Status of B hcK

1
Status of B? hcK

• Stefania Ricciardi (Royal Holloway)
• for the hc group
• BABAR-UK Meeting, Bristol, November 13th 2002

2
The hc group (since 2000 A.D.)
BRISTOL Nick Barlow Phil Clark Marc Kelly
SACLAY G. Hamel de Monchenault Witold
Kozanecki Melanie Langer Georges London
MANCHESTER Frank Jackson
IRVINE Dieter Best MIT Gabriella Sciolla
ROYAL HOLLOWAY Chris Marker S.R.
Joined group in spring/summer 2002
3
Outline

• Recent achievements
• Sin2b
• Branching Fractions
• Current Studies
• More decay modes
• Improved selection
• Efficiency variation across D.P.
• Background studies
• Future Plans
• hc width
• Publication(s)

4
Sin2b with B0 ? hc K0s
Theoretically clean golden CP 1 mode
Experimentally more challenging only hadronic
decay modes with low individual branching
fractions Backgrounds relative high compared to
other CP-1 modes with leptonic decay of ccbar
system
Summer 2002 Measurement based on 132 events
selected out of full sample (run1run2)
88million BBbar events Including J/y region B0 ?
KsKp K0s B0 ? KKp0 K0s Purity
63 (accounting for 13.1 peaking bkg)
hc
J/y
5
Sin2b PRL Vol 89, n. 20 just
published (11 November 2002)
Supporting internal Etac-CP documentation
BAD381,BAD442
B0 ? hc K0s
6
Branching Fractions hep-ex/0203040 (Moriond
QCD,2002)
Supporting Etac-BF docs BAD222,BAD336

• Analysis based on Run1 data only ( 22.7 million
  U(4S)?BB)
• Searching for
• 
  BF (PDG 2002)
• 1. hc ? KsKp- c.c. (1.8 ? 0.6)
• 2. hc ? KK-p0 (0.9 ? 0.3)
• 3. hc? 2(KK-) (2.1 ? 1.2)

Combining 1 and 2 we obtained BF( B ? hc K)
( 1.50 ? 0.19 ? 0.15 ? 0.46) x 10-3 BF( B0 ? hc
K0) ( 1.06 ? 0.28 ? 0.11 ? 0.33) x 10-3
Decay 3 was Not included in final result because
of poor-known BF(hc? 4K)
7
Other experiments

• BF(B?hCK) measured by CLEO
• On 10 fb-1 and hC?KSKp
• BF(B?hCK) (0.69 0.23 0.08 0.20) 10-3
• BF(B0?hCKS) (1.09 0.48 0.12 0.31) 10-3
• Recent Belle results hep-ex/0208047
• On 29.1 fb-1, Modes hC?KSKp, hC?KKp0, hC?pp
• BF(B?hCK) (1.25 0.14 0.11 0.38) 10-3
• BF(B0?hCKS) (1.23 0.23 0.14 0.33) 10-3
• GhCBelle2002 (29 8 6) MeV/c2
• Evidence for signal also in hC?KKp (charged B)

8
New decay modes hc ? pp (Dieter Best )
BF (0.12 0.04)
On 82 fb-1 (Preliminary Selection under study)
Blind signal region
B0
B
Present efficiency (26.9? 0.3) Expected Signal
39.5 ? 0.4 Expected Background 5.7 ? 0.4
Present efficiency (18.1? 0.2) Expected
Signal 26.6 ? 0.2 Expected Background
4.9 ? 0.4
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New decay modes hc ?hpp (Phil Clark)
BF (4.9 1.8)
Cut optimization close to completion Reconstruct
ed h? gg On data a clear peak shows up after
having applied all studied cuts h
Mass,helicity g (energy,LAT) p0 veto
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hc ? ff (Chris Marker)
BF (0.71 0.28)
DE
Another 4 charged-K final state Cut on KK-
invariant mass ? 14 MeV/c2 from
Mf effective for background rejection Loose PID
requirements (4 NN-NotAPi)
Charged mode Just un-blinded
MES
B Estimated efficiency 17.8 Expected signal
19 Expected background 0.14
After unblinding Signal
16.6 Background 0.40
B0 Estimated
efficiency 18.6 Expected signal
7 Expected background 0.05
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Improved Selection New skim

