BaBar ventures into the non
B-physics world :
R from ISR and Pentaquark
Searches
Nicolas Berger, SLAC
For the BaBar Collaboration
Outline
• Measuring R
–
–
–
–
Why ?
Why use ISR ?
Exclusive Analyses
Inclusive Analysis
• Search for Pentaquarks
– Motivation
– Q+  pK0S
– X5  Xp
– X5  LK
• NOT shown here: Many More related analyses:
–
–
–
–
–
inclusive Lc, Xc, h, f studies
inclusive p,K,p spectra,
studies of fragmentation models
DsJ, X(3870)
Searches for charmed pentaquarks, Q++... and more!
Nicolas Berger, Cornell Seminar
2
Hadronic Cross-sections
from Initial-state Radiation
Motivation(1) : Standard Model Fits
• Fit SM parameters using as inputs:
– W, Z parameters (MW, GW MZ, GZ, sHad0, Rl, AFB0,l)
– Leptonic asymmetries (Al(Pt), Al(SLD))
– Heavy flavors (RX, AX, AFB0,X, X=b,c)
– Weak Mixing Angle (sin2qefflept(QFBHad),
sin2qW(NuTeV/E158), QW(Cs))
– mt, DaHad(5)(MZ2).
low-Q2 data now excluded
• Results globally consistent
• Can measure mH indirectly (loop effects)
F. Teubert, ICHEP
2004
mH  114 69
45 GeV
log mH  2.06  0.21
5)
D2 (log mH )  D2 (exp)  D2 (mt )  D2 (Da (Had
)  D2 (a s )
(0.21)
2
All observables
except NuTeV
(0.12)
2
(0.13)
2
(0.10)
2
(0.04)
2
Not the largest contribution to the error
since BES 2002 results but still large!
Nicolas Berger, Cornell Seminar
4
Hadronic Contributions to Da
•
•
•
a(q2=0) is the most precisely measured
constant of nature, but we need a(MZ2)
=> “Run” a to MZ2
a ( M Z2 ) 
Hadrons
Ward identity: only the vacuum polarization
contributes -- Hadronic part ?
Had=
 Had ( s0 )   Had (0) 
Contour integral (Analyticity):
Im s
s0
•
4mp2

s0
p

4 mp2
Im  Had ( s )
ds
s ( s  s 0 )  i
s (e  e   Hadrons )
R( s ) 
s 0 (e  e       )
Re s
Born
cross-section
1
  d
2
Im
Optical theorem (Unitarity):
a (0)
a (0)

1  Da ( M Z2 ) 1   ( M Z2 )   (0) 
a
  R( s)
3
2
aM Z2 
R( s )
Da Had ( M )  
P
ds
4 mp s ( s  M 2 )
3p
2
Z
2
Z
Nicolas Berger, Cornell Seminar
5
Motivation(2) : Hadronic Contributions to (g-2)
Contributions to the Standard
Model (SM) Prediction:
Units
of
10-10
a 
SM
( g  2) 
 aQED  aW eak  ahad.VP  aLBL
2
Pure
QED
Electroweak
Corrections
Hadronic Vacuum Polarization (LO)
e+ett
Hadronic VP
(HO)
Light-by-Light
Scattering
Kinoshita, Nio
hep-ph/0402206
Czarnecki et al.
hep-ph/0212229)
Davier, Hoecker, Eidelman and Zhang
hep-ph/0308213
Hagiwara et al.
hep-ph/0312250
Melnikov, Vainshtein
hep-hp/0312226
a
11,658,471.9
15.4
696.3
711.0
-9.79
13.6
Da
0.2
0.3
6.2exp  3.6rad
5.0exp  0.8rad  2.8SU(2)
0.09
2.5
Can be expressed as
a dispersion integral
for R(s)
a 
a
 11,614,098 10 10
2p
Total SM Prediction for e+e- (hep-ph/0308213):
aSM  (11 659 180.9  7.2had  3.5LBL  0.4QED+EW ) 1010
BNL 2004 Measurement (hep-ph/0401008):
aExp  (11 659 208 .0  5.8) 1010
ahad , LO
2.5s
discrepency!
Nicolas Berger, Cornell Seminar
a 
 
