We report on the B physics prospects from the Fermilab Tevatron, summarizing
the B physics goals of the CDF and DO experiments using their upgraded
detectors. We discuss the time schedule for completion of the detector upgrades
and summarize the current measurement of the CP violation parameter sin(2 beta)
at CDF.Comment: Final version as it will appear in Proceedings of XIX International
  Symposium on Lepton and Photon Interactions at High Energies, Stanford
  University, August 9-14, 1999. 8 pages plus title page; 5 figure

Abe F.

MANFRED PAULINI

English

arXiv

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BRIEF REPORT FROM THE TEVATRON

The authors report on the B physics prospects from the Fermilab Tevatron, summarizing the B physics goals of the CDF and D0 experiments using their upgraded detectors. They discuss the time schedule for completion of the detector upgrades and summarize the current measurement of the CP violation parameter sin 2{beta} at CDF

Paulini, M.

UNT (University of North Texas) Digital Library

F Fermi National Accelerator LaboratoryFERMILAB-Conf-00/007-ECDF and D0Brief Report from the TevatronM. PauliniFor the CDF and D0 CollaborationsLawrence Berkeley National LaboratoryBerkeley, California 94720Fermi National Accelerator LaboratoryP.O. Box 500, Batavia, Illinois 60510January 2000To appear in the published proceedings of the XIX International Symposium on Lepton and PhotonInteractions at High Energies, Stanford University, Stanford, California, August 9-14, 1999Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the United States Department of EnergyDisclaimerThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any oftheir employees, makes any warranty, expressed or implied, or assumes any legal liability orresponsibility for the accuracy, completeness, or usefulness of any information, apparatus,product, or process disclosed, or represents that its use would not infringe privately ownedrights. Reference herein to any specic commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily constitute or imply itsendorsement, recommendation, or favoring by the United States Government or any agencythereof. The views and opinions of authors expressed herein do not necessarily state or reectthose of the United States Government or any agency thereof.DistributionApproved for public release; further dissemination unlimited.Copyright NoticationThis manuscript has been authored by Universities Research Association, Inc. under con-tract No. DE-AC02-76CH03000 with the U.S. Department of Energy. The United StatesGovernment and the publisher, by accepting the article for publication, acknowledges thatthe United States Government retains a nonexclusive, paid-up, irrevocable, worldwide licenseto publish or reproduce the published form of this manuscript, or allow others to do so, forUnited States Government Purposes.CDF/PUB/BOTTOM/PUBLIC/5200FERMILAB-Conf-00/007-EVersion 1.0January 7, 2000Brief Report from the TevatronManfred PauliniLawrence Berkeley National LaboratoryBerkeley, California 94720, USA(Representing the CDF and D Collaborations)AbstractWe report on the B physics prospects from the Fermilab Tevatron, summarizingthe B physics goals of the CDF and D experiments using their upgradeddetectors. We discuss the time schedule for completion of the detector upgradesand summarize the current measurement of the CP violation parameter sin 2at CDF.Plenary talk presented atXIX International Symposium on Lepton and Photon Interactions at High EnergiesStanford University, August 9-14, 1999.Brief Report from the TevatronManfred PauliniLawrence Berkeley National LaboratoryBerkeley, California 94720, USA1 IntroductionIt might appear surprising to include a report from the Fermilab Tevatron, a proton-antiproton collider, in a session about \Brief Reports from the B factories". Doesthis mean the Tevatron would qualify as a B factory? There are two advantages ofstudying B physics at the Tevatron. First, all B hadrons are produced; not onlycharged and neutral B mesons as at the B factories but also B0S mesons and b-baryons. The second advantage is the b quark production cross section, which isabout 1 nb at the (4S) resonance while it is about 50 b for pp collisions atps =1:8 TeV. This is an enormous cross section which is about 50,000 times larger at theTevatron than at the B factories. It resulted in about 5  109 bb quark pairs beingproduced during the 1992-1995 data taking period of the Tevatron, called Run I. Toillustrate the enormous b production rate at the Tevatron, we compare the yield offully reconstructed