HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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B0(s) h+h’- decays at CDF
HEP2005 International Europhysics Conference on High Energy Physics
July 21st – 27th, 2005 – Lisboa, Portugal
Diego Tonelli
Istituto Nazionale di Fisica Nucleare, Pisa
for the CDF Collaboration
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Motivation
Joint study of B0 and B0
s 2-body decays into charged kaons and pions (KK, and K): a privileged insight into flavor physics and a useful tool in searching for New Physics.
CDF has simultaneous access to both B0 /B0
s h+h'- decays: flavor physics program complementary to Y(4S).
R. Fleischer PLB459:306-320, 1999 - constrain hadronic unknowns with SU(3) symmetry. Use approximated s d quark symmetry (i.e. measure jointly B0
and B0s) to extract phase .
WEAK
amplitude theoretically
clean
HADRONIC/ EW
theoretically uncertain
TREE PENGUIN
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Motivation (cont’d)
Fleischer’s method needs: time-dependent asymmetries in b-flavor tagged samples, size of SU(3) breaking, sin(2) and ms CDF ultimate long term goal.
Currently accessible BR can constrain theory too: compare CDF measurements with allowed regions in spaces of B0 +- and B0
s K+K- observables (Y(4S) and theory): a probe for both and NP
Fleischer and Matias PRD66: 054009,2002 - London and Matias PRD70:031502, 2004.
…many other interesting measurement, e.g. s/s in B0
s K+K- see talk by M.
Donega’ - Friday 17.08 Room 5.
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
4/16Experimental challenge #1: write signal events to tape
S/N at production ~10-9;
high track multiplicity per event;
generic final states (2 tracks, K and/or ) in huge QCD BCKG.
Crucial role of trigger:
Reconstruct silicon tracks online. Trigger on displaced secondary vertices with ~30 m impact parameter (IP) resolution.
B
Primary vertex
Secondary vertex
PLANE TO THE BEAM
IP(B)
IP(h1)
pT(h1)
pT(h2) pT(B)
large (B) large B decay length and IP of tracks;
pp bb + X B from primary vertex, small IP of B.
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Analysis overview
SIGNAL RECONSTRUCTION unbiased optimization of the selection
requirements (use MC and data)
FIT OF COMPOSITION Unbinned ML fit: kinematics
and dE/dx to distinguish each B0
(s) h+h'- mode
BR RATIOS and ASYMMETRIES Correct raw fit results for
trigger / selection efficiencies (use MC and data)
dE/dx CALIBRATIONS
Accurate calibrations of dE/dx with D*+
decays
CONTROL SAMPLES B0
s and B0 exclusive decays in J/X and D
SIGNAL SIMULATIONRealistic MC
sample
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
6/16Experimental challenge #2: signal extraction
Unbiased optimization of selection cuts: maximize S/(S + B) with signal from MC and background from data sidebands.
isolation: fraction of pT carried by the B candidate after fragmentation. Rejects 15% of signal and 400% of background.
B - space
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
7/16Experimental challenge #3: peak composition
Excellent CDF mass resolution:
5 silicon layers + drift chamber measure pT in 1.4 T solenoidal field with 132 cm lever arm
resolution ~ (0.7 0.1 pT)%
Still, the four (expected) major modes overlap into an unresolved mass peak.
Extract composition statistically with an unbinned 5-dimensional ML fit. Combine information from:
kinematics (mass and p);
particle ID (dE/dx).
B0s modes
B0 modes
simulated signals
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Peak composition handle 1: kinematics
-mass vs signed momentum imbalance: (1- pmin/pmax)qmin discriminates among modes (and flavors in K modes).
B0 +- + c.c.
B0s K+K- + c.c.
B0 K-+ B0 K+-
B0s K+- B0
s K-+
MC MC MC
MCMCMC
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Peak composition handle 2: specific ionization in the drift chamber
Tracks have hits in drift chamber:
96 layers, |η| ≤ 1.0; 44 cm < r < 132 cm, 30k channels; σ(hit) ~ 180 μm; dE/dx encoded in hit pulse-width.