 3p 
2 

4 mp2
2

R( s)  m

K ( s) ds


s  s

“QED kernel”
function (closed form)
6
Experimental Status for R, DaQED and a
Da
had
a  R( s )  M Z2 

ds
(M )  
P
2 
3p 4 m s  s  M Z 
p
2 
2

R( s)  m
a 
had
a  

K ( s) ds
 

 3p  4 mp2 s  s

2
Z
2
s [GeV]
•Same integral form for a
and DaQED.
•low-s region crucial for a.
• DaQED sensitive to full
accessible range
Error due
to radiative
corrections
Hagiwara et al. (2003)
Nicolas Berger, Cornell Seminar
Davier et al. (2003) 7
Recent Progress in R Measurements
KLOE
hep-ex/0407048
• ISR Method
• Untagged photons
(outside calorimeter)
CMD-2 : E. Solodov,
Talk at ICHEP 2004
(Variable beam Energy)
BES
hep-ex/0210042
(Variable beam Energy)
Nicolas Berger, Cornell Seminar
8
The BaBar Detector
BaBar SVT
•5 double-sided Si layers
•Vertex Reconstruction, Tracking
•Hit resolution 20-40 m
BaBar DIRC
•Quartz Cherenkov radiator
•Covers 80% of solid angle
•Particle ID above 600 MeV/c
BaBar DCH
• 40 layers, axial and stereo wires.
• Covers 92% of solid angle
• dpt/pt ~ 0.5 -1.5 %
• Particle ID up to 600 MeV/c
BaBar EMC:
• 6580 CsI(Tl) crystals
• Covers 91% of solid angle but
inner rings degraded by beam
background.
• E resolution ~2 % at high E.
Nicolas Berger, Cornell Seminar
9
BaBar Particle ID
Cherenkov Angle
(Kaon from D*-  D0 p , D0  K- p+ sample)
Nicolas Berger, Cornell Seminar
All Events
10
PEP-II Luminosity
• PEP-II is an asymmetric e+ecollider with a CM energy of
10.58 GeV.
• Peak luminosity = 9.2 1033 cm-2s-1
• Integrated luminosity = 244 fb-1.
• Analyses presented here use
89-123 fb-1.
Nicolas Berger, Cornell Seminar
11
ISR atU(4S) Energies
e+
Hadrons
e-
s  s'
Eg 
2 s
*
• Hard photon: Eg* = 3-5.3 GeV
at s’ = 0-7 GeV.
 No beam-gas events
•ISR/FSR separation
• High event fiduciality with cuts on g
polar angle
• Hadronic system collimated by recoil.
• Harder spectrum
 better detection efficiency.
 Reduced dependence on had. model.
– FSR contribution is expected to be
small, well separated from ISR
– Separated with angular analysis.
•Mass resolution
– Limited by photon E resolution
– Exclusive analyses : excellent results
from kinematic fits.
– Not a problem for Dahad.
Nicolas Berger, Cornell Seminar
12
MC Studies
s  s' 
ds

x 

( s, x)  W ( s, x).s 0 ( s (1  x))
s


dx

“Radiator
a 1  x 2  1  cosq min


W
(
s
,
x
)

log

(
1

x
)
cos
q
function” (LO)
min 

p x(1  x)  1  cosq min

Born crosssection:
KKMC event generator
s’<8 GeV
15.3 < qg < 137.3o
stotal = 90.2 pb
spp = 18.7 pb
In 200 fb-1,
ds/ds’ [pb/2.5 MeV]
3.8M
(pp: 3.5 M)
2.6M
5.7M
BES 2002:
~250K events
Level 1
Events In 200 fb-1 :
Ntotal = 18 million
Npp = 3.7 million
Level 3
KKMC
KKMC
Triggering
Efficiencies
“BG Filter”
= Level 4
s’ [GeV]
Nicolas Berger, Cornell Seminar
s’ [GeV]
13
Overview of Exclusive Analyses
• Common features
– Perform kinematic fits with
constraints :
• In solid boxes presented here ,
• in dashed boxes in progress .
• E,p conservation
• Resonance masses
– Use fit c2 to discriminate signal
and background.
– Use particle Identification to
select/reject kaons and protons
p+p-h
p+p-
p+p-p0
K+KK0SK0L
p+p-p+pp+p-p0p0
fp0
fh
K+K-p+pK+K-K+K-
J/y
DD*
K+K-p/h
K0Kp
Nicolas Berger, Cornell Seminar
pp
14
e+e-  p+p-p+p-g
• Perform kinematic fits with mg = 0 for 4p, 2K2p,
4K hypotheses
c24p
– Accept events with good c2.
– Reject if good c2 in “neighbor” modes
– For 4p mode, c24p < 30 and c22K2p > 10
Non-ISR
Background MC
• Identify kaons using Cherenkov angle and dE/dx.
• Normalize cross-sections w.r.t e+e-  +-g
Signal MC
M4p

