A summary of recent results on B rare decays from the CDF and D0 experiments
operating in Run II of the Fermilab Tevatron is given; analyzed decay modes are
B_{d,s}--> hh, B_{d,s}--> mu^{+}mu^{-}, and B--> mu^{+} mu^{-}h. Data samples
are relative to 1 fb^{-1} or more integrated luminosity of p-pbar collisions at
sqrt(s) = 1.96 TeV. All reported results are in agreement with Standard Model
predictions and consistent with B-Factories analyzes.Comment: Proceedings of the Moriond QCD and Hdronic Interactions 2007
  Conference, La Thuile, March 17-24, 200

Scuri, Fabrizio

English

arXiv

A summary of recent results on B rare decays from the CDF and D0 experiments operating in Run II of the Fermilab Tevatron is given; analyzed decay modes are B{sub d,s} {yields} hh, B{sub d,s} {yields} {mu}{sup +}{mu}{sup -}, and B {yields} {mu}{sup +}{mu}{sup -} h. Data samples are relative to 1 fb{sup -1} or more integrated luminosity of p{bar p} collisions at {radical}s = 1.96 TeV. All reported results are in agreement with Standard Model predictions and consistent with B-Factories analyzes

UNT (University of North Texas) Digital Library

MEASUREMENTS OF B RARE DECAYS AT THE TEVATRONF. SCURIon behalf of the CDF and D0 collaborations.Istituto Nazionale di Fisica Nucleare, Sezione di Pisa,Largo B. Pontecorvo 3, I-56127 Pisa, ItalyA summary of recent results on B rare decays from the CDF and D0 experiments operating inRun II of the Fermilab Tevatron is given; analyzed decay modes are Bd,s → hh, Bd,s → µ+µ−,and B → µ+µ− h. Data samples are relative to 1 fb−1 or more integrated luminosity of pp¯collisions at√s = 1.96 TeV. All reported results are in agreement with Standard Modelpredictions and consistent with B-Factories analyzes.1 IntroductionThe large production of all kinds of b-hadrons at the Tevatron offers the opportunity to studyrare decays also in the Bs and b-baryon sectors, exploiting a physics program complementary tothe B-Factories.The bottom anti-bottom production cross-section σ(bb¯) at the Tevatron is O(105) larger thanproduction in e+e− colliders at the Υ(4s) or Z0 energy scale; however, the inelastic cross-sectionis a factor 103 larger than σ(bb¯) and the branching ratios of rare b-hadron decays are O(10−5) orlower; therefore, interesting events must be extracted from a high track multiplicity environmentand detectors need to have very good tracking and vertex resolution, wide acceptance and goodparticle identification, highly selective trigger. Both CDF and D0 detectors, whose detaileddescription can be found elsewhere 1, match those requirements.The following decays modes are analyzed here: charmless Bd,s → h+h−, Bd,s → µ+µ−,and B → µ+µ− h. All those rare decay modes are interesting in the search of New Physicscontributions, each mode with its own peculiarity: charmless B → hh decays are a useful toolfor probing CKM inferring on the α and γ angles of the Unitarity Triangle; they are alsosensitive to New Physics effects both in the Penguin diagram contributions to the process andvia anomalies in the CP Asymmetry ACP .The Standard Model prediction of the Branching Ratio for flavor-changing neutral current(FCNC) processes like Bs → µ+µ− is very suppressed: B(Bs → µ+µ−)SM = (3.35±0.32)×10−9(M.Blanke et al. 2); a slightly higher value for the BR upper limit was recently estimated inConstrained Minimal Flavor Violation 3: B(Bs → µ+µ−)CMFV < 7.42 × 10−9 (95% C.L.);the leptonic branching fraction of the Bd decay is suppressed by a factor | Vtd/Vts |2 in theCKM matrix elements leading to a SM predicted BR of O(10−10). The decay amplitude ofBd,s → µ+µ− can be significantly enhanced in some extensions of the SM, such as, for instance,the type-II two-Higgs-doublet-model (2HDM), where the BR depends only on MH+ and on tanβ,the ratio between the vacuum expectation values of the two neutral Higgs fields; in this case 4,B(B → µ+µ−)2HDM ∝ (tanβ)4. In the minimal super-symmetric standard model (MSSM) thedependence on tanβ is even stronger, B(B → µ+µ−)MSSM ∝ (tanβ)6, leading to an enhancementof orders of magnitude 5 in case of large values of tanβ.The b → s µ+µ− transition in the B→ s-meson µ+µ− modes allows the study of FCNC inmore detail through