heavy b hadrons at tevatron

FPCP2004, Daegu Andrei Nomerotski (Fermilab) 1

Heavy B Hadrons at Tevatron

Andrei Nomerotski (Fermilab)

Main Injectorand Recycler

DD

Tevatron


Introduction

Tevatron produces B hadrons inaccessible at B-factories Previous results mostly from LEP and Run I Tevatron

Cross sections are large but so are the backgrounds (bb) 100b at 2 TeV ((bb) 1nb at B factories) Mostly soft Pt processes : Triggers are very important

In Run II, Tevatron has two experiments doing B-physics : CDF and DZero Take data the third year Both had major upgrades for Run II

With magnetic field and Tracker DZero is much better suited for B-physics than before

With 0.5 fb-1 per experiment on tape Tevatron has world largest samples of heavy B hadrons


DZero Detector Excellent coverage of Tracking and Muon Systems 2 T Solenoid, polarity inversed weekly Quiet Muon Trigger with muon Pt measurement at Level1

by toroids Fine segmentation Calorimeter and Preshower

SMT H-disks SMT F-disks SMT barrels


CDF Detector Large Tracking

volume in magnetic field – excellent mass resolution

Particle ID capabilities : TOF, dE/dx in drift chamber

Large bandwidth (50 kHz) Level1 Trigger and Displaced Track Silicon Trigger at Level2

Access to purely hadronic B samples


Datasets Tevatron performance progressed very well in 2004 0.5 fb-1 per experiment by September 2004 Typical analyses use ½ of total luminosity


Will talk about Bs and b Mass Measurements at CDF

Observation of narrow B** mesons at DZero Observation of Bc at DZero

Branching Fractions of hadronic modes Bs and b (CDF)

Semileptonic samples of Bs and b (DZero)

Bs oscillations (DZero)

Bs and b lifetimes (DZero/CDF)

Summary


Bs and b Masses (1)

Taking advantage of good mass resolution CDF greatly improved mass accuracy for Bs and b

Possible after careful calibration of the mass scale of the tracker Material Field Track errors


Bs and b Masses (2)

World’s best single measurements In agreement with previous results


B** Spectroscopy : Theory

B** are orbitally (L=1) exited states of B meson

In general there are two wide states and two narrow states Narrow states decay through D-wave Wide states decay through S-wave

Properties of B** are very similar to D** mesons For charm mesons, M(D*)-M(D) ~ 140-145 MeV For bottom, M(B*)-M(B) ~ 46 MeVTheory: Splitting within a doublet has 1/m_Q

corrections For non-strange charm, M(D**)-M(D) ~550-600 MeVExpect similar behavior for B mesons M( D*2)-M(D1) ~ 32-37 MeV

Expect this to be ~ 10-15 MeV for M(B*2)-M(B1)


DZero : D** in Semileptonic B Decays

Observed merged D10(2420) and D2*0(2460)

wrong-sign combinations

Preliminary result on product branching ratio

Br(B {D10,D2*0} X) Br({D1

0,D2*0} D*+ -) = 0.280 0.021 (stat) 0.088 (syst) %

D*- + mass


B** Spectroscopy : Experiment

B** have been observed before at LEP and CDF in Run I but the narrow states haven’t been resolved

DZero observed B** in B modes using exclusive B decay channels

Experiment B reconstruction

BJ mass (MeV) BJ width

ALEPH exclusive 5695±18 53±16

CDF (μD)+π 5710±20 -----

DELPHI inclusive B + π 5732±21 145±28

OPAL inclusive B + π 5681±11 116±24


Used exclusive B meson samples with J/psi in final state

L = 350 pb-1

7217±127

2826±93

624±41

DZero : B** analysis (1)


DZero : B** analysis (2) Add charged pion coming from the Primary

Vertex to exclusively reconstructed B Since ΔM between B**+ and B**0 is expected to

be small compared to resolution all channels are combined

Dominant decay modes B*

2 B or B* B1 B* B* B

Since photon is not reconstructed two narrow B** states produce three peaks in ΔM

In addition there are wide states which cannot be distinguished from non-resonant background


BB *2

From fit:

N = All B**

536±114events

First Observation of Separated States

~7σ signif.