p+p-p+p-
cross-section
(89.3 fb-1)
Covers entire
spectrum
(~60K evts)
events/0.025 GeV
e+e-
data
Average BG fractions
data
ISR Background
Non-ISR
Background MC
Nicolas Berger, Cornell Seminar
15
Resonant Structures in e+e-  p+p-p+p-g
J/Yp+p-p+p-
Y(2S)J/Yp+p-
a2
r0
r0
y(2S)
excluded
from
these
plots
M4p = 2.3-3.0 GeV
MC
Data
Mpp (GeV/c2)
f2(1270) or
f0(1370) ?
Assuming PDG values for
B(J/Y  ),
G(J/Y,Y2S)  ee):
PDG: (4.01.0).10-3
B( J /y  p p p p  )  (3.61  0.26  0.26) 103
B(y (2S )  J /y (    )p p  )  (36.1  1.5  2.8)%
Would be interesting to
compare with J/Yp0p0 BF
from e+e-  p+p-p0p0g...
Work in progress!
Nicolas Berger, Cornell Seminar
PDG: 31.02.8 %
16
e+e-  K+K-p+p-g
e+e-  K+K-p+pcross-section (89.3 fb-1)
• Require 1 or 2 Kaon IDs
c22K2p < 20, c24p > 30, c24K > 20.
• Negligible background
• Good agreement with DM1,
higher ECM reach.
• Systematics: Kaon ID,
Efficiency.
Assuming PDG value of G(J/Y  ee):
B( J /y  K  K p p  )  (6.09  0.50  0.53) 103
Nicolas Berger, Cornell Seminar
PDG: (7.22.3).10-3
17
e+e-  K+K-p+p-g : Resonant Structures
•K*(892) Kp
dominates
•Little K*K*
• f,r in K+K- and
pp spectra with
K*(892) bands
excluded
•Hint of ff0(980),
ff0(600) ?
f
K*0
r0
Excluding the
K*(892) bands
f band
Nicolas Berger, Cornell Seminar
18
e+e-  K+K-K+K-g
e+e-  K+K-K+Kcross-section (89.3 fb-1)
Assuming PDG value of G(J/Y  ee):
B( J /y  K  K  K  K  )  (6.7  1.0  1.1) 103
PDG: (7.03.0).10-3
• Require 3 or 4 Kaon IDs
c24K < 20, c22K2p > 20
• Negligible background
• First measurement ever of
the e+e-  K+K-K+K-g crosssection.
• Dominated by systematics:
No large
f signal
– Particle ID
– Luminosity
– Tracking efficiency
– Acceptance losses
Nicolas Berger, Cornell Seminar
19
e+e-  J/Yg  +-g
e+e-  +-g
•Require E,p balance, 1C fit
with mg = 0.
•Backgrounds mostly ISR
processes, use muon ID.
•Get sJ/Y from ratio of peak
to continuum events.
s~ MeV
BABAR 88.4 fb-1
ISR luminosity at s’=m2
Cross-section given by:
s

