Transcript Charmonium Production at BaBar Jamie Boyd University of Bristol On behalf of the Photon 2003, Frascati 7th-11th April 2003 Collaboration.

Charmonium Production at
BaBar
Jamie Boyd
University of Bristol
On behalf of the
Photon 2003, Frascati
7th-11th April 2003
Collaboration
Overview
•
•
BaBar detector & PEP-II performance
c measurements in 2 photon events
–
–
Measurement of the c width
Observation of c(2S)
•
J/ production using ISR events
•
Understanding J/ production in B decays as a test of nonrelativistic QCD:
•
Preliminary Result!
–
Measurement of the J/ total width
–
Branching fractions: B+  J/p L and B0  J/p p
Summary of new exclusive B decays to charmonium
All of the above analyses represent new or
newly updated results
April 10th , 2003
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BaBar Detector
Detector of
Internally Reflected
Cherenkov light
1.5T solenoid
Instrumented Flux Return
Identifies muons and neutral hadrons
Identifies particles by their
Cherenkov radiation
e+ (3.1GeV)
K- separation>3.4 for P<3.5GeV/c
e- (9GeV)
Silicon Vertex Tracker
Measures origin of charged particle
Trajectories + dE/dx
97% efficiency
Drift CHamber
Measures momentum of charged particles + dE/dx
(pT)/PT=0.13%PT0.45%
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ElectroMagnetic Calorimeter
Measures energy of electrons and photons
(E)/E=1.33%E-1/42.1%
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PEP-II Performance
PEP-II has provided 100fb-1 to date exceeding design
specifications
Integrated Luminosity
Daily luminosity
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c production in 2 events
• c lowest lying charmonium state
• c width poorly determined
• New Babar result using 1715 ± 70 signal
events
e  e   e  e  C
+
C  K K 
0
S
-
• Use J/ ISR events as cross check of
the detector resolution model
• Don’t detect the electrons
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c production in 2 events - Analysis strategy
c
J/
Spectrum fitted with:
J/: Gaussian
c: Gaussian  Breit-Wigner
Bkg.:Exponential
Free parameters:
MJ/ψ , MJ/ψ  Mηc , σ J/ψ , Γηtotc , (bkgr.)
Mηc  MPDG
J/ψ  (M J/ψ  M ηc ) fit
σ ηc  σ J/ψ  0.8 MeV from MC
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c production in 2 events - Results
2
TOT

33
.
3

2
.
5

0
.
8
MeV/c
C
MC  2983.3 1.2 1.8MeV/c2
c width
c mass
PDG
2
M JFIT
/  M J /  1.8MeV / c
MC  2983.3 1.2 1.8MeV/c2
Dominant Syst errors:
April 10th , 2003
TOT
 33.3  2.5  0.8MeV/c2
C
MeV/c2
MeV/c2
FIT
PDG
2
M

