Beauty Baryon Decays @ LHCb

Beauty Baryon Decays @ LHCb

Steven Blusk

Beauty 2014, Edinburgh, Scotland, July 14-18, 2014

On behalf of the LHCb collaboration

Syracuse University

2

Beauty baryons @ LHCbBeauty baryons are produced copiously in LHCb,opening up new avenues for study and improved precision of their properties and decays.

Production MassLifetimeNew decay modesCP asymmetries

Other studies, for a future BEAUTY meeting…Rare decays, e.g. LbLm+m-.

1 fb-1 result (PLB 725, 2013) being updated to 3 fb-1.

Probe CKM elements Vcb, Vub in LbLcln and Lbpln decaysExcited b-baryon statesbc-baryons

3

Detector & data sets

Precision vertex detector (sip~ 20 um), tracking sp/p ≈ 0.5% Excellent particle identification, including hadron separation to ~100 GeV High bandwidth trigger, ~2-5 kHz to tape, hadronic, EM and muonic final states.

Wide & flexible physics scope: b, c, quarkonia, W, Z’s, exotics, jets, etc. Analyses based on:

2011, 1 fb-1 @ 7 TeV 2012, 2 fb-1 @ 8 TeV

4

Menu for this talk

B(LbLcp) arXiv:1405.6842

Xb- and Wb

- lifetimes arXiv:1405.1543

Xb0 mass, lifetime & production properties arXiv:1405.7223

Lb/Xb

0 D0ph± decays arXiv:1311.4823

LbJ/ypK- and LbJ/ypp- arXiv:1406.0755

Search for Lb/Xb0 KSph± arXiv:1402.0770

First observation of LbLc+ D(s)

- arXiv:1403.3606

arxiv:1405.6842

arxiv:1405.1543

arxiv:1405.7223

arxiv:1311.4823

arxiv:1406.0755

arxiv:1402.0770

arxiv:1403.3606

5

Reconstructing hyperons from b decay

Average b-momentum in LHCb ~ 100 GeVE.g. LbJ/yL, 30 GeV L g≈30 <d> ≈ 2.5 m

2.3

m

“Long”

6


Average b-momentum in LHCb ~ 100 GeVE.g. LbJ/yL, 30 GeV L g≈30 <d> ≈ 2.5 m

Hyperons reconstructed if they decay upstream of TT.

2.3

m“Downstream”

7


Going beyond Lb .. Example: Xb

-J/yX-, X- Lp- Get hit 2X …. t(X-)~164 ps, t(L)~260 ps

2.3

m“Downstream”

8

Production, BFs Mass and Lifetimes

9

Lb Lcp BF LHCb-PAPER-2014-004arXiv:1405.6842submitted to JHEP1 fb-1• State of affairs, pre-2014:

– “Golden mode” for Lb decays only known to ≈ 70% precision!

• Use 45,000 fully reco’d LbLcp+ and 106,000 B0D-p+ decays.

0 +4.0 -32.6( ) 5.7 10b cB p -

-L L

arxiv:1405.6842

10




• Anatomy:

0

0

0

0

( ) ( ) ( ) ( ) ( ) ( )

b c bT b c c

TT dB D

N p fpK pN p B D D K f

p

p

p pp p p

-

-

- - L L L

- -

L L L

cor

cor

B BB B

Scale factor between thetwo analyses

0 +4.0 -32.6( ) 5.7 10b cB p -

-L L

LHCb, PRD 85, 032008 (2012)

Measured in semileptonic

analysis

Measured here,in LbLcp

decays

arxiv:1405.6842

11




• Anatomy:

0

0

0

0

( ) ( ) ( ) ( ) ( ) ( )

b c bT b c c

TT dB D

N p fpK pN p B D D K f

p

p

p pp p p

-

-

- - L L L

- -

L L L

cor

cor

B BB B

Scale factor between thetwo analyses

BF measured to 8% precision! Huge leap forward in precision!

