LHCb Results on Flavour Physics

Transcription

1 55 th International Winter Meeting on Nuclear Physics, January 2017, Bormio LHCb Results on Flavour Physics Stefania Ricciardi STFC, RAL On behalf of the LHCb Collaboration

2 Outline Introduction to Flavour and LHCb 2016 selected highlights on mixing, CPV and FCNC Mixing and CPV with B semileptonic decays CKM angle gamma CPV in baryonic decays CPV search with charm mesons Anomalies in B 0 K* 0 mm Other recent anomalies and tensions Lepton Flavour Universality B s,d mm Future LHCb prospects Focus of this talk: new physics searches at LHCb with beauty and charm hadrons Other important LHCb physics results (spectroscopy, heavy ions) will be covered in the talk by Giovanni Passaleva 26/01/2017 Stefania Ricciardi, RAL 2

3 Flavour in Valtellina If you Google for Flavour 26/01/2017 Stefania Ricciardi, RAL 3

4 Different flavours of slopes Great excitement with just u and d quarks! 26/01/2017 Stefania Ricciardi, RAL 4

5 3 generations: hic est flavour physics! Flavour == several copies of the same gauge representation 3 up-type and 3-down type quarks with same quantum charges but different masses /01/2017 Stefania Ricciardi, RAL 5

6 3 generations: hic est flavour physics! Flavour == several copies of the same gauge representation 3 up-type and 3-down type quarks with same quantum charges but different masses and different couplings to W boson * Complex couplings CP violation 26/01/2017 Stefania Ricciardi, RAL 6

7 Why is flavour physics interesting? Standard Model flavour puzzle: why 3 generations, what is the origin of the hierarchy observed in the fermion masses and quark mixing parameters (and why so different from lepton mixing anarchy?) Cosmology Amount of CPV in Standard Model not sufficient to explain the observed matter-antimatter asymmetry in the Universe. New sources of CPV required by baryogenesis. Discovery potential far beyond the energy frontier via studies of forbidden or SM suppressed processes, such as FCNC FCNC Flavour Changing Neutral Current forbidden at tree-level in SM 26/01/2017 Stefania Ricciardi, RAL 7 Z 0

8 Indirect searches for New Physics FCNC occur only at loop level: box or penguin diagrams. Sensitive to BSM contributions from new particles that can mediate the loops. Two examples: SM BSM Flavour mixing New particles? Rare decay BSM? New particles can be virtually produced sensitivity limited by precision, not by collision energy. Sensitivity to new particles up to ~100 TeV can be reached at LHCb [A. Buras et al. JHEP1411(2014)121] 26/01/2017 Stefania Ricciardi, RAL 8

9 Why beauty and charm? PRODUCTION Large beauty and charm crosssections in pp collisions at LHC 7-13 TeV center of mass energy In LHCb acceptance: s(cc ) = mb O(10 12 ) cc pairs/fb -1 Run2 at 13 TeV underway Already 2fb -1 on-tape Results presented here from 3 fb -1 Run1 at 7-8TeV s(bb) = mb O(10 11 ) bb pairs/fb -1 DECAY b and c are the heaviest quarks that form bound hadrons Many decay channels Long lifetime O(10-12 s) enables precise measurement of production and decay vertex 26/01/2017 Stefania Ricciardi, RAL 9

10 LHCb detector RICh detectors e(k) ~ 95% for 5% p K misid MUON system e(m) ~ 97% for 1-3% p m misid JINST 3(2008) S08005 IJMPA 30 (2015) Interaction point B 4Tm 4Tm B VELO s IP ~20mm (high p T tracks) TRACKING System Dp/p = % ( GeV) CALORIMETERS ECAL: s E /E ~ 1% 10%/ E Single arm forward spectrometer, large acceptance for bb in forward region 2<h<5 26/01/2017 Stefania Ricciardi, RAL 10