Interpreting the peaks as

273±59 events

131±30 events BBBB ***

2 ;

BBBB **1 ;


DZero : B** analysis (4) Fitting M distribution

Three relativistic Breit-Wigner functions convoluted with Gaussian resolution

Theory motivated assumptions : and equal Br for two B*2 decay

modes

Results M(B1) = 5724 ± 4(stat) ± 7(syst) MeV

M(B*2-B1) = 23.6 ± 7.7(stat) ± 3.9(syst) MeV

= 23 ± 12(stat) ± 9(syst) MeV

f1 = 0.51 ± 0.11(stat) ± 0.21(syst)

f1 is relative yield of B1 meson

Systematic errors are dominated by fit assumptions and for by uncertainty of

mass resolution


Neutral B**

Charged B**

DZero : B** analysis (5)

Consistency checks: Separate fits for

neutral and charged B

No signal if charged pion is not coming from Primary Vertex


DZero: Bc Meson (1)

Last of ground state mesons to be definitively observed

Theory Lifetime 0.3 - 0.5 ps Mass 6.4 ± 0.3 GeV

Only previous evidence : CDF Run I result

20.4 signal+6.2- 5.5

mass 6.4 ± 0.39 ± 0.13 GeV

= 0.46 0.03 ps+0.18

- 0.16


DZero: Bc Meson (2)

Bc+

+

+-

PV

Use tri-muon final state J/and tight third form a

good vertex Select 231 J/ X candidates Bc is not fully reconstructed

backgrounds are very important Bkg with fake muon estimated

with J/+track data control sample separated into prompt and non-prompt components

bb/cc backgrounds are small due to vertex requirement

Include contributions to signal from Feed-down from Bc (2S) X Bc J/ X


Dzero : Bc Meson (3) Plot invariant mass of

three muons Not exclusive

reconstruction Use MC to get mass

template shapes

Do combined likelihood fit to invariant mass and pseudo-proper time distribution

Number of Bc candidates: 95±12±11


Mass log likelihood

Mass :

5.95 ± 0.34 GeV +0.14

- 0.13

DZero: Bc Meson (4)

Mass, GeV

Results of the fit :

Lifetime :

0.45 ± 0.12 ps +0.12

- 0.10

Main systematics Mass : signal sample composition, MC signal modeling, fraction of prompt bkg Lifetime : Bias from vertexing algorithm, fraction of prompt bkg Both could be improved


Bc : Other Properties

b

b

c

c

Bc

Fragmentation process b Bc + c dominated production Charm quark should form weakly

decaying charmed hadron in vicinity of Bc

Measured probability to have muon within ± 90o of Bc candidate 5 ± 2 % for signal sample 1% for background sample


Branching Rates for Bs and b

Poorly known – see PDG summary below


CDF : Br for hadronic modes

CDF collected excellent hadronic samples of Bs and b decays using Track Trigger

Measured Br of several decay modes Earlier results

Br(BsDs)/Br(B0D)=1.4±0.2(stat)±0.5(syst) Br(bc) = 6.0±1.0(stat)±0.8(syst)±2.1(Br) x10-3


CDF : Br (Bs Charmless BVV decay Track Trigger :

Two oppositely charged tracks with Pt > 2 GeV at Level 1 Impact Parameter > 0.12 mm at Level 2

Normalized to Bs J/ decay Br(Bs = (1.4+-0.6(stat)+-0.2(syst)+-0.5(Br)) 10-5


CDF : Charmless bp and bpK decays

M()

Charmless b decays may have large direct CPV Proceeds via CKM suppressed and/or penguin

