$^{40}$Institute for High Energy Physics, Protvino, Russia $^{41}$Petersburg Nuclear Physics Institute, St. Petersburg, Russia $^{42}$Stockholm University, Stockholm, Sweden, and Uppsala University, Uppsala, Sweden $^{43}$Lancaster University, Lancaster, United Kingdom $^{44}$Imperial College London, London SW7 2AZ, United Kingdom $^{45}$The University of Manchester, Manchester M13 9PL, United Kingdom $^{46}$University of Arizona, Tucson, Arizona 85721, USA $^{47}$University of California, Riverside, California 92521, USA $^{48}$Florida State University, Tallahassee, Florida 32306, USA $^{49}$Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA $^{50}$University of Illinois at Chicago, Chicago, Illinois 60607, USA $^{51}$Northern Illinois University, DeKalb, Illinois 60115, USA $^{52}$Northwestern University, Evanston, Illinois 60208, USA $^{53}$Indiana University, Bloomington, Indiana 47405, USA $^{54}$Purdue University Calumet, Hammond, Indiana 46323, USA $^{55}$University of Notre Dame, Notre Dame, Indiana 46556, USA $^{56}$Iowa State University, Ames, Iowa 50011, USA $^{57}$University of Kansas, Lawrence, Kansas 66045, USA $^{58}$Kansas State University, Manhattan, Kansas 66506, USA $^{59}$Louisiana Tech University, Ruston, Louisiana 71272, USA $^{60}$University of Maryland, College Park, Maryland 20742, USA $^{61}$Boston University, Boston, Massachusetts 02215, USA $^{62}$Northeastern University, Boston, Massachusetts 02115, USA $^{63}$University of Michigan, Ann Arbor, Michigan 48109, USA $^{64}$Michigan State University, East Lansing, Michigan 48824, USA $^{65}$University of Mississippi, University, Mississippi 38677, USA $^{66}$University of Nebraska, Lincoln, Nebraska 68588, USA $^{67}$Rutgers University, Piscataway, New Jersey 08855, USA $^{68}$Princeton University, Princeton, New Jersey 08544, USA $^{69}$State University of New York, Buffalo, New York 14260, USA $^{70}$Columbia University, New York, New York 10027, USA $^{71}$University of Rochester, Rochester, New York 14627, USA $^{72}$State University of New York, Stony Brook, New York 11794, USA $^{73}$Brookhaven National Laboratory, Upton, New York 11973, USA $^{74}$Langston University, Langston, Oklahoma 73050, USA $^{75}$University of Oklahoma, Norman, Oklahoma 73019, USA $^{76}$Oklahoma State University, Stillwater, Oklahoma 74078, USA $^{77}$Brown University, Providence, Rhode Island 02912, USA $^{78}$University of Texas, Arlington, Texas 76019, USA $^{79}$Southern Methodist University, Dallas, Texas 75275, USA $^{80}$Rice University, Houston, Texas 77005, USA $^{81}$University of Virginia, Charlottesville, Virginia 22901, USA and $^{82}$University of Washington, Seattle, Washington 98195, USA (Dated: January 12th 2010) 

We present a measurement of the differential cross section for t ¯ t events produced in p ¯ p collisions at √$_{s}$ = 1 . 96 TeV as a function of the transverse momentum ( p T ) of the top quark. The selected events contain a high- p T lepton ( ℓ ), a large imbalance in p T , four or more jets with at least one candidate for a b jet, and correspond to 1 fb − 1 of integrated luminosity recorded with the D0 detector. Objects in the event are associated through a constrained kinematic fit to the t ¯ t → W bW ¯ b → ℓνb q ¯ q ′ ¯ b process. Results from next and next-to-next-to-leading-order perturbative QCD calculations agree with the measured differential cross section. Comparisons are also provided to predictions from Monte Carlo event generators using QCD calculations at different levels of precision. 

The transverse momentum ( p$_{T}$ ) of top quarks in t ¯ t events provides a unique window on heavy-quark pro- duction at large momentum scales. In the standard model (SM), the lifetime of the top quark is far shorter than the characteristic hadron-formation time of quan- tum chromodynamics (QCD), which provides access to 

PACS numbers: 14.65.Ha,12.38.Qk,13.85.Qk 

the properties and kinematics of a “bare” quark, such as mass, charge, spin, and p$_{T}$ , that are almost unaffected by bound-state formation or final-state interactions [8]. The top quark is unique in that it has a mass close to the scale of electroweak symmetry breaking. Detailed studies of the properties of this bare quark beyond the measure- 

