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Nicola Neri on Behalf of the Lhcb Collaboration Presenting Also Result from Atlas and CMS

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Nicola Neri on Behalf of the Lhcb Collaboration Presenting Also Result from Atlas and CMS 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.
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