(QCD,EW) Expected Br ~ (1-2) 10-6

Normalized to B hh process

Search window in M() optimizes separation from B hh

772 ±13 events expected 767 observed

Br(b hh < 22 x 10-6


DZero : Bs semileptonic modes

Excellent yield for all semileptonic modes Collected by Single Muon Triggers without online lifetime

cuts

Used for Bs oscillations and lifetime measurements


μ+

π -

K+K-

φ

D-S

BS

μ+

Tagging muonY, cm

X, cm

Oscillated BS candidate

Opposite Side Muon tagging applied to semileptonic BS

sample Re performance of taggers see G.Borissov’s talk

Example of tagged BS candidate Two same sign muons are detected MKK=1.019 GeV, MKKπ=1.94 GeV PT(μBs)=3.4 GeV; PT(μtag)=3.5 GeV


DZero : Bs Mixing Projections Plan to use both semileptonic and

hadronic Bs samples More statistics in semileptonics Better proper decay time resolution

in hadronics (no ) Have access to hadronic Bs sampe

triggering on opposite side muon Muon is used as high purity tag Work in progress - see signals

Also hardware upgrades in 2005 L3 bandwidth will be increased from

50 to 100 Hz in 2005 Semileptonic sample limited by L3

and offline CPU – expect large gain in yield

Upgrade to 250 Hz under review Partial silicon upgrade

New beampipe with smaller diameter Add another innermost layer of

silicon (Layer0) with analog cable readout

Layer0 + L3 BW upgrades

No upgrades


DZero: b c

sample Reconstructs b c in two c decay modes

c Ks p c

Samples will be used for lifetime ratio measurements

350 pb-1

Second peak interpreted

as c

c mass agrees with PDG

350 pb-1


Naive quark spectator model predicts equal lifetimes for all B hadrons (but Bc)

(NLO) QCD Heavy Quark Expansion predicts deviations in rough agreement with data

Experimental and theoretical uncertainties are comparable

Lifetime differences probe the HQE to 3rd order in QCD / mb

Goal: measure the ratios accurately

B Hadron Lifetimes

Dzero: Recent result from semileptonic modes(B+)/(B0) = 1.093 0.021 (stat) 0.022 (syst)


Exclusive modes : Bs Lifetime J/ modes are golden at the Tevatron since they

allow for simple di-lepton trigger with low Pt threshold

CDF : BsJ/ ( KK) based on 240 pb-1

12 parameter maximum likelihood fit

(Bs) = 1.369 ± 0.100 ps-0.010+0.008


250 pb-1

DZero : Exclusive Bs Sample

DZero accumulated the largest sample of

exclusive Bs J/decays J/


DZero : Bs Lifetime

BsJ/ BdJ/ Ks*0

250 pb-1 250 pb-1

Bd0) = 1.473 ±0.023 ps-0.050

+0.052Bs) = 1.444 ±0.020 ps-0.090+0.098

Bs)/B0) = 0.980 ±0.003-0.070+0.075

Use two similar topologies BsJ/ and BdJ/ Ks*0 to measure lifetime ratio

Simultaneous Likelihood fit to mass and lifetime distribution


DZero : b Lifetime Reconstruct b J/ Use process with similar

topology Bd0 J/ Ks to

measure the ratio

Result is statistically limited

Bd0) = 1.397 ±0.031 ps-0.098

+0.107

b) = 1.221 ±0.043 ps-0.179+0.217

b)/B0) = 0.874 ±0.028-0.142+0.169


Summary So far Tevatron experiments were doubling samples

every year – that may continue

Exciting prospects for heavy B hadrons Expect great improvement in accuracy of lifetime and

Br measurements Measurement of sms within reach

There are still particles to discover in this sector: bbb , doubly heavy baryons

Be ready for new results

heavy b hadrons at tevatron

Documents

b mesons

experiment b

opalinclusive b

delphiinclusive b

b hadrons inaccessible

cdfobservation of narrow

p b1 b

semileptonic b decays