B mesons between the CLEO experiment and CDF. In a datasample of about 3000 pb 1, CLEO reconstructs about 200 B mesons decaying intoJ= K+ [1] while CDF nds in a sample of about 100 pb 1 of data a signal of about1000 J= K+ events with a good signal-to-background ratio [2].The goal of the B factories is to discover CP violation in B0 ! J= K0Sdecays.CDF has already presented a measurement of CP violation in the B meson system [3],measuring the time-dependent asymmetry in the yield of J= K0Sevents coming froma B0 versus B0:ACP (t)  N(B0(t)) N(B0(t))N( B0(t)) +N(B0(t))= sin 2 sinmdt: (1)This asymmetry is directly related to the CP violation parameter sin 2.1.1 CDF Measurement of sin 2Here, we briey summarize CDF's initial measurement of sin 2. Figure 1(a) showsthe J= K0Syield at CDF, where 395  31 events have been identied. This is cur-rently the world's largest sample of fully reconstructed J= K0Sevents. Measuring a(a) (b)(Mµµππ-MB)/σMevents050100150200-20 -10 0 10 20ct (cm)true asymmetry ∆m floating ∆m fixed-1 0 1 2sin2β-2-1012340 0.05 0.1 0.15 0.2 0.25Figure 1: (a) Normalized mass distribution of J= K0Scandidates. (b) True asymme-try sin 2 as a function of the reconstructed J= K0Sproper decay length. The eventswith low decay length resolution are shown separately on the right.CP asymmetry requires knowing whether the J= K0Soriginated from a B0 or B0meson. This is usually referred to as B avour tagging. Several methods of B avourtagging exist. Some of them exploit the other B hadron in the event and search fora lepton from the semileptonic decay of the other B hadron or determine the netcharge of the jet produced by the other b quark. These two methods are called leptontagging and jet charge tagging, respectively. The B avour can also be determinedby searching for pions which are produced through fragmentation or B mesons incorrelation with the B meson of interest. This method is known as same side tagging.B avour tagging is the crucial element for a CP violation measurement at theTevatron. The gure of merit quantifying how well a avour tagging algorithm worksis the so-called eective tagging eciency "D2. Here, " is the eciency for obtaining aparticular avour tag, and D is the dilution dened by the number of right tags (NR)and the number of wrong tags (NW ): D = (NR NW )=(NR+NW ). CDF determinedthe tagging power of various tagging methods with data measuring the time depen-dence of B0 B0 avour oscillations. Such a measurement serves as a demonstrationthat a particular avour tag does work in a hadron collider environment and deter-mines its "D2. Figure 2(a) shows the measured mixing asymmetries as a functionof proper decay length using a same side tag [2, 4]. From this measurement CDF(a)(b)Figure 2: (a) Measured asymmetries as a function of proper decay length using a sameside tag for the decay signatures: D0`+ (top), D `+ (middle), and D `+ (bottom).(b) Fraction of mixed events as a function of proper decay length using a jet chargeand lepton avour tag.extracts md = (0:471+0:078 0:068  0:034) ps 1 and the eective tagging eciency for thesame side tag to be "D2 = (1:80:40:3)%. As another example, Figure 2(b) showsthe fraction of mixed events as a function of proper decay length using a jet charge andlepton avour tag [5]. This measurement yields md = (0:500  0:052  0:043) ps 1as well as "D2 = (0:91 0:10 0:11)% and "D2 = (0:78 0:12 0:08)% for a leptontag and jet charge tag, respectively.Applying all three tagging methods to CDF's sample of J= K0Sevents gives theCP asymmetry distribution shown in Figure 1(b). The data prefer a positive asymme-try, resulting in a measurement of sin 2 = 0:79 0:39 0:16. This can be translatedinto a limit on sin 2 being positive (0 < sin 2 < 1) at 93% condence level. Thisis the best direct measurement of CP violation in the B system to date. With thisresult, CDF demonstrated that a CP violation measurement is feasible at the Teva-tron in Run II. Returning to our initial question, we think the Tevatron does qualifyas a B factory capable of measuring CP violation.2 The Tevatron in Run IIThe most important element of the Tevatron upgrade for Run II is the Main Injector.It is a new 150 GeV accelerator half the circumference of the Tevatron, which willForwardPreshowerSilicon Tracker Fiber TrackerSolenoid Central Preshower125 cm50cm20cm=3=1.6Figure 3: Left: Cross section of the upgraded D detector. Right: Longitudinal viewof the D tracking system.increase the antiproton intensity into the Tevatron, providing 20 times higher lumi-nosities. The Main Injector project was nished in June 1999 with the rst