After many upgrades to the CDF detector and to the accelerator complex, Run
II began in April 2001. The new detector has improved capabilities for charm
physics, and first results from the analysis of early Tevatron Run II data are
reported here.Comment: 6 pages, 4 figures, contribution to the DIS2003 workshop, St.
  Petersbur

Meyer, Arnd

English

arXiv

After many upgrades to the CDF detector and to the accelerator complex, Run II began in April 2001. The new detector has improved capabilities for charm physics, and first results from the analysis of early Tevatron Run II data are reported here

Meyer, A.

UNT (University of North Texas) Digital Library

Fermilab FERMILAB-Conf-03/283-E  October 2003NEW CHARM(ONIUM) RESULTS FROM CDFARND MEYER (for the CDF Collaboration)III. Physikalisches Institut A, RWTH Aachen, Physikzentrum52056 Aachen, GermanyE-mail: meyera@fnal.govAfter many upgrades to the CDF detector and to the accelerator complex,Run II began in April 2001. The new detector has improved capabilitiesfor charm physics, and rst results from the analysis of early TevatronRun II data are reported here.1 IntroductionAfter the very successful Tevatron Run I (1992-1995), colliding protons andantiprotons with a center of mass energy ofps = 1:8TeV, the accelerator andthe colliding beam experiments CDF and D were upgraded for Run II. On theaccelerator side, the beam energy has been increased from 900GeV to 980GeV.A new proton storage ring, the \Main Injector", has been built, and the sametunnel houses the \Recycler" storage ring, which will improve the rate at whichantiprotons can be accumulated, and may also be utilized to reuse antiprotonsafter recovering them from the Tevatron. The bunch spacing in the Tevatronhas been reduced from 3:5 s to 396 ns. The results shown below are based onearly Run II data corresponding to an integrated luminosity of up to 69 pb 1,i.e. comparable to the Run I data set (R L dt ' 110 pb 1).The CDF detector [1] is designed for general purpose use, with a largetracking system inside a uniform 1:4T solenoidal magnetic eld, 4 calorimetry,and a muon detection system. The entire tracking system has been replacedfor Run II, consisting of a Silicon tracking system with typically seven layers atradii of 1:5cm to 28cm, and the Central Outer Tracker (COT), an open cell driftchamber for the precise momentum measurement of charged tracks, using up to96 space points. Between the COT and the solenoid is the new Time-of-Flightdetector (TOF), which together with the momentum measurement providesparticle identication by determining a particle's mass. The three-level triggersystem and the data acquisition system [2] have been signicantly enhancedfor Run II. Traditionally triggering on heavy avor physics at hadron collidersrelies on a lepton signature; examples are the decay of the J= into + or semileptonic b decays. With the Silicon Vertex Tracker (SVT) [3] at thesecond trigger level CDF has introduced a novel method to obtain heavy avor12decays. The SVT uses COT tracks as seeds to a parallelized pattern recognitionin the Silicon vertex detector. The following linearized track t returns trackparameters with nearly oine resolution on a time scale of 15 s. Originallydesigned to select hadronic B decays the SVT also collects a large sample ofcharm hadrons. All of the measurements shown here, with the exception of theJ= cross section, are based on data samples collected with the SVT.2 Prompt D Meson Cross SectionsThere is no published measurement of the charm cross section from the Teva-tron. With the advent of the SVT this measurement is possible in Run II, andit is of theoretical interest due to the larger than expected beauty cross sec-tions compared to next-to-leading order QCD calculations. The measurementshown here, based on the analysis of 5:8 pb 1 of data, makes use of four fullyreconstructed decay modes: D0 ! K +, D+ ! D0+ with D0 ! K +,D+ ! K ++, and D+s ! + with ! K+K .The contributions from prompt and secondary charm are