In this contribution to the panel discussion on ``The Future of Hadron B
Experiments'' held at the 8th International Conference on B Physics at Hadron
Machines (Beauty 2002) at Santiago de Compostela, Spain, we explore the physics
potential for B physics at CDF and DO in five years and beyond. After a brief
introduction to precision flavour physics, we concentrate our discussion on the
future of CP violation by evaluating the prospects for measuring the CKM angles
beta, gamma and alpha at the Tevatron Collider experiments CDF and DO by the
end of Run II.Comment: Posting for the archives: Contribution to Panel Discussion on "The
  Future of Hadron B Experiments". Pub. Proceedings Beauty 2002: 8th
  International Conference on B Physics at Hadron Machines, Santiago de
  Compostela, Spai

Anikeev

Aubert

Buras

Datta

Gilman

Gronau

Manfred Paulini

Paulini

Quinn

Snyder

English

arXiv

Crossref

Future of B physics at CDF and DØ

In this contribution to the panel discussion on ''The Future of Hadron B Experiments'' held at the 8th International Conference on B Physics at Hadron Machines (Beauty 2002) at Santiago de Compostela, Spain, June 17-21, 2002, we explore the physics potential for B physics at CDF and D0 in five years and beyond. After a brief introduction to precision flavour physics, we concentrate our discussion on the future of CP violation by evaluating the prospects for measuring the CKM angles {beta}, {gamma} and {alpha} at the Tevatron Collider experiments CDF and D0 by the end of Run II

Paulini, M.

