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Lhcb-TALK-2016-187.Pdf LHCb RESULTS ON EXOTICS AND PENTAQUARK STATES Marco Pappagallo University of Bari & INFN on behalf of LHCb collaboration QCD@Work 27-30 June 2016, Martina Franca, Italy OUTLINE Ø LHCb Experiment + Ø Search for Pentaquarks Pc à J/ψ p − Ø Amplitude Analysis of Λb àJ/ψ p K Decays − Ø Model Independent Analysis of Λb àJ/ψ p K Decays − Ø Amplitude Analysis of Λb àJ/ψ p π Decays ± ± Ø Search for a tetraquark X(5568) àBs π Ø Amplitude Analysis of B+ à J/ψ ϕ K+ Decays QCD@Work, 27-30 Jun 2016 M. Pappagallo 2 THE LHCb DETECTOR JINST 3 (2008) S08005 Tracking system TT, IT/OT Muon system Vertex Locator (VELO) 3 Primary and secondary Vertex reconstruction Interaction Point RICH detector Calorimeters PID K, π e, γ, π0, n QCD@Work, 27-30 Jun 2016 M. Pappagallo 3 DATASET √s = 7 and 8 TeV Run I Run II (expected 5 fb-1) √s = 13 TeV QCD@Work, 27-30 Jun 2016 M. Pappagallo 4 CERN Accelerating science Sign in Directory CERN press office Français English N ew s S p or Media visits News Calendar Resources Contact us t W ea Updates Press releases th er S S c h i op en HYSICAL CERN’s LHCb experiment reports c E L e ar & th a E P r observation of exotic pentaquark particles p g nv Tr a e ir av EVIEW r o el B ti H n 2015 14 Jul 2015 y c a m P l d e R S a e n c u r t UGUST ie l o Geneva, 14 July 2015. Today, the LHCb experiment at CERN’s Large Hadron Collider has reported the n R ETTERS ce in n 14 A c discovery of a class of particles known as pentaquarks. The collaboration has submitted a paper ed on C 14 it o L reporting these findings to the journal Physical Review Letters. J or l u , B l ly B i “The pentaquark is not just any new particle,” said LHCb spokesperson Guy Wilkinson. 2 C d 0 e “It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons 1 N r 5 e Articles published week ending w d and neutrons, in a pattern that has never been observed before in over fifty years of experimental S s ci w is searches. Studying its properties may allow us to understand better how ordinary matter, the en eb c ce si o protons and neutrons from which we’re all made, is constituted.” & te v E e Our understanding of the structure of matter was revolutionized in 1964 when American physicist, nv r ir s Member Subscription Copy Murray Gell-Mann, proposed that a category of particles known as baryons, which includes protons o A n n D m V and neutrons, are comprised of three fractionally charged objects called quarks, and that another e e E n w R Library or Other Institutional Use Prohibited Until 2017 category, mesons, are formed of quark-antiquark pairs. Gell-Mann was awarded the Nobel Prize in t T IS E physics for this work in 1969. This quark model also allows the existence of other quark composite p M e E states, such as pentaquarks composed of four quarks and an antiquark. Until now, however, no n N t T conclusive evidence for pentaquarks had been seen. a qu LHCb researchers looked for pentaquark states by examining the decay of a baryon known as Λ b a (Lambda b) into three other particles, a J/ψ - (J-psi), a proton and a charged kaon. Studying the rk spectrum of masses of the J/ψ and the proton revealed that intermediate states were sometimes + + involved in their production. These have been named P c (4450) and P c (4380) , the former being clearly visible as a peak in the data, with the latter being required to describe the data fully. “Benefitting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states”, says LHCb physicist Tomasz Skwarnicki of Syracuse University. "More precisely the states must be formed of two up quarks, one down quark, one charm quark and A one anti-charm quark.” n i (s llu Earlier experiments that have searched for pentaquarhkso have sproved inconclusive. Where the LHCb w tra experiment differs is that it has been able to look for pentaiqnuarks tfirom many perspectives, with all g n pointing