evidence for a near threshold structure in the j from b j k decay at cdf l.
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Evidence for a Near-Threshold Structure in the J/  from B +  J/ K + Decay at CDF. Kai Yi University of Iowa (for CDF Collaboration) Fermilab, March 17, 2009 .  - discovery J/  (cc) discovery  (bb) discovery. History—from strange to bottom discovery.

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evidence for a near threshold structure in the j from b j k decay at cdf
Evidence for a Near-Threshold Structure in the J/ from B+J/K+ Decay at CDF

Kai Yi

University of Iowa

(for CDF Collaboration)

Fermilab, March 17, 2009

history from strange to bottom discovery

 -discoveryJ/ (cc) discovery  (bb) discovery

History—from strange to bottom discovery






  • 1964 1968 1974 1974 1977
  • Heavy flavor spectroscopy helped turn quarks into a reality!
  • B+J/K+ decay includes b,c,s,u quarks
quark model

b u d

c c

Quark Model
  • Six quarks exist in Standard Model
  • charm/bottom/top called heavy
  • no free quarks, they have to be bound
  • top so heavy, it decays before forming bound states
  • Baryons are bound states of three quarks
  • Mesons are bound states of quark and anti-quark
  • quarkonia: quark and its own antiquark
  • Quark model works pretty well
  • Challenged by newly discovered charmonium-like states
x 3872 2003

PRL 91, 262001




M=3871.8±0.7±0.4 MeV

< 3.5 MeV @ 90% CL

mass ~70 MeV > predictions (2003)

+- peak at high value like a ρ (2003)


JPC = 1++ or 2-+

y 3940 j y 4260 j 2005
Y(3940)J/, Y(4260)J+---2005

PRL 94, 182002

PRL 95, 142001


M≈4259±8 MeV

≈88 23 MeV


M≈3940±11 MeV

≈92±24 MeV

Above DD && DD* threshold,

tiny Branching Fraction expected

New mass and width from BaBar:

M 3914+3.8-3.42.0,  34+12-8 5 MeV

at the J/ threshold ?

Well above DD && DD* threshold,

tiny Branching Fraction expected

JPC=1--, plus Y(4350), Y(4660)

too many 1-- ?

z 4430 2s 2008

PRL 100, 142001


M≈4433±4 MeV

≈44 ±17 MeV

Needs confirmation

The first charged charmonium-like

new state, if confirmed

Many more new states…

They do not (easily) fit into charmonium

Beyond (qq) mesons: exotic mesons?

exotic mesons qcd predictions

c u

u c

g g

c g c

Exotic Mesons—QCD predictions
  • Multi-quark mesons
  • molecule, diquark-antidiquark
  • Hybrid mesons
  • quark-antiquark-gluon
  • Glueball
  • gluonic color singlet states
  • Explore more channels to understand
  • How about J/ψϕ? (threshold @4.116 GeV, VV, C=+)
  • (cc) with a mass above 4.116 GeV, expect tiny branching fraction
charmonium hybrid j
Charmonium hybridJ/ψϕ ?

PRD 57, 5653 (1998)

F. Close et al


J/ψϕis also accessible to 0-+, 2-+

(0-+ ,1-+ ,2-+) masses are expected near Y(4260), E. Eichten

multi quark states j
Multi-quark statesJ/ψϕ ?

arXiv:0902.2803 (new)

N. V. Drenska et al

J/ψϕis well motivated!

How to search?

Inclusive? Challenge!

Through B decays!

search structures j through b decays

Experimentally easy to search through clean BJ/K channel

  • -- taking advantage of B lifetime and narrow B mass window
  • -- BJ/ψϕK is OZI suppressed, so low physics background
Search structuresJ/ through B decays

PRL 84,1393

PRL 91, 071801

vacuum polarization

gluon coupling

the current status
The current status
  • The current status through B J/ K:

BaBar 2003, PRL 91, 071801

CLEO, PRL 84,1393

23 B+

13 B0

J/ and ee

J/ and ee, 10 B+ and B0

  • statistically limited, no structures reported
why search at cdf
Why search at CDF?
  • B hadrons at Tevatron are:
  • copiously produced
  • boosted
  • --vertex separation
  • --boost low pT daughters
  • CDF has:
  • excellent mass resolution
  • excellent vertexresolution
  • reasonable hadron PID
  • CDF detector


cdf detector
CDF detector
  • Muon: μ ID
  • ToF: TOF
  • COT: track p
  • dEdx
  • Silicon: track p
  • vertex
cdf di muon trigger
CDF Di-muon trigger

pT > 1.5 GeV both muons

Scale to ~2.7 fb-1, ~20M J/with silicon hits

used for this analysis

cdf hadron pid

dEdx residual

CDF Time-of-flight: Tevatron store 860-12/23/2001


dE/dx parameterized using D*+(-)→D0π+(-) sample

dE/dx efficiency ~100%

Excellent resolution

Time-of-Flight acceptance+efficiency ~60%

CDF hadron PID

Main background: prompt pions, need PID to suppress

TOF mass

Make use of both dEdx and ToF for hadron PID

summarizing dEdx and ToF into a log-likelihood ratio

cdf hadron pid16
CDF hadron PID

K-π separation



Typical B decay daughter momentum ~GeV

analysis strategy














Vertex separation

Particle Identification

  • I) Reconstruct B+ as:
  • B+ J/ +
  • J/+-
  • +-
  • II) Search for structure in J/ mass spectrum inside B+ mass window
Analysis strategy
the challenge
The challenge
  • Start with typical requirements for B hadron at CDF:
  • --p(2) for B+ vertex fit>1%
  • --pT(track)>0.4 GeV,
  • -- >=4 r- silicon hits
  • --pT(B+)>4 GeV
  • --mass window:
  • J/ (50 MeV) and  ( 7 MeV)
  • constrain +- toJ/ PDG mass value
  • NOT applied yet: Lxy and kaon PID

B+ mass

Typical hadron collider environment

applying l xy
Applying Lxy
  • Maximize S/√(S+B) for B+J/K+ signal, has nothing to do with J/
  • Maximized cuts: Lxy>500 m, kaon LLR>0.2

+Lxy>500 um

B+ mass

Lxy Reduce background by a factor of ~200

applying l xy and kaon pid
Applying Lxy and kaon PID

Gaussian function

mean fixed to PDG

rms fixed to resolution (5.9 MeV)


define 3 as B+ signal region

(17.7 MeV obtained from MC)

Purity ~80% in B+ region

Kaon PID reduce background by a factor of ~100

clear B+J/K+ signal

control channels
Control channels
  • We also reconstruct two control channels with similar cuts:
  • ~3 000BsJ/, ~50 000B+J/K+
  • before Lxy and kaon LLR cuts
  • Clean control signals after Lxy and kaon LLR cuts
  • cross check and efficiency evaluation


~ 800 events


~21k events

background reduction factor

Before Lxy>500 um, kaon LLR>0.2

After Lxy>500 um, kaon LLR>0.2

Background reduction factor

Reduce background by a factor of 20 000 by using Lxy and kaon PID cuts while keeping about 20% of signal as estimated by control channels.

Any background under ?

verify b j k
Verify B+J/K+
  • Investigate components of B+ peak
  • --relax K+K- mass window to:
  • [1.0,1.04] MeV
  • --do B+ sideband subtraction for K+K-
  • --fit to sideband subtracted K+K- mass
  • A P-wave relativistic BW only fit to
  • data with 2 probability 28%, no
  • f0K+K- or K+K- phase space
  • components with our ϕ mass window
  • Conclusion
  • pure B+J/K+ for B+ peak
  • negligible B+J/f0K+, J/K+K-K+ components

II) Search for structures in

J/ψϕ spectrum from B

investigate j mass spectrum in mc
InvestigateJ/mass spectrum in MC
  • MC simulated phase space, full detector simulation


  • MC events smoothly distributed in Dalitz plot
  • No artifacts in the J/ mass spectrum
  • How about reflections from other B hadrons?
investigate j mass spectrum in mc28
InvestigateJ/mass spectrum in MC
  • We simulate generic B hadron decays with a J/ in the final state and
  • we identified a contamination channel: Bs(2S), (2S)J/+-

