vided a long detailed ummary of what i known about the B meon branching fraction, and life time. Mot of the information they reported on the B meon br

Transcription

1 An Update on CLEO' Study of B Meon Decay Bernard Gittelman Cornell Univerity - thaca New York, USA ntroduction The family of meon wa dicovered at Fermilab[1] in At that time, purely by coincidence the CESR torage ring had been deigned and wa under contruction. Contruction of the CLEO- detector had alo begun. n 1978, the exitence of the (1S) and (2S) reonance were conrmed at the DORS torage ring of DESY[2], and from their meaurement of the e + e?! (1S) croection, it became clear that the reonance are bet decribed a b b quark pair, not tt. CESR began operation at the end of The CLEO (and CUSB) Collaboration began data taking. n 1980, CLEO (and CUSB) publihed obervation of the (1S), (2S), (3S)[3], and the (4S)[4]. The (4S), i a much wider reonance and i believed to decay excluively to B B meon. Over the next ix to eight year, many general propertie of B meon decay were meaured at DORS and CESR. n 1988, CESR hut down and the CLEO- detector wa replaced by the CLEO- detector. The new CLEO- detector conit of a better reolution tracking ytem and electromagnetic calorimeter. Figure 1 i an illutration of the CLEO- detector. Our undertanding of the B meon decay ha continued to improve with the CLEO- detector, but today we only undertand approximately 50% of the B decay. Thi paper i a decription of the tatu of our undertanding today compared with the Particle Data Group review publihed in Undertanding of B Meon Decay in 1996 n the 1996 Review of Particle Phyic[5], the Particle Data Group pro- 1

2 vided a long detailed ummary of what i known about the B meon branching fraction, and life time. Mot of the information they reported on the B meon branching fraction came from publication of the ARGUS Collaboration at DESY and publication of CLEO at Cornell. A ummary of the \larget" B meon branching fraction lited in the 1996 Review of Particle Phyic i given in Table 1. n the Standard Model, the b quark decay under the weak interaction to the c or u quark. From early experiment, it wa evident that the b! u interaction i more than an order of magnitude weaker than the b! c (See for example the b! ul and the B! X c l branching fraction lited in Table 1.). B meon decay are uually decribed by the diagram hown in gure 2 (Since the main decay are to c quark, the diagram hown in gure 2 do not include the b! u tranition.). The rt et of branching fraction in Table 1 are the emileptonic decay mode. Thee are the implet decay mode to decribe. They all proceed via the tree diagram. The lited branching fraction, for example Br(B! Xl) = (10:4 0:4)%, i uppoed to repreent the branching fraction for l = e or l =. The total emileptonic branching fraction include B! Xe; B! X, and B! X. The branching fraction to electon and muon are expected to be very cloe to identical. However, the branching fraction to lepton, which have never been meaured, are expected to be only 0:3 a large, becaue of the large ma (The factor 0.3 come from the phae pace). The um over electron, muon and tau emileptonic decay i 2:3(10:40:4) = (23:90:9)%. The econd group of branching fraction in Table 1 are the 2 body decay of the B meon in which the W boon materialize into a ud, (i.e., + or + ). One notice that the B + branching fraction are time larger than the B o '. The diagram decribing the B +! + D o decay are the tree and the color upreed hown in gure 2. The B o! + D? decay proceed through the tree and the W exchange diagram. f the W exchange amplitude i a large a the color upreed amplitude, thi would imply that color upreed amplitude i in phae with the tree, and the W exchange amplitude i out of phae. The third group of branching fraction in Table 1 are the 2 body decay of the B meon into a D () D (). Thee excluive two body mode add up to (5:5 2:0)%. The incluive yield of D coming from B decay wa lited a (8:6 2:2)%, which implie 64% of the B! XD are two body. The incluive decay of B meon to D meon in Table 1 add up to (82:2 6:0)%. Thee include the D meon coming from emileptonic decay 2