to the same conclusion. It’s as if tShe previous searchesf wivere lo ooking for silhouettes in the c e f dark, whereas LHCb conducted the seaprch witihe the lights on, and fr otmi all oanngles. The next step in the a n gh e analysis will be to study how the quarks arre boundt tiosgether within the petnl taqu aprks. tic t y- os l s bo s “The quarks could be tightly boIund,” said LHCbe p hysicis ta Liming Zhang of Tsinnghua iUbniversity, “or t w c t d le they could be loosely bound in a sort aof meson-baryaonl molectuhle, in which the meseond and blaryon feel s le e q yo Volumea residua 115,l stron gNumber force simi la7r to the one f bi inding protonsd and neuLtrons to form nuclei.”ua u rs th ar rk t o More studies will be needed to distinguish bettw peen these possibeilities, angd to see what else s) f q r p e u ed e H ar ic nt ad ks te a r in d qu on a to a p rk C e ex . ol nt is lid aq t i e ua Published by n r rk th ha p e v ar 1 e tic 96 a le 0 nn s American Physical Society s o uc bu u h t n as , m ce t u d ho c th se h e s lik e e di en t s a h co t e v LH H e C ig ry b gs o b f a os n on e p w ar tic le b ef or e it, Observation of J/ψ p resonances consistent with - pentaquark states in Λb à J/ψ p K decays [LHCb: PRL 111 (2013) 102003] QCD@Work, 27-30 Jun 2016 M. Pappagallo 5 - FIRST OBSERVATION OF Λb àJ/Ψ K p [LHCb: PRL 111 (2013) 102003] Why did LHCb arrive first? The decay was not observed before! ü J/ψ à Large trigger efficiency ü 4 Tracks àLarge detection efficiency ü Large Λb production LHCb: JHEP 08(2014)143 LHCb: Chin. Phys. C40, (2016) 011001 μ- J/ψ μ+ Λb K- p p p QCD@Work, 27-30 Jun 2016 M. Pappagallo 6 OBSERVATION OF A NARROW BAND IN THE Λb DALITZ PLANE [LHCb: PRL 115, 07201 (2015)] Selection updated with the full Run I dataset (3fb-1) 0 26k Λb candidates. Background ~ 5.4% ] Λ*(1520) 2 26 LHCb [GeV p 24 ψ 2 J/ m 22 20 18 16 2 3 4 5 6 2 2 mKp [GeV ] Ø Efficiency flat over the “Dalitz” plot Ø Cross checks: 0 ü Veto BsàJ/ψKK & B àJ/ψKπ after swapping the mass hypothesis of the Λb daughters: p ßàK or p ßà π ü Clone and ghost tracks carefully removed ü Not a partially reconstructed Ξb decay QCD@Work, 27-30 Jun 2016 M. Pappagallo 7 UNEXPECTED NARROW PEAK IN m(J/Ψ p) [LHCb: PRL 115, 07201 (2015)] Λ*(1520) Ø A lot of structures in m(pK-)! Ø Could it be a reflection of the interfering Λ*’sà pK-? 6D Amplitude analysis QCD@Work, 27-30 Jun 2016 M. Pappagallo 8 FIT WITH ∧*àpK STATES ONLY [LHCb: PRL 115, 07201 (2015)] 2200 data 800 total fit 2000 background (a) LHCb 700 (b) LHCb 1800 Λ(1405) Λ(1520) 1600 Λ(1600) 600 Λ(1670) 1400 (1690) Events/(15 MeV) Λ Events/(15 MeV) 500 1200 Λ(1800) (1810) Λ 400 1000 Λ(1820) Λ(1830) 800 Λ(1890) 300 600 Λ(2100) Λ(2110) 200 400 Λ(2350) Λ(2385) 100 200 0 0 1.4 1.6 1.8 2 2.2 2.4 2.6 4 4.2 4.4 4.6 4.8 5 m [GeV] K p mJ/ψp [GeV] Use of extended model, so all possible known Λ* amplitudes: mKp projection looks fine, but the fit projection can’t reproduce the peaking structure in J/ψ p QCD@Work, 27-30 Jun 2016 M. Pappagallo 9 ADDING PCàJ/Ψp AMPLITUDES [LHCb: PRL 115, 07201 (2015)] Reduced Λ* model + 2 states decaying to J/ψ p Best fit has JP=(3/2-, 5/2+), also (3/2+, 5/2-) & (5/2+, 3/2-) are preferred 800 700 (b) LHCb 600 Events/(15 MeV) 500 400 + Pc(4450) 300 200 + Pc(4380) 100 0 4 4.2 4.4 4.6 4.8 5 mJ/ψp [GeV] State Mass (MeV) Width (MeV) Fit fraction (%) + Pc(4380) 4380 ±8±29 205±18±86 8.4±0.7±4.2 + Pc(4450) 4449.8±1.7±2.5 39 ± 5±19 4.1±0.5±1.1 QCD@Work, 27-30 Jun 2016 M. Pappagallo 10 + DO WE REALLY NEED 2 PC ’S? YES [LHCb: PRL 115, 07201 (2015)] m(Kp) >2 GeV nd + Clear need for the 2 broad Pc where the Λ*àpK- contribution is the smallest 500 Combined Pc LHCb Pc(4450) 400 Pc(4380) 300 Corrected events/(0.1) 200 Evidence of an interference pattern in the angular 100 distribution 0 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 cos( ) Pc QCD@Work, 27-30 Jun 2016 M.
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