J/y
(s) 
12 p 2 Gee B
m s
 W ( s, x0 ),
m2
x0  1 
s
GJ /y  ee BJ /y     0.330  0.008  0.007 keV
With PDG values
for B(J/Y  )
and B(J/Y  e+e-):
GJ /y  ee  5.61  0.20 keV
GJ /y  94.7  4.4 keV
Nicolas Berger, Cornell Seminar
In agreement
with world
average
+ better error.
20
• New results (Summer 2004):
– Measurement of 3pi form factor
on a wide energy range
– Measurement of B(J/Y  3p
• 4C fit requiring E,p
conservation, p0 mass (using
photon angles but not energy)
Events/0.01 GeV/c2
e+e-  p+p-p0g
BaBar
124 fb-1
higher
’s ?
• Backgrounds from
– e+e-  K+K-p0g, e+e-  npg
– e+e-  qq  p+p-p0p0
– Background level :
• 0.5-1.5% in , f regions
• Rises to 15-50% at higher masses
• Known to ~25% below 2 GeV
• Detection efficiency ~10%,
weak dependence on M3p.
• Mass resolution: 6, 7, 9 MeV/c2
at , f, J/y masses.
Solid: Signal MC
Points: data
e+e-  K+K-p0g
e+e-  p+p-p0p0
Nicolas Berger, Cornell Seminar
21
Structures in e+e-  p+p-p0g
• Fit the f mass region, including ’ and ’’
•

•
•
f
Fix relative phases to
• -f : (1637)
• - : 180
•  -  : 0
Assume PDG values for G, Gf.
We get:
B  ee B  3p   (6.70  0.06  0.27) 105
PDG: (6.350.11)%
Bf  ee Bf  3p   (4.30  0.08  0.21) 105
fit c2/d.o.f = 146/148
PDG: (4.590.14)%
B '  ee B '  3p   (0.82  0.05  0.06) 106
B ' '  ee B ' '  3p   (1.3  0.1  0.1) 106
M  '  1350  20  20 MeV/c 2 PDG: 1400-1450 MeV/c2


G '  450  70  70 MeV
PDG : 180-250 MeV
M  ''  1660  10  2 MeV/c 2
PDG: 1670 ± 30 MeV/c2
G ''  230  30  20 MeV
PDG: 315 ± 35 MeV
Nicolas Berger, Cornell Seminar
22
e+e-  p+p-p0g: J/y and Cross-Section
NJ/y = 92034
From sJ/y, we extract:
GJ /y  ee BJ /y  3p   0.122  0.005  0.08 keV
Using G(J/y ee)= 5.610.20 keV from the
e+e-  J/Yg  +-g results, we have:
BJ /y  3p   (2.18  0.19) %
PDG: (1.500.20)%
BES 2003: (2.100.12)%
SND
BaBar Preliminary
Cross-Section:
• Overall normalization error
~5% below 2.5 GeV.
• Consistent with SND data
for M3p < 1.4 GeV.
• Inconsistent with DM2 results.
DM2
Nicolas Berger, Cornell Seminar
23
Inclusive ISR Analysis
•Goal : extract DaHad to 3-4 % between 0-7 GeV.
•ISR Selection
–Require unmatched cluster with ECM > 3 GeV
–s’ given by Eg.
•Efficiency
–Triggering efficiency ~98%, can be calibrated to below 1%.
–Photon fiducial detection inefficiency ~10%, can be calibrated
to few % level.
–Weak dependence on hadronization model.
•Luminosity
–Extracted from standard U(4S) luminosity using MC prediction
for the “radiator function”.
–Uncertainty on U(4S) luminosity ~ 1%, and < 1% for MC
calculations (KKMC generator).
Nicolas Berger, Cornell Seminar
24
• Energy resolution ~3%, affects the spectrum, especially
at low s’.
• However, we measure integrals of R(s)/s, not R(s)/s
itself:

had
a


4 mp2
R( s )  K ( s ) 

ds,
s  s 
Da had ( M Z2 )  

4 mp2
R( s)  1

s  s  M Z2

ds


Eg [GeV]
Energy Resolution effects
• Smearing  events move in s’; Problem only if weight
function is non-uniform.
–
–
OK for DaHad
Does not work for a
s’ [GeV]
Smeared spectrum
(Crystal Centers)
Smeared spectrum
(All Clusters)
MC spectrum
Smeared spectrum
(Crystal centers)
Smeared spectrum
(All clusters)
MC Spectrum
x