0 +4.0 -32.6( ) 5.7 10b cB p -

-L L

• B(LcpKp) common to both analyses cancelation of large syst. error

LHCb, PRD 85, 032008 (2012)

Measured in semileptonic

analysis

Measured here,in LbLcp

decays

arxiv:1405.6842

12

Xb- and Wb

- lifetimes• Reconstruct Xb

- J/yX-, X- Lp- and Wb- J/yW-, W- LK-, with Lpp-.

LHCb-PAPER-2014-010arXiv:1405.1543submitted to PLB

3 fb-1

313±20 58±8

arxiv:1405.1543

13

Xb- and Wb

- lifetimes• Reconstruct Xb

- J/yX-, X- Lp- and Wb- J/yW-, W- LK-, with Lpp-.

LHCb-PAPER-2014-010arXiv:1405.1543submitted to PLB

3 fb-1

313±20 58±80.100.09

0.260.21

( ) 1.55 0.03 ps

( ) 1.54 0.05 psb

b

t

t

- -

- -

X

W

Best precision to date. Consistent with the recent CDF results

0.530.40

( ) 1.32 0.14 0.02 ps

( ) 1.66 0.02 psb

b

t

t

-

- -

X

W

CDF, PRD 89, 072014 (2014)

(See talk by J. Rosner)

arxiv:1405.1543

14

Studies of the Xb0 baryon - 1

• Until recently, little known about the Xb0 baryon.

– Lifetime unmeasured– Mass only known to ~2.5 MeV (Lb mass known to ~0.3 MeV)– Relative production rates ? Are prod. properties (pT, h) similar to Lb ?

LHCb-PAPER-2014-021arXiv:1405.7223Accepted in PRL

3 fb-1

arxiv:1405.7223

15




• In Xb, Wb studies, decays with J/y+hyperons have been ‘the work horse’.– Use CF decays, J/y for triggering, well-displaced vertices from hyperons with narrow

widths. Hadron ID helpful, but not crucial.– In LHCb, large boosts, large ct leads to a reduction in total efficiency for hyperon reco.


3 fb-1

arxiv:1405.7223

16






• To play into LHCb’s strengths, use Cabibbo-suppressed decays … no hyperons!

• Despite 3 X lower BF, still win big in total acceptance.


3 fb-1

0 , b c c pKp p - - X X X CF CS ( ) ~ 0.34( ) ( ) ( )

c

c

B pKB B B p

pp p p p

-

- - - -

X X X X L L

arxiv:1405.7223

17






• To play into LHCb’s strengths, use Cabibbo-suppressed decays … no hyperons!

• Despite 3 X lower BF, still win big in total acceptance.

• Excellent normalization mode (identical final state): LbLcp, LcpKp !– Most systematics cancel at 1st order in relative measurements.– Small differences in momentum spectra and lifetime of Xc vs Lc pKp


3 fb-1

0 , b c c pKp p - - X X X CF CS ( ) ~ 0.34( ) ( ) ( )

c

c

B pKB B B p

pp p p p

-

- - - -

X X X X L L

arxiv:1405.7223

18


LbLc+p- Xb

0Xc+p-

~188,000 LbLc+p-

~3,800 Xb0Xc

+p-

0

0

0

0( ) 172.44 0.39 0.17

M( ) 5791.80 0.39 0.17 0.26

M

MeV

eV

b

b b

b

M

LX

X - L

Mass of Xb0 ~5X more precise than prev. best from

LHCb

Precision mass


3 fb-1

arxiv:1405.7223

19


LbLc+p- Xb

0Xc+p-

~188,000 LbLc+p-

~3,800 Xb0Xc

+p-

0

0

0

0( ) 172.44 0.39 0.17

M( ) 5791.80 0.39 0.17 0.26

M

MeV

eV

b

b b

b

M

LX

X - L

Mass of Xb0 ~5X more precise than prev. best from

LHCb

Lifetime of Xb0 baryon measured relative to that of Lb.