3 of the B meon. Mot of the ret of B meon decay are into Charmonium or Charm-Baryon. Adding the 1:14 0:06 and the 6:4 1:1 to the 82:2 6:0%, one ha accounted for (89:7 6:1)% of B meon decay. ncluive B Meon Decay Branching Fraction During the pat few year, CLEO ha made many remeaurement of incluive branching fraction in B meon decay. The mot recent CLEO meaurement on the incluive branching fraction are lited in Table 2. Thee reult are generally conitent but a little more accurate than thoe hown in Table 1. The eparate meaurement of emileptonic decay of B + and B o meon wa rt made via full recontruction of the B meon hadronic decay in the event then examining how often there wa a lepton coming from the remaining B meon decay[6]. Although thi method wa very clear and imple, it wa tatitically limited by the mall ample of fully recontructed B (or B) meon. The reult lited in Table 2 were obtained by partial recontruction of B o! D + l? ; D +! + D o, detecting only the lepton and the + [7]. Having collected a very large ample of partially recontructed B o and meauring how often there i alo a lepton amongt the leftover track coming from the other B meon decay, the emileptonic branching fraction of the B o wa determined. To obtain the B?! X o l? branching fraction, the reult of thi analyi wa then combined with a previou analyi[13] in which the emileptonic branching fraction averaged over charged and neutral B meon wa meaured. The reult indicate the B o branching fraction i 0:53% larger than the B +, which i indicate the B o lifetime i 0:53% longer than the B +. However, the uncertainty i large enough o that the branching fraction could be equal. The incluive decay to D meon in table 2 are the reult of oberving how often it wa poible to recontruct a D o (via D o! K? + ) and how often it wa poible to recontruct D + (via D +! K? + + ) in a et of event coming from (4S) decay. The ame analyi wa ued to meaure the incluive B branching fraction to D + and D o by meauring how often it i poible to recontruct a D + and how often a D o. One hould undertand the incluive D branching fraction include D meon coming from D decay. Normally, the D meon from B meon decay originate from the b quark tranition, b! cw?. However, D meon can come from B meon decay by the W?! c. Both the tree and the color upreed diagram (ee gure 2) 3

4 Table 1. Summary of Major B Meon Branching Fraction known in 1996 ( Number from PDG Review[5] ) Decay Mode B + B o Admixture B! Dl (%) (%) B + and B o (%) 1:6 0:7 1:9 0:5 B! D l 5:3 0:8 4:6 0:3 B! D l 2:7 0:7 B! X c l 10:1 2:3 10:3 1:0 B! Xl 10:4 0:4 b! ul 0:18 0:05 B! D + 1:34 0:18 0:78 0:14 B! D + 1:55 0:31 0:73 0:15 B! D + 0:53 0:05 0:30 0:04 B! D + 0:52 0:08 0:26 0:04 B! DD + 1:7 0:6 0:7 0:4 B! D D + 0:1 0:07 1:2 0:6 B! DD + 1:2 1:0 2:0 1:5 B! D D + 2:3 1:4 1:9 1:2 B! XD + 8:6 2:2 B! D? X 24:2 3:3 B! D o X 58:0 5:0 B! K 0:10 0:014 0:075 0:021 B! K + +? 0:14 0:06 B! K +? 0:11 0:06 B! K 0:17 0:05 0:16 0:03 B! X 1:14 0:06 B! Charm-Baryon 6:4 1:1 4

5 can lead to D from B decay. A meaurement of how often the B meon decay to a D meon and how often to a D meon ha been made[9]. Thi wa carried out by uing the fact that the (4S) decay to B B. One of the two B meon i tagged via the ign of the lepton in it emileptonic decay. Only high momentum lepton (p l > 1:4 GeV/c) are ued, to eliminate lepton from emileptonic D decay. The other B meon i aumed to have the oppoite avor (Correction are made for the B o $ B o mixing of the neutral B meon). Having tagged the avor of one of the B meon, the D meon coming from that ame B meon i known to have an explicit avor. Thi D meon, which come from the tagged B meon, i identied via the angular correlation. Since the lepton ha a momentum greater than 1.4 GeV/c, the D meon mut be moving at an angle greater than 90 o away from the lepton in order to conerve momentum. The D meon from the other B meon are iotropic, o the avor of the D meon in the ame hemiphere a the lepton wa tudied. From the number in Table 2, one ee that 90% of the D meon from B decay come from the c quark that originate from the b! cw? tranition and 10% come from the W boon. The B! XD incluive branching fraction were meaured by tudying the number of D meon and their momentum pectrum at the (4S) No attempt wa made to tag the avor of the B meon or it charge. From the D momentum pectrum it wa concluded that the D i almot alway coming from the W boon. To obtain the branching fraction, 12:11%, it wa aumed that the B + and B o branching fraction to D are the ame. Thi value i ignicantly larger than the 1996 PDG value (ee Table 1.). The mot intereting new incluive reult i the meaurement of the B decay to X[12]. The 17:6% branching fraction i much larger than one might expect. Some of the meon come from the D and D meon that are in the B meon decay. The contribution from feed down ha been etimated from the incluive B! D ; D o?, and D branching fraction and the incluive branching fraction of each of thee three charm meon. The branching fraction etimate are Br(B! DX! X 0 ) = (2:5 0:5)%, and Br(B! D X! X 0 ) = (2:8 0:6)%. Subtracting thee lead to the concluion (12:3 1:8)% of B decay produce meon directly. meon are often decribed a partly an reonance, but thi 12:3% branching fraction i much larger than the incuive Br(B! X) = (3:5 0:7)%[5]. 5

