The X(3872) at the Tevatron

Transcription

1 The X(387) at the Tevatron Ulrich Kerzel, University of Karlsruhe for the CDF and D0 collaborations BEAUTY 005

2 Physics at the Tevatron observe p p collisions at s =1.96 TeV 1 fb -1 luminosity delivered early June huge inelastic cross-section: 5000 times bigger than for b b triggers are essential! events polluted by fragmentation tracks, underlying events need precise tracking and good resolution dedicated trigger for J/Ψ µ + µ - trigger events where m(µ + µ - ) around m(j/ψ) high quality J/Ψ events with large statistics channel J/Ψ e + e - much more challenging in hadronic environment 4th June 005 U.Kerzel, University of Karlsruhe Beauty005

3 CDF: precise tracking: (silicon vertex detector and drift chamber) important for B physics: direct trigger for displaced vertices D0: excellent muon system and coverage large forward tracking coverage new in RunII: magnetic field D0 has joined the field of B physics 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 3

4 Observation of X(387) at CDF and D0 Candidates / 10 MeV/c 800 Dfl PRL 93,1600 (004) D0 ψ(s) Candidates / 10 MeV/c X(387) M + - µ µ (GeV/c ) M µ - M µ + - (GeV/c ) + µ - π + π - µ 0 hep-ex/ J/ψ µµ Candidates/ 5 MeV/c PRL 93,07001 (004) CDF II J/ψ π + π - J/ψ π ± π ± hep-ex/03101 no signal in wrong-sign combination, i.e. X ++, X J/ψππ Mass (GeV/c ) M = ± 3.1(stat) ± 3.0(syst.) MeV/c M = ± 0.7(stat) ± 0.4(syst) MeV/c σ = 17± 3 MeV/c σ = 4.9 ± 0.7 MeV/c reported widths are compatible with detector resolution 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 4

5 Observation of X(387) at CDF and D0 Original observation by Belle: m(π + π - ) clusters at large values D0: demand m(π + π - ) > 0.5 GeV/c as default cut CDF: separately plot m(j/ψ π + π - ) for m(π + π - ) > 0.5 GeV/c and m(π + π - ) < 0.5 GeV/c no apparent signal for m(π + π - ) < 0.5 GeV/c Candidates/ 5 MeV/c PRL 93,07001 (004) CDF II M(π + π - ) > 0.5 GeV/c hep-ex/ M(π + π - ) < 0.5 GeV/c J/ψπ + π - Mass (GeV/c ) 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 5

6 X(387): central vs. forward PRL 93,1600 (004) D0 hep-ex/ D0: large muon coverage reconstruct X(387) in central and forward part of the detector Ψ(S) and X(387) behave very similar in both rapidity ranges 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 6

7 X(387) properties compare fraction of yields w.r.t initial selection PRL 93,1600 (004) Dfl D0 hep-ex/ ψ(s) X(387) Fraction p > 15 GeV T y < 1 (i.e, central) L xy < 0.01 cm cos(θ ) < 0.4 π Comparison isolated cos(θ µ ) < 0.4 isolation: p(x) / p(x + charged tracks in cone R = 0.5) θ π, θ µ : boost one of the pions (muons) in dipion (dimuon) rest-frame, L xy : distance (PV decay vertex) * M/p t X(387) behaves similarly to the Ψ(S) 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 7

8 X(387) production fraction from B Define pseudo-proper decay time: cτ = M(J/Ψπ+ π ) p t (J/Ψπ + π ) L xy PV decay Lxy = (~x decay ~x prim ) ~p t ~p t Unbinned LogL fit (simultaneously for cτ and M): Mass: signal: Gaussian BG : nd order polynomial for BG Proper time: signal: exponential BG : pos., 1 neg. exponential all folded with Gaussian due to resolution 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 8

9 X(387) production fraction from B fraction from B decays: Ψ(S): 8.3 ± 1.0 (stat.) ± 0.7 (syst.) % X(387): 16.1 ± 4.9 (stat.) ± 1.0 (syst.)% X(387) behaves similarly to the Ψ(S) (with given uncertainties) 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 9

10 X(387) production fraction from B Consistency check: overlay m(j/ψ π + π - ) spectrum with prediction from LogL data is described well N.B. almost no prompt signal for cτ > 100 µm 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 10

