Production and decay of heavy flavour baryons Nicola Neri on behalf of the LHCb collaboration presenting also result from Atlas and CMS INFN - Sezione di Milano FPCP 2015 25-29 May 2015 - Nagoya, Japan Outline ‣ Introduction to b-baryon physics ‣ Experimental results ‣ Conclusions Nicola Neri 2 Production and decay of HF baryons - FPCP 2015 Introduction to b-baryon physics Nicola Neri 3 Production and decay of HF baryons - FPCP 2015 Physics motivations ‣ At LHC b-baryons are produced in unprecedented quantities ➝ opens a new field in flavour physics for precision measurements 0 - Most precise measurement of |Vub| using ⇤ b pµ−⌫¯µ decays [arXiv:1504.01568] ! - Mass, lifetimes and branching ratios measurements ‣ b-baryon physics is a relatively unexplored territory: - search for physics beyond the Standard Model (SM) in rare decays and CP violation - useful QCD laboratory in different energy regime with respect to light baryons. Experimental anchor point for QCD models Nicola Neri 4 Production and decay of HF baryons - FPCP 2015 Beautiful baryons ‣ Baryons are fermions composed by 3 quarks ‣ State function antisymmetric under exchange of equal-mass quarks qqq = color space, spin, flavour | iA | iA ⇥ | iS ‣ SU(4) multiplets for baryons made of (u,d,s,b) observed quarks - B= bottomness, Y=hypercharge, I3= Isospin z-component - SU(4) symmetry heavily broken - large b-quark mass - particles in SU(4) multiplets have same spin and parity Nicola Neri 5 Production and decay of HF baryons - FPCP 2015 b-baryons states q2 s, ` S, J ‣ b-baryons ( bq 1 q 2 ) as QCD L = ` + `0 `0 laboratory: q1 - m b m q 1 q 2 simplified dynamics b ground state p + + - b quark in the limit m b j =0 , 1 j = L + s (L = 0) !1(m 4.8GeV) effective static colour field b ⇠ - heavy baryon properties determined by dynamics of diquark system in b- quark color field - Ground state baryons ( L = 0) with spin-parity J P =1 / 2 + , 3 /2+ characterised by the spin-party of p + + the diquark system j =0 , 1 1 + 3 + J P = (J P = not shown) 2 2 Nicola Neri 6 Production and decay of HF baryons - FPCP 2015 b-baryon rare decays 0 ⇤ pµ−⌫¯ ‣ Access to |Vub| CKM element, b ! µ form factors f ( ⇤ b p ) determined by Lattice! QCD. Experimentally very challenging, Vub achieved unprecedented See Greg Ciazerek talk for precision more details 3 V =(3.27 0.23) 10− | ub| ± ⇥ arXiv:1504.01568, submitted to Nature 0 + ‣ Angular analysis of b-baryon ⇤b ⇤µ µ− flavour-changing neutral current ! decays, e.g. b s transitions, is sensitive to physics! beyond Standard Model (SM) arXiv:1503.07138, submitted to JHEP See Christian Linn talk for more details Nicola Neri 7 Production and decay of HF baryons - FPCP 2015 Experimental results Nicola Neri 8 Production and decay of HF baryons - FPCP 2015 b-baryon production ‣ Production cross-section strongly depends on pT of b-hadron : f 0 /fd - different b-quark fragmentation function ratio ⇤ b measured at 0 0 LEP and at LHC, where f ⇤ 0 = P ( b ⇤ b ) and fd = P (b Bd) b ! ! f 0 /fd - measurement of ⇤ b vs pT of b-quark is cleaner to interpret. Expected a slow dependence in that case arXiv:1505.02771 JHEP 08, 143 (2014) PRD85, 032008 (2012) Note: LEP average not included in the fit. LHCb measurements are not independent Nicola Neri 9 Production and decay of HF baryons - FPCP 2015 Production kinematic dependence 0 + 0 + ‣ Use clean ⇤ ⇤ ⇡ − (45K) , B D ⇡ − (106K) exclusive b c ! decays to measure! dependance of f 0 /f d on b-hadron ⇤b kinematics, e.g. pT, pseudorapidity η. ‣ Measure where and x = pT , ⌘ Data sample 1fb-1 at 7 TeV - JHEP08(2014)143 0 + 3.05 < ⌘ < 3.2 0 + ⇤b ⇤c ⇡− B D ⇡− 3.05 < ⌘ < 3.2 ! ! Nicola Neri 10 Production and decay of HF baryons - FPCP 2015 Production kinematic dependence f 0 /fd ‣ Absolute value of ⇤ b from LHCb semileptonic analysis Phys. Rev. D 85 (2012) 032008 - obtain most precise branching ratio measurement of b-baryon to date (8% precision) 0 + stat. syst. semileptonic (B D ⇡−) JHEP08(2014)143 analysis B ! Exponential dependence vs pT Linear dependence vs η Nicola Neri 11 Production and decay of HF baryons - FPCP 2015 0 ⇤ b production cross-section 0 ‣ Measurement of differential production cross-section for ⇤ b 0 + using ⇤ J/ ⇤ decays with J/ µ µ−, ⇤ p⇡− b ! ! ! PLB 714 (2012) 136–157 ‣ pT distribution falls faster than measured b-mesons spectra and than predicted spectra from NLO MC POWHEG and leading-order MC PYTHYA 0 0 ‣ Cross-section ratio σ ( ⇤ b ) / σ ( ⇤ b ) consistent with 1 and constant vs pT, and rapidity |y| Nicola Neri 12 Production and decay of HF baryons - FPCP 2015 0 Observation of ⌅b⇤ ‣ New resonant state compatible with 0 3 + ⌅⇤ (usb) J P = ,j =1 b 2 ‣ Signal reconstruction involves three 21 signal events significance >5σ secondary vertices, ⌅ b− , ⌅ − , ⇤ and a dimuon pair 00 ‣ Theory predicts m ( ⌅ ) m ( ⌅ − ) <m ⇡+ b − b 00 + no strong decay ⌅ b ⌅ b− ⇡ consistent with experimental! results p ⇡− PRL 108, 252002 (2012) 0 ⇤ ⇡− ⌅b− δm = m(⌅⇤ ) m(⌅−) m + = 14.84 0.74 0.28 MeV b − b − ⇡ ± ± µ− 108 14 + 0 µ J/ ± m(⌅⇤ ) = 5945.0 0.7 0.3 2.7(PDG) MeV b ± ± ± ⌅− 0 ⌅− + Γ(⌅b⇤ )=2.1 0.74 MeV b ⇡ ± 0 ⌅b⇤ Nicola Neri 13 Production and decay of HF baryons - FPCP 2015 Two new ⌅ b− baryon resonances 1 + 0 (dsb) J P = ,j =1 ‣ Study ⌅ b ⇡ s− mass spectrum: 2 ⌅b0 2 3 + new resonances consistent with ( dsb ) J P = ,j =1 ⌅b⇤ 2 121 12 ± 237 24 ± -1 0 0 3fb data at 7-8 TeV - PRL 114, 062004 (2015) δm = m(⌅ ⇡−) m(⌅ ) m b − b − ⇡− Nicola Neri 14 Production and decay of HF baryons - FPCP 2015 ⌅ b− helicity angle distributions ‣ Flat distribution if J=1/2 or J>1/2 but zero longitudinal polarisation ‣ Cannot determine J value. However, data are consistent with quark model predictions J=1/2 and J=3/2 (if not or weakly polarised) PRL 114, 062004 (2015) 0 ⌅⇤ ⌅b− b ⇡− a =0.89 0.11 a =0.88 0.11 ± + ± ⌅c ✓ Helicity angle definition h 0 ⇡− (0, ) ⌅b ⇤ − ⇡− ⌅b Nicola Neri 15 Production and decay of HF baryons - FPCP 2015 0 ⌅ b lifetime