11 Introduction to Flavour and LHCb 2016 selected highlights on mixing, CPV and FCNC o o o o o B-Mixing and CPV CKM angle gamma CPV in baryonic decays CPV search in charm Anomalies in B 0 K* 0 mm Other recent anomalies and tensions o Lepton Flavour Universality o B s,d mm Future LHCb prospects B-MIXING 26/01/2017 Stefania Ricciardi, RAL 11

12 B s mixing B flavour eigenstates do not coincide with mass eigenstates, i.e., B L,H = p B 0 + q B 0 B-mixing or B-flavour oscillation = periodical transformation of a B (B 0 or B s ) into its own antiparticle as a function of time. Oscillation frequency Dm = m H m L B s fast oscillation requires: excellent decay time reconstruction Clean samples of self-tagged decays B s D s - p + and B s D s + p - Flavour-Tag production Mixed if different flavour at decay and production Unmixed if equal flavour at decay and production LHCb(1 fb -1 ) : Dm s = ± ± ps -1 most precise measurement to date SM: Dm s = 17.3 ± 1.5 ps -1 New J. Phys. 15 (2013) 05321

13 B 0 mixing 3fb -1 update in 2016 Dm d measured with full Run-1 data sample (3 fb -1 ) and semileptonic B 0 decays Mixing frequency directly related to mixing asymmetry A (t) = Nunmix t N mix t N unmix t +N mix t = cos ( m dt) Mixing asymmetry projections in 4 tagging categories with different mistag rates: B 0 D - m + n m X B 0 D* - m + n m X Eur. Phys. J.C (2016) 76:412 Dm d = ± 2.1 ± 1.0 ns -1 Most precise single measurement - compatible and similar precision to world average 26/01/2017 Stefania Ricciardi, RAL 13

14 CPV in B mixing 3fb -1 update in 2016 CPV in B mixing if P B q B q P B q B q, q=s,d PRL 117 (2016) Predicted to be very small in SM a sl s = 2.22 ± 0.27 x 10-5 a sl d = -4.7 ± 0.6 x 10-4 D0 measurement of like-sign dimuon 3.2s from SM PRL105(2010) sensitive to both a sl d and a sl s LHCb measures a sl s using untagged semileptonic decays: B s D s- m + nx A raw = N D s μ + N D s + μ N D s μ + +N D s + μ a sl s = (0.39 ± 0.26 ± 0.20)% Most precise measurement to date And in good agreement with SM 26/01/2017 Stefania Ricciardi, RAL 14

15 Introduction to Flavour and LHCb 2016 selected highlights on mixing, CPV and FCNC o o o o o B-Mixing and CPV CKM angle gamma CPV in baryonic decays CPV search in charm Anomalies in B 0 K* 0 mm Other recent anomalies and tensions o Lepton Flavour Universality o B s,d mm Future LHCb prospects MORE ON CPV 26/01/2017 Stefania Ricciardi, RAL 15

16 CKM Unitarity Triangle- Reminder V ud V us V ub V CKM = V cd V cs V cb V CKM = V td V ts V tb Wolfenstein parameterisation V ud V ub * + V cd V cb * + V td V tb * = 0 g a CP b 26/01/2017 Stefania Ricciardi, RAL 16

17 CKM angle g An increasingly precise picture..but still room for New Physics at O(20%) level Precision CKM metrology required Still large experimental uncertainty on g from direct measurements CKMFITTER g = UTFIT g = 70.5 ± 5.7 Above averages dominated by LHCb results g can be measured from tree level decays only SM benchmark negligible BSM contributions negligible theoretical uncertainties Several experimental challenges V ub mediated transitions Small BF involved Fully hadronic decays 26/01/2017 Stefania Ricciardi, RAL 17