M


1
.
8
MeV/c
for Mc uncertainty on mass scale
J /
J /
for c uncertainty in background parameterization (0.7MeV/c2)
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c production in 2 events - c(2S)
BaBar preliminary results:
N(ηc (2S))  86  23
totC ( 2 S )  20  10  4 MeV/c 2
MC ( 2 S )  3632.2  5.0  1.8 MeV/c 2
Theory:
3583 Mηc (2S)  3640 MeV/c2
Ebert et al., Phys. Rev. D62, 034014 (2000)
Eichten, Quigg, Phys. Rev. D49,5845 (1994)
Lahde, Riska, hep-ph/0112131
Mηc (2S)  3654 6  8 MeV/c
Belle:
(in excl. B decays): tot  55 MeV/c2
c ( 2 S )
2
Crystal Ball:
(in (2s) decays)
April 10th , 2003
Mηc (2S)  3594 5 MeV/c2
totc (2S )  8.0 MeV/c2
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J/ production in ISR events
• Study ISR e+ e- ->  +- events in the +- mass range around
the J/ mass (2.8 – 3.2GeV/c2)
• Fit to the J/ mass spectrum to measure J/ parameters
• ~10% of ISR events have a photon which falls in the
detector acceptance
• High statistics due to large luminosity so fully reconstruct
both muons and photon
• Event selection
•
•
•
E*>3GeV
Muon ID E(EMC)<0.4GeV, p>0.5GeV/c
Kinematic cuts |Etotal-Ebeams|<1.5GeV, <0.07rad
• 1C Kinematic fit – mass of the recoil against the di-muon
system constrained to be 0 (photon hypothesis)
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J/ production in ISR events – Method
In ISR
d J / ( s, x)
Probability that ISR photon
has energy fraction x
 W ( s, x). 0 ( s(1  x))
dx
Integrating and adding in J/ lineshape:
 J / (s) 
12ee
m.s.tot
2
m
.W (s, x0 ); x0  (1  )
s
Measuring total cross section gives:
ee
tot
 eeB
Substituting in PDG values for B and Bee allows measurement
ee
of ee and tot
Bee 
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tot
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J/ production in ISR events - Method
Fit the di-muon mass spectrum with:
2nd order polynomial
(from simulation)
f (m)  c[ R  H (m; M J / , G )  NRPDF (m)]
J/ lineshape (from simulation) convoluted with
Gaussian (detector resolution)
main fit parameter
Obtain total cross section from R
vis
d

 JBorn
1
Total dM
/
K
R  Born .
vis
d

ISR dM
 ISR K
Efficiency systematics cancel in this ratio
April 10th , 2003
K corrects for FSR
Processes = 1.110.01
(from simulation)
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J/ production in ISR events - Results
~70k selected events, ~8000 in peak
BABAR
Preliminary
Background:
< 0.1% in peak
< 0.3% in NR region
χ 2 /ndf  124/144
Preliminary
Total
2
results: J /  94.7  4.4keV/c
PDG:
2
JTotal

87
5
keV/c
/
Jee/  5.61 0.20keV/c2
Jee/  5.26  0.37keV/c2
(Dominant systematic is error on K from FSR, and uncertainty on J/ lineshape)
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J/ production in ISR events - Interference
Line shape with/without interference
•Interference between J/ production and
convoluted with detector resolution
non-resonant component
•Effects the shape of the distribution but
has very little effect on the total cross
section
•Taken into account as a systematic error
(0.3%)
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J/ production in ISR events – the future…
This is just the beginning for charmonium production in
ISR at BaBar
Also looking at J/, (2S) production in hadron decays
modes
BABAR
Preliminary
J/->+-+-
(2S)->J/++Eventual goal is to measure RHAD(s) using ISR at BaBar
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BJ/X experimental observation
An excess at low momentum in the inclusive production
of charmonium mesons in B decay at the U(4S) has been
observed compared to the non-relativistic QCD prediction
(excess corresponds to a branching fraction ~10-4)
Possible source includes:
•intrinsic charm
color singlet component of B
NRQCD
data
•production of sdg
hybrid with J/
•Rate enhanced due
to B decay to J/
baryon-antibaryon
Phys.Rev. D67, 032002 (2003)
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B+  J/pL and B0  J/pp analysis
These processes can be enhanced by exotic QCD resonances in intermediate states
e.g. (baryonium, pentaquark, nuclear-bound quarkonium)
B+  J/pL
B0  J/pp
p
l+l-,l=,e
l+l-,l=,e
Key elements of the analysis are the separation of low momentum protons
from Kaons (DIRC, dE/dx) - 98 % efficiency, less than 1% misidentification
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B+J/ pL results
4 events in
signal region
with an
expected
background of
0.210.14
Prob.(4, expecting 0.21 0.14) is equal to 2.5x10-4 (3.5 )
Bayesian analysis, uniform prior 0 gives:
-6
-6
B(B+J/ pL)=(12 +9
)x10
90%
CL
upper
limit
26x10
-6
Efficiency uncertainty is dominant systematic
April 10th , 2003
Submitted to PRL
hep-ex/0303036
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B0J/ pp results
1 event in signal region
Expected 0.640.17 background events, one observed.
90% CL upper limit 1.9x10-6
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This is not an explanation of the excess
• Measured branching fractions order of magnitude
too low to explain excess
• Each of the possible QCD exotic resonances (baryonium,
pentaquark, nuclear-bound quarkonium) that could be
involved foresee a monoenergetic particle (J/ , p, L) in the
B frame
No evidence
for Exotic
resonance
production
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Summary of exclusive B decays to Charmonium
(4.4  1.4  0.5) x 10-5
Measured
Branching fractions
And Upper Limits
at 90% CL
(5.1  1.9  0.5) x 10-5
< 9.2 x 10-6
< 2.7 x 10-5
< 6.3 x 10-5
10- 5
(11.6 +8.5 )x10-6
- 5.6
< 1.9 x 10-6
10- 6
(4.6  0.7  0.6) x 10-5
(1.6  0.6  0.4) x 10-5
10- 5
Phys.Rev.Lett. 90, 091801 (2003)
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Summary
• New measurement of the c width
– Agrees with large width measurements by Belle
2
TOT

