on behalf of the LHCb collaboration

Transcription

1 CONSTRAINING THE CKM ANGLE AT L. CARSON School of Physics and Astronomy, James Clerk Maxwell Bilding, Mayfield Road, Edinbrgh EH9 3JZ, UK on behalf of the collaboration The experiment is a general prpose forward spectrometer operating at the Large Hadron Collider, optimised for the stdy of B and D hadrons. has collected 3 fb 1 of integrated lminosity, which provides an nprecedentedly large sample of B hadron decays to final states involving charmed hadrons. These decays offer many complementary ways to measre the angle / of the CKM triangle. The latest combination of measrements to provide a vale of / is presented, along with the first measrements of GPviolating ob servables in B+ + DK+ and B+ + D7r+ decays with D + KK±7r'f final states. The first observations of a nmber of 1>baryon decays that have the potential to contribte to measrements of / are also reported. 1 Introdction The CKM parameter is crrently the least wellconstrained angle of the CKM triangle. Combi nations made in smmer 212 by the CKMFitter 1 and UTFit 2 collaborations, before the inclsion of measrements from, gave = (66 ± 12) and = (76 ± 1) respectively. Measrements of can be made sing B decays that are mediated only by treelevel transitions, for example B decays to open charm mesons. Since these transitions are nlikely to be affected by New Physics, they provide a "standard candle" to measre the Standard Model (SM) vale of The vale of measred in this way can then be compared to vales measred sing B decays mediated by looplevel transitions, for example B decays to light charmless hadrons. A significant difference between these vales wold indicate a New Physics contribtion to the loop processes. This docment presents the latest reslts from the experiment 3 measring CFviolating observables in hadronic B decays to open charm. Reslts from timeindependent analyses of B++ DK+ and B + + D7r+ decays, with varios final states of the D meson, are combined to give a first vale for The first analysis of B+ + DK+ and B + + D7r+ decays with D + KK±7r'f final states is also described. Finally, stdies of bbaryon decays to D ph and Ach final states (where h represents a charged pion or kaon) are reported. Most of the reslts reported here are based on data corresponding to 1 fb 1 of integrated lminosity, collected in 211 at a centreofmass energy of 7 TeV, while some reslts also inclde the 2 fb 1 of data collected in 212 at a centreofmass energy of 8 TeV. 2 Gamma combination from timeindependent analyses of B+ + DK+ and B+ + D7r+ In general, timeindependent methods of measring from hadronic B decays to open charm take advantage of the interference between b + c and b + transitions at treelevel, where

2 the D final state is accessible to both D and If. The most commonly sed B decays are B+ +DK+ and B+ + DJr+. Aside from the weak phase y, these analyses also measre the hadronic parameters rb(d) and Dn(D) where the ratio of the favored to sppressed B(D) decay amplitdes is rs(d)ei(bb(dj). The method to extract these hadronic parameters and depends on the D final state. The three methods discssed in this docment are sally referred to by the initials of the athors of the paper(s) that first proposed the method. There is the "GLW" method 4, where the D decays to a GP eigenstate, the "ADS" method 5 where the D decays to a qasiflavorspecific state, and the "GGSZ" method 6 where the D decays to a selfconjgate threebody final state. has pblished measrements, all based on 1 fb1 of data, sing D + Jr+Jr, K+ K and K±Jr'f in a twobody ADS and GLW analysis 7, D + K±Jr'f7r+Jr in a forbody ADS analysis 8, and D + KJr+Jr and D + KK+ K in a GGSZ analysis 9. These measrements have been combined, sing a freqentist approach, to obtain a combined vale for 1. In addition to the measrements, CLEOc measrements are also sed to constrain some of the parameters of the relevant D systems 11. The experimental likelihoods are combined as where A are the experimental observables (sch as, Rep+, x+, etc), and a are the physics parameters (sch as y, rs, etc). Confidence intervals are then obtained from this likelihood in a freqentist way. The confidence intervals are rescaled to accont for ndercoverage and neglected correlations between systematics. The effects of D If mixing, and of possible GP violation in the D decays, are taken into accont. The confidence intervals for and rs from a combination of the DK and Drr measrements are shown in Fig. 1. The 68% confidence interval for is [55.4, 82.3]. Following the pblication of Ref. 1, performed a preliminary pdate of the GGSZ analysis with D + Krr+rr and D +KK+K final states, sing 3 fb1 of data 12. This reslt has been sed to make a preliminary combination 13 with the 1 fb1 analyses that were sed for the pblished combination described above. The preliminary combination ses measrements from B+ +DK+ decays only. The reslting confidence interval for is shown in Fig. 2. Also shown is a comparison of the confidence interval for from the preliminary combination with that from a combination of B+ +DK+ measrements based only on the 1 fb1 dataset. The preliminary measrement of from this combination is = (67± 12) The measrements sed for this combination were inclded in the global CKM fits for the first time in reslts presented at the smmer conferences in 213. The fitted vales for were = (68.:1::) from CKMFitter, and (7.1 ± 7.1) from UTFit. = 1 ' 1 ' ia' LW W W!OOlWIWIW 1 ' Lc_Lc_,_'1! Figre 1 Confidence intervals, reslting from the combination of the DK and D7r measrements, for / (left), and TB (right). [OJ r