18 g CKM angle g from B ± DK ± Favoured B - u V cb Suppressed u K - D 0 B - D 0 K - r e i D f D K - D r B e i( -g ) r D B e i D A( B A( B - A( D A( D D D f f 0 0 D D K K ) ) - - ) ) B - u V ub u D 0 K - i r B e ( -g ) B D 0 K - All unknowns from data No hadronic uncertainties Methods and D final states GLW : f D = KK, pp [Gronau-London-Wyler] PLB 253,483(1991), PLB 265, ) ADS : f D = Kp, Kppp [Atwood-Dunietz-Soni] PRL 78,257(1997), PRD 63,036005(2001) GGSZ : f D = K S pp, K S KK [Giri-Grossman-Soffer-Zupan] PRD 68,054018(2003) GLS :f D = K S Kp [Grossman Ligeti-Soffer] PRD 67,071301(2003) Same methods apply to B - Dp -, but interference smaller 26/01/2017 Stefania Ricciardi, RAL 18

19 CKM angle g from B ± DK ± 3fb -1 update in 2016 PLB 760 (2016) 117 Analysis includes: D to KK, pp, Kp, K3p, 4p D Kp ADS suppressed-mode Small yields but large asymmetry B ± [p ± K ] K ± B ± [p ± K ] p ± CPV at 8s in B DK 553 ± 34 events 1360 ± 44 events 26/01/2017 Stefania Ricciardi, RAL 19

20 CKM angle g from B ± DK ± 3fb -1 update in 2016 PLB 760 (2016) 117 Analysis includes: D to KK, pp, Kp, K3p, 4p D Kp ADS suppressed-mode Small yields but large asymmetry B ± [p ± K ] K ± B ± [p ± K ] p ± CPV at 8s in B DK 553 ± 34 events 1360 ± 44 events First measurement of CP parameters from D 4p. Large yields B ± [p ± p p ± p ] K ± B ± [p ± p p ± p ] p ± 1497 ± 60 events ± 150 events CP fraction F + = / (External input from CLEO) CPV at 2.7s in B DK Opposite sign to ADS as expected From predominantly CP-even GLW 26/01/2017 Stefania Ricciardi, RAL 20

21 g: combination of B DK results Frequentist method combining 71 observables depending on 32 parameters Compatible results obtained also with alternative Bayesian approach New update in 2016 JHEP 12 (2016) 087 g = Most precise determination of g from a single experiment As all input measurements are statistically limited, uncertainty should reach ~4 with Run2 26/01/2017 Stefania Ricciardi, RAL 21

22 g from B s D s K 3fb -1 update in 2016 update, not yet in g combination D s± K not self-tagged, both B 0 s and B 0 s can decay to it Time-dependent required Measurement unique to LHCb b c b u A CP ( Bs ( t = 0) Ds K ) - ( B s ( t ( t) ( B ( t = 0) D K ) + ( B s ( t s s 0 = 0) D = 0) D + s + s K K - - ) ) C cos( Dmst) - S sin( Dmst) = cosh( D t / 2) + Asinh( D t / 2) 2 2r S = 2r 1- r sin( - ( g - 2b )) 2 s A = cos( - ( g - 2b )) C = - 2 s 1+ r 1+ r 1+ r 2 s LHCb-CONF s 26/01/2017 Stefania Ricciardi, RAL 22

23 CPV in baryons decay New in 2016 arxiv: Non-negligible CPV effects predicted within SM in charmless L b decays Interfering amplitudes with similar size and large relative weak phase in L b pppp or L b ppkk V ub V ud * V tb V td * First observation of L b pppp 4-body final states Triple product asymmetries C T C T = p ( - p ph ph = p ( + p ph ph ) ) L b 6646+/- 105 events Observables largely insensitive to production and charge detection asymmetries (advantage over simple decay rates) 26/01/2017 Stefania Ricciardi, RAL 23 L b

24 CPV with baryons New in 2016 arxiv: NO PV Observables: 0 PV 0 CPV CPV Searches of localised P- and CP-violating asymmetries in distinct region of the phasespace. Two different binning schemes used. Data consistent with NO P violation CPV at 3.3s level (combining both schemes) First evidence of CPV in baryon sector 26/01/2017 Stefania Ricciardi, RAL 24

