b and c Spectroscopy at LHCb Giulia Manca (on behalf of the LHCb Collaboration) Universita` degli Studi di Cagliari & I.N.F.N.

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1 b and c Spectroscopy at LHCb Giulia Manca (on behalf of the LHCb Collaboration) Universita` degli Studi di Cagliari & I.N.F.N. Rencontres de Moriond QCD, La Thuile (IT), 9-15 th March 13

2 Outline The LHCb Detector Theory and motivation Selected results B c and B hadrons Exotic spectroscopy Conclusions and outlook G.Manca, Moriond QCD 13

3 RICH1 & RICH ε K K 95% π K mis-id: 5% beam 1 LHC and LHCb Pseudorapidity acceptan < η < 5 Calorimeters ECAL: σ E /E 1% 1%/ E[GeV] beam "LHC pp collider : 1-13 at s =.76, 7, 8 TeV Tot L 3 fb -1 " " "In 13 LHCb also collected pa data -> Tot L nb -1!! " " VELO σ IP μm for high-p T tracks Tracking System Δp/p =. 4%@5 GeV/c to. 6%@1 GeV/c Muon System ε μ μ 97% π μ mis-id: 1 3% 1 11 Uncertainty on Luminosity in these analyses : 3.5-5% (JINST 7 (1) P11 ) G.Manca, Moriond QCD 13 3

4 Why Spectroscopy? " Different QCD models predict different masses, "lifetimes, branching ratios, spin-parity etc. "for many c- and b-hadrons. Further confirmation and testing of models of the heavy quark interactions is provided by c- and b-hadron spectroscopy In some cases observation of new particles or new modes can help the theorists to build the big picture! G.Manca, Moriond QCD 13 4

5 B c Physics Bc unique meson with two open heavy flavours, bc - - or bc Intermediate charmonium/bottomonium First observed CDF in 1998 in B c ->J/ψl ν, fully reconstructed in B c ->J/ψπ LHCb already measured the mass and "production with.37 fb -1 in B c ->J/ψπ Two new B c decay modes observed at LHCb!! B c ->ψ(s) π B c ->J/ψ D s (*) Phys.Rev.Lett. 96 (6) 8 NEW Candidates / (1 MeV/c ) Predicted B c Mass Spectrum 6 LHCb data Total Signal 5 Background N(B c )=179± M(J/ψπ ± ) (MeV/c ) G.Manca, Moriond QCD 13 5 Figure 1: Invariant mass distributions of selected B! J/ K candidates (right). The results of the fit

6 LHCb Preliminary B c -> J/ψ D s (*) : Introduction LHCb-PAPER-13-1 First observation of this mode! D s First analysis to use full 111 dataset 3 fb -1, at s = 7 and 8 TeV We measure the ratio : B D s = B D s! (K K ) B (B c! J/ D s ) B (B c! J/ ) = 1 B D s Theory predictions disagree! "tot B c!j/ " tot B c!j/ D s N (B c! J/ D s ) N (B c! J/ ), References [see Pag.16] Simple approach [B ] Simple approach [B ] G.Manca, Moriond QCD 13 6

7 LHCb Preliminary B c -> J/ψ D s (*) : Results LHCb-PAPER-13-1 NEW Very clear signals of B c ->J/ψ D s (*), "with D s * -> D s γ/π, D s ->(KK) π Fits: Background : exponential Signal: "B c ->J/ψ D s : Gaussian "B c ->J/ψ D s * : Sum of two " helicity amplitudes from MC A and A ±± " " Candidates/(5 MeV/c ) Candidates/(1 MeV/c ) 5 B c ! J/ D s m(j/ D s ) B c ->J/ψ D s * GeV/c LHCb Preliminary B c ->J/ψ D s " Significance >7σ for each! Using the B c ->J/ψ π as normalisation channel we can measure the ratios : Main systematic: B(D ->φ(->k K )π ) Agreement with simplest approach, tension with other results m(j/ D s ) GeV/c.9±.57(stat)±.4(syst).37±.56(stat)±.1(syst) G.Manca, Moriond QCD 13 7