separated by uti-lizing the impact parameter distribution of the reconstructed D meson sam-ples. Mesons originating from B decays exhibit a large impact parameter. At to the impact parameter distribution yields prompt production fractionsof 88:6  0:4(stat)  3:5(sys)%, 88:1  1:1  3:9%, 89:1  0:4  2:8%, and77:33:82:1% for D0, D+, D+, and D+s , respectively, averaged over the fullanalyzed pT range. The measured prompt dierential cross sections are shownin Fig. 1. They are compared to a next-to-leading order QCD calculation [4],and a xed order next-to-leading log calculation [5]. The calculations are lowerthan, but compatible with the data.3 mD+s  mD+ Mass DierenceThe measurement of the mD+s mD+ mass dierence provides a test for HeavyQuark Eective Theory and lattice QCD. While many precision measurementsof meson masses can be expected from Run II, the analysis shown here couldalready be carried out with a modest amount of luminosity.The mass dierence measurement relies on D+s and D+ decays into +with  ! K+K , as shown in Fig. 2. Using the same decay mode has theadvantage of cancelling systematic uncertainties. The unbinned likelihood t ofthe mass spectrum results in mD+s  mD+ = 99:410:38(stat)0:21(sys)MeV,with uncertainties comparable to the world average [6]. This measurementconstitutes the rst published Run II result from CDF [7].3)  [GeV/c]0(DTp5 10 15 20  [nb/GeV/c]T)/dp0(Dσd102103104  [nb/GeV/c]T)/dp0(DσdCDF Run II preliminary Meson Differential Cross Section0D)  [GeV/c]+(D*Tp5 10 15 20  [nb/GeV/c]T)/dp+(D*σd10102103104  [nb/GeV/c]T)/dp+(D*σdCDF Run II preliminary Meson Differential Cross Section+D*)  [GeV/c]+(DTp5 10 15 20  [nb/GeV/c]T)/dp+(Dσd10102103104  [nb/GeV/c]T)/dp+(DσdCDF Run II preliminary Meson Differential Cross Section+D)  [GeV/c]+s(DTp5 10 15 20  [nb/GeV/c]T)/dp+ s(Dσd110102103  [nb/GeV/c]T)/dp+ s(DσdCDF Run II preliminary Meson Differential Cross Section+sDFigure 1: Dierential cross section for the four reconstructed D mesons. The-oretical predictions from Kniehl et al. (dashed line with dotted line indicatinguncertainty) and Cacciari et al. (full line with shaded band as uncertainty) arecompared to the data. The theoretical uncertainties are based on varying therenormalization and factorization scales independently by factors of 0.5 to 2.4 Cabibbo Suppressed Decays and CP ViolationUtilizing the large sample of D0 mesons in 65 pb 1 integrated luminositycollected with the secondary vertex trigger, relative branching fractions aremeasured,  (D0!K+K ) (D0!K+ ) = 9:38 0:18(stat) 0:10(sys)% and  (D0!+ ) (D0!K+ ) =3:686 0:076(stat) 0:036(sys)%, comparing favorably with the current bestmeasurement [8]. In the analysis, the D0 candidate is combined with a chargedslow pion to form a D meson; in this way, backgrounds are reduced, and thecharge of the slow pion from the D decay serves as an unbiased tag of the D0avor. Examples of the reconstructed decays are shown in Fig. 3.The CP violating decay rate asymmetries A =  (D0!f)  ( D0!f) (D0!f)+ ( D0!f)are alsomeasured. It is found that A(D0 ! K+K ) = 2:0  1:7(stat)  0:6(sys)%and A(D0 ! + ) = 3:0  1:9(stat)  0:6(sys)%, comparable to previous4]2 mass [GeV/cπKK1.80 1.85 1.90 1.95 2.00 2.052Entries per 2 MeV/c050100150200250300350400 CDF Run II, 11.6 pb-1KK→φ, πφ→s, D+DUnbinned likelihood fit projectedCDF Run II Preliminary0 4 8 12 16pT(J/ψ) GeV/c10-11101102dσ/dp T(|y|<0.6) . Br(J/ψ→µµ) nb/(GeV/c)Data with stat. uncertaintiesSystematic uncertaintiesFigure 2: Left: The reconstructed D+ ! + and D+s ! + massdistribution. Right: The inclusive J= cross section dierential in pT forjy(J= )j < 0:6.measurements [9].5 Search for the FCNC Decay D0 ! + The search for the avor changing neutral current (FCNC) decay D0 ! + is another example of an analysis that greatly benets from the SVT trigger, byproviding the well measured normalization mode D0 ! + . The branchingratio is O(10 13) in the Standard Model, but can be enhanced up to B(D0 !