6 Table 2, ncluive B Meon Branching Fraction from CLEO Decay Mode Branching Fraction (%) Reference Semileptonic Decay B +! X o l + 10:25 0:57 0:65 [7] B o! X? l + 10:78 0:60 0:69 [7] ncluive Decay to D meon Auming an Equal Admixture of B B o o and B + B? B! D o X + B! D o X 63:6 1:4 2:6 [8] B! D + X + B! D + X 23:5 0:9 2:4 [8] B! D o X + B! D o X 24:7 1:2 2:5 [8] B! D + X + B! D + X 23:9 1:5 1:7 [8] ncluive Flavor Senitive Decay to D meon (lv) for D meon from b! c, (uv) for D meon from W?! c B! D o X + B! D + X (lv) 79:2 3:9 [9] B! D o X + B! D? X (uv) 7:9 2:2 [9] ncluive B! D Decay B +! D + X = B o! D + X 12:11 0:39 1:63 [10] ncluive B! Charmonium Decay B! X = B! X 1:12 0:04 0:06 [11] B! X = B! X Direct 0:80 0:08 [11] B! 0 X = B! 0 X 0:34 0:04 0:03 [11] B! c1x = B! c1x 0:40 0:06 0:04 [11] B! c2x = B! c2x 0:25 0:10 0:03 [11] B! Charmonium (total) 1:79 0:15 from above ncluive B Decay to X (B! X) 17:6 1:1 1:2 [12] 6

7 Excluive B Meon Decay Branching Fraction The um of all the excluive branching fraction lited in Table 1 add up to (15:6 2:1)%, (16:6% for B +, 17:4% for B o ). n recent year, many other 2 body nal tate have been earched for. Mot of thee are \rare B decay"[14]. The excluive nal tate lited in Table 1 have been remeaured. The new CLEO reult for thee and a few other are given in Table 3. There have been everal new meaurement of emileptonic decay. For the b! c nal tate, there have been no eriou change. The D1l o ha been meaured. There have alo been meaurement of the b! u nal tate, l and l. The branching fraction of the excluive b! cl nal tate that have been oberved add up to 7:0% which i only 67% of the incluive branching fraction. The oberved b! u nal tate add up to 0:043% compared with the incluive rate of 0:18% from Table 1, i.e., only 25% of the b! ul i undertood. The excluive two body charm decay in which the W boon materialize a a ; or D have been remeaured. Mot of the reult agree with the earlier meaurement and are more accurate. The remeaurement on B! K () have imilar reult. Summary- What Fraction of B Meon Decay are \Undertood" Theoretically, the Semileptonic decay of B meon are the eaiet to undertand, becaue there i only one hadronic vertex. Originally[25], the emileptonic branching fraction wa etimated to be approximately 16%. After independent meaurement at DORS, CESR, and LEP, we nd the branching fraction i ignicantly maller. The generic average of the CLEO meaurement give the incluive branching fraction, Br( B! Xl) = (10:5 0:89)%: Although uing QCD correction, theorit have recently uggeted the B emileptonic branching fraction could be a low a 12%, the CLEO reult i a theoretical challenge. Furthermore, only a fraction of the of the hadronic content of the emileptonic decay have been meaured. Summing over the 7

