HEP2005 Lisboa - July 21 st, 2005Diego Tonelli, CDF - Pisa 1/16 B 0 (s) h + h’ - decays at CDF HEP2005 International Europhysics Conference on High Energy

HEP2005 Lisboa - July 21st, 2005 Diego Tonelli, CDF - Pisa

1/16

B0(s) h+h’- decays at CDF

HEP2005 International Europhysics Conference on High Energy Physics

July 21st – 27th, 2005 – Lisboa, Portugal

Diego Tonelli

[email protected]

Istituto Nazionale di Fisica Nucleare, Pisa

for the CDF Collaboration


2/16

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


3/16

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.


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.


5/16

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


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


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


8/16

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


9/16

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.


10/16

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


11/16

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:


12/16

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)


13/16

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%


14/16

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).


15/16

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.


16/16

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-).


17/16

ADDITIONAL MATERIAL


18/16

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


19/16

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!


20/16

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


21/16

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


22/16

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


23/16

Systematics - detailed


24/16

Raw physics results


25/16

Raw physics results


26/16

Corrected results


27/16

Correlation matrix

Legenda


28/16

p.d.f. projection: momentum imbalance


29/16

p.d.f. projection: |p(1)| + |p(2)|


30/16

p.d.f. projection: dE/dx


31/16

p.d.f. projection: dE/dx


32/16

Momentum p.d.f.

p p

Monte Carlo Binned ML fit

signal

background


33/16

dE/dx model


34/16

Silicon Vertex Trigger


35/16

Silicon Vertex Trigger (cont’d)

(35 33) m SVT beam

= 48m

SVT


36/16

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:


37/16

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

Documents

HEP2005 Lisboa - July 21 st, 2005Diego Tonelli, CDF - Pisa 1/16 B 0 (s) h + h’ - decays at CDF HEP2005 International Europhysics Conference on High Energy