• Main changes
• Same PID selector at skim and analysis level
• Better understanding of efficiency
• Removed ? cut and replaced with p cut

n ? cosine of helicity angle under B-gthcK
hypothesis
p
Old analysis cuts
Old skim ?lt1.1
Correlation between n (p,MX) Cutting part of
J/y signal
New skim analysis cut
Mx (Gev/c2)
12
Improved selection re-optimization of old
modes (Nick Barlow, Marc Kelly)
Old procedure (Run1)
New procedure

• Un-smeared SP3 MC
• for signalbackground
• low statistics in background
• due to lack of generic MC
• Use PDG BF(hc?X) and
• CLEO BF(B ? hcK) for signal yield
• Fisher only used photons from
• B candidate
• Cutcount analysis
• optimized all cuts including
• m_ES, DE,m_etac

• SP4 fully-corrected MC for signal
• (PID/pi0 killing neutral energy
  shif/smearing)
• DE sidebands of data for background
• Use our Run1 measurement
• BF(B ? hcK) x BF(hc?X)
• Fisher retrained using all photons
• ML fit to m_ES,m_etac,maybe DE
• Optimized all other cuts
• (including n to reduce higher
• combinatorial background of new
  skim)

13
Example Fisher optimization (Nick Barlow, Marc
Kelly)
KsKp K
Signal

• Important to reduce continuum
• Trained independently for each decay
• mode using off-resonance data for bkg
• and MC for signal
• Based on 18 quantities including
• 9 CLEO energy-cones and various
• event-shape variables

Bkg
KKp0
KsKp
4KK
Old gt0.0 New gt -0.08
Old gt -1.4 New gt -0.48
Old gt0.5 New gt 0.16
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New selection summary
(Nick Barlow, Marc Kelly)
Main cuts are relaxed. Will benefit of higher
efficiency smaller systematics
15
Expected Yields
(Nick Barlow, Marc Kelly)
Expected higher significance in all channels
Charged
Neutral
16
Sources of background

• Full MC studies showed
• Pure combinatorial
• typically 20-30 according to mode
• Peaking background
• Mainly due B decays to exact matches (10-20)
• For example for KsKp Ks final state, scaled to
  80.8/fb
• Partial reconstruction negligible
• Inclusive hc
  negligible
• These MC studies suffered from unknown BF, low
  statistics
• ? CANNOT rely on MC for absolute yield estimation
  of background

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Determination of signal and background

• 2D unbinned maximum likelihood fit to mX, mES
  used for sin2b
• B?hCK
• Gaussian in mES
• BW x Gaussian in mX
• B?J/yK
• Gaussian in mES
• Gaussian in mX
• Peaking Bkg
• Gaussian in mES
• flat in mX
• Combinatorial
• Argus in mES
• flat in mX

Old skim/selection Full data sample
MKsKp
Major assumptions to be verified
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PravdaMC studies (SR)
Fast MC interfaced to TrackErr for track
smearing High efficiency wrt SP4 kaons and pions
do no decay Additional killing per track required
set at 5 in these studies Good agreement for
most important distributions in this analysis
we can use it to check background shapes
KsKp K
DE
Blue Signal SP4 Red Signal Pravda
mES
mKsKp
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PravdaMC Generic B production (SR)
We interfaced Pravda to our reconstruction
code and we could generate 500 /fb of generic B0
and B in about 1 month CPU time 50 h/fb
(mainly due to reconstruction) on Linux public
queues _at_ SLAC Total 50K hours
PravdaMC B Generic (500/fb)

• We can then
• Verify assumptions
• on background estimation
• Isolate individual contributions
• of different background
• components
• Study fit systematics due
• to different bkg composition