8 LHCb Preliminary B c -> J/ψ D s (*) : Discussion LHCb-PAPER-13-1 NEW References [see Pag.16] Simple approach [B ] Simple approach [B ] Theory predictions disagree! In the Simple approach we assume that the spectator diagram dominates and that factorisation holds; then we can write the ratios as : BRs taken "from the PDG.9±.57(stat)±.4(syst).37±.56(stat)±.1(syst) G.Manca, Moriond QCD 13 8

9 LHCb Preliminary B c Mass Measurement The low energy release (Q-value) in the B c ->J/ψ D s decay allows a precise measurement of the B c mass Main source of uncertainty: D s mass knowledge! Averaged with PDG m(d s )= ±.33 MeV/c NEW LHCb-PAPER-13-1 Writing : m(d s ) = m(d ) [m(d )-m(d )] [m(d s ) m(d )] = ±. MeV/c measured by LHCb [LHCB-PAPER-13-11] m(b c ) m(d s ) = ± 1.44(stat) ±.11(syst) MeV/c. m(b c ) = ± 1.44(stat) ±.36(syst) MeV/c. Most precise single measurement to date! Systematic uncertainties: Source m(b c ) m(b c ) m(d s ) D s mass.16 - Energy Loss Correc5ons.5.1 world Momentum Scale Uncertainty.3.1 Fit Model.5.5 TOTAL ± G.Manca, Moriond QCD 13 9

10 B c -> ψ(s) π arxiv: LHCb searched for this decay in 1 fb -1 s= 7 TeV data, observing it for the FIRST TIME Events selected with Boost Decision Tree (BDT) trained on B c -> J/ψπ Fit: Crystal ) Candidates / ( 1. MeV/c Ball exponential Measured: LHCb M(J/ψ π ) (MeV/c ) Data Total fit Signal Combinatorial bkg Partially reconstructed bkg B c J/ψ K ) Candidates / ( 1.5 MeV/c LHCb M(ψ(S)π ) (MeV/c ) (b) Data Total fit Signal Combinatorial bkg Partially reconstructed bkg "B c -> ψ(s) π N(B Figure 1: The invariant c -> ψ(s)π mass ) = ε distribution of B c candidates reconstructed as (a) B c " B c -> J/ψπ rel x =.5±.68(stat)±.14(syst)±.6(B) J/ψ π and (b) N(B B c c -> J/ψπ ) ψ(s)π. Black dots with error bars show the data, the thick blue solid line the fit of the data, the dashed red line the signal distribution, the dotted green line the combinatorial background, the Main dot-dashed systematic: violet line BDT the selection Theory predicts : LHCb-PAPER-1-54 partially reconstructed background, and the thin light blue line is the background from the B c J/ψ K channel. bservation of B ψ(s)π bservation of B ψ(s)π heoretical predictions B( ( ) ) ~.13.4 B( ~ 84 where.13 /.4 N is the B( ) / ) number of selected signal events and ε is the total efficiency. [ PRD 68 (3) 94 The number ; PRD 49 of (1994) signal events 3399 ; isprd obtained 56 (1997) by fitting 4133 the ; B c 85 mass B(ψ(S)->µµ) spectrum in Figure 1. PRD 61 () 86 The 341 signal ; arxiv: is modelled with a] double-sided Crystal Ball function [4]. The tail parameters are determined from the G.Manca, simulation. Moriond The QCD main 13 background component for both 1 channels 88 is combinatorial, and it is modelled with an exponential function. At the lower end of the Theoretical predictions B( ( ) ) LHCb-PAPER-1-54 [ PRD 68 (3) 94 ; PRD 49 (1994) 3399 ; PRD 56 (1997) 4133 ; PRD 61 () 341 ; arxiv: ] Dataset: 1 fb of data collected in 11 at s = 7 TeV B J/ψπ used as control channel N(B c -> J/ψπ ) = 595±9 Partially reconstructed events Dataset: 1 fb of data collected in 11 at s = 7 TeV N(B c -> ψ(s)π ) = ±5 Combinatorial Background Uncertainty from B(J/ψ->µµ)