additional observables, such as the dimuon invariant mass m(µ+µ−), andthe forward-backward asymmetry of the s-quark in the dimuon system.A summary of recent results from the Tevatron experiments is given in the following sectionfor all modes; quoted values refer to integrated luminosities varying from about 1 fb−1 to about2 fb−1, depending on the specific analysis, and covering the Tevatron Run-II data taking periodfrom 2002 to beginning of 2007.FERMILAB-CONF-07-163-E2 Tevatron result summary for B rare decaysHadronic decays of the B mesons into two charged tracks are studied in an efficient way bythe CDF experiment, exploiting the high performances of its peculiar Secondary Vertex Trigger(SVT), designed to select events with vertexes displaced with respect to the primary vertex andwhose full description can be found elsewhere 6. Details of the event selection procedure and ofthe analysis method can be found in a recent CDF publication 7.Partially reconstr.B-decaysCombinatorialbackgrounda)PRb)PRc)Figure 1: a): M(pipi) invariant mass distributions; b) Probability Ratio for B0 → K+pi−; c) Probability ratio forBs → K−pi+.The invariant mass m(pipi) after cut optimization is shown in figure 1a); about 6500 signalevents accumulate in the signal region; individual modes overlap in a single peak as shown by thesignal composition (filled colored areas) estimated via Monte Carlo and including full detectorsimulation. The signal composition in real data is measured with a likelihood fit, combininginformation from kinematics (mass and momentum) and particle identification; details of the fitprocedure can be found elsewhere 7.Table 1: CDF results with 1 fb−1 large sample for B(B → h+h−).Decay mode BR × 106B0 → pi+pi− 5.10 ± 0.33(stat.) ± 0.36(syst.)B0 → K+K− 0.39 ± 0.16(stat.) ± 0.12(syst.)Bs → K+K− 24.4 ± 1.4(stat.) ± 4.6(syst.)Bs → pi+K− 5.0 ± 0.75(stat.) ± 1.0(syst.)Bs → pi+pi− 0.53 ± 0.31(stat.) ± 0.40(syst.)Measured branching ratios for individual modes are summarized in table 1; values for theBd modes are consistent with the B-Factories results, while the Bs modes are CDF exclusive.The very good separation power between B0 and B¯0 achieved with the likelihood fit isshown in figure 1b) for the raw asymmetry of the B0 → K+pi− mode ; the probability ratioPR = pdf(B0)/[pdf(B0) + pdf(B¯0)] is based on probability density functions (pdf) using 5observables (M(pi1, pi2), p1 + p2, the charged pion momentum um-balancing 7, and the particleidentification ID1 and ID2). With this method, the first measurement of direct CP asymmetry(ACP ) in the Bs system was done, figure 1c). CDF results on ACP for the Kpi modes are givenin the following equations:ACP (B0d → K+pi−) =N(B¯0d→K−pi+)−N(B0d→K+pi−)N(B¯0d→K−pi+)+N(B0d→K+pi−) = −0.086± 0.023(stat.)± 0.009(syst.)ACP (B0s → K−pi+) = N(B¯0s→K+pi−)−N(B0s→K−pi+)N(B¯0s→K+pi−)+N(B0s→K−pi+)= −0.39± 0.15(stat.)± 0.08(syst.)(1)Tevatron and B-Factories results on ACP (B0d → K+pi−) agree; Tevatron confirms the differencein sign w.r.t. ACP (B+ → K+pi0). The measured value of ACP (B0s → K−pi+) (1) can becompared with the value obtained with the Lipkin test 8, based on minimal assumptions, justSM with SU(3) symmetry; in this case, the following equation holds:ACP (B0s → K−pi+) = −ACP (B0d → K+pi−) ·B(B0d → K+pi−)B(B0s → K−pi+)· τ(B0d)τ(B0s )≈ 0.37 (2)In equation 2 the values of ACP (B0d → K+pi−) and B(B0d → K+pi−) are taken from the HeavyFlavor Averaging Group 9, B(B0d → K+pi−) is the CDF resulted quoted in table 1, and thelifetime ratio is set equal to one.The two Tevatron experiments adopt similar procedures to search for Bs → µ+µ− events; ablind cut optimization is made using signal Monte Carlo samples and signal sidebands for esti-mation of the background in the data sample. The B+ → J/ψ K+ mode is used as normalizationchannel in the BR estimation. Similar discriminating observables (secondary vertex displace-ment, B pointing angle to the primary vertex, B isolation) are used to construct a LikelihoodRatio (LR); optimal values of LR for event counting are obtained with different methods. Themain difference in the two analyzes is the definition of the signal window in the µ− µ invariantmass spectrum (figure 2); a 360 MeV/c2 wide search region including Bd and Bs is defined byD0, two different regions, 120 MeV/2 wide and centered in the Bd and Bs nominal masses areused by CDF, quoting separate limits; D0 assumes B(Bd → µ+µ−)  B(Bs → µ+µ−) andquotes the overall value as a conservative limit on B(Bs → µ+µ−).