20
Pravda MCstudy of bkg shape
2.75 lt MX lt 2.85 GeV/c2
2.85 lt MX lt 2.95 GeV/c2
MES plots in MX slices KsKp K reconstructed
from B generic J/y and hc signal removed at
generator level
2.95 lt MX lt 3.05 GeV/c2
3.05 lt MX lt 3.15 GeV/c2
Peaking bkg
Preliminary flat combinatorial Positive
slope found for peaking
events (from fit in MX slices)
3.15 lt MX lt 3.25 GeV/c2
Combinatorial bkg
MX
MES
21
Dalitz Plot studies (Gautier Hamel de
Monchenault)
Dalitz plot from ?? ? ?c ?Ks0K?
M(Kp-)
Large resonant component hc ? K(1430)K ? KsKp
See K(1430) bands hc ? K K- ? Ksp K hc ?
K0 Ks ? Kp Ks
M(Ksp?)
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Dalitz Plot transformation(Frank Jackson)
MC generates non-res. 3-body decays ? Efficiency
variation across phase-space to be corrected
MC
Phase space boundary shape in m2(Kp) vs m2(Ksp)
is not convenient

• 2D efficiency corrections in
• Rectangular phase-space
• CosqH(p) vs m(Kp)
• No boundary problems
• (method by W. Dunwoodie)

CosqH(p)
Efficiency variation After cuts must be
parameterized
m(Kp)
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Dalitz Efficiency Correction/1(Frank Jackson)
10 M(Kp) slices
Combined B0 and B to increase stat. - all
analysis cuts - Legendre polynomials parameteriza
tion Pi(cosq), i1,L
Coefficients determined using a
summation/integration technique based on the
orthogonality of the polynomials
Efficiency
dN d(cosq)
NToT ?? aiPi(cosq)
1 NToT
dN d(cosq)
ai ? Pi(cosq) d(cosq)
1 NToT
? ?j Pi(cosqj), j1,NToT
Cos qH (p)
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Dalitz Efficiency corrections/2 (Frank
Jackson)
Efficiency
Efficiency Parameterization in place In each
M(Kp) slice e(cos q) 2e0 1/2 ? ai Pi(cos
q) Found Legendre moments up to P2 Next
step evaluate errors on ai and corrected
efficiencies
a1
a2
m(Kp)
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A To-Do list to BF publication

• Complete background studies
• extend Pravda MC studies to all channels,
  verification of
• identified background contributions with
  Full MC where possible
• Complete efficiency corrections study over
  Dalitz Plot
• New modes
• finalize cut optimization and unblind (ff done)
• ML extraction of yields on new skim,new cuts
• (RooFit)tools already in place
• All modes study systematic errors
• done for old modes on Run1 Data/SP3 MC
• Main contributions PID efficiency, tracking
  efficiency, background model
• To be repeated for all modes on Run1Run2/SP4

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Measurement of hc width
Important cross-check comes from B??cK (?c
?Ks0K?)
?? ? ?c ?Ks0K? (B.Meyer,GHM)
The width is a parameter of 2D MaxL fit On old
skim G(hc) 32.9 ? 5.0 (stat) MeV In good
agreement with BaBar gg measurement and
significantly higher than PDG (16.0 /- 3.4
MeV)! Next update result study systematic
error
G(hc) 31.9 ? 2.5 (stat) ? 1.3(syst) MeV
(BAD 261)
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Conclusions
Group effort to include hcK0s in Sin2b had a
successful end Moving ahead for BF refereed
publication including 3 additional hc decay
modes and refined analysis Aiming to
end-of-winter (early 2003) Very much wanted
include into publication width measurement with
exclusive decays Nice short-term project
awaiting for a volunteer 3 PHD thesis close to
the End (almost DR Chris, Frank, Nick) And1
New Mum (Melanie) Other channels and analysis
available to smart students Willing to join this
group (hc ? KKp, rr, baryons)