11 arxiv:13.17 Measurement of Λb,Ξb-,Ωb- masses Candidates / ( MeV/c ) 4 LHCb Ξb J/ψ Ξ LHCb Ωb J/ J/ψ Ω LHCb mass measurement - fit (b) mass measurement - fit (c)! J/ mass measurement - fit 5 b! b! J/ LHCb Candidates / ( MeV/c ) Candidates / ( 8 MeV/c ) J/ψ Λ 18 (c) Ωb J/ψ Ω LHCb (b) Ξb J/ψLHCb Ξ (a) Λb b b ψ Λ) 8 M(J/ [MeV/ c] 8 M(J/ψ Ξ ) [MeV/ c] M(J/ψ Ω ) [MeV/ c] Gaussian functions with common4 mean Gaussian Signal: single Gaussian function Signal: single function with61 fixed width 1 D [1.3 fb1] M(J/ψ Ξ ) [MeV/ c1]] CDF I [11 pb ] = Widths: 6.4 ±.5 (stat) MeV/c D [1.3 fb 1 M(J/ ψ Ω ) [MeV Width: 7.8 ±.7 (stat) MeV/c final result final result nal: two Candidates / ( 8 MeV/c ) 18 (a) Λb J/ψ Λ 16 b Candidates / ( 5 MeV/c ) Candidates / ( 5 MeV/c ) b-baryon status: 16 predicted ground states World s best measurements!!! Λ b, Ξb and Ωb baryons observed mass measurement - fit! J/ mass measurement - fit b! J/ / mass measurement - fit Their masses measured by simple cut based analysis on 1. fbb -1 data final result Width: 7. MeV/c (fixed) = 1.5 ± 1.3 (stat) MeV/cCDF [4. fb ] Ξ J/ψ Ξ M(J/ψ Λ) [MeV/ c] CDF [4. fb ] LHCb [35 pb ] 111 ± 1 (stat) Yield: 19 ± 5 (stat) Signal:Yield: single Gaussian function Yield: 687 ± 11 (stat) CDF [4. fb ] Ξ Ξ π Signal: single Gaussian wit ATLAS [4.9 fb ] PDG [1] 671 ± 4 Mass: ±.9 (stat) MeV/c Mass: 646. ±.function (stat) MeV/ Signal:±two functions with common mean Mass: Gaussian (stat) MeV/c Width: 7.8 ±.7 (stat) MeV/c PDG [1] ±. Average ±.6 Width: 7. MeV/ fb ] Yield: 111 ±LHCb 1[1.(stat) LHCb [35 pb 1. fb ] LHCb [1. fb ] ±.5 (stat) MeV/c Widths: = Background: exponential function Background: exponential function kground: exponential function Yield: 19 ± 5 Mass: ±.9 New average ±.4 CDFLHCb average(stat) ±.1 MeV/c New average ±.9 CDF II [ pb ] 1 b b c = 1.5 ± 1.3 (stat) MeV/c Mass: 646. ± Yield: 687 ± 11576(stat) function 65 [MeV/ c] Λ mass 8/19 R. Ma rki b-baryon mass measurements at LHCb 61 exponential R. Ma rki b-baryon mass measurements at LHCbBackground: 9/19 R. 615 Ma rki b-baryon mass Ξ mass [MeV/ c ] Ω mass [MeV/c ] Mass: scale ±.13 (stat) MeV/c [References on Pag.17] exponential function LHCb measurement Background: Main systematic : momentum b b LHCb measurement M( b ) = ±.13 (stat) ±.45 (syst) MeV/c 8/ Background: Combining with 1 result from LHCb b LHCb measurement R. Ma rki b-baryon mass measurements at LHCb 11 ) = ±.9 (stat) ±.4 (syst) MeV/c exponentialm( function M( ) = 646. ±. (stat) ±.5 (syst) MeV/c b b 9/19 R. Ma rk M( b ) M( b ) = 176. ±.9 (stat) ±.1M( (syst) MeV/c b ) M( b ) = 46.4 ±. (stat) ±.4 (syst) MeV/c G.Manca, Moriond QCD 13