UNT (University of North Texas) Digital Library

Fermilab FERMILAB-Conf-03/028-E  February 2003Future of B Physics at CDF and DManfred Paulini 1Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, U.S.A.Contribution to Panel Discussion on\The Future of Hadron B Experiments"AbstractIn this contribution to the panel discussion on \The Future of Hadron B Exper-iments" held at the 8th International Conference on B Physics at Hadron Machines(Beauty 2002) at Santiago de Compostela, Spain, June 17-21, 2002, we explore thephysics potential for B physics at CDF and D in ve years and beyond. After abrief introduction to precision avour physics, we concentrate our discussion on thefuture of CP violation by evaluating the prospects for measuring the CKM angles,  and  at the Tevatron Collider experiments CDF and D by the end of Run II.1Representing the CDF and D Collaboration.1IntroductionThis report contains my contribution to the panel discussion on \The Future of HadronB Experiments" held at the 8th International Conference on B Physics at Hadron Ma-chines (Beauty 2002) at Santiago de Compostela, Spain, June 17-21, 2002. The panel waschaired by Fred Gilman, also current chair of HEPAP, who charged the panel membersto evaluate the physics potential for B physics at Hadron Machines in ve years andbeyond [1]. In my contribution, I discussed the future of B physics at the two Teva-tron Collider experiments CDF and D at the end of Run II. More information aboutB physics prospects at the Tevatron in Run II and beyond can be found in Ref. [2].Since the oÆcial start of the Fermilab Tevatron Run II in March 2001, much workhas gone into commissioning the CDF and D detectors. Both experiments were takingphysics data and presenting rst physics results at the time of this conference in summer of2002 [3]. The goal for the rst phase of Run II (Run IIa) is to collect a data sample of about2 fb 1 until 2004. After a short shutdown of about 6 months, Fermilab's current planforesees a high-luminosity running period of the Tevatron with an integrated luminosity ofpossibly  10 fb 1 delivered until the turn-on of the LHC in 2007. The most importantupgrades for CDF and D consist of replacing their silicon vertex detectors by moreradiation tolerant devices to allow for collecting 10-15 fb 1 of pp collision data.Toward Precision Flavour PhysicsIn the 1990's, particle physics was dominated by a decade of precision electroweak physicswith measurements from LEP, SLD, the Tevatron and various xed target experiments.The progress made in that decade can be summarized in the constraints on the Higgsboson mass as known in 1999. In the famous MW versus Mtop plane, the Tevatron andLEP measurements on MW , the CDF and D results on Mtop as well as constraints fromvarious indirect measurements are displayed in Figure 1(a). As indicated, the StandardModel (SM) prefers a light Higgs Boson mass. Ten years earlier, in 1989, the top quarkwas not yet discovered and the W boson mass was only known with a precision of about1.5 GeV=c2. Enormous progress has been made in this decade of precision electroweakphysics.With the turn-on of the e+e  B factories in 1999, the physics community started totalk about particle physics moving from a decade of precision electroweak physics towarda decade of precision avour physics. A lot of progress in understanding avour physicshas already been achieved in the past 4-5 years. In 1998, we had no information onCP violation in the B system which was discovered in 2001 [4], and the constraints fromjVubj, B mixing and CP violation in the kaon system were quite coarse. Much progresshas been made since then as can be seen in Figure 1(b) showing the constraints on theposition of the apex of the unitarity triangle from jVubj, B mixing, K and sin 2. Thisplot has been taken from the 2002 Review of Particle Properties [5].According to the chair of this panel on \The Future of Hadron B Experiments", FredGilman, for the rst time there exist now two independent tests of the CKM mechanism180.180.280.380.480.580.6130 140 150 160 170 180 190 200Mtop (GeV/c2)MW (GeV/c2 )1002505001000Higgs Mass (GeV/c2 )TEVATRONMW-Mtop contours : 68% CLLEP2LEP1,SLD,νN data(a)(b)Figure 1: (a) Constraints on the Higgs boson mass as of 1999 from measurements of MWand Mtop from the Tevatron, LEP2 and indirect results. (b) Constraints on the positionof the apex of the unitarity triangle from jVubj, B mixing,  and sin 2 as of 2002 (fromRef. [5]).in the Standard Model [1]. Rate measurements of jVubj as well as B0 and B0smixingconstrain the position of the apex of the unitarity triangle as illustrated in Figure 2(a).The second independent test comes from CP violation in the kaon system (K) and theB system (sin 2) as displayed in Figure 2(b). Both tests through rate measurements andCP violation are in striking agreement as illustrated in Figures 2 and 1(b).A Look into the FutureWhen the \wise (wo)man" is asked to have a look into the future of B physics at hadronmachines, (s)he might do two things. First, (s)he might take a step back and recommend00.20.40.60.81-1 -0.5 0 0.5 100.20.40.60.81-1 -0.5 0 0.5 1(a) (b)Figure 2: Illustration of the two independent tests of the CKM unitarity triangle through(a) rate measurements (jVubj and B mixing) and (b) CP violation (K and sin 2).2K0Lνν0π  K0Lπ  0 e  e+ -ε /ε’K νν+ +π  B lldB llXdB Xd νν|V  /V  |ub cbηρ0-1 1 21 0.51.5γαβACBεB -B0 0Figure 3: An ideal CKM unitarity triangle indicating the dierent constraints from K de-cays and B physics (from Ref. [6]).to get a \grand view". For the topic of this panel discussion, the \grand picture" ispresented in Figure 3 taken from Ref. [6]. In this diagram an ideal view of the CKMunitarity triangle is given indicating the dierent constraints from K decays (K, 0=,K0L ! 