25 No CPV in charm yet 3fb -1 update in 2016 LHCb largest data sample of charm decays to charged tracks Unique environment with up-type quarks D 0 mixing firmly established Expected tiny level of CPV in SM <10 --2, which could be enhanced by NP DA CP = A CP ( D K K ) - A LHCb 0.6 fb -1 : DA CP = (-0.82 ± 0.21)%, evidence of CPV PRL108(2012) ( D p p CP ) A CP ( D = ( D f ) - ( D f ) + ( D f ) f ) 3fb -1 update in 2016, using D + D 0 π + and D D 0 π samples DA CP PRL (2016) = ( )% supercedes our previous measurement A A CP CP ( KK) ( pp ) arxiv: = ( )% = ( )% NO CPV but sensitivity has reached per mill level 26/01/2017 Stefania Ricciardi, RAL 25

26 Time-dependent CPV with D 0 K + K - and D 0 p + p - D* tagged sample, O(10 6 ) decays Asymmetry A CP (t) measured in bins of decay proper-time Preliminary 3fb -1,2016 LHCB-CONF Data split by magnet polarities and years Consistent results, no slope no CPV A CP ( t) a dir CP t - D A Slope A measures indirect CP violation Detection asymmetries corrections checked on D 0 K - p + control sample Most precise measurement of these observables Also unbinned analysis available on same data sample, consistent results (LHCB-CONF ) 26/01/2017 Stefania Ricciardi, RAL 26

27 Introduction to Flavour and LHCb 2016 selected highlights on mixing, CPV and FCNC o o o o o B-Mixing and CPV CKM angle gamma CPV in baryonic decays CPV search in charm Anomalies in B 0 K* 0 mm Other recent anomalies and tensions o Lepton Flavour Universality o B s,d mm Future LHCb prospects RARE DECAYS 26/01/2017 Stefania Ricciardi, RAL 27

28 B 0 K *0 (892)m + m - 3fb -1 update in 2016 JHEP 11 (2016) 047 Differential branching fraction of B 0 K *0 (892)m + m - P-wave only determined for the first time Measured S-wave fraction, F S Fit to M(Kpmm), M(Kp) and helicity angle cos(q K ) F S = ± ± for 796 < M(Kp) < 996 MeV and 1.1 <q 2 <6.0 GeV 2 Most precise measurements of the differential branching fraction to date In good agreement with the SM predictions 26/01/2017 Stefania Ricciardi, RAL 28

29 B 0 K *0 m + m - angular analysis 3fb -1 update in 2016 Four-body final states System described by dimuon invariant mass q 2 and =(q l, q K,f) Angular distributions sensitive to New Physics Observables: I i I i for B 0 The observables depend on Wilson coefficients (short-distance physics, evaluated perturbatively, universal) and on hadronic form factors for B K* transition (longdistance physics, evaluated through lattice QCD or LCSR) 26/01/2017 Stefania Ricciardi, RAL 29

30 B 0 K *0 m + m - angular distribution The CP-averaged angular distribution can be explicitely written as JHEP 02(2016) 104 F L = Fraction of longitudinal polarisation of the K *0 A FB = Forward-backward asymmetry of dimuon system LHCb F L and A FB in good agreement with SM Blake, Lanfranchi, Straub Prog.Part.Nucl.Phys. 92 (2017) /01/2017 Stefania Ricciardi, RAL 30

31 B 0 K *0 m + m -, P 5 observable 3fb -1 update in 2016 Set of observables with reduced hadronic uncertainties can be defined using ratios JHEP 02(2016) fb fb -1 Independent of form-factors at leading order S.Descotes-Genon et al., JHEP01(2013)048 LHCb has performed the first full angular analysis of B 0 K *0 m + m - Global analysis of LHCb results on CP-averaged observables at 3.4s from SM LHCb local tension with SM prediction Belle data consistent with LHCb 2.1s from SM, arxiv: /01/2017 Stefania Ricciardi, RAL 31