4 mp2
s’ [GeV2]
Nicolas Berger, Cornell Seminar
R ( s ) 
1

s  s  M Z2

 ds


s’ [GeV2]
25
Event Selection
• Remove QED background:
tt
Before p0 veto
– Radiative Bhabhas
– e+e-  gg, including g  e+e– Virtual Compton scattering
• Keep e+e-  ttg, g, substract MC
prediction
Signal
(KKMC)
cc, uds
– Must retain high efficiency
– Problems for t e modes but branching
fractions well known.
• Significant backgrounds from
e+e-  uu,dd  p0X and e+e-  tt  p0X,
with p0 faking an ISR photon. Reject using
– Explicit p0 veto (if other photon found)
– Shower shape cuts (for “merged p0” case)
– Event Shape cuts
Efficiency
Fiducial Efficiency
After p0 veto
After QED Veto
After p0 Veto
g
ttg
Sufficient purity
can be obtained
up to s’~ 6 GeV
with efficiency
~80% of fiducial
s’ [GeV]
Nicolas Berger, Cornell Seminar
s’ [GeV]
26
Pentaquark Searches
Experimental Overview
• New, exotic resonances observed:
– Q+ : seen nK or pK decays by many experiments
– X / X0 : seen by NA49
– Qc : A charmed partner to Q+ seen by HERA
Inclusive
CLAS
Many sightings,
but masses
don’t agree…
NA49
• However, many negative results as well:
• Q+ : CDF, HyperCP, E690, HERA-B, Aleph, Delphi…
• X : CDF, E690,HERA-B, WA49
Nicolas Berger, Cornell Seminar
28
Theory Overview
B(Q+  pK0S) = 25%
• Several models predict
a 10+8 multiplet of
SU(3)f for non-charm
pentaquarks (doesn’t
include HERA’s QC+)
• A 27 multiplet also
possible (Q++)
• Assume J = ½.
In red, states
covered in this talk.
In green, searches
not shown here
B(X5--  X-p-) < 50%:
= S-K-, also Xpp…
–50% for pK0/nK+
–50% K0S/K0L
Q+ |ududs
pK0S
N50 |udd(dd,ss)
N5+ |uud(dd,ss)
LK+
LK0S
S5- |dds(dd,ss)
N5 may be below
LK threshold
S50 |uds(dd,ss)
Xp-
X5- |dss(dd,ss)
LK-
•BFs to LK depend
on 10-8 mixing
 model-dependent
S5+ |uus(dd,ss)
pK0S
X  K+
X5- - |sdsdu
•Searches in LK only
sensitive to octet
states
X50 |uss(dd,ss)
Xp+ / LK0S
Nicolas Berger, Cornell Seminar
X5+ |ususd
X0p
29
Hadron Production Rates in e+e• Look at multiplicity of
hadrons per spin state in
e+e- collision events.
• Weak dependence on
quark content, spin,…
• Strong dependence on
mass
• Pentaquarks may not be
too different from other
hadrons.
• Normalizing to L(1520)
may not be a good idea.
Nicolas Berger, Cornell Seminar
30
Search for Q+ pK0S
BaBar 123 fb-1
• Proton selection using dE/dx
and Cherenkov, clean over
wide momentum range.
Lc
• Use K0S  p+p-.
• Expected Resolution on Q+
mass ~ 2 MeV, would be
most precise so far.
• Can also look for S5+.
• Large signal for Lc+  pK0S
 Lc
Q+
Better resolution for
Q+ since near threshold
Nicolas Berger, Cornell Seminar
31
Search for Q+ pK0S (and S5+)
G = 1 MeV: s < 183 fb @ 95% c.l.
G = 8 MeV: s < 363 fb @ 95% c.l.
B(Q+  pK0S) = 25%
taken into account
Events / 2 MeV/c2
Events / 2 MeV/c2
Q+(1540)
Q+(1540)
Nicolas Berger, Cornell Seminar
Q+
Events / 2 MeV/c2
3.5 < p* < 4.0 GeV/c
0.0 < p* < 0.5 GeV/c
X
S5
?
?
?
S5+  pK0S
32
Search for Q+ pK0S : Lc+ Signal
• 100K LC’s in data
sample
• Resolution 5-7 MeV
Lc+
3.5 < p* < 4.0 GeV/c
0.0 < p* < 0.5 GeV/c
M(pK0S) [GeV/c2]
Nicolas Berger, Cornell Seminar
M(pK0S) [GeV/c2]
33
Search for X50/-- X-p±
Xp, BaBar 123 fb-1
Look for inclusive
production of :
X*(1530)
Xc0