11 The m(π + π - ) mass spectrum Distribution of m(π + π - ) constrains quantum numbers J PC shape depends on: decay of (π + π - ) sub-system: (π + π - ) in s,p,d wave (i.e. intermediate sub-resonances or not) relative angular momentum between (µ + µ - ) and (π + π - ) (and detector acceptance, efficiency, etc.) e.g. for decay chain: X J/Ψ ρ, ρ π + π - dγ X Γ dm =m X J/Ψρ (m ππ ) m ρ Γ ρ ππ (m ππ ) ππ ππ (m ππ m ρ) +m ργ ρ(m ππ ) for broad resonances (kinematic factors vary across width) µ Γ A BC =Γ k 0,A BC k 0 L+1 µ f(k ) ) ³ mm0 f(k 0 form-factor 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 11

12 The m(π + π - ) mass spectrum Challenge: Large background, rather low X(387) yield sideband-subtraction difficult, instead: slicing technique impose bin borders in m(π + π - ) as additional cuts fit resulting (π + π - µ + µ - ) mass spectrum obtained yield shows variation with m(π + π - ) Candidates / 5 MeV/c CDF II Preliminary, 360 pb 65 < M(ππ) < 650 MeV/c 10 ± 38 (stat.) X's < M(ππ) < 710 MeV/c 165 ± 35 (stat.) X's J/ψππ Mass [GeV/c] 4th June 005 U.Kerzel, University of Karlsruhe Beauty < M(ππ) < 765 MeV/c 18 ± 30 (stat.) X's need to be careful at kinematic borders

13 The m(π + π - ) mass spectrum if (π + π - ) in S-wave state: shape needs to be modelled compare to multipole expansions if (π + π - ) form sub-resonance: shape follows Breit-Wigner e.g. decay via ρ 0 π + π - (no kinematics, form-factor here) dγ ρ dm ππ Γ (m ππ M ρ ) +Γ /4 (PS) X(387) yield per 0 MeV/c ππ Mass [GeV/c ] 4th June 005 U.Kerzel, University of Karlsruhe Beauty CDF II Preliminary, 360 pb X(387) J/ψπ + π - J/ψ ρ J/ψ ππ Phase-Space Multipole Expansions for c c: 3 S 1 1 P 1 x 5 m(π + π - ) favours high end of mass spectrum compatible with intermediate ρ 0 π + π - resonance also 3 S 1 multipole-expansion for charmonium possible no charmonium candidate at that mass 3 S 1 also has J PC = 1 non-observation by BES (Γ(e + e - )B(π + π - J/Ψ) < 10 C.L. ) 3 D J hep-ph/ notation: n s+1 L J (J PC )

14 X(387) with J/Ψ e + e - Reconstruction of J/Ψ e + e - very difficult in complex hadronic environment dedicated J/Ψ e + e - trigger use neural-network based approach to identify soft e ± (p t > GeV/c) reject e ± from conversions based on neural network approach add γ at J/Ψ vertex to accommodate Bremsstrahlung X(387) reconstructions follows J/Ψ π + π - case (replace cut on m(π + π - ) by cut on Q = m X m J/ Ψ m ππ ) strong radiative tail able to reconstruct X(387) in this channel! 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 14

15 What is the X(387)?? Charmonium? 1 P 1, i.e. h 0 c (1+- ) predicted at 3950 MeV/c why is the 1 P 1 h c not seen in J/Ψ π + π -? Belle: cosθ J/Ψ distribution does not fit 1 1 D ( -+ ) pos. C-parity 1 3 D ( -- ), 1 3 D 3 (3 -- ) then also decay: X χ c1 γ, X χ c γ if charmonium, very unusual properties! charmed molecule? hybrid state, i.e.? Deuson? c cg (hep-ex/ ) notation: n s+1 L J (J PC ) 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 15

16 DeRujula, Georgi, Glashow (1977): Charmed molecules? X(387)?? possible formation of 4q molecules : D D, D D D D D D,D D J/ decay via: J/Ψρ 0,J/Ψη 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 16

17 Deuson model (Törnqvist) X(387) similar to deuteron: composed of two objects bound by π 0 exchange Prediction: J PC = 1 ++ or 0 -+ (otherwise potential too weak or repulsive) small binding energy: narrow resonance, big object isospin breaking: X J/Ψ ρ 0, ρ 0 π + π - allowed X J/Ψ σforbidden for any isoscalar σ X J/Ψ π 0 π 0 forbidden D π 0 D 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 17