+ ) ' 3:5  10 6 in R-parity violating models of Supersymmetry. In a datasample corresponding to an integrated luminosity of 69pb 1 no candidate eventis observed (Fig. 4) with 1:70:7 background events expected. After correctingfor relative acceptance an upper limit of B(D0 ! + )  2:4  10 6 at 90%CL is set, improving the current best limit [10] of 4:1  10 6.6 Measurement of the J= Cross SectionOne of the surprises of Run I was the direct production cross section for J= and (2S) mesons [11], which turned out to be orders of magnitude larger than thetheoretical expectation in the Color Singlet Model. While later calculationswithin the framework of non-relativistic QCD, including intermediate coloroctet states, are in broad agreement with the data, there is continued interestin the subject; in particular measurements of the J= and  (2S) polarizationappear to be in conict with the theory, albeit not with convincing statisticalsignicance.5]2 Mass [Gev/cππ1.76 1.78 1.8 1.82 1.84 1.86 1.88 1.9 1.922Entries/2MeV/c0200400600800100012001400160018002000 π]ππ[→π0D→*D  69± = 36970DN-14 pb±CDF RunII Preliminary            65]2 Mass [GeV/cπK1.8 1.82 1.84 1.86 1.88 1.9 1.922Entries/0.9MeV/c0500100015002000250030003500π]π[K→π0D→*D 340± = 935600DN-14 pb±CDF RunII Preliminary           65]2KK Mass [GeV/c1.75 1.8 1.85 1.9 1.952Entries/2.5MeV/c050010001500200025003000 π[KK]→π0D→*D-14 pb±CDF RunII Preliminary             65 140± = 83200DNFigure 3: Reconstructed D0 decay modes for branching ratio and CP asym-metry measurements. Note that in the KK (right) and  (left) modes thereections are well separated.For Run II the muon trigger momentum thresholds at CDF were loweredto  1:4GeV, thus allowing to trigger on J= 's at rest for the rst time. Usinga data sample of 39:7pb 1 the inclusive dierential cross section in bins of theJ= transverse momentum has been measured for J= rapidities jy(J= )j < 0:6(Fig. 2). The region pT < 5 GeV is covered for the rst time. The total crosssection has been determined to be (pp ! J= X; jy(J= )j < 0:6)  B(J= !+ ) = 240  1(stat)+35 28(sys) nb. In the future, the determination of theprompt production cross section, more precise data at large pT , polarizationmeasurements, and similar measurements of  (2S), (1S), (2S), and (3S)production will shed further light on the production mechanisms for heavyvector mesons.References[1] CDF II Collaboration, The CDF-II Detector: Technical Design Report,Fermilab-Pub-96-390-E (1996)[2] A. Meyer, The CDF Data Acquisition System for Tevatron Run II, CHEP 2001Conference, proceedings and Fermilab-Conf-01-242-E (2001)[3] W. Ashmanskas et al., Nucl. Instrum. Meth. A447, 218 (2000)[4] B.A. Kniehl and G. Kramer, private communication; B.A. Kniehl, G. Kramerand B. Potter, Nucl. Phys. B597, 337 (2001)[5] M. Cacciari and P. Nason, private communication; M. Cacciari, M. Grecoand P. Nason, JHEP 9805, 007 (1998); M. Cacciari and P. Nason,Phys. Rev. Lett. 89, 122003 (2002)6CDF Run II Preliminary02550751001.8 1.85 1.9 1.95Mππ (GeV)events/MeV Normalization mode:1371 ± 53  D0→π+π-in the mass search window∫ L dt = 69pb-1CMU fiducialCDF Run II Preliminary01231.8 1.85 1.9 1.95Mµµ (GeV)events/MeVD0→µ+µ- Search0 events in the ±2σ search windowFigure 4: Search for D0 ! + . Left: Mass spectrum for the normalizationmode D0 ! + ; the search window is indicated by the shaded area. Right:Dimuon candidate events; the search window is indicated by the hatched area.[6] K. Hagiwara et al., Phys. Rev. D66, 010001 (2002)[7] CDF II Collaboration, Measurement of the Mass Dierence m(D+s) m(D+) atCDF II, Fermilab-Pub03/048-E (2003), submitted to Phys. Rev. D[8] FOCUS Collaboration, Phys. Lett. B555, 167 (2003)[9] CLEO Collaboration, Phys. Rev. D65, 092001 (2002)[10] BEATRICE Collaboration, Phys. Lett. B408, 469 (1997)[11] CDF Collaboration, Phys. Rev. Lett. 79, 572 (1997) and 85, 2886 (2000)

New charm (onium) results from CDF

http://digital.library.unt.edu/ark:/67531/metadc738729/

New Charm(onium) Results from CDF

Abstract

Similar works

Full text

Available Versions

UNT (University of North Texas) Digital Library