Measurement of Inclusive Jet Cross Sections in <em>Z/γ*( -&gt; e⁺e⁻) + jets Production in <em>pp</em> Collisions at s√=1.96   TeV

Article

Reference

Measurement of Inclusive Jet Cross Sections in Z/γ*( -> e

e

) + jets Production in pp Collisions at s√=1.96   TeV

CDF Collaboration

CLARK, Allan Geoffrey (Collab.), et al.

Abstract

Inclusive jet cross sections in Z/γ∗ events, with Z/γ∗ decaying into an electron-positron pair, are measured as a function of jet transverse momentum and jet multiplicity in pp collisions at s√=1.96   TeV with the upgraded Collider Detector at Fermilab in run II, based on an integrated luminosity of 1.7   fb−1. The measurements cover the rapidity region |yjet|30  GeV/c.

Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.

CDF Collaboration, CLARK, Allan Geoffrey (Collab.), et al . Measurement of Inclusive Jet Cross Sections in Z/γ*( -> e

e

) + jets Production in pp Collisions at s√=1.96   TeV. Physical Review Letters, 2008, vol. 100, no. 10, p. 102001

DOI : 10.1103/PhysRevLett.100.102001

Available at:

http://archive-ouverte.unige.ch/unige:38509

Disclaimer: layout of this document may differ from the published version.

1 / 1

Measurement of Inclusive Jet Cross Sections in Z=

! e

e

jets Production in p p Collisions at

p s

1:96 TeV

T. Aaltonen,²³J. Adelman,¹³T. Akimoto,⁵⁴M. G. Albrow,¹⁷B. A´ lvarez Gonza´lez,¹¹S. Amerio,⁴²D. Amidei,³⁴ A. Anastassov,⁵¹A. Annovi,¹⁹J. Antos,¹⁴M. Aoki,²⁴G. Apollinari,¹⁷A. Apresyan,⁴⁷T. Arisawa,⁵⁶A. Artikov,¹⁵ W. Ashmanskas,¹⁷A. Attal,³A. Aurisano,⁵²F. Azfar,⁴¹P. Azzi-Bacchetta,⁴²P. Azzurri,⁴⁵N. Bacchetta,⁴²W. Badgett,¹⁷

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Y. Zheng,^8,rand S. Zucchelli⁵

(CDF Collaboration)

1Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China

2Argonne National Laboratory, Argonne, Illinois 60439, USA

3Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain

4Baylor University, Waco, Texas 76798, USA

5Istituto Nazionale di Fisica Nucleare, University of Bologna, I-40127 Bologna, Italy

6Brandeis University, Waltham, Massachusetts 02254, USA

7University of California, Davis, Davis, California 95616, USA

8University of California, Los Angeles, Los Angeles, California 90024, USA

9University of California, San Diego, La Jolla, California 92093, USA

10University of California, Santa Barbara, Santa Barbara, California 93106, USA

11Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain

12Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

13Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA

14Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia

15Joint Institute for Nuclear Research, RU-141980 Dubna, Russia

16Duke University, Durham, North Carolina 27708

17Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

18University of Florida, Gainesville, Florida 32611, USA

19Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy

20University of Geneva, CH-1211 Geneva 4, Switzerland

21Glasgow University, Glasgow G12 8QQ, United Kingdom

22Harvard University, Cambridge, Massachusetts 02138, USA

102001-2

23Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland

24University of Illinois, Urbana, Illinois 61801, USA

25The Johns Hopkins University, Baltimore, Maryland 21218, USA

26Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany

27Center for High Energy Physics: Kyungpook National University, Daegu 702-701, Korea;

Seoul National University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746, Korea;

Korea Institute of Science and Technology Information, Daejeon, 305-806, Korea;

Chonnam National University, Gwangju, 500-757, Korea

28Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

29University of Liverpool, Liverpool L69 7ZE, United Kingdom

30University College London, London WC1E 6BT, United Kingdom

31Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain

32Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

33Institute of Particle Physics: McGill University, Montre´al, Canada H3A 2T8;

and University of Toronto, Toronto, Canada M5S 1A7

34University of Michigan, Ann Arbor, Michigan 48109, USA

35Michigan State University, East Lansing, Michigan 48824, USA

36University of New Mexico, Albuquerque, New Mexico 87131, USA

37Northwestern University, Evanston, Illinois 60208, USA

38The Ohio State University, Columbus, Ohio 43210, USA

39Okayama University, Okayama 700-8530, Japan

40Osaka City University, Osaka 588, Japan

41University of Oxford, Oxford OX1 3RH, United Kingdom

42University of Padova, Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy

43LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France

44University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

45Istituto Nazionale di Fisica Nucleare Pisa, Universities of Pisa, Siena and Scuola Normale Superiore, I-56127 Pisa, Italy