12 Number of candidates / (.5 MeV) X(387) Quantum Numbers has been checked with simplified Monte Carlo samples, X(387) discovered by Belle fit(3) results are shown but in Fig. nature 1 and Table still 1. Thefitdoesnot unclear account for QED radiative corrections and hence underestimates the masses. Using a simulation LHCb measured the X mass and cross section in 1 and now performed the J PC measurement in 1 fb -1 based on PHOTOS [19] the biases on the X(387) and s masses are = found 7TeV to be.7 ±. MeV/c Measurement of quantum numbers (J PC and. ±. MeV/c,respectively. The fitted mass) values crucial are corrected!! for these biases and the uncertainties propagated in the estimate of the sys- If 1 (D D * molecule, Tetra-quarks, tematic error. χ c1 ( 3 P 1 )) or - (η c (1 1 D )) X reconstructed from B decays : ψ(s) 55 6 prove the stability of the fit, the parameter c is fixed to the value obtained from the same-sign pion sample. In total, the fit has eight free parameters: three yields (ψ(s), X(387) and background), two masses (ψ(s) and X(387)), one resolution parameter, and two background shape parameters. The correctness of the fitting procedure fully simulated Monte Carlo samples, and samples containing a mixture of fully simulated Monte Carlo signal events and same-sign background events taken from the data. The LHCb 387 Several other sources of systematic effects on the mass measurements are considered. For each source, the complete analysis is repeated (including / the track fit and the momentum scale calibration when needed) under an alternative assumption, and the observed change in the central value of the fitted masses relative to the nominal results assigned as a systematic uncertainty. The dominant source σ=4.±.5 of uncertainty 7 X(387) is the calibration σ=5.5±.5 of the momentum scale. MeV/c Based on checks performed MeV/c with reconstructed signals of various 6 mesons decaying into two-body final states (such 5 Table 1 Results of the fit to the J/ψπ 4 π invariant mass distribution of Fig M(π π J/ψ) - M(J/ψ) [MeV] 1 Number of background events 7394 ± arxiv: amounts corresponding to the.1 % relative precision with which the length scale along the beam axis is known [6]. Other small uncertainties arise due to the limited knowledge of the X(387) width and the modeling of the resolution. The former is estimated by fixing the X(387) width to.7 MeV/c instead of zero, as suggested by the likelihood published by Belle [7]. The latter is estimated by fixing the ratio σ X(387) /σ ψ(s) using the covariance estimates Fig. 1 Invariant mass distribution of J/ψπ π (points with statistical error bars) and same-sign J/ψπ ± π ± (filled histogram) candidates. The curves are the result of the fit described in the text. The inset shows a zoom of the X(387) region Fit: Symmetric Crystal Ball Function linear background N( B ->ψ(s)k ) = 564±76 Fit parameter or derived quantity ψ(s) X(387) Number of signal events 3998 ± ± 6 Mass m [ MeV/c ] ± ±.48 N( B ->X(387)K ) = 313±6 (68% purity) Resolution σ [ MeV/c ].54 ± ±.8 Signal-to-noise ratio in ±3σ window B -> ψ(s)k used as control channel Figure 1: Distribution of M for B! J/ K candidates. The fits of the (S) and X(387) signals are displayed. The solid blue, dashed red, and dotted green lines represent the total fit, signal component, and background component, respectively. G.Manca, Moriond QCD 13 1 Eur. Phys. J. C7 (1) 197