e e  X5 X , X5  X p 
0
e e  X5 X , X50  X p 
• Apply loose particle ID on proton
• Use displaced vertices:
Xp, BaBar 123 fb-1
– ct(L) = 7.9 cm,
– ct(X-) = 4.9 cm
• Select masses near the nominal L
and X- masses
• Control particles:
–
–
X*0(1530)  X-p+
Xc0(2470)  X-p+
Nicolas Berger, Cornell Seminar
34
Search for X5-- X-pG = 1 MeV: s < 22.0 fb @ 95% c.l.
G = 18 MeV: s < 33.7 fb @ 95% c.l.
Limits on
s  B(X5--  X-p-)
Xp, BaBar 123 fb-1
• Exotic
channel
 No
features
• No sign of
the NA49
particle
X5—-(1862)
Nicolas Berger, Cornell Seminar
35
Search for X50 X-p+ : X50, X*0 and Xc0
Xp, BaBar 123 fb-1
NX*  5000
s=7.3 MeV/c2
X*(1530)
123 fb-1
X50(1862)
NXc  2000
s=9.3 MeV/c2
X*(1530)
Xc0
Nicolas Berger, Cornell Seminar
36
Search for N5/X5  L K
• Look at K = K+,K-,K0S
• LK only sensitive to octet states, not
antidecuplet
• Require tight proton selection.
• For L and K0S, cut on angle between flight
direction and momentum direction.
• Backgrounds mostly real L and K
• S0K searches also performed for S0  Lg, can
probe antidecuplet, but more BG (soft
photon).
L
Mpp [GeV]
K0S
Mpp [GeV]
Nicolas Berger, Cornell Seminar
37
Search for X50  L K0S
G = 1 MeV: s < 82.8 fb @ 95% c.l.
G = 18 MeV: s < 204.7 fb @ 95% c.l.
Limits on
s  B(X50  LK0S)
X50(1862)
LK0S
123 fb-1
XC0
X C0
123 fb-1
Nicolas Berger, Cornell Seminar
NXc  00
s = 5.9 MeV
38
Search for X5-  L KG = 1 MeV: s < 83.6 fb @ 95% c.l.
G = 18 MeV: s < 181.0 fb @ 95% c.l.
LK
123 fb-1
W
123 fb-1
Nicolas Berger, Cornell Seminar
NW  00
s = 3.0 MeV
39
Search for N5+ L K+
We have
B(Lc+  L K+) = 6.7 10-4
B(Lc+  L p+p0) = 3.6%
B(Lc+  L K+K0) = 0.6%
LK
123 fb-1
So modes with particles
missing/mis-ID’d can have
large contributions.
NLc  00
s = 5.3 MeV
Lc+ feed-down
L c+
L c
123 fb-1
Nicolas Berger, Cornell Seminar
40
Searches in S0K Modes
no W, below
threshold
SK+
SKSK0S
SK0S
SK-
SK+
Bottom line: Less clean than LK, same features, no Pentaquarks
Nicolas Berger, Cornell Seminar
41
Results in Perspective
•Assume
–B(Q+  pK0S) = 25%
–B(X5--  X-p-) = 50%
•Assume pentaquarks
from udsc, not bb
•No model-independent
results for LK, since BFs
not known
•Limits can be placed
with respect to other
baryons.
•Limits stand below
expectations for:
– Q5+ by a factor of 8-15
– X5-- by a factor of 4-6
Nicolas Berger, Cornell Seminar
42
Conclusions
• Promising prospects for ISR at BaBar
– Coverage of wide energy ranges
– Advantageous kinematics, radiative corrections situation.
• Many Exclusive ISR channels already measured; more in
progress (pp, h, h’, pp, KK…).
• Inclusive ISR analysis can provide a precise measurement of
DaHad.
• Several analyses of inclusive hadronic spectra are in
progress.
• Pentaquark searches have yielded negative results so far.
However, they have highlighted potential for study of
charmed and non-charmed Baryons.
Nicolas Berger, Cornell Seminar
43
Backup Slides
e+e-  p+p-p+p-g
Nicolas Berger, Cornell Seminar
45
e+e-  p+p-p+p-g
Nicolas Berger, Cornell Seminar
46
2K 2p Structures
Nicolas Berger, Cornell Seminar
47
More 2K 2p Structures
All Events
Nicolas Berger, Cornell Seminar
Events with the other
Kp combination in the
K* band.
48