beamcirculating at that time.Run II of the Tevatron has originally been dened as 2 fb 1 being delivered intwo years to the collider experiments. Run II has recently been extended beyondthe initial two years with 2 fb 1, to continue until 2006 with no major shutdowns,maximizing the delivered luminosity to a total of up to 15 fb 1. The current Fermilabschedule xes the start of Run II in March 2001.2.1 D Detector UpgradeThe D detector upgrade is built on previous strengths, combining excellentcalorimetry with good muon coverage and purity. A cross section of the upgraded Ddetector is shown in Figure 3. The most important improvement is a superconductingsolenoid (B = 2 T) providing signicantly improved tracking capabilities (see righthand side of Figure 3). A central ber tracker consisting of eight superlayers of scintil-lating bers allows a measurement of the charged particle momentum. Together withthe silicon micro-strip tracker, a momentum resolution of (pT )=pT = 0:002 pT will beachieved. The silicon tracker consists of six barrels with four layers each (r and rzreadout) and 12+4 forward disks reaching out to 1.25m in z. In addition, improve-ments to the muon system will allow enhanced muon triggering for pT > 1:5 GeV=c(jj < 2). Central and forward preshower detectors will improve electron identica-CalorimeterDrift ChamberSilicon Vertex DetectorMuon ChambersBeampipeMagnetCOT0.51.01.52.00 .5 1.0 1.5 2.0 2.5 3.0END WALLHADRONCAL.SVX II5 LAYERS303 00SOLENOIDINTERMEDIATE SILICON LAYERSCDF Tracking Volume = 1.0  = 2.0END PLUG EM CALORIMETEREND PLUG HADRON CALORIMETER  = 3.0nnnm mFigure 4: Left: Schematic cut-away view of the CDF II detector. Right: Longitudinalview of the upgraded CDF tracking system.tion and triggering on electrons with pT > 1 GeV=c (jj < 2:5). Finally, an impactparameter trigger detecting tracks from displaced vertices is under development.The current D schedule expects the central and forward preshower fabricationas well as the central ber tracker project to be completed by June 2000. The silicontracker will be nished by September 2000 and the full tracking system installed andhooked up a few weeks later. The muon system will be in place by November 2000and the calorimeter electronics by January 2001, allowing D to be rolled in andready for beam by February 2001.2.2 CDF Detector UpgradeThe goal for the CDF detector upgrade is to maintain detector occupancies atRun I levels, although many of the detector changes also provide qualitatively im-proved detector capabilities. A schematic view of the CDF II detector is shown inFigure 4. One major improvement is to the charged particle tracking system (seeFigure 4), vital for the B physics program at CDF. A new silicon vertex detectorwill consist of ve layers of double sided silicon from radii of 2.9 cm to 10 cm. Thesilicon detector will include three modules covering the entire pp luminous region. Inaddition, an intermediate silicon layer consisting of two double-sided silicon sensorsat larger radii permits stand-alone silicon tracking out to jj = 2. A new open celldrift chamber (COT) will operate at a beam crossing time of 132 ns with a maximumdrift time of 100 ns. The COT consists of 96 layers arranged in four axial and fourstereo superlayers. It also provides dE/dx information for particle identication.The upgrades to the muon system almost double the central muon coverage whileFlavour tag "D2 Run I "D2 Run IISame side tag (1:8 0:4  0:3)% 2.0%Jet charge tag (0:78  0:12  0:08)% 3.0%Lepton tag (0:91  0:10  0:11)% 1.7%Kaon tag { 2.4%Table 1: Summary of eective B avour tagging eciencies "D2 measured at CDFin Run I and corresponding projections for Run II.a new scintillating tile plug calorimeter will give good electron identication up tojj = 2. New front-end electronics will be installed, and a DAQ upgrade will allowthe operation of a pipelined trigger system. Finally, two additional upgrade projectssignicantly enhancing the B physics capabilities of the CDF II detector have beenapproved. These include the installation of a low-mass radiation hard single-sidedsilicon detector with axial strips at very small radius of  1:6 cm, as well as theinstallation of a time-of-ight system employing 216 three-meter-long scintillator barslocated between the outer radius of the COT and the superconducting solenoid.The current CDF schedule foresees cosmic ray running of the detector at thebeginning of 2000 and expects the COT to be installed in April 2000. A commissioningrun will take place from August to November of 2000. The silicon upgrade will becomplete by September 2000 and installed