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

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

Reconstructing hyperons from b decay

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

Reconstructing hyperons from b decay

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

10

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.

• 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

11

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.

• 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

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

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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)

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

15

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 ?

• 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.

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

3 fb-1

16

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 ?

• 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.

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

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

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

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

17

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 ?

• 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.

• 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

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

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

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Studies of the Xb0 baryon - 2

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

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

3 fb-1

19

Studies of the Xb0 baryon - 2

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

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

3 fb-1

20

Studies of the Xb0 baryon - 3

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

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

3 fb-1

21

Studies of the Xb0 baryon - 3

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

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

3 fb-1

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.

24

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.

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

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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.

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

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

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

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

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

FirstObservation

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

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

Nor

m. m

ode

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

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

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):

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

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.