and mass measurements 3fb-1 data at 7-8 TeV - PRL 113, 032001 (2014) ‣ Measure lifetime relative to ⇤ 0 and mass difference m ( ⌅ 0 ) m ( ⇤ 0 ) b b − b 0 + + + 0 + + + ⇤ ⇤ ⇡−, ⇤ pK−⇡ ⌅ ⌅ ⇡−, ⌅ pK−⇡ b ! c c ! b ! c c ! (180.5 0.5) 103 3775 71 ± ⇥ ± ‣ Ratio of efficiency corrected yields vs time (1/⌧⇤0 1/⌧⌅0 )t N 0 (t)/N 0 (t)=e b − b ⌅b ⇤b Lifetime ratio from a fit using exponential function Nicola Neri 16 Production and decay of HF baryons - FPCP 2015 0 ⌅ b lifetime and mass measurements PRL 113, 032001 (2014) 0 ⇤b lifetime measurements ⌧⇤0 =1.479 0.009 0.010 ps b ± ± PLB, 734, (2014) 122 ‣ Measure ⌧⇤0 =1.449 0.036 0.017 ps b ± ± first measurement PRD 87, 032002 (2013) ⌧⇤0 =1.503 0.052 0.031 ps b ± ± JHEP 07 (2013) 163 0 0 2 ‣ Measure m ( ⌅ b ) m ( ⇤ b ) = 172 . 44 0 .39 0.17 MeV/c − x4± precision± improvement 0 ‣ Measure relative production rate ⇤ b mass measurements m⇤0 = 5619.36 0.26 MeV b ± PRL 112, 202001 (2014) m⇤0 = 5619.7 0.7 1.1 MeV assuming naive Cabibbo factors b ± ± PRD 87, 032002 (2013) obtain f(⌅0)/f(⇤0) 0.2 b b ⇡ Nicola Neri 17 Production and decay of HF baryons - FPCP 2015 lifetime and mass measurements ⌅b− 3fb-1 data at 7-8 TeV - PRL 113, 242002 (2014) 0 0 ‣ Measure lifetime relative to ⇤ and mass difference m ( ⌅ − ) m(⇤ ) b b − b 0 + + + 0 0 + ⇤ ⇤ ⇡−, ⇤ pK−⇡ ⌅− ⌅ ⇡−, ⌅ pK−K−⇡ b ! c c ! b ! c c ! (220.5 0.5) 103 1799 46 ± ⇥ ± Nicola Neri 18 Production and decay of HF baryons - FPCP 2015 ⌅ − lifetime and mass results b PRL 113, 242002 (2014) Ratio of efficiency vs decay time Ratio of efficiency corrected yields vs decay time ‣ Measure x2 precision improvement 0 ‣ Using LHCb results relative to ⌅ b we obtain ‣ Results consistent with predictions from heavy quark expansion (HQE) Nicola Neri 19 Production and decay of HF baryons - FPCP 2015 0 Observation of ⇤ J/ p ⇡ − decay b ! - Large interference between tree and penguin amplitudes. 0 JHEP07(2014)103 Measure relative BR wrt ⇤ J/ pK − and search for CPV b ! 3 3 V V λ VtbVtd λ ( Vus = λ) / cb cd ⇠ / ⇠ | | 0 0 ⇤ J/ p⇡− 2102 61 ⇤b J/ pK−11179 109 b ! ± ! ± Nicola Neri 20 Production and decay of HF baryons - FPCP 2015 Search for CP violation ∆A 3fb-1 data at 7-8 TeV ‣ Measurement of CP cancel production and proton JHEP07(2014)103 reconstruction asymmetries 0 0 0 + (⇤ J/ ph−)= (⇤ J/ ph−)+ (⇤ ) (h )+ (p) Araw b ! ACP b ! Aprod b − Areco Areco 0 0 ∆A = (⇤ J/ p⇡−) (⇤ J/ pK−) CP Araw b ! − Araw b ! 0 0 + + = (⇤ J/ p⇡−) (⇤ J/ pK−)+ (⇡ ) (K ) ACP b ! − ACP b ! Areco − Areco 0 0 (5.7 2.4 1.2)% 2.2σ from zero raw(B J/ K⇤ )=( 1.10 0.32 0.0.6)% ± ± ⇡ A ! − ± ± ‣ No indications of large local CP asymmetries in Dalitz plane ‣ Rich resonant structure in m ( p ⇡ − ) , no evidence for exotics in m(J/ p),m(J ⇡−) ‣ BR compatible with expected value 0.08: CKM x phase space factor Nicola Neri 21 Production and decay of HF baryons - FPCP 2015 0 (0) Search for ⇤ b ⇤ ⌘ decays ! arXiV:1505.03295 ‣ b-baryons decays to final states with ⌘ , ⌘ 0 not yet Submitted to JHEP observed.