0 and K+ ! +) as well as B physics (jVubj, B mixing, rare decays andCP violation in form of the angles ,  and ). The second advice the wise (wo)manmight oer is to look at your older friends. If you want to know how you'll appear in veyears from now, look at your older friends and see what they are right now. The olderfriend of B physics is kaon physics. Currently, the virtue of kaon experiments is to testthe Standard Model by measuring modes that are theoretically clean such as K0L ! 0and K+ ! +. Thus, the goal of B physics in ve years and beyond should be to testthe SM by concentrating on theoretically clean modes. These will also allow to nd newphysics in an unambiguous way. In the remainder of this paper, we will therefore focuson testing CP violation through theoretically clean B decay modes.The Future of CP ViolationIn the following, we assume a data sample of 15 fb 1 for the quoted prospects which wouldcorrespond to the luminosity that can possibly be reached by the end of the TevatronRun II. We will mainly concentrate on prospects determined at CDF as they were moreaccessible than prospects from D.The Angle  from B0 ! J= K0SCDF's most important B physics goal in Run II is the study of CP violation in theB system. The golden decay B0 ! J= K0S is the mode which all experiments will use to3obtain precision measurements of sin 2. For Run IIa with 2 fb 1 of data, CDF expects20,000 fully reconstructed B0 ! J= K0S decays. With an expected eective taggingeÆciency of "D2  9:1%, CDF will measure sin 2 with an uncertainty of about 0.05. Dexpects a similar precision. The systematic uncertainty on sin 2 is dominated by theuncertainty on the dilution which is determined by large control samples of J= K data.Thus this uncertainty scales with statistics. Since we do not see a limiting systematicuncertainty, the precision on sin 2 will scale with the integrated luminosity resultingin an uncertainty of 0.02 in 15 fb 1 competitive with expected measurements at thee+e  B factories.CP Asymmetry in B0s! J= While the CP asymmetry in B0 ! J= K0S measures the weak phase of the CKM matrixelement Vtd, CP asymmetry in B0s! J=  measures the weak phase of the CKM matrixelement Vts. The latter CP asymmetry is expected to be very small in the StandardModel, on the order of a few percent. In the context of testing the Standard Model, thismode has the same fundamental importance as measuring sin 2 but is most accessibleat a hadron collider. An observation of a large CP asymmetry would be a clear signal ofnew physics.In Run I, CDF's yield of J=  was about 40% of J= K0S which results in an expectationof about 8000 J=  events in Run IIa. The magnitude of the CP asymmetry in B0s!J=  is modulated by the frequency of B0smixing. This requires to resolve B0soscillations.There is an additional complication in this decay mode, if the J=  nal state is not a pureCP eigenstate. In this case, an angular analysis is necessary to determine the mixture ofCP even and CP odd states in this decay channel. With 15 fb 1 of data in Run II, CDFexpects a resolution of 0.03-0.06 on the CP asymmetry in B0s! J=  for ms  20 ps 1depending on the CP content of the nal state.CP Asymmetry in B0s! J= (0)Measuring the CP asymmetry in B0s! J= (0) decays is very similar to measuring it inB0s! J=  with two dierences. First, the J=  and J= 0 nal states are CP eigen-states. Therefore no angular analysis is needed and no degradation of the CP asymmetryoccurs. Second, the presence of photons in the nal state makes these modes more diÆcultto detect at CDF since the CDF calorimeter was not designed to measure low energy pho-tons with good resolution. However, CDF is capable of detecting these signals as shownin Figure 4. Here, in the invariant diphoton mass spectrum clear signals of 0 !  and !  are observed in CDF Run I data.Scaling from the expected number of B+ ! J= K+ events, the rate of B0 to B0spro-duction and the expected relative branching ratios, CDF expects about 8000 B0s! J= events in Run II. Studies of J= events in Run I indicate that a mass resolution of40 MeV=c2 and a signal-to-background ratio of 1:2 appears achievable. For ms  20 ps 1and a proper time resolution of t  0:045 ps, CDF expects to measure the CP asymmetryin B0s! J=  with an uncertainty on the order of 0.1.4(a) (b)Figure 4: Invariant diphoton mass distribution showing (a) 0 !  and (b)  ! signals in CDF Run I data.The Angle  from B0s! D sK+A good candidate to determine the CKM angle  is the decay mode B0s! D sK+ measur-ing sin . In this mode, CP violation occurs via interference of the quark level processesb! cus and b! ucs through direct and mixed decays. Since B0soscillations are expectedto have a small CP violating phase, the relative weak phase of this decay is ei . Penguincontributions are expected to be small but there is a strong phase Æ present which cannotbe reliably calculated with present theoretical techniques and needs to be extracted fromdata. The time dependent decay rates for all four processes B0s= B0s! DsK are ttedwith a two-fold ambiguity in Æ and .The reduction of backgrounds, in particular physics backgrounds from the Cabibboallowed process B0s! D s +, is the primary challenge for CDF in extracting the B0s!D sK+ signal. Exploiting the D sK+ invariant mass as well as dE/dx information of thenal state particles, studies at CDF show that a signal-to-background ratio of 1/6 