TIME OF FLIGHT
Accurate, time dependent dE/dx calibration using ~95% pure K / samples from ~70k decays:
D*+ D0 + [K-+] + + c.c.
Strong D*+ decay tags the D0 flavor.
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Peak composition handle 2: dE/dx (cont’d)
Angle, gas pressure, time and hit-multiplicity dependences corrected.
1.4 K/ separation at p > 2 GeV/c
( 60% of “perfect” separation)
Residual gain fluctuations cause correlated dE/dx shifts: measured and included in the fit of composition.
corrected
raw
corrected
raw
dE/dx vs dE/dx vs hits
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Raw fit results
~900 evts/180 pb-1 in initial CDF data, taken with still non optimized detector/trigger. Now much better: ~2700 / 360 pb-1
What we measure:
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Efficiency/acceptance corrections
Correct for relative acceptance, trigger and selection effic.: 5 -10%
Kinematics and nuclear interaction efficiencies (Monte Carlo)
Trigger-bias: correct for dE/dx-dependent trigger efficiency (D+ data)
Isolation efficiency, measured from exclusive decays (B0 and B0s data)
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Dominant systematic uncertainties
dE/dx track-to-track correlations (partially reduces with statistics);
B-meson masses input to the fit (reduces with statistics);
Relative isolation efficiency between B0s and B0
(reduces with statistics);
Effect of final state radiation;
Trigger bias on efficiency;
Charge-dependence of dE/dx;
Background shape;
Charge asymmetries in background;
Others.
(stat. ~ 7.8%) syst. ~ 1.2%
(stat. ~ 17%) syst. ~ 15%
(stat. ~ 24%) syst. ~ 14%
(stat. ~ 29%) syst. ~ 13%
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Final results: B0s sector
B0s K
+K- decay established. BR ratio may favor large SU(3) breaking as predicted from sum rules (Khodjamirian et al. PRD68:114007, 2003).
Allows first comparisons with Y(4S) and theory expectations, test of NP.
No evidence for B0s K
-+, set a limit a factor ~40 better than PDG04.
Great improvement on annihilation mode B0s -+. A factor >100 below
PDG04 (time-evolutions of B0s -+ and B0
s K-K+ assumed the same).
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Final results: B0 sector
ACP compatible with B-factories, systematic uncertainty comparable as well, Babar statistic uncertainty just ~30% better with same sample size. With currently available data (3x statistics), we expect < 4.5% statistical uncertainty to be compared with current world best: 2.2% (Belle).
Limit on pure annihilation/exchange mode B0 K
+K-. A factor ~2 above B-factories, expect much better performance on current sample.
Consistent with B-factories. Valuable cross-check for other measurements.
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Concluding remarks
CDF has unique joint access to B0 / B0
s h+h'- modes: rich physics program complementary to B-factories. Results shown ready for PRL submission in first B0
(s) h+h'- paper from an hadronic collider:
B0s K
+K- decay established and BR measured (first B0s PP observed);
x100 improvement with respect to PDG04 on the upper limit on BR(B0
s +-) and x40 improvement on the limit on BR(B0s K
-+);
measurement of ACP (B0 K
+-) with small systematics.
Just the beginning: now 900 pb-1 on tape, of which 360 ready for analysis with ~2x increase in yield/pb-1 (optimized efficiencies), improved mass resolution (better tracking alignment and reconstruction). By end of 2005 we expect:
Observe B0s K
-+ and reduce to ~10% statistical error on BR(B0s K
+K- );
ACP (B0 K
+-) much closer to Y(4S) with ~4% statistical uncertainty;
World best limits on BR(B0s +-) and on BR(B0
K+K-).
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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ADDITIONAL MATERIAL
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The Tevatron pp colliderSuperconducting proton-synchrotron: 36 p 36 p bunches
collision every 396 ns at √s = 1.96 TeV
Luminosity…………………………….: record peak is 1.3 1032 cm-2 s-1
~ 10 pb-1 / week recorded on tape
# interactions / bunch-crossing……..: < N >poisson = 6 (at 2 1032 cm-2s-1)
Luminous region size………………..: 30 cm (beam axis) 30 m (transverse) need long Si-vertex small wrt c(B) ~ 450 m
2005, regularly exceeds 1032 cm-2s-1
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Delivered Luminosity
Stable data taking efficiency: ~85%
The results shown here from an analysis that uses ~180 pb-1
Ap
ril
2001
Feb
2002
first data for
analyses
data for physics
detector commiss.