L b lifetime now known to high precision (see talk by P. Gandini) Perform sim. fit in bins of decay time, correct by relative efficiency (from simulation)

o ob b

0

0

1 1( ) ( )

= cor b

cor b

tNN

e t tL X

X

L-

0

0 0

0

( ) / ( ) 1.006 0.018 0.01

( ) 1.477 0.026 0.014 0.013

0

psb

b b

b

t t

tL

X

X L

1st measurement of Xb0 lifetime

Lb and Xb0 lifetimes equal to within 2%

Consistent with expectations from HQE

Precision mass


3 fb-1

arxiv:1405.7223

20


Can also study the relative production rate vs (pT, h)

Steep pT dependence of Lb/B0 production

also in Xb0!

(see talk by Maria Zangoli)

Relative production rate, integrated.

0 0Consistent with / 0.2 with above assumptionsb bf fX L

≈1 ≈0.1

Semileptonic

LbLcp+ scaled


3 fb-1

arxiv:1405.7223

21


We also have a VERY CLEAN sample of Xc+ decays

( ) 181.51 0.14 0.10

M( ) 2467.97 0.14 0.10 0.14 MeV

MeV

c

c c

c

M

L

X

X - L

Mass of Xc+ ≈4X more precise than WA

Can also study the relative production rate vs (pT, h)

Steep pT dependence of Lb/B0 production

also in Xb0!

(see talk by Maria Zangoli)

Relative production rate, integrated.

0 0Consistent with / 0.2 with above assumptionsb bf fX L

≈1 ≈0.1

Semileptonic

LbLcp+ scaled


3 fb-1

arxiv:1405.7223

22

New decaymodes & CPV

studies

23

Lb/Xb0 D0ph± LHCb-PAPER-2013-056

arXiv:1311.4823PRD 89, 032001 (2014)

1 fb-1

The LbD0pK decay can be used to measure the weak phase g, ala B0 D0K*0.

Usual trick..• Both diagrams are O(l3)• Exploit interference for final

states common to D0 and D0.

arxiv:1311.4823

24


arXiv:1311.4823PRD 89, 032001 (2014)

1 fb-1




Start with CF D0Kp decay, to first observe these decays.

arxiv:1311.4823

25


arXiv:1311.4823PRD 89, 032001 (2014)

1 fb-1




Several first observations in Lb and Xb0 decays!

Start with CF D0Kp decay, to first observe these decays.

Good prospects for g with larger data set

arxiv:1311.4823

26

LbJ/ypK- and LbJ/ypp- CP violation not yet observed in the baryon sector. The decay LbJ/ypK recently observed by LHCb most precise t(Lb) (see P. Gandini talk). The CS decay, LbJ/ypp-, unobserved prior to this analysis, has 2 amplitudes, tree & penguin

with different weak phase NP can enter in the penguin and give rise to direct CPV.

LHCb-PAPER-2014-020arXiv:1406.0755|Submitted to JHEP

3 fb-1

arxiv:1406.0755

27

LbJ/ypK- and LbJ/ypp- CP violation not yet observed in the baryon sector. The decay LbJ/ypK recently observed by LHCb most precise t(Lb) (see P. Gandini talk). The CS decay, LbJ/ypp-, unobserved prior to this analysis, has 2 amplitudes, tree & penguin

with different weak phase NP can enter in the penguin and give rise to direct CPV.

0

0

( / ) (8.24 0.25 0.42)%( / )

b

b

B J pB J pK

y py

-

-

L

L

First observation of LbJ/ypp-

0 0( / ) ( / ) (5.7 2.3 1.2)%

CP b bJ p J pKy p y- - L - L

A A A

Direct CPV wrt favored mode (|P/T|SM <<1)

LHCb-PAPER-2014-020arXiv:1406.0755|Submitted to JHEP

3 fb-1

arxiv:1406.0755

28

Charmless: Search for Lb/Xb0 KSph±

• Prior to this analysis, no 3-body charmless decays of b-baryons had been observed. Like B decays, 3-body charmless b-baryon decays contains penguin contributions NP can enter.