8 Table 3, Excluive B meon Decay Branching Fraction from CLEO Decay Mode B + B o Reference (%) (%) Semileptonic Decay B! Dl 1:94 0:15 0:34 1:87 0:15 0:32 [15] B! D l 5:13 0:54 0:64 4:49 0:32 0:39 [16] B! D1l o 0:56 0:13 0:09? [17] B! l 0:018 0:004 0:004 [18] B! l 0:025 0:004 0:007 [18] Excluive Two Body Charm Decay B! D 1:35 0:12 0:15 0:81 0:11 0:18 [19] B! D 1:68 0:21 0:28 0:74 0:10 0:14 [19] B! D 0:55 0:04 0:05 0:29 0:04 0:06 [19] B! D 0:434 0:033 0:038 0:281 0:011 0:022 [20] B! DD + 1:26 0:22 0:29 0:87 0:24 0:22 [21] B! DD + 0:87 0:27 0:20 1:00 0:35 0:25 [21] B! D D + 1:40 0:43 0:39 0:93 0:23 0:19 [21] B! D D + 3:10 0:88 0:75 2:03 0:50 0:43 [21] B! D? D + < 0:12 [22] B! D D < 0:18 [22] B! D? D + < 0:22 [22,26] Excluive B! Charmonium Decay B! K 0:102 0:008 0:007 0:085 0:013 0:006 [23] B! K 0:141 0:023 0:024 0:132 0:017 0:017 [23] B! 0:0056 0:0027 < 0:0058 [24] B! < 0:077 < 0:025 [24] B!! < 0:027 [24] 8

9 meaured charm hadronic tate, one ha Br( B! (D + D + D )l) = (7:00 0:85)% Therefore, we undertand (7:00 0:85)=(10:5 0:89) = (67:0 13:7)% of emileptonic branching fraction. From the CLEO meaurement of the avor dependence of the decay of B meon to D meon, we know the Br( B! DX) = (79:2 3:9)% (i.e., from b! c at the lower vertex). Auming the excluive emileptonic branching fraction to ' are 0.3 time the branching fraction to electron and/or muon, and adding the excluive emileptonic decay to e', ', and ', we have for the total excluive emileptonic branching fraction Br( B! D (;) (e + + )) = (2:3 (7:00 0:85) = (16:1 2:0)% The excluive two body decay reulting in a D meon add up to Br( B! D+D +D+D +DD +D D +DD +D D ) = (8:81:2)% (Thi wa calculated from the number in Table 3, averaging over B + and B o.) Putting the above number together, the incluive B! DX decay are \undertood" at the level, Br( B! D () (l D )) = (16:1 2:0) + (5:73 1:17) + (3:07 0:35) = (24:9 1:8)% Thi i (24:9 1:8)=(79:2 3:9) = 0:31 0:03 of the incluive D meon coming from the b! c vertex. The average of excluive nal tate with charmonium that have been meaured add up to (0:23 0:03)%. The excluive baryon nal tate have not yet been fully recontructed. Therefore, we have an excluive undertanding of (24:9 1:8 + 0:23 0:03) = (25:1 1:8)% of the B decay. n term of incluive branching fraction, in the B! DX decay, the X repreent lx 0, D X 00, and X 000. Here X 0 include the ' coming from D or D which we know omething about, but X 00 and X 000 are not known. From the value of the branching fraction B! DX = (79:2 3:9)%, we calculate, Br( B! DX 000 ) = B! D(X? lx 0? D X 00 ) = (79:2 3:9)? (2:3 (10:5 0:89))? (12:1 1:7) 9 = (42:9 4:7)%

10 Thi mean we know nothing about (42:9=79:2) = 54% of the incluive B! DX decay. The total incluive branching fraction, (excluding the \rare" decay) add up to Br(B! DX + charmoniumx 0 + baryonx 00 ) = = (79:2 3:9) + (1:8 0:2) + (6:4 1:1) = (87:4 4:1)% CLEO ha recently made many meaurement of rare decay (and upper limit of rare decay)[14]. However, the total um of the meaured mode and the upper limit on rare B decay branching fraction i le than 2 10?3, o there i no need to include thee at thi time. The concluion i one mut invent non-rare decay mode and look for them. Acknowledgement would like to thank Giancarlo Moneti and Ed Thorndike of the CLEO Collaboartion for ueful comment, correction, and dicuion related to thi paper. The hopitality of the organizer of the Quark-98 Seminar in Suzdal made thi viit to Ruia, my rt in ten year, warm and intereting. Reference [1] Obervation of a new group of reonance at 10 GeV decaying to muon pair S.W. Herb et al., Phy. Rev. Lett. 39; 252(1977): [2] Conrmation of the exitence of the (1S) and (2S) C. Berger et al., Phy. Lett. 76B; 243(1978): C.W. Darden et al., Phy. Lett. 78B; 246(1978): J.K. Bienlein et al., Phy. Lett. 78B; 360(1978): C.W. Darden et al., Phy. Lett. 80B; 419(1979): [3] Obervation of Three Upilon State D. Andrew et al., Phy. Rev. Lett. 44; 1108(1980): T. Bohringer et al., Phy. Rev. Lett. 44; 1111(1980): 10