32 Global fits to b s data In OPE, B decay amplitude is expressed by: H eff = 4G F 2 V CKM C i O i i O i describe long-distance physics (non-perturbative) C i Wilson coefficients, short-distance physics (perturbative) Two examples of global fits to b s data: constraints on Wilson coefficients Altamannshofer and Straub arxiv: C i = C i SM + C i NP Descotes-Genon et al arxiv: Branching fractions Angular observables SM SM Vector Axial-vector Consistent picture: data favours modified vector coupling C 9 C 9 NP 0 at about 4s 26/01/2017 Stefania Ricciardi, RAL 32

33 Interpretation of b s anomalies NP Vector-like contribution could come from a Z with a mass of a few TeV OR? SM Vector-like contribution could be mimicked by poorly understood charm-loop contributions that may produce a di-muon pair via a virtual photon Lyon and Zwicky, arxiv: Altmannshofer, W. & Straub, D.M. Eur. Phys. J. C (2015) Ciuchini et al., JHEP 06(2016)116 More effort on-going to clarify picture: e.g., measure C 9 (q 2 ) dependence (different from charm loops and NP contribution) Current statistics not sufficient to draw conclusions 26/01/2017 Stefania Ricciardi, RAL 33

34 Introduction to Flavour and LHCb 2016 selected highlights on mixing, CPV and FCNC o o o o o B-Mixing and CPV CKM angle gamma CPV in baryonic decays CPV search in charm Anomalies in B 0 K* 0 mm Other recent anomalies and tensions o Lepton Flavour Universality o B s,d mm Future LHCb prospects OTHER ANOMALIES 26/01/2017 Stefania Ricciardi, RAL 34

35 Lepton Universality Test: e/m SM b sll flavour universality Expect: R K BF B K m m ) = = 1 O( BF( B K e e ) ( -3 Theoretically clean: hadronic uncertainties cancel in the ratio Experimentally challenging: electronreconstruction (Bremsstrahlung tail) B + K + e + e - ),e +,e- LHCb Run-1 (3 fb -1 ) for 1<q 2 <6 GeV 2 : R K LHCb 2.6s from SM LHCb PRL 113(2014) BaBar PRD 86(2012) Belle PRL 103 (2009) = R K =0.8 consistent with angular anomalies in b smm in some class of NP models E.g [Altmannshofer et al, PRD 89 (2014) ] 26/01/2017 Stefania Ricciardi, RAL 35

36 Lepton Universality Test: m/ (*) ( B D R( D ) = (*) ( B D (*) ) m ) 1 due to phase-space SM prediction theoretically very clean Sensitive to NP: e.g. charged Higgs, leptoquark LHCb measured R(D*) with mnn Experimental challenge: missing neutrinos LHCb result at 2.1s from SM R( D*) = LHCb, PRL115,111803(2015) SM NP NP 4s HFAG average of all R(D) and R(D*), including Belle, Babar, LHCb 4s from expectations More measurements of other b c n processes under way at LHCb. Also using B s, B c, L b decays 26/01/2017 Stefania Ricciardi, RAL 36

37 First observation of B s m + m - FCNC decay, very rare in SM SM NP Nature 522(2015)68 BF can be significantly altered in many BSM models First observation (6.2 s) of B s m + m - BR = ( ) x 10-9 compatible with SM at 1.2s 2s First evidence (3s) of B 0 m + m - BR = ( ) x compatible with SM at 2.2s 26/01/2017 Stefania Ricciardi, RAL 37

38 FUTURE PROSPECTS 26/01/2017 Stefania Ricciardi, RAL 38

39 L=3-4x10 32 L=4x10 32 L=20x10 32 LHCb LHCb 3 fb -1 Today 8 fb -1 LHC Operation PLAN 26/01/2017 Stefania Ricciardi, RAL 39

40 LHCb LHCb 3 fb -1 Today LHCb Upgrade 8 fb fb -1 by 2030 LHCb upgrade: new 40 MHz read-out with fully software trigger 26/01/2017 Stefania Ricciardi, RAL 40