13 decays as found by studying the K mass distribution. The angular X(387) J PC correlations in the B Measurement decay carry information about the X(387 quantum numbers. To discriminate between the 1 and assignments we use th likelihood-ratio test, which in general provides the most powerful arxiv: test between two h Analysis performed potheses in 5D, []. considering The PDF all for angular eachcorrelations J PC hypothesis, in B decay J X, is defined in θ ππ# the 5D angula The PDF for space each J PC is f( (cos X, cos, X,, cos J/, X,J/ )bythenormalizedproductofth, π ) X(387) ρ π - P( J X )= M( J X ) ( )/I(J X ), where I(J X )= R M( J X ) ( )d. J/ψ(1S) Thee K θ expected decay matrix element (M) squaredandofthereconstruction X(387) e ciency ( µ "built as a product of the expected matrix element and the "reconstruction efficiency. cienc is averaged over the Angular correlations X(387)! (77)J/, (77)! go in here, decay [6,16,8]. The observed M( ) distributio ϕ X(387) -ϕ ππ is in good agreement with this expressed simulation. in the The lineshape µ of the (77) resonance ca J/ψ(1S) π- change slightly depending onhelicity the spin formalism hypothesis. The µ - e ect on ( ) ρ isπ foundtobever Helicity amplitudes can be expressed falls into the region where the probability density for the 1 small and is neglected. We follow the approach adopted in Ref. [1] simulated experiments is ϕ J/ψ(1S) ) -ϕ Without free parameters : J PC = 1 high. Integrating the 1 to predict ππ the matr distribution from 1 to t data gives CL (1 )=34%. Wealso compare the binned distribution ϕof X(387) single-event -ϕ J/ψ(1S) log-likelihood-ratios with sweights applied, elements. The angular correlations are obtained using helicity X(387) formalism, With a complex parameter (α) : J PC = - ln[p( i, ˆ )/P( i 1 )], between the data and the simulations. The shape of this distribution in data is consistent with the 1 simulations and inconsistent with the simulations, as illustrated in Fig. 3. To discriminate between the two hypotheses we built a test statistic t= ratio of the likelihoods of the two J PC X X values, such that M( J X ) 7 1 = A t > -> 1 J/, D J X (, J/ X, X, X) favoured LHCb 6 µ= 1,1 t < -> - J/, = 1,,1 1 PC - PC favoured Simulated J = Simulated J =1 RESULTS: D 1, ( 1 5,, ) D 1 J/, ( µ J/, J/, J/ ) t Data prefers the 1 hypothesis! J "(tested with simulation) where are particle helicities and D J 1, 1 - hypotesis rejected with > 8σ PDF = Probability Density Function B mass (M( )) using a simulation [3 7] that θ J/ψ(1S) assumes th µ - are Wigner functions [13 15]. The helicit G.Manca, Moriond QCD Number of experiments / bin t data t = - ln[ L( )/L(1 ) ] Figure : Distribution of the test statistic t for the simulated experiments with J PC = and = ˆ (black circles on the left) and with J PC =1 (red triangles on the right). A Gaussian fit to the distribution is overlaid (blue solid line). The value of the test statistic for the data, t data, is shown by the solid vertical line.

14 RESULTS: X(387) J PC Measurement: tests t Data prefers the 1 hypothesis! J More tests/validations : Density of signal events w w Data prefer the value of α=(.67,.8) in agreement with "Belle (.64,.7) [Phys. Rev. D84 (11) 54] Checking the shape " w Going to one dimension Data PC Simulated J =1 PC - Simulated J = LHCb Number of candidates / all candidates Data PC Simulated J =1 PC - Simulated J = cosθ ππ >.6 arxiv: LHCb ln[ P( ) / P(1 ) ] cosθ X P P G.Manca, Moriond QCD

15 Conclusions and Outlook LHCb has a rich program in spectroscopy which is flourishing with the new data!! Many important results already achieved (new decay modes observed, unique first measurements ) Many more available but not shown today for time issues: Prompt charm cross section [arxiv:13.864] B s * and Λ b * observation [arxiv: , Phys. Rev. Lett. 19 (1) 173 ] Study of D sj decays to D K S and D K final states [J. High Energy Phys. 1 (1) 151] Still about fb -1 of data to be analysed!! There will be many more news As usual G.Manca, Moriond QCD 13 15

16 References B c -> J/ψ D s (*) G.Manca, Moriond QCD 13 16

17 References Baryon Masses [] Particle Data Group, J. Beringer et al., Review of particle physics, Phys. Rev. D86 (1) 11. [4] D collaboration, V. Abazov et al., Observation of the doubly strange b baryon b, Phys. Rev. Lett. 11 (8) 3, arxiv: [5] CDF collaboration, T. Aaltonen et al., Observation of the b baryon and measurement of the properties of the b and b baryons, Phys. Rev. D8 (9) 73, arxiv: [6] D collaboration, V. Abazov et al., Direct observation of the strange b baryon b, Phys. Rev. Lett. 99 (7) 51, arxiv: [16] ATLAS collaboration, G. Aad et al., Measurement of the b ATLAS experiment, arxiv: lifetime and mass in the [17] CDF collaboration, D. Acosta et al., Measurement of b hadron masses in exclusive J/ decays with the CDF detector, Phys. Rev. Lett. 96 (6) 1, arxiv:hep-ex/ G.Manca, Moriond QCD 13 17