(~1300 pb-1)(~500 pb-1)a)b)Figure 2: a), b): D0 Likelyhood Ratio LR vs. µ− µ invariant mass; blue lines set the LR optimal value; c) CDFµ− µ invariant mass vs. LR; red and blue boxes define the search areas for Bd and Bs respectively.Tevatron results on Bs → µ+µ− are summarized in table 2; a statistical combination is madeby D0 to quote the overall limit from two data taking periods, before (run IIa) and after (runIIb) insertion of a new inner layer in silicon vertex detector.Table 2: Tevatron result summary for Bs → µ+µ−; (*) D0 run IIa and IIb combined result.Exp. Int. Lum. Bs events Bd events B(Bs → µ+µ−) B(Bd → µ+µ−)pb−1 Expected Obs. Expected Obs. 90%(95%) C.L. 90%(95%) C.L.CDF 780 1.27±0.37 1 2.45±0.40 2 < 8.0 · 10−8(10) < 2.3 · 10−8(3)D01300 (run IIa)500 (run IIb)0.8 ±0.21.5 ±0.512- - < 7.5 · 10−8(9.3)(*) -CDF and D0 analyzes to reconstruct the B→ µ+µ− hs modes are similar; each signal isnormalized to the analogous B→ J/ψ hs mode after a blind cut optimization and backgroundestimation from the signal sidebands; details of the procedure can be found elsewhere 10.CDF results for the Bu,d modes, obtained with 1 fb−1, are summarized in table 3; they arein good agreement with those from the B-Factories 11 and have similar uncertainty.Table 3: CDF result summary for the Bu,d → h µ+µ− modes;Mode Evts. in the signal region Estimated bkg. BR·10−6B+ → µ+µ−K+ 90 45.3±5.8 0.60±0.15(stat.)±0.04(syst.)Bd → µ+µ−K∗0 35 16.5±3.6 0.82±0.31(stat.)±0.10(syst.)CDF and D0 limits for B(Bs → φ µ+µ−) are shown in table 4; CDF uses a Bayesianapproach to extract its limit, while D0 confidence interval is constructed within the Feldman-Cousins scheme.Table 4: Tevatron result summary for Bs → φ µ+µ−;Exp. Int.Lum. Observed events Expected events BRCDF 920 pb−1 11 3.5±1.5 < 2.4 · 10−6(90% C.L.)D0 450 pb−1 0 1.6±0.6 < 3.3 · 10−6(90% C.L.)3 ConclusionsTevatron is demonstrated to be a good place to study B rare decays offering different possibilitiesto constrain more and more New Physics in the Bs → µ+µ− and b→ s µ+µ− modes; moreover,a physics program complementary to the B-Factories can be exploited in the Bs → h+h− sector.CDF made the first observation of the Bs → K−pi+ mode whose direct CP asymmetry appearsto be large in agreement with expectation.Tevatron current values for the limits on B(Bs → µ+µ−) are entering the 10−8 territory; D0current best limit is the first Tevatron result with 2 fb−1 integrated luminosity. Any signal atTevatron before its run II program end (∫Ldt ∼ 8 fb−1) will be evidence of New Physics.CDF and D0 are beginning the exploration of the b → s µ+µ− field; upper limits forB(Bs → φ µ+µ−) obtained with less than 1 fb−1 are close to the SM prediction, CDF reportednew results on B(Bu,d → s µ+µ−) in general agreement with the B-Factories; significantlyimproved results will come soon.References1. CDF Collaboration, D.Acosta et al, Phys. Rev. D 71, 032001 (2005),D0 Collaboration, V.M.Abazov et al, Nucl. Instrum. Methods A 565, 463 (2006).2. M. Blanke et al., JHEP 610, 003 (2006)3. T. Hurth, submitted to Nucl. Phys. B, hep-ph/0612231.4. H.E Logan and U. Nierste, Nucl. Phys. B 586, 39 (2000)5. K.S. Babu and C.F. Kolda, Phys. Rev. Lett. 84, 228 (2000)6. W. Ashmanskas et al, Nucl. Instrum. Methods A 518, 532 (2004).7. CDF Collaboration, A. Abulencia et al, Phys. Rev. Lett. 97, 211802 (2006)8. H.J. Lipkin,Phys. Lett. B 621, 126 (2005)9. http://www.slac.standford.edu/xorg/hfag10. D0 Collaboration, V.M. Abazov et al.,Phys. Rev. D 74, 031107(R) (2006)CDF Collaboration, CDF public note 8543, Nov. 30, 200611. BaBar Collaboration, B. Aubert et al.,Phys. Rev. D 73, 092001 (2006)Belle Collaboration, K. Abe et. al., ICHEP04, Beijing, 16-22 Aug. 2004, hep-ex/0410006.

Measurements of B rare decays at the Tevatron

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Measurements of B Rare Decays at the Tevatron

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