41 LHCb projected statistical uncertainties BF(B d μμ) BF(B s μμ) LHCb Run 1& fb -1 LHCb Upgrade- Run3&4 - ~ fb -1 Theory ~100% ~35% ~5% s 0 A FB (B d K μμ) 6% 2% 7% g (B DK) negligible LHCb-PUB f s (B s J/yf) ~0.003 A (D KK) 0.2 x x Statistical uncertainties will stay larger than theoretical ones for many years! 26/01/2017 Stefania Ricciardi, RAL 41

42 Conclusions Many new LHCb results published this year (>50 papers!) Only a few, selected ones, presented here Increasing experimental precision and good agreement with SM for most of the flavour observables: Mixing in the B d (and B s ) system CPV in mixing with semileptonic Bs decays (asl s ) CKM-g from direct CPV in B DK decays First evidence of CPV in baryonic decays (L b ) No observation of CPV in D 0 decays Some measurements showing interesting tensions with SM: Some exclusive b sm + m - branching fractions B 0 K *0 m + m - angular distributions (2016 first full angular analsys) Hints of lepton non universality in B Kll and B Dln decays B 0 m + m - branching fraction (too high?) New Physics or unaccounted uncertainties or statistical fluctuations? Most results using LHC Run-1, 3fb -1 ; b and c-quark data-samples from Run-2 on tape is already more than twice larger (accounting for larger cross-sections at 13TeV) Plans to collect 50fb -1 by end of LHC Run-4 (2030) with upgraded detector 26/01/2017 Stefania Ricciardi, RAL 42

43 THANK YOU 26/01/2017 Stefania Ricciardi, RAL 43

44 Flavour physics indirect discoveries 1970: c-quark predicted (GIM mechanism) to explain smallness of K L mm 1974: first J/y observation 1973: 3 rd generation introduced (Kobayashi & Maskawa) to explain CP violation in kaon decays, e K 1977: first b-quark observed 1994: first top-quark observed 1974: charm mass predicted from Dm K (K 0 -mixing) 1987: Argus hints of large top mass from Dm B (B 0 -mixing) 1994: top-mass measured 26/01/2017 Stefania Ricciardi, RAL 44

45 CKM constraints evolution An increasingly precise picture.. 26/01/2017 Stefania Ricciardi, RAL 45

46 FCNC b smm decays b s (and b d) transitions only occur at loop level in SM b s (and b d) transitions at loop or tree level via NP. E.g., Penguin diagram Penguin diagram Box diagram Box diagram Tree diagram Several observables: decay rates, CP asymmetries, angular distributions 26/01/2017 Stefania Ricciardi, RAL 46

47 Exclusive b sm + m - decay rates B + K + m + m - B 0 s K 0 m + m - B 0 s fm + m - JHEP 06 (2014) 133 B + K *+ m + m - JHEP 06 (2014) 133 B 0 K *0 m + m - JHEP 09(2015) 179 L b Lm + m - JHEP 06 (2014) 133 JHEP 08 (2013) 131 JHEP 06 (2015) 115 All lower than predicted! But large uncertainties in the SM prediction from hadronic form factors 26/01/2017 Stefania Ricciardi, RAL 47

48 Amplitude phase-differences in B + K + m + m - Observed tensions need sizeable long-distance effects in dimuon mass regions far from the pole-masses of the resonances to be explained in terms of charm-loop contributions First measurement of the phase difference between the short-distance and the narrow resonant contributions to the B + K + mm decay New Submitted to EPJC arxiv degenerate solutions corresponding to phases ±p/2, ±p/2 [J/y. y(2s)] Fit to dimuon mass-distribution: - Long distance (resonances) contributions modelled with relativistic Breit-Wigner with individual magnitude and phases - Short distance with effective field theory: C 9 and C 10 floating, B K form factors from predictions Same strategy could be applied to B 0 K *0 mm (complicated due to different helicity amplitudes contributing with different phases) Also BF measurement of non-resonant component compatible with previous but smaller than SM Negligible interference far from pole If C 10 set to 0, fit favours region with C 9 <C 9 SM 26/01/2017 Stefania Ricciardi, RAL 48