18 Back up G.Manca, Moriond QCD 13 18

19 Bc->J/psi Ds Uncertainties on the ratio of Br Bc->J/psi Ds/pi G.Manca, Moriond QCD 13 19

20 Bc->J/psi Ds Different binning scheme Candidates/(1 MeV/c ) 5 15 Candidates/(1 MeV/c ) B c! J/ D s LHCb Preliminary m(j/ D s ) GeV/c m(j/ D s ) GeV/c Figure A.5: Mass distributions for J/ D s pairs. The overlaid curve represents the fit results described in text. This is a rebinne dversion of Fig G.Manca, Moriond QCD 13

21 X(387) Quantum numbers Figure 1: Distribution of M for B! J/ K candidates. The fits of the (S) and X(387) signals are displayed. The solid blue, dashed red, and dotted green lines represent arxiv: the X(387) total fit, signal discovered component, by and Belle background >1yrs component, ago but respectively. its nature still unclear Measurement of quantum numbers crucial in sheding light on this state decays as found by studying the K mass distribution. The angular correlations Possibilities: 1(D D * in the B molecule? decay carry information Tetra-quarks? χ c1 ( 3 about P 1 ) OR - the X(387) (η c (1 1 D )) quantum numbers. To discriminate between the 1 and assignments we use the likelihood-ratio test, which in general provides the most powerful test between two hypotheses []. The PDF for each J PC hypothesis, 387 J X, is defined in the 5D angular space (cos X, cos, X,, cos / J/, X,J/ )bythenormalizedproductofthe expected decay matrix element (M) squared andofthereconstructione ciency ( ), P( J X )= M( J X ) ( )/I(J X ), where I(J X )= R M( J X ) ( )d. Thee ciency is averaged over the mass (M( )) M /, using a simulation [3 7] that assumes the, /,,, (,, ) /, ( /, /, / ) X(387)! (77)J/ =, /,, (77)! decay [6,16,8]. The observed M( ) distribution =,, is in good agreement with this simulation. The lineshape of the (77) resonance can cos, cos,,, cos /, change slightly depending on the spin hypothesis., / The e ect on ( ) Helicity coupling /, : no free parameter if 1 isfoundtobevery small and is neglected. We follow the approach adopted in Ref. [1] to predict the matrix elements. The angular correlations one complex are obtained parameter using the( ) helicity if formalism, LHCb performed the measurement in 1fb -1 of data s=7tev 5-dimensional analysis 1 Likelihood ratio test X to discriminate X the two hypotheses M( J X ) = µ= 1,1 J/, = 1,,1 A J/ ln L /L 1 D 1, (,, ) D 1 J/, ( µ J/, J/, J/ ) favored 1 favored, D J X (, J/ X, X, X) where are particle helicities and D J 1, are Wigner functions [13 15]. The helicity G.Manca, Moriond QCD 13 1,

22 NEW Λ b * First Observation!! Two narrow states are observed in Λ b π π - spectrum in L=1. fb -1 data Expected at J P = 1/ - and 3/ - Λ b peak arxiv: G.Manca, Moriond QCD 13

23 NEW Λ b * First Observation!! Two narrow states are observed in Λ b π π - spectrum in L=1. fb -1 data Expected at J P = 1/ - and 3/ - arxiv: G.Manca, Moriond QCD 13 3

24 NEW Λ b * First Observation!! Two narrow states are observed in Λ b π π - spectrum in L=1. fb -1 data Expected at J P = 1/ - and 3/ - arxiv: Yield width Significance Λ b (591) 16.4± MeV/c Λ b (59) 49.5±7.9.7MeV/c 4.6 σ 1.1 σ " " " " stat syst Λ b mass Main systematics: " Signal/background modelling, momentum scale Limits on natural widths (95% C.L.) : G.Manca, Moriond QCD 13 4