46University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

47Purdue University, West Lafayette, Indiana 47907, USA

48University of Rochester, Rochester, New York 14627, USA

49The Rockefeller University, New York, New York 10021, USA

50Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, University of Rome ‘‘La Sapienza,’’ I-00185 Roma, Italy

51Rutgers University, Piscataway, New Jersey 08855, USA

52Texas A&M University, College Station, Texas 77843, USA

53Istituto Nazionale di Fisica Nucleare, University of Trieste/ Udine, Italy

54University of Tsukuba, Tsukuba, Ibaraki 305, Japan

55Tufts University, Medford, Massachusetts 02155, USA

56Waseda University, Tokyo 169, Japan

57Wayne State University, Detroit, Michigan 48201, USA

58University of Wisconsin, Madison, Wisconsin 53706, USA

59Yale University, New Haven, Connecticut 06520, USA (Received 23 November 2007; published 11 March 2008)

Inclusive jet cross sections in Z= events, with Z= decaying into an electron-positron pair, are measured as a function of jet transverse momentum and jet multiplicity inppcollisions atps

1:96 TeV with the upgraded Collider Detector at Fermilab in run II, based on an integrated luminosity of1:7 fb¹. The measurements cover the rapidity region jy^jetj<2:1 and the transverse momentum range p^jet_T >

30 GeV=c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.

DOI:10.1103/PhysRevLett.100.102001 PACS numbers: 13.85.t, 12.38.Qk, 13.87.a

The measurement of the inclusive production of colli- mated jets of hadrons in association with aZ= boson in pp collisions provides a stringent test of perturbative quantum chromodynamics (pQCD) [1], and is sensitive to the presence of new particles decaying into Z=

jets final states. At the leading order (LO) in pQCD, Z=jet events are driven by the processes gq!

Z=qand qq!Z=g, while higher orders con- tributions, including additional parton radiation, produce mutiple jets in the final state. Next-to-leading order (NLO) pQCD predictions [2] forZ=jets production are only available for jet multiplicities N_jet up to N_jet 2. The understanding of Z=jets final states from data is therefore crucial since they also constitute important irre-

ducible backgrounds in searches for new physics. Previous results [3] from run I at the Tevatron have been compared with LO plus parton shower Monte Carlo predictions af- fected by large scale uncertainties. This Letter reports new and more precise measurements of the inclusive jet cross sections in Z=!ee production using 1:7 fb¹ of data collected by the CDF experiment in run II. The data are compared to NLO pQCD predictions including non- perturbative contributions.

The CDF II detector is described in detail elsewhere [4].

The detector has a charged particle tracking system im- mersed in a 1.4 T magnetic field aligned coaxially with the beam line that provides tracking coverage in the pseudor- apidity [5] rangejj 2. Segmented sampling calorime- ters, arranged in a projective tower geometry, surround the tracking system and measure the energy of interacting particles for jj<3:6. The central electromagnetic and hadronic calorimeters cover the regionjj<1, while the end-wall hadronic calorimeter provides forward coverage out to jj<1:3. Forward electromagnetic and hadronic calorimeters cover the regions1:1<jj<3:6and1:3<

jj<3:6, respectively. The calorimeters are instrumented with finely segmented detectors to measure the shower profile at a longitudinal depth close to the location of a typical electromagnetic shower maximum. Cherenkov counters in the region3:7<jj<4:7measure the number of inelasticppcollisions to compute the luminosity [6].

Samples of simulated inclusive Z=!ee jets events are generated using the PYTHIA 6.216 [7]

Monte Carlo generator. CTEQ5L [8] parton distribution functions (PDFs) are used for the proton and antiproton.