3 3 Timeindependent analyses of B++DK+ and B++ DJr+ with D+ KK±Jr final states has made the first stdy of GP violation in B+ + DK+ and B+ + Dir+ decays with D+ KK±Ir final states, sing 3 fb1 of data 14. This is the first time an "ADSlike" analysis has been performed with a SinglyCabibboSppressed ( SCS) final state 15. The final states are labelled OppositeSign ( OS) or SameSign ( SS ) by comparing the charge of the kaon from the D decay with the charge of the initial B meson. The analysis of the threebody D final state reqires knowledge of how the average interference amplitde (1'KsK11:) and strong phase difference (8KsK11:) vary across the D Dalitz plot. This information is taken from measrements by the CLEO c collaboration 16. The analysis measres the yield ratios (R) and charge asymmetries (A) between OS and SS final states, and between DK and Dir final states. Combining this information with the CLEOc measrements allows 1, rb, rd and 8B to be extracted. The analysis is performed across the whole D Dalitz plane, and also in a restricted region arond the K>± resonance, to take advantage of the higher coherence factor (1'KsK11:) in that region. Examples of the fits to the invariant mass of the B candidates are shown in Fig. 3. The measred vales of the observables are shown in Table 1. The scans of the x2 probability over the 1 rs parameter space are shown in Fig. 4, for the fit to the whole D Dalitz region and the fit to the region arond the K>± resonance. It can be seen that the constraints from this analysis are consistent with those obtained by from other final states. With a larger dataset, this analysis will provide valable constraints on 1..l y..l y.8 Preliminary % 1! !ff' Prelimi=y [OJ 1()() [OJ Figre 2 Left: confidence interval for from the preliminary combination of DK measrements inclding the 3 fb 1 GGSZ analysis. Right: comparison with the combination of DK measrements based only on the 1 fb 1 dataset. The prple (green) interval corresponds to the pdated (1 fb 1 only) combination. N' <..l " 5 1 Figre fk,;kk+]d K (c) Sm, Incl. combinatorics B + Signal MisID Partially reconstrcted 2 " 5 3 ct;' 3 :>" 52 1 Sm, incl. combinatorics Signal Partially reconstrcted m([kn+jd re+) [MeV/c2] Distribtions of the invariant mass of the B candidates for two sbsamples of the data the SS (left), and the OS B + + D11:+ (right). The fit PDFs are sperimposed. B + DK

4 Table 1: Reslts for B +, DK+ and B+, D7r+ observables measred in the whole Dalitz region, and in the region arond the Kd resonance. The first ncertainty is statistical and the second is systematic. Whole Dalitz plot K*± window 2.57±.13 ± ±.58±.25 Rss;os,n".92±.9±.4.84±.11±.3 RnK/D",ss RnK/n",os.66±.9±.2.56±.13±.2.4±.91±.18.26±.19±.29 Ass.DK.233±.129± ±.28±.26 Aos,D K.25±.24±.1.12±.28±.1 Ass,D".52±.29±.17.54±.43±.17 Aos,D" Observable 4 Stdies of bbaryon decays to Dph and Ach final states Compared to the bmeson sector, the bbaryon sector remains largely nexplored. Decays sch as Ag _, D A and Ag _, DpK can be sed to measre 17. The first step towards this goal is to observe sch decays. Using 1 fb1 of data, has made the first observation of the Ag _, DpK decay 18, where the D meson is reconstrcted sing the Cabibbofavored D _, KJr+ decay mode. Decay modes having a similar final state to Ag _, DpK are also stdied, namely Ag _, Dvrr, Ag _, AtIr and Ag _, AtK, where the At baryon is reconstrcted sing the Cabibbofavored At_, pkir+ decay mode. A loose selection, based on rectanglar cts, is applied to measre the ratio of branching fractions of the favored decays Ag _, AtIr and Ag _, Dp7r. The invariant mass distribtions of candidates passing this loose selection are shown in Fig. 5 for the AtJr (left) and Dp7r (right) final states. The ratio of branching fractions is measred to be where the first error is statistical and the second systematic. The largest systematic ncertainty is de to knowledge of the efficiency of the PID cts sed to separate protons from kaons and pios. The charm hadron branching fractions are inclded in the qoted ratio to avoid dependence on the poorlyknown At_, pkjr+ branching fraction. A tighter selection, based on a Boosted Decision Tree, is sed to search for the previosly nobserved modes where the "bachelor" particle from the bbaryon decay is a kaon rather than a pion. The invariant mass distribtions of candidates passing this tighter selection are shown in Fig. 6 for the DpK (left ) and AtK (right) final states. In the DpK final state, peaks Figre 4 Scans of the x2 probability over the r rb parameter space for (a) the whole Dalitz fit and (b) the fit inside the Kd region. The confidence regions for 1, 2 and 3 standard deviations are shown in dark, medim and light ble respectively. The crrent measrement of rand rb is indicated by the black data point.