(Bs(2S), (2S)J/ +-) B+J/K+ due to kaon mis-identification

  • Bs contamination at M>1.56 GeV,
  • cut it off for simplification

20 times Luminosity of data

search for structures in j mass data
Search for structures in J/mass--Data


Three-body Phase Space Background shape is different from data

An near threshold enhancement is observed

robustness test
Robustness test


Default cuts



SVX hits3

  • Extensive cross checks by varying
  • Lxy, kaon PID LLR, B+ mass window,
  • vertex probability, # of silicon hits,…
  • Robust against variations
  • More signal but with more background
search for structures in j mass data32
Search for structures in J/mass--Data
  • We model the Signal (S) and Background (B) as:
  • S: S-wave relativistic Breit-Wigner B: Three-body decay Phase Space

Yield =145

m = 1046.3 2.9 (stat) MeV/c2

Width = 11.7 +8.3-5.0 (stat) MeV

Convoluted with resolution

(1.7 MeV)


√(-2log(Lmax/L0 ))=5.3, need Toy MC to determine significance for low statistics

significance study
Significance study
  • We determine significance from simulation (Toy MC):
  • --Using Three-body decay Phase Space only to generate the m spectrum
  • --Find the most significant fluctuation for each trial
  • anywherein m between 1.02 and 1.56 GeV
  • width between 1.7 MeV (resolution) and 120 MeV (10X observed width)
  • --Count it if -2log(Lmax/L0 ) (-2Δln) ≥ -2Δln value in data

P-value: 9.3X10-6

(3.1 million total trials)

corresponding to 4.3


significance study34

Cross check:

  • --fit -2Δln distribution with 2 Probability Density Function to get n (d.o.f):
  • --calculate p value using 2 PDF as cross check
Significance study

P-value by integrating 2 PDF: 6.5X10-6, corresponding to 4.3, consistent with counting

Best estimation of significance

More conservative


  • Most conservative: Phase Space and flat background for non-B background, 3.8
  • Including systematics:
  • Yield =145
  • m = 1046.3 2.9 (stat) 1.2 (syst) MeV/c2
  • Mass = 4143.0  2.9 (stat) 1.2 (syst) MeV/c2 (adding J/ψ mass)
  • Width = 11.7 +8.3-5.0 (stat) 3.7(syst) MeV
  • Significance: at least 3.8σ for most unphysical conservative background
  • Width indicates a strong decay
  • tentatively name it as Y(4140)
what is it
What is it?


  • Well above
  • charm pair threshold
  • Expect tinyBF to J/
  • Does not
  • fit into charmonium
  • Close J/ threshold
  • like Y(3940)
  • arXiv:0903.2529[hep-ph]
  • molecular?
  • Determine JPC (c=+)? Need statistics
  • --increase efficiency, reduce background
  • --add more data, 5σ
  • --investigate efficiencies against angles?
  • More channels for this structure?
  • --open charm pair?
  • Note: Search for potential more structures?
  • B+(2S)K+, B+K+, BsJ/
  • (nS), …

Mass = 4143.0  2.9 (stat) 1.2 (syst) MeV/c2

Width = 11.7 +8.3-5.0 (stat) 3.7(syst) MeV

JPC=??+ tentatively name it as Y(4140)


Stay tuned!

backup 1


~ 400 fb-1


220 fb-1 m

Backup 1

J/ee is difficult

but not impossible

Trigger is gone 

backup 2
Backup 2

Not close from the PDF comparison although they both have C=+


backup 3
Backup 3


exotic j pc
Exotic JPC
  • For qq meson system, let L to be the orbital angular momentum.
  • The meson spin J is given by |L-S|<J<|L+S|,
  • where S=0 (antiparallel quark spin) or 1 (parallel quark spin)
  • The parity P and charge parity C of the meson system can be expressed as:
  • P=(-1)L+1
  • C=(-1)L+S
  • In the configuration of P=(-1)J, S=1, CP=+1, 
  • Exotic JPC (not allowed for qq meson):
  • 0--, 0+-,1-+,2+-,…
  • But exotic mesons can have these JPC due to additional degree of freedom.
  • Identify exotic JPC is helpful to identify exotic mesons