ThePYTHIAsamples are created using a special tuned set of parameters, denoted asPYTHIA-TUNE A [9], that includes enhanced contributions from initial-state gluon radiation and secondary parton interactions between proton and antiproton beam remnants and provides an accurate de- scription of the measured jet shapes and energy flows in Z=!ee jets final states [10]. Monte Carlo samples for background processes are generated using

PYTHIA-TUNE A. The samples are passed through a full CDF detector simulation (based on GEANT3 [11] where the GFLASH [12] package is used to simulate the energy deposition in the calorimeters) and reconstructed and ana- lyzed with the same analysis chain as for the data.

Events are collected using a three-level trigger system [13]. At the first-level trigger, events are required to have a central electromagnetic calorimeter cluster (jj<1) with E_T [5] above 8 GeV and an associated track with p^track_T above8 GeV=c. Similarly, at the second-level (third-level) trigger, a central electromagnetic cluster with E_T >

16 GeV (E_T >18 GeV) and an associated track with p^track_T >8 GeV=c (p^track_T >9 GeV=c) are required. The events are then required to have two electrons [14] with E^e_T>25 GeV and a reconstructed invariant mass in the range66< M_ee<116 GeV=c² around theZboson mass.

The electron candidates are reconstructed using criteria described in [15]. In this study, one electron is required to be central (j^ej<1) and fulfill tight selection cuts, while the second electron is required to pass a looser selection and to be either central (CC final-state con- figuration) or forward with 1:2<j^ej<2:8 (CF final- state configuration). The trigger efficiencies for CC and CF configurations are 99:960:01% and 97:90:3%, respectively. The events are selected to have a recon- structed primary vertex with z position within 60 cm around the nominal interaction point, and at least one jet with corrected transverse momentum p^jet_T;cor>30 GeV=c (see below), rapidity [5] in the range jy^jet_calj<2:1, and R_ejet>0:7, where R_ejet denotes the distance (y space) between the jet and each of the two electrons in the final state. The final sample contains 6203, 650, 57, and 2 events with at least one, two, three, and four jets, respectively.

Jets are reconstructed in data and Monte Carlo simulated events using calorimeter towers with transverse momenta [16] above 0:1 GeV=c. The towers associated with the reconstructed electrons in the final state are excluded from the jet search. Jets are searched for using the midpoint algorithm [17] with cone radius R0:7and a merging/

splitting fraction of 0.75, starting from seed towers with transverse momenta above1 GeV=c. The same algorithm is applied to the final state particles in the Monte Carlo generated events, excludingZ=decay products, to define jets at the hadron level [18].

The rapidity and azimuthal angle of the jets, y^jet_cal and ^jet_cal, are well reconstructed in the calorimeter with a resolution better than 0.05 units in bothyand. The mea- sured jet transverse momentump^jet_T;calsystematically under- estimates that of the hadron-level jet. For p^jet_T;cal values about 30 GeV=c, the jet transverse momentum is under- estimated by about 30%. The systematic shift decreases with increasing p^jet_T;cal down to about 11% for p^jet_T;cal>

200 GeV=c. This is mainly attributed to the presence of inactive material and the noncompensating nature of the calorimeter [19]. An average correction, as a function of p^jet_T;calandy^jet_cal, is applied to the measuredp^jet_T;calto account for these effects [20]. The measured p^jet_T;cal also includes contributions from multipleppinteractions per crossing at high instantaneous luminosity. Multiple interactions are identified via the presence of additional primary vertices reconstructed from charged particles. For each jet,p^jet_T;calis corrected for this effect by removing a certain amount of transverse momentum, ^mi_pT 1:060:32 GeV=c, for each additional primary vertex in the event, as determined from data [20].

The main backgrounds to the Z=!ee jets sample arise from inclusive jets and Wjets events, and are estimated from the data. First, an inclusive jet data

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sample is employed to estimate the probabilityf_e^jetfor a jet to pass a given electron selection. The probabilities are parametrized as a function of p^jet_T;cal and are typically around 0.001 (0.02) for tight (loose) central electrons and 0.005 for forward electrons. Second, a sample of events in data with exactly one reconstructed tight central electron is selected. For each jet in the event, theE^e_T of a fake elec- tron is determined, and the invariant mass of the tight- central electron and jet final state is then computed.

Event-by-event, all electron-jet combinations that fulfill the E^e_T cuts and with an invariant mass within 66<

Mejet<116 GeV=c² are considered in the background calculation, where each combination is weighted by the corresponding f_e^jet value and divided by the number of accepted electron-jet combinations in the event. The total inclusive jets and Wjets background is then computed in each measured distribution. Other background con- tributions from tt, Z=!ee , WW, WZ, ZZ, and Z=! jets final states are estimated using Monte Carlo samples. The total background in in- clusiveZ=!ee jets production is about12%for N_jet 1, and increases up to about17%forN_jet 3.