5 are observed at both the Ag and :=:g masses. The significances of these peaks are 9." for the Ag + DpK signal, and 5.9" for the :=:g + DpK signal. Both decays are therefore observed for the first time, with ratios of branching fractions measred to be B(Ag + DpK).73 ±.8+.56, B(Ag+ Dop7r) f3g x B(sg + DpK ) =.44 ±.9 ±.6, faob X B(Ag + DpK) _ where the first error is statistical and the second systematic. The ratio of fragmentation fnctions fb "" / fabo is inclded in the qoted ratio, as its vale is crrently nmeasred. The DpK mass spectrm is also sed to precisely measre the difference between the masses of the :=:g and Ag baryons: m.,,o m 11.o = ± 2.4 ±.5 MeV/c2, b b :> <t;' AbtA;nsignal Partially rec. AtA;KBgJt D(sl1C '",...; :> 16 ::;s <t;' '" ::;s :::::., (;j h ro '". :... M(D p1q [MeV/c2] M(A;1n [MeV/cZJ Figre 5 Invariant mass distribtions for Ag + A;+7r (left) and Ag loose selection. : n A > DpKsignal Partially rec. A?Dp7tA> o*px tdpksignal ' <..>..... > ::;s :::::., (;j ro M(DpK) [MeV/c2] Partially rec.,...; (;j ' <..>..... > s<loo A> Dp1tsignal + Drnr (right) candidates passing the AtA;Ksignal Partially rec. At r.;7t AtA;1ttA;Ksignal M(A;K) [MeV/c2] Figre 6 Invariant mass distribtions for DpK(left) and A;" K (right) candidates passing the tighter selection.

6 where the first error is statistical and the second systematic. For both the ratios of branching fractions and the mass difference, the largest systematic ncertainty is de to the modelling of the backgrond contribtions to the DpK mass fit. The measrement of the mass difference can be combined with the measrement of maob in the Ag + J/'If;A decay mode 19 to give m"o. = ± 2.4 ±.7 MeV./c2, where the first error is statistical and the second is systematic and incldes the error on ma g This is the most precise measrement of m3g to date. In the A/; K final state, a prominent peak is observed at the Ag mass. There is also evidence for a peak at the sg mass, with a significance of 3.3a. The ratios of branching fractions are measred to be where the first error is statistical and the second systematic. For both ratios of branching fractions, the largest systematic ncertainty is de to the modelling of the backgrond contribtions to the.a.t 'T{ mass fit. The ratios of branching fractions measred in this anaiysis are consistent with expectations based on consideration of the CKM matrix elements involved in the dominant decay processes. References J. Charles et al., Er. Phys. J. C 41, 1 ( 25) M. Bona et al., JHEP 1, 81 ( 26 A. A. Alves Jr. et al., JINST 3, S85 (28) M. Grona and D. London, Phys. Lett. B 253, 483 ( 1991 ) M. Grona and D. Wyler, Phys. Lett. B 265, 172 ( 1991 ) D. Atwood, I. Dnietz and A. Soni, Phys. Rev. Lett. 78, 3257 ( 1997) D. Atwood, I. Dnietz and A. Soni, Phys. Rev. D 63, 365 ( 21 ) A. Giri, Y. Grossman, A. Soffer and J. Zpan, Phys. Rev. D 68, 5418 ( 23) A. Polektov et al., Phys. Rev. D 7, 723 (24) A. Bandar, Proceedings of BINP special analysis meeting on Dalitz analysis, npblished ( 22) A. A. Alves Jr. et al., Phys. Lett. B 712, 23 ( 212) A. A. Alves Jr. et al., Phys. Lett. B 723, 44 ( 212) A. A. Alves Jr. et al., Phys. Lett. B 718, 43 ( 212) A. A. Alves Jr. et al., Phys. Lett. B 726, 151 ( 213) N. Lowrey et al., Phys. Rev. D 8, 3115 (29) A. A. Alves Jr. et al., CONF2134 ( 213) A. A. Alves Jr. et al., CONF2136 ( 213) A. A. Alves Jr. et al., PAPER21368, sbmitted to Phys. Lett. B Y. Grossman, Z. Ligeti and A. Soffer, Phys. Rev. D 67, 7131R ( 23) J. Insler et al., Phys. Rev. D 85, 9216 ( 212) I. Dnietz, Z. Phys. C 56, 129 ( 1992) Fayyazddin, Mod. Phys. Lett. A 14, 63 ( 1999) A. Giri, R. Mohanta and M. Khanna, Phys. Rev. D 65, 7329 (22) A. A. Alves Jr. et al., Phys. Rev. D 89, 321 ( 214) A. A. Alves Jr. et al., Phys. Rev. Lett. 11, 1821 (213)