11 [4] Obervation of a Fourth Upilon State in e + e? Annihilation D. Andrew et al., Phy. Rev. Lett. 45; 219(1980): G. Finnocchiaro et al., Phy. Rev. Lett. 45; 222(1980): [5] Particle Data Group Review, Phy.Rev.D 54; 1(1996) [6] Semileptonic Branching Fraction of Charged and Neutral B Meon M.Athana et al., Phy. Rev. Lett. 73; 3503(1994), (erratum, Phy. Rev. Lett. 74; 3090(1995)) [7] Study of the B 0 Semileptonic Decay Spectrum at the (4S) Reonance M. Artuo et al., Phy. Lett. B 399; 321(1997): [8] The ncluive Decay B! DX and B! D X L. Gibbon et al., Phy. Rev. D 56; 3783(1997): [9] Flavor-Specic ncluive B Decay to Charm T.E. Coan et al., Phy. Rev. Lett. 80; 1150(1998): [10] Meaurement of B! D + X Decay D. Gibaut et al., Phy. Rev. D 53; 4734(1996): [11] ncluive Decay of B Meon to Charmonium R. Balet et al., Phy. Rev. D 52; 2661(1995): [12] The ncluive Decay B! X Y. Kubota et al., Phy. Rev. D 53; 6033(1996): [13] Meaurement of the B Semileptonic Branching Fraction with Lepton Tag B. Barih et al., Phy. Rev. Lett. 76; 1570(1996): [14] Search for Excluive Charmle Hadronic B Decay D.M.Aner et al., Phy. Rev. D 53; 1039(1996): Evidence for Penguin-Diagram Decay: Firt Obervation of ::: R. Ammar et al., Phy. Rev. Lett. 71; 674(1993): Obervation of B +!!K + and Search for Related B Decay Mode T. Bergfeld et al., Phy. Rev. Lett. 81; 272(1998): 11

12 [15] Meaurement of the B! D` Partial Width and Form Factor Parameter M. Athana et al., Phy. Rev. Lett. 79; 2208(1997): [16] Meaurement of the B! D ` Branching Fraction and jv cb j B. Barih et al., Phy. Rev. D 51; 1014(1995): [17] nvetigation of Semileptonic B Meon Decay to P-Wave Charm Meon A. Anataov et al., Phy. Rev. Lett. 80; 4127(1998). [18] Firt Meaurement of the B! ` and B! (!)` Branching Fraction J. Alexander et al., Phy. Rev. Lett. 77; 5000(1996): [19] Excluive Hadronic B Decay to Charm and Charmonium Final State M.S. Alam et al., Phy. Rev. D 50; 43(1994): [20] New Meaurement of B! D Branching Fraction G.Brandenburg et al., Phy. Rev. Lett. 80; 2762(1998): [21] Meaurement of B! D + X Decay D. Gibaut et al., Phy. Rev. D 53; 4734(1996): [22] Search for the Decay B 0! D ()+ D ()? D.M. Aner et al., Phy. Rev. Lett. 79; 799(1997): [23] Meaurement of the Decay Amplitude and Branching Fraction of B! J= K and B! J= K Decay C.P. Jeop et al., Phy. Rev. Lett. 79; 4533(1997): [24] Study of B! M. Bihai et al., Phy. Lett. B 369; 186(1996): [25] B Meon Decay, B. Gittelman, S. Stone High Energy Electron-Poitron Phyic, World Scientic (Singapore), (1988) [26] Recently there ha been a meaurement of the branching fraction, Br(B! D? D + ) = (7:8 +5:4?3:8 1:5) 10?4. Thi ha been ubmitted to the Van Couver conference, CLEO CONF 98-07; CHEP

13 ??Helium Reervoir Muon Chamber????? PTL??? Time?? Superconducting Coil Barrel Shower Detector Drift Chamber Detector Micro-Beta Quadrupole Vertex Detector End Cap Time of Flight Pole Tip Shower Detector of Flight Scintillator Magnet Yoke Meter FG. 1 Side View of the CLEO- Detector 13

14 TREE d B b W c u c D, D*, D** u, d COLOR SUPPRESSED b c B W c, K, K* u, d W Exchange B o b W c D + D + D 0 d u K 0 FG. 2 The Electro-Weak-Theory Diagram ued to Decribe the Mot Likely Decay of the B Meon 14