Raw inclusive jet differential cross sections as a function ofp^jet_T;corare defined asd=dp^jet_T;corL¹ N_jet^cor=p^jet_T;cor, whereN^cor_jet denotes the total number of jets in a givenp^jet_T;cor bin,p^jet_T;cor is the size of the bin, andLis the luminosity.

N_jet^cor is corrected bin-by-bin for background contributions and trigger inefficiencies. The measured cross sections are then corrected for acceptance and smearing effects back to the hadron level usingPYTHIA-TUNE AMonte Carlo event samples, and a bin-by-bin unfolding procedure that also accounts for the efficiency of theZ=!eeselection criteria. The final results refer to hadron-level jets with p^jet_T >30 GeV=c and jy^jetj<2:1, in a limited and well- defined kinematic range for the Z= decay products:

E^e_T>25 GeV, j^e1j<1:0, j^e2j<1:0 or 1:2<j^e2j<

2:8,66< M_ee<116 GeV=c², andR_ejet>0:7. In order to avoid any bias on the correction factors due to the particular PDF set used, which translates into slightly different simulated p^jet_T;cal distributions, the PYTHIA-TUNE A Monte Carlo event sample is reweighted until it accu- rately follows the measured p^jet_T;cal spectra. The unfolding factorsUp^jet_T;cor ^d

dp^jet_T = ^d

dp^jet_T;corare computed separately for the different measurements and vary between 2.0 at low p^jet_T and 2.3 at highp^jet_T .

A detailed study of the systematic uncertainties was carried out [10]. A 1:5% uncertainty on the trigger efficiency translates into1:5%and0:06%uncertainties on the cross sections for CF and CC configurations, re- spectively. The uncertainty on thep^jet_T dependence of the electron identification efficiency introduces a5%uncer- tainty on both CC and CF results. The measured jet en-

ergies are varied by2% at lowp^jet_T;cal to 2:7%at high p^jet_T;cal to account for the uncertainties on the absolute energy scale in the calorimeter [20]; this introduces un- certainties on the final measurements which vary between 5% at low p^jet_T and12% at highp^jet_T . They^jet depen- dence of the average correction applied top^jet_T;calintroduces a 2% uncertainty on the measured cross sections, ap- proximately independent of p^jet_T . The uncertainty on ^mi_pT has a negligible effect on the measured cross sections. The uncertainty on the p^jet_T;cal dependence of fe^jet introduces a 15%uncertainty on the inclusive jets andWjets back- ground estimation, that translates into a less than 2%

uncertainty on the measured cross sections. A conservative 30%uncertainty on the normalization of the rest of the background contributions, as extracted from Monte Carlo samples, introduces a less than 1% effect on the final results. If the unfolding procedure is carried out using unweighted PYTHIA-TUNE A, the effect on the measured cross sections is less than1%. Positive and negative devia- tions with respect to the nominal cross section values are added separately in quadrature to define the total system- atic uncertainty. The final results are obtained from the combination of CC and CF measurements. Finally, a5:8%

uncertainty on the total luminosity [15] is included in the measured cross sections.

Figure1(a)shows the measured inclusive jet differential cross sections as a function ofp^jet_T inZ=!ee jets production, withN_jet 1andN_jet 2, compared to NLO pQCD predictions. The data are reported in Table I. The cross sections decrease by more than 3 orders of magnitude asp^jet_T increases from30 GeV=cup to about300 GeV=c.

The NLO pQCD predictions are computed using theMCFM

program [2] with CTEQ6.1M PDFs [21], with the renor- malization and factorization scales set to ² M_Z²p²_TZ, and using a midpoint algorithm with R 0:7 and R_sep1:3 [22] to reconstruct jets at the parton level. Values for R_sep between 1.0 and 2.0 change the theoretical prediction by less than 2%. A variation of by a factor of two (half ) reduces (increases) the theoretical predictions by10%to15%. The uncertainties on the NLO pQCD predictions due to the PDFs were computed using the Hessian method [23]. They vary from4%at lowp^jet_T to10%at highp^jet_T .