33
.
3

2
.
5

0
.
8
MeV/c
C
– Observation of the c(2S)
• J/ production in ISR events
– Preliminary measurement of the total J/ width
2
JTotal

94
.
7

4
.
4
keV/c
/
– Preliminary measurement of the e+e- J/ width
Jee/  5.61 0.20keV/c2
• New Exclusive B decays to charmonium
– J/ Baryon anti-Baryon processes cannot explain the excess
of J/ production at low p* in B decays
April 10th , 2003
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BACK UP SLIDES…
What is Mes and DeltaE
etaC event selection
Systematics on ISR J/ widths
J/ baryon anti-baryon event selection
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Exclusive B reconstruction variables
• The variables MES and E
•
E is the difference between the B candidate energy and the
*
*
expected energy
E  EB  Ebeam
•
MES is the B candidate mass with the beam energy used as the
candidates energy
*2
*2
M ES  Ebeam  pB
• Nearly uncorrelated
• Very useful for distinguishing signal
from, background (continuum & B background)
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c production in 2 events – Event Selection
• Do not reconstruct the e+e• Select 2 photon events
• Etot(lab) <9GeV (suppresses B decays)
• pT <0.5GeV/c
• Fully reconstruct the C(KSK+- )
• Ks ->+• 0.491<M(+-)<0.503 GeV/c2
• Cos (Ks) > 0.99
• Apply Particle Id on charged K candidate (dE/dX &
DIRC)
• Fit the KSK+- vertex (prob(2)>0.01)
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J/ production in ISR events –
Systematic Errors
Summary of the systematic errors on the J/ parameters
Statistical error on K factor 0.9%
Systematic error on K factor 1.3%
(Varying cut values)
Background uncertainty
0.5%
Simulation of J/ lineshape
1.4%
Interference
0.3%
Total
2.2%
(MC / varying background cuts)
(fit with or without muon bremsstrahlung)
(see slide 13)
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B -> J/ Baryon anti-Baryon – Event Selection
• Reconstruct J/ -> e+e- or +• 2.95<Mee<3.13 GeV/c2 or 3.06<M<3.13 GeV/c2
• Particle Id on the electron candidates (EMC, dE/dX,
DIRC) and muon candidates (EMC, IFR)
• Particle Id on Proton candidates (dE/dX, DIRC)
• Lambda candidates reconstructed in L-> p+- mode
• 1.10<Mp<1.13 GeV/c2
• L vertex >2mm from J/ vertex
• Cut on difference between expected B energy and B
candidate energy (E) & Mes (B-mass with the beam energy
used to improve the resolution)
• Efficiencies
• 4.9  0.9% (B+-> J/ Lp), 18.4  2.4% (B0 -> J/ pp)
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