in the SM:
dσ(e±g → e±g)
dˆt
=
πλ2
2M8
S
ˆ u
ˆ s2
?2ˆ u3+ 4ˆ u2ˆt + 3ˆ uˆt2+ˆt3?.
For a given point in the (x,Q2) plane, the e±p cross section is then given by
d2σ(e±p → e±X)
dxdQ2
(x,Q2) = q(x,Q2)dσ(e±q)
dˆt
+ ¯ q(x,Q2)dσ(e±¯ q)
dˆt
+ g(x,Q2)dσ(e±g)
dˆt
,
where q(x,Q2), ¯ q(x,Q2) and g(x,Q2) are the quark, antiquark and gluon densities in the
proton, respectively.
5
Page 14
3.4Quark form factor
Quark substructure can be detected by measuring the spatial distribution of the quark
charge. If Q2≪ 1/R2
modified, approximately, to:
eand Q2≪ 1/R2
q, the SM predictions for the cross sections are
dσ
dQ2
=
dσSM
dQ2
?
1 −R2
e
6
Q2
?2?
1 −R2
q
6
Q2
?2
,
where Reand Rqare the rootmeansquare radii of the electroweak charge of the electron
and the quark, respectively.
4Data samples
The data used in this analysis were collected with the ZEUS detector at HERA and
correspond to an integrated luminosity of 48pb−1and 63pb−1for e+p collisions collected
in 199497 and 19992000 respectively, and 16pb−1for e−p collisions collected in 199899.
The 199497 data set was collected at√s = 300GeV and the 19982000 data sets were
taken with√s = 318GeV.
The analysis is based upon the final event samples used in previously published cross
section measurements [18–20]. Only events with Q2> 1000GeV2are considered. The
SM predictions were taken from the simulated event samples used in the cross section
measurements, where selection cuts and event reconstruction are identical to those ap
plied to the data. Neutral current DIS events were simulated using the Heracles [21]
program with Djangoh [22,23] for electroweak radiative corrections and higherorder
matrix elements, and the colordipole model of Ariadne [24] for the QCD cascade and
hadronization. The ZEUS detector was simulated using a program based on Geant
3.13 [25]. The details of the data selection and reconstruction, and the simulation used
can be found elsewhere [18–20].
The distributions of NC DIS events in Q2, measured separately for each of the three
data sets, are in good agreement with SM predictions calculated using the CTEQ5D
parameterization [26,27] of the parton distribution functions (PDFs) of the proton. The
CTEQ5D parameterization is based on a global QCD analysis of the data on high energy
leptonhadron and hadronhadron interactions, including highQ2H1 and ZEUS results
based on the 1994 e+p data. The ZEUS data used in the CTEQ analysis amount to less
than 3% of the sample considered in this analysis. In general, SM predictions in the Q2
range considered here are dominantly determined by fixedtarget data at Q2< 100GeV2
and x > 0.01 [28].
6
Page 15
5Analysis method
5.1Monte Carlo reweighting
The contact interactions analysis was based on a comparison of the measured Q2distri
butions with the predictions of the MC simulation. The effects of each CI scenario are
taken into account by reweighting each MC event of the type ep → eX with the weight
w =
d2σ
dxdQ2(SM+CI)
d2σ
dxdQ2(SM)
?????
true x,Q2
. (4)
The weight w was calculated as the ratio of the leadingorder5cross sections, Eq. (1),
evaluated at the true values of x and Q2as determined from the fourmomenta of the
exchanged boson and the incident particles. In simulated events where a photon with
energy Eγis radiated by the incoming electron (initialstate radiation), the electron energy
is reduced by Eγ. This approach guarantees that possible differences between the SM and
the CI model in eventselection efficiency and migration corrections are properly taken into
account. Under the assumption that the difference between the SM predictions and those
of the model including contact interactions is small, higherorder QCD and electroweak
corrections, including radiative corrections, are also accounted for.
5.2Limitsetting procedure
For each of the models of new physics described above, it is possible to characterize
the strength of the interaction by a single parameter: 4π/Λ2for contact interactions;
(λLQ/MLQ)2for leptoquarks; λ/M4
the quark form factor. In the following, this parameter is denoted by η. For contact inter
actions, models with large extra dimensions and the quark form factor model, scenarios
with positive and negative η values were considered separately.
Sfor models with large extra dimensions; and R2
qfor
For a given model, the likelihood was calculated as
L(η) =
?
i
e−µi(η)·µi(η)ni
ni!
,
where the product runs over all Q2bins, niis the number of events observed in Q2bin
i and µi(η) is the expected number of events in that bin for a coupling strength η. The
5Note that CIs constitute a nonrenormalizable effective theory for which higher orders are not well
defined.
7
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