Heavy ﬂavour spectroscopy at LHCb - LPHElphe.epfl.ch/publications/2012/ICHEP_b-baryons.pdf ·...

Heavy flavour spectroscopy at LHCbICHEP2012

36th International Conference for High Energy Physics

R. Marki on behalf of the LHCb collaboration

Ecole Polytechnique Federale de Lausanne (EPFL)

5 July 2012

1/22 R. Marki Heavy flavour spectroscopy at LHCb

Outline

Motivation and status

The LHCb experiment at CERN

Mass measurements of ⇤0b, ⌦

�b , ⌅�b and ⌅0

b

First observation of excited ⇤0b baryons

Observation of excited DsJ mesons

Summary and plans


Motivations for heavy quark hadron spectroscopy

Di↵erent QCD models predict di↵erent masses, lifetimes,branching ratios, spin-parity etc. for many c- and b-hadrons.

Further confirmation and testing of models of the heavy quarkinteractions is provided by c- and b-hadron spectroscopy

b-baryon status: 16 predicted ground states

Weakly decaying: ⇤0b, ⌅

0b ,

⌅�b and ⌦�b baryons observed

Strongly decaying: only charged⌃±b observed

Some first excited states seen

c-meson status:

Remaining puzzles incs states


The LHCb experiment at CERN

LHCb - single-arm forward spectrometer at the LHC

Recording pp collisions withp

s = 7 TeV (in 2011) and 8 TeV (in 2012)

Optimized for measurements in heavy-flavour physics

Comprizes tracking detectors, RICH detectors, calorimeters and muon chambers.

The tracking system: Vertex Locator (VeLo), Tracker Turicensis (TT),Inner-Tracker (IT) and Outer Tracker (OT)


Mass measurements at LHCb

Many mass measurementsperformed at LHCb

Good mass resolution

Example: currently worldbest ⇤0

b mass measurementwith 35 pb�1 of 2010 data1.

]2) [MeV/cΛ ψM(J/5500 5550 5600 5650 5700 5750

)2Ev

ents

/ ( 5

MeV

/c

0

10

20

30

40

50

60

70

80

LHCb (d)

Λ ψ J/→ bΛ

LHCb ⇤0b mass measurement

M(⇤0b) = 5619.19 ± 0.70 (stat) ± 0.30 (syst) MeV/c2

Also recent ATLAS measurement2

M(⇤0b) = 5619.7 ± 0.7(stat) ± 1.1(syst) MeV/c2

! Consistent with the LHCb value.1Physics Letters B 708 (2012) 2412ATLAS-CONF-2012-055


Momentum calibration at LHCb

Crucial ingredient for mass measurements is momentum scalecalibration.

[per mille]α-0.5 0 0.5

(2S)Υ

(1S)Υ

(2S)ψ

ψJ/0D0DsK

[per mille]α-0.5 0 0.5

LHCb

Momentum scaled by factor 1� ↵ such that the invariantmass of J/ ! µ+µ� is reconstructed at the PDG value.

Systematics evaluated by the spread in calibration of otherwell known two-body decays (D0, K 0

S , etc.).


⌅�b and ⌦�

b mass measurements

Before the first LHCb measurement, both ⌅�b and ⌦�b baryonshave been observed but there was a very significant inconsistencyregarding the ⌦�b mass.

Value measured or predicted for M⌦�b

DØ3 6165 ± 10 ± 13 MeV/c2

CDF4 6054.4 ± 6.8 ± 0.9 MeV/c2

Theory5 6052.1 ± 5.6 MeV/c2

DØ measurement of ⌦�b mass is more than 6 standard deviationsaway from the CDF one !

Also: only the CDF value is in agreement with main QCD models.

3Phys. Rev. Lett. 101:232002 (2008)4Phys. Rev. D80:072003 (2009)5Annals Phys. 324:2-15 (2009)


⌅�b ! J/ ⌅� and ⌦�b ! J/ ⌦� mass measurements - Fits

Using 0.62 fb�1

of 2011 data

Single gaussian fit

Width fixed to MC

]2 ) [MeV/c-Ξ ψM(J/5600 5700 5800 5900 6000 6100

)2Ev

ents

/ ( 1

0 M

eV/c

0

5

10

15

20

25

30

35

40

45

PreliminaryLHCb

-Ξ ψ J/→ -bΞ

]2 ) [MeV/c-Ω ψM(J/5600 5800 6000 6200 6400 6600

)2Ev

ents

/ ( 2

0 M

eV/c

0

2

4

6

8

10

12PreliminaryLHCb

-Ω ψ J/→ -bΩ

Yield:72.2 ± 9.4

Yield:13.9 +4.5

�3.8


⌅�b ! J/ ⌅� and ⌦�b ! J/ ⌦� mass measurements - Systematics

Source of uncertainty ⌅�b ! J/ ⌅� ⌦�b ! J/ ⌦�

Momentum calibration:

Average momentum scale 1.2 2.1⌘ dependence of momentum scale < 0.1 < 0.1

Detector description:

Energy loss correction < 0.1 < 0.1Mass fitting:

Signal model 0.1 0.1Background model < 0.1 0.7

Total systematic uncertainty 1.2 2.2

Biggest systematic uncertainty from momentum calibration

Final result [LHCb-CONF-2011-060]

M⌅�b

= 5796.5 ± 1.2 (stat.) ± 1.2 (syst.) MeV/c2

M⌦�b

= 6050.3 ± 4.5 (stat.) ± 2.2 (syst.) MeV/c2

! in agreement with CDF and not with DØ.9/22