• Opens up an interesting window to explore CPV in the b-baryon sector across the Dalitz plot.• BFs normalized to the kinematically similar B0KSp+p- decay.

LHCb-PAPER-2013-061arXiv:1402.0770JHEP 04 (2014) 087

1 fb-1

Sign

al ch

anne

ls

M(KSpp) [ MeV ] M(KSpp) [ MeV ]

M(KSpK) [ MeV ] M(KSpK) [ MeV ]

Nor

m. m

ode


FirstObservation

arxiv:1402.0770

29

Charmless: Search for Lb/Xb0 KSph±

• Prior to this analysis, no 3-body charmless decays of b-baryons had been observed. Like B decays, 3-body charmless b-baryon decays contains penguin contributions NP can enter.

• Opens up an interesting window to explore CPV in the b-baryon sector across the Dalitz plot.• BFs normalized to the kinematically similar B0KSp+p- decay.

LHCb-PAPER-2013-061arXiv:1402.0770JHEP 04 (2014) 087

1 fb-1

Sign

al ch

anne

ls


M(KSpK) [ MeV ] M(KSpK) [ MeV ]

Nor

m. m

ode


0

0

0 0

/0 0

0 0

0 0

0 0

0 0

0 0

0 0

( ) 0.25 0.04 0.02 0.02( )

( ) 0.07 @90% CL( )

( ) 0.03 @90% CL( )

( ) 0.02 @90% CL( )

db

b

b

b Sf f

S

b S

S

b S

d S

b S

d S

B K pB B K

B K pKB B Kf B K pf B B Kf B K pKf B B K

pp p

p p

pp p

p p

L

-

-

-

-

-X

-

-X

-

L

L

X

X

0 0 0 0( ) ( ( ) ) 0.22 0.13 0.03

CP b S b c SK p K pp p- - L - L L

A A A

See paper for additional Lb BFs

Measure direct CPV relative to CF modeLbLc(pKS)p- (penguins should be negligible)

Consistent with zero.

FirstObservation

arxiv:1402.0770

LbLc+ D(s)

-

30

LHCb-PAPER-2014-002arXiv:1403.3606PRL 112, 202001 (2014) 3 fb-1

First observation of b-baryons decaying to double-charm final states

Consistent with expected Cabibbo suppression

LbLc+Ds

- LbLc+D-

Yield~4,600 Yield~260

Bonus: Get most precise Lb mass measurement from measured mass difference M(Lb )– M(B0):

arxiv:1403.3606

LbLc+ D(s)

-

31

LHCb-PAPER-2014-002arXiv:1403.3606PRL 112, 202001 (2014) 3 fb-1

First observation of b-baryons decaying to double-charm final states

Consistent with expected Cabibbo suppression

B(LbLcDs): Normalize to B(B0D-Ds+), but relative yield strong function of pT.

Measure double ratio, same pT dependence, which cancels in ratio.

Several world best BF measurements

LbLc+Ds

- LbLc+D-

Yield~4,600 Yield~260

Bonus: Get most precise Lb mass measurement from measured mass difference M(Lb )– M(B0):

LHCb 0

0b c s

s

DB D D

-

-

L L

0

0b c

B Dpp

-

-

L L

arxiv:1403.3606

32

Summary• b-baryon rate at LHCb very large, 1 Lb for every 2 B0!• Production, decays, b-baryon properties and CPV are

beginning to be probed.– Lifetime of Xb

0 went from unmeasured 2% precision (t(Lb) known to ~1%)

– Mass of Xb0 went from ±2.5 MeV ~0.4 MeV, almost on par with Lb!

• Other high yield modes of b-baryons are also being explored that exploit the excellent PID in LHCb.

• Expect more on rare decays, Vcb, Vub,

excited baryonic states soon..

The future is bright for b-baryon studies @ LHCb.

Documents

Beauty Baryon Decays @ LHCb