The theoretical predictions include parton-to-hadron correction factors C_hadN_jet; p^jet_T that approximately ac- count for nonperturbative contributions from the under- lying event and fragmentation into hadrons (see Table I).

In each measurement,C_hadis estimated using thePYTHIA- TUNE A Monte Carlo samples, as the ratio between the nominal p^jet_T distribution and the one obtained by turning off both the interactions between proton and antiproton remnants and the string fragmentation in the Monte Carlo

samples. The correction decreases as p^jet_T increases from about 1.2 (1.26) at p^jet_T of 30 GeV=c to 1.02 (1.01) for p^jet_T >200 GeV=c for N_jet 1 (N_jet 2), and is domi- nated by the underlying event contribution. In order to estimate the uncertainty onC_had,PYTHIAsamples are gen- erated with a different set of parameters, denoted asTUNE DW[24], that governs the underlying event activity and also describes the Z=!ee jets final states. The un- certainty onC_hadis about10%(17%) at lowp^jet_T and goes down to1%at highp^jet_T forN_jet 1(N_jet 2). The ratios between data and theory as a function ofp^jet_T are shown in Figs.1(b)and1(c). Good agreement is observed between the measured cross sections and the nominal theoretical predictions. A ² test, where the sources of systematic uncertainty on the data are considered independent but fully correlated across p^jet_T bins, and the uncertainty on

C_hadis also included, gives a²probability of99%(22%) forN_jet 1(N_jet 2).

Figure 2 shows the cross sections _Njet for Z=!ee jets events up to N_jet 3. The measured event cross sections are ₁ 7003 146stat⁴⁸³₄₇₀syst 406lum fb, ₂ 695 37stat⁵⁹₆₀syst 40lum fb, and ₃ 60 11stat⁸₈syst 3:5lum fb, for N_jet 1, N_jet 2, and N_jet 3, respectively. The data are compared to LO and NLO pQCD predictions. The parton-to-hadron non- perturbative corrections vary between 1.1 and 1.4 as N_jet increases. The LO pQCD predictions underestimate the measured cross sections by a factor about 1.4 approxi- mately independent of N_jet. For N_jet 1 and N_jet 2, this corresponds to ² probabilities of 0:07% and2:7%, respectively. Good agreement is observed between data and NLO pQCD predictions, with ² probabilities better than83%.

In summary, we report new results on inclusive jet production in Z=!ee events in pp collisions at TABLE I. Measured inclusive jet differential cross section in Z=!ee+jets production as a function ofp^jet_T withNjet

1andN_jet 2. The systematic uncertainties are fully correlated across p^jet_T bins. The parton-to-hadron correction factors C_hadp^jet_T; N_jetare applied to the pQCD predictions.

p^jet_T ^d

dp^jet_T stat syst lum Chad stat syst GeV=c fb=GeV=c parton!hadron

Z=!ee jets N_jet 1

30 – 35 413:313:3^30:4_31:324:0 1:2090:0100:134 35– 41 263:39:4^18:3_17:415:3 1:1460:0100:096 41– 47 178:37:5^12:0_11:610:3 1:1140:0110:077 47–54 128:55:9^8:7_8:47:5 1:0970:0120:066 54 – 62 80:54:3^5:5_6:04:7 1:0860:0130:059 62 –72 52:53:2^4:4_4:33:0 1:0780:0130:053 72 –83 34:22:4^2:5_2:82:0 1:0720:0150:049 83–110 16:01:1^1:5_1:30:9 1:0630:0120:043 110 –146 4:90:5^0:5_0:50:3 1:0510:0120:035 146 –195 1:10:2^0:1_0:10:06 1:0400:0080:027 195– 400 0:080:03^0:01_0:010:005 1:0210:0050:013

Z=!ee jets N_jet 2

30 – 38 52:93:5^5:3_4:63:1 1:2620:0220:217 38– 47 37:02:8^2:9_2:82:1 1:2070:0240:169 47–59 21:21:8^1:9_1:91:2 1:1640:0250:130 59 –79 10:51:0^0:9_1:00:6 1:1230:0240:093 79 –109 5:70:6^0:7_0:50:3 1:0870:0260:062 109 –179 0:880:15^0:09_0:100:05 1:0520:0200:030 179 – 300 0:150:04^0:02_0:020:009 1:0260:0100:008 [fb/(GeV/c)] jet T/dpσd