can beachieved and a signal of 850 B0s! D sK+ events can be expected in 2 fb 1. Thus, aninitial measurement of  should be possible at CDF in the beginning of Run II. Withinthe rst 2 fb 1 of data, the expected error on sin(  Æ) is 0.4 to 0.7 depending on theassumed background levels. By the end of Run II, an uncertainty near 0:2 for  may beachievable.The Angle  from B  ! D0K In a similar manner, the angle  can be determined from the decays B  ! D0K  andB  ! D0K  with D0= D0 ! K. The advantage is that these modes are self-tagging5and no time-dependent measurement is necessary. One needs to just measure branchingfractions of these decays. However, the decay B  ! D0K  is particularly problematic dueto the small expected branching ratio. All these decay modes have signicant physics andcombinatoric backgrounds that must be reduced to acceptable levels to make this methodfeasible. CDF expects to collect a small sample of about 100 signal candidates with thetwo-track hadronic trigger in 2 fb 1. There is optimism that the physics backgroundcan be brought down to the same level as the signal, but there could be considerablecombinatoric background. If the combinatoric background can also be reduced to a levelcomparable to the signal, CDF would be in the position to measure  with an uncertaintyin the order of 10-20Æ in 2 fb 1. At this point it is not clear whether this can be scaled toa 5Æ measurement on  with 15 fb 1 at the end of Run II.The Angle To date, there are only two methods considered to be clean extractions of the CP phase fromB decays. Each method has its own particular diÆculties. Originally it was suggestedto use the time dependent CP asymmetry in B0 ! +  to obtain . In order to removethe \penguin pollution", it is necessary to perform an isospin analysis ofB !  decays [7]including the decay mode B0 ! 00 which is diÆcult to measure. The second methodis the Dalitz-plot analysis of B0 !  ! + 0 decays [8]. The problem here is tounderstand the continuum background and the correct description of !  decays.In a recent paper by London and Datta [9], a new method to measure the CP phase has been suggested using decays B0=B0s! K() K(). Because the branching ratios forB ! K() K() are rather small,O(10 6), and because B0sdecays are involved, this methodis most appropriate for hadron colliders, in particular since no 0 detection is needed. Thebasic idea is to consider the pure b! d penguin decays B0 ! K0 K0 and B0 ! K K andrelate their time dependent decay rate to the corresponding B0sdecay modes into K0 K0and K K assuming U -spin symmetry. Using a double ratio in which the SU(3)-breakingeects largely cancel, the theoretical uncertainties are estimated to be at most 5% [9]. Thepotential weakness of this method is an up to 16-fold ambiguity in extracting  whichcan be reduced by considering other K() K() nal states. This constitutes a promisingmethod for a potentially clean measurement of . CDF expects to collect about 100-200B ! K() K() decays with its hadronic track trigger in 1 fb 1.ConclusionIn this contribution to the panel discussion on \The Future of Hadron B Experiments"held at the Beauty 2002 conference, we made an attempt to discuss the question \Quovadis, B physics?", where is B physics going in ve years and beyond by representing theB physics prospects at CDF and D. There exists a long laundry list of modes to measureat the B factories, the Tevatron and 3rd generation B experiments (BTeV, LHCb). In thekaon system two clean tests of the Standard Model have been identied, K0L ! 0 andK+ ! +, but it is not clear which are the \smoking gun modes" in the B system.6Precision measurements of sin 2, B0s! J=  and possibly B ! K() K() decays arelikely good candidates.Going back to looking at the \grand picture", the relation of the CKM matrix to thequark mass hierarchy, avour physics, the Higgs mechanism and electroweak symmetrybreaking, it would be desirable to have a well dened path with clean Standard Modeltests to be performed in the B system. Since this path is not obvious at this point, theonly answer can be to continue strengthening the planned experimental eorts (Run IIb,BTeV, LHCb) to ask questions to nature by doing experiments in order to test the avoursector of the Standard Model until it breaks. Let me conclude with a quote from WoodyAllen which does not only relate to the lack of access to divine counseling but also to thefunding situation in US high energy physics: \If only God would give me some clear sign!Like making a large deposit in my name at a Swiss bank."References[1] F. Gilman, these proceedings and private communication.[2] K. Anikeev et al., FERMILAB-PUB-01-197 (2001) [arXiv:hep-ph/0201071].[3] M. Paulini (for the CDF Collaboration), these proceedings;FERMILAB-CONF-03/010-E (2002).[4] B. Aubert et al. [BABAR Collaboration], Phys. Rev. Lett. 87, 091801 (2001);K. Abe et al. [Belle Collaboration], Phys. Rev. Lett. 87, 091802 (2001).[5] F. Gilman, K. Kleinknecht and B. Renk \The Cabibbo-Kobayashi-Maskawa Quark-Mixing Matrix", in K. Hagiwara et al. (Particle Data Group),Phys. Rev. D 66, 010001 (2002).[6] A. J. Buras, [arXiv:hep-ph/0101336].[7] M. Gronau and D. London, Phys. Rev. Lett. 65, 3381 (1990).[8] A. E. Snyder and H. R. Quinn, Phys. Rev. D 48, 2139 (1993);H. R. Quinn and J. P. Silva, Phys. Rev. D 62, 054002 (2000) [arXiv:hep-ph/0001290].[9] A. Datta and D. London, Phys. Lett. B 533, 65 (2002) [arXiv:hep-ph/0105073].7

Future of B Physics at CDF and D0

Future of B Physics at CDF and DO

Future of B Physics at CDF and DO

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