by January 2001. The full CDF II detectorwill be ready for collisions by March 2001.3 Run II B Physics ProspectsWhen discussing the Run II B physics prospects in this section, we will refer to adata sample of 2 fb 1 delivered in two years. We will focus on the prospects for theCDF experiment. D has similar expectations.For a measurement of sin 2, CDF expects 10,000 J= K0Sevents in 2 fb 1 withthe J= decaying to muon pairs and K0S! + . With the enhanced tracking andvertexing capabilities, extended lepton coverage and better particle identication,CDF will improve the eective avour tagging eciencies for the dierent taggers asdetailed in Table 1 to a total "D2 of approximately 9.1%. With this, CDF expects tomeasure sin 2 with an uncertainty of 0:07. Figure 5 shows the current CDF resulton sin 2 in the (; )-plane where the light shaded area indicates the present 1uncertainty. To illustrate the improvements in Run II, the dark shaded area displaysthe expected error on sin 2 in Run II with 2 fb 1.With respect to other CP modes, CDF plans to measure the time dependence00.20.40.60.81-1 -0.5 0 0.5 1Figure 5: Illustration of the current CDF result on sin 2 in the (; )-plane (lightshaded area) and expected improvement in Run II (dark shaded area).of the CP asymmetry in B0 ! +  decays, determining sin 2. CDF will use adisplaced track trigger which will trigger on hadronic tracks from long-lived particlessuch as B hadrons. With a fast track trigger at Level 1, CDF nds track pairs inthe COT with pT greater than 1.5 GeV=c. At Level 2, these tracks are linked intothe silicon vertex detector, and cuts on the track impact parameter d > 100 m((d)  25 m) are applied. CDF expects to collect 4000-7000 B !  events,assuming B(B0 ! + ) = (4:7+1:8 1:5  0:6)  10 6 as measured by CLEO [6]. Inaddition, there will be about four times more B ! K decays. The implications ofthis background for an extraction of sin 2 at CDF are still under study.For a measurement of sin  in Run II, CDF can use B0S mesons. A signal of about700 B0S= B0S ! DSK events is expected. This might allow for an initial measurementof sin  with 2 fb 1 in Run II.B0 B0 and B0S B0S avour oscillations measure the Cabibbo-Kobayashi-Maskawamatrix elements jVtdj=jVtsj. The recently approved detector upgrades play an impor-tant role in CDF's prospects for measuring B0S mixing. The additional inner layerof silicon improves the time resolution from t = 0:060 ps to 0.045 ps. This will beimportant if mS is unexpectedly large. The time-of-ight system will enhance theeectiveness of B avour tagging, especially through same side tagging with kaonsand opposite side kaon tagging, to a total "D2  11:3%. CDF expects a signal of15,000-23,000 fully reconstructed B0S ! D S +; D S + + events from the two-track hadronic trigger in 2 fb 1. For 20,000 B0S events, a 5 measurement of mSwill be possible at CDF for mS values up to 40 ps 1. The current limit on mS is14.3 ps 1 [7] at 95% C.L. Note, physics with B0S mesons will be unique to the Tevatronuntil the turn-on of the LHC in 2006.4 ConclusionsThe CDF and D detector upgrades are well under way with data taking startingin March 2001. There are excellent prospects for B physics in Run II, allowing ameasurement of sin 2 with an uncertainty of 0.07. A discovery of B0S mixing ispossible for mS values up to 40 ps 1. The extension of Run II until 2006 willfurther increase the sensitivity and the B physics potential at the Tevatron. CDFand D are looking forward to joining the party with the B factories.References[1] C. P. Jessop et al. [CLEO Collaboration], Phys. Rev. Lett. 79, 4533 (1997).[2] F. Abe et al. [CDF Collaboration], Phys. Rev. D59, 032001 (1999).[3] T. Aolder et al. [CDF Collaboration], hep-ex/9909003. Accepted for publicationin Phys. Rev. D.[4] F. Abe et al. [CDF Collaboration], Phys. Rev. Lett. 80, 2057 (1998).[5] F. Abe et al. [CDF Collaboration], Phys. Rev. D60, 072003 (1999).[6] Ron Poling, these proceedings.[7] Guy Blaylock, these proceedings.DiscussionMichail Danilov (ITEP, Moscow): What is the sensitivity of the D experimentfor B physics studies in Run II?Paulini: As mentioned in my presentation, the prospects for D are similar to theones at CDF. D expects about 8500 J= K0Sevents with J= ! +  but theyplan to also trigger on e+e  pairs resulting in additional 6500 J= K0Sevents. From atime-dependent analysis, D expects to measure sin 2 with an uncertainty of 0.07.In addition, an impact parameter trigger project has recently been approved allowingD to detect B !  events and also to explore B0S B0S mixing.

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