10-1

1 10 102

103

104

105

×20) 1 jet inclusive (

≥ -) + +e

→e γ*(

Z/

2 jets inclusive

≥ -) + +e

→e γ*(

Z/

(a)

CDF Data L = 1.7 fb-1 Systematic uncertainties NLO MCFM CTEQ6.1M Corrected to hadron level

sep=1.3 (Z), R 2 + pT 2 = MZ 2 µ0

0/2 µ µ = 0 ; µ µ = 2

PDF uncertainties

Data / Theory

0.7 0.8 0.9 1 1.1 1.2

1.3 Z/γ*(→e⁺e^-) + ≥1 jet inclusive

(b)

[GeV/c]

jet

pT

30 100 200

Data / Theory

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

2 jets inclusive

≥ -) + +e

→e γ*(

Z/

(c)

FIG. 1 (color online). (a) Measured inclusive jet differential cross section as a function of p^jet_T (black dots) in Z=! ee jets withN_jet 1;2compared to NLO pQCD predic- tions (open circles). For clarity, the measurement forN_jet 1is scaled up (20). The shaded bands show the total systematic uncertainty, except for the5:8%luminosity uncertainty. (b) and (c) Data/theory ratio as a function ofp^jet_T forN_jet 1andN_jet 2, respectively. The dashed and dotted lines indicate the PDF uncertainty and the variation with of the NLO pQCD pre- dictions, respectively.

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s

p 1:96 TeV for jets with p^jet_T >30 GeV=c and jy^jetj<2:1, based on 1:7 fb¹ of CDF run II data. The measured cross sections are well described by NLO pQCD predictions including nonperturbative corrections.

We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions.

This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Founda- tion; the A.P. Sloan Foundation; the Bundesministerium fu¨r Bildung und Forschung, Germany; the Korean Science and Engineering Foundation and the Korean Research Foundation; the Science and Technology Facilities Council and the Royal Society, UK; the Institut National de Physique Nucleaire et Physique des Particules/CNRS;

the Russian Foundation for Basic Research; the Comisio´n Interministerial de Ciencia y Tecnologı´a, Spain; the Euro- pean Community’s Human Potential Programme; the Slovak R&D Agency; and the Academy of Finland.

aIFIC(CSIC-Universitat de Valencia), 46071 Valencia, Spain.

bVisitor from Universidad Iberoamericana, Mexico D.F., Mexico.

cVisitor from Queen Mary, University of London, London, E1 4NS, England.

dVisitor from University de Oviedo, E-33007 Oviedo, Spain.

eVisitor from University Libre de Bruxelles, B-1050 Brussels, Belgium.

fVisitor from University of Athens, 15784 Athens, Greece.

gVisitor from University of Bristol, Bristol BS8 1TL, United Kingdom.

hVisitor from TX Tech University, Lubbock, TX 79409, USA.

iVisitor from University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.

jVisitor from University College Dublin, Dublin 4, Ireland.

kVisitor from University of Heidelberg, D-69120 Heidelberg, Germany.

lVisitor from University of CA Santa Cruz, Santa Cruz, CA 95064, USA.

mVisitor from University of Cyprus, Nicosia CY-1678, Cyprus.

nVisitor from Nagasaki Institute of Applied Science, Nagasaki, Japan.

oVisitor from University of CA Irvine, Irvine, CA 92697, USA.

pVisitor from Cornell University, Ithaca, NY 14853, USA.

qVisitor from University of Manchester, Manchester M13 9PL, England.

rVisitor from Chinese Academy of Sciences, Beijing 100864, China.

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) [fb] -e+ e→*γ BR(Z/× jetsNσ

102

103

104

105

(a)

CDF Data L = 1.7 fb-1 Systematic uncertainties NLO MCFM CTEQ6.1M corrected to hadron level

sep=1.3 (Z), R 2 + pT 2 = MZ 2 µ0

0/2 µ µ = 0 ; µ µ = 2 NLO scale NLO PDF uncertainties LO MCFM hadron level

jets

≥ N

1 2 3

Ratio to LO

1 1.2 1.4 1.6 1.8 (b)

FIG. 2 (color online). (a) Measured cross section for inclusive jet production in Z=!ee events as a function of N_jet compared to LO and NLO pQCD predictions. The shaded bands show the total systematic uncertainty, except for the 5:8%

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