18 Further properties by B-factories BaBar: search for charged partner X ± J/Ψ ρ ± expect twice the rate if X is part of iso-triplett no signal found Belle: (hep-ex/ ) (hep-ex/ ) 4 σ evidence for decay X(387) J/Ψ γ evidence for decay X J/Ψ π + π π 0 Swanson: 1 ++ D D (hep-ph/03119) has contribution of X J/Ψ ω, ω π + π π 0 search for X χ c1 γ, X χ χ γ no signal found C = +1 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 18

19 Conclusions & Outlook X(387) observed at CDF and D0 with high statistical significance already many properties determined: behaves similar to Ψ(S): isolation, cos(θ π,µ ), rapidity y fraction from B decays π + π - mass distribution experimental evidence seems to point to: X(387) has positive C parity X(387) compatible with molecular interpretation π + π - spectrum compatible with intermediate ρ 0 hypothesis yet to come: determination of J PC (CDF), decay modes with photons (D0),... 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 19

20 BACKUP 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 0

21 The Tevatron p p collisions CDF D0 Tevatron RunI: data taking period at s =1.8TeV Main injector and recycler RunII: major upgrades to collider and detectors s =1.96 TeV 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 1

22 Tevatron performance Running well - both peak luminosity and integrated luminosity Currently ~15 pb -1 / week delivered 1 fb -1 delivered in beginning of June. 4th June 005 U.Kerzel, University of Karlsruhe Beauty005

23 CDF: precise tracking: (silicon vertex detector and drift chamber) important for B physics: direct trigger for displaced vertices D0: excellent muon system and coverage large forward tracking coverage new in RunII: magnetic field D0 has joined the field of B physics 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 3

24 Physics at the Tevatron large b production rates: σ(p p, η < 1.0) 0µb 10 3 times bigger than Υ(4S)! spectrum quickly falling with p t Heavy and excited states not produced at B factories: B c,b s,b, Λ b, Σ b,... enormous inelastic cross-section: triggers are essential events polluted by fragmentation tracks, underlying events need precise tracking and good resolution! 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 4

25 Dedicated trigger J/Ψ µ + µ - Evaluate muon chamber info on trigger level: trigger events where m(µ + µ - ) around m(j/ψ) high quality J/Ψ events large statistics available N.B. channel J/Ψ e + e - much more challenging in complex hadronic environment! 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 5

26 Likelihood function for measuring fraction from B define likelihood: L =Π N h i i=1 f Sig ((1 f LL ) L P + f LL L LL ) + ³1 f Sig L B L i = F i (cτ) M i (m) composed of lifetime and mass functions mass component: M Sig (m) =G(m m 0, σ 0 ) M B (m) =a 0 + a 1 (m m) +a (m m) Signal: Gaussian, m 0, σ 0 from full fit Background: nd degree polyn. lifetime component: exponential with Gaussian resolution F(cτ )=R(cτ 0 cτ, σ τ ) exp( cτ 0 /τ Sig ) 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 6

27 Systematics for measuring fraction from B mass window shift window at fixed width of 130 MeV/c vary width of mass window: MeV/c fit model vary parameterisations, e.g. Gaussians instead of 1, etc. (negligible for X(387)) multiple candidates (L xy dominated from J/Ψ decay) randomly select one candidate take highest/lowest p t candidate take candidate with largest m(π + π - ) take candidate with smallest error on L xy take candidate with lowest χ in vertex fit fit bias generate many pseudo-experiments (Toy-MC) from original fit define pulls and check for deviations from Gaussian at zero 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 7

28 Systematics for m(π + π - ) measurement Yield systematics: compare yield from Gaussian with counting bin entries replace background parametrisation A (α+1)(x x 0) α βe (x up x low ) α+1 βx x 0 : turn-on value e βx low e βxup x low, x up : fit range with polynomial (n.b. special treatment for points at kinematic boundary) vary fit window size from 00 MeV/c to 150, 50 MeV/c Efficiency systematics: efficiency correction determined from MC measure p t spectrum from data, vary parameters 4th June 005 U.Kerzel, University of Karlsruhe Beauty005 8