Jul
2002
~ 900 pb-1 on tape
1 fb-1 milestone!
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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The Good
bb production x-section O(105) larger than e+e- at (4S) /Z0. Incoherent strong production of all b-hadrons: B, B0, Bs, Bc, b, b .
The Bad
Total inelastic x-section ~ 103 (bb). BRs’ for interesting processes O(10-6).
…and The Ugly
Messy environments with large combinatorics.
Heavy Flavor physics at the Tevatron
CDF
Need highly selective trigger
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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7-8 silicon layers1.6< r <28 cm |z|<45 cm |η| ≤ 2.0, cosθ = 0.964σ(hit) ~ 14 μm
Time-of-flight100 ps @150cmp, K, π id
96 layer drift chamber |η| ≤ 1.044 < r < 132 cm, 30k channelsσ(hit) ~ 170 μm dE/dx for p, K, π id
Tile / fiber endcapcalorimeter 1.1 < |η| <3.5
coverage to||≤1.580% in
132 ns front endCOT tracks @L1SVX tracks @L230000 /300 / 70 Hz~no dead time
Some resolutions:pT ~ (0.7 0.1 pT)%J/Ψ mass ~15 MeVEM E ~ 16%/√EHad E ~ 100%/√Ed0 ~ 6+22/pT μmPrimary vtx ~10 μmSecondary vtx r-Φ ~ 14 μmr-z ~ 50 μm
1.4 T magnetic fieldLever arm 132 cm
CDF Detector Upgrades
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Triggering bs’ (and cs’)
Di-lepton
B charmonium Rare B
Two muons with:
pT> 1.5 GeV ||< 1
pT> 2.5-4.5 GeV ||<2
electron or and displaced track
Semileptonic decays
Electron () with:
pT> 4 (1.5) GeV ||< 1
and one track with:
pT > 2.0 GeV IP > 120 m
Two displaced tracks
n-body hadronic B
Two tracks with:
pT > 2.0 GeV
pT > 5.5 GeV
IP > 120 (100) m
Displaced track trigger at Level 2: a revolution in hadronic environment ! Makes it accessible rare hadronic decays with high S/B.
conventional new approach
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Systematics - detailed
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Raw physics results
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Raw physics results
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Corrected results
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Correlation matrix
Legenda
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p.d.f. projection: momentum imbalance
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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p.d.f. projection: |p(1)| + |p(2)|
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p.d.f. projection: dE/dx
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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p.d.f. projection: dE/dx
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Momentum p.d.f.
p p
Monte Carlo Binned ML fit
signal
background
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dE/dx model
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Silicon Vertex Trigger
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Silicon Vertex Trigger (cont’d)
(35 33) m SVT beam
= 48m
SVT
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B0s K+K- lifetime
B0 lifetime from PDG04. B0s K+K- lifetime depends on:
- s/s : width difference between “long” and “short”
eigenstates-the relative composition in short and long-lived components
Assume Standard Model s = d and s / s = -0.12 0.06 B0
sK+K- is expected almost 100% “short-eigenstate” Fleischer and Matias:PRD66-054009,2002)
Therefore the lifetime of B0s K+K- is determined as:
HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa
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Physics Motivations (backup)
The combination of Bd and Bs decays provides a promising way to extract CP-related physical parameters avoiding the “penguin pollution”. (R. Fleischer PLB459 (1999) 306)
Assume U-spin symmetry (d s), the ACP are function of the CKM angles and and of the amplitude ratio P/T (~ dei) 4 equation with 4 unknowns (, , d, ). A combined fit of the 4 CP asymmetries measures , and P/T ratio.
Above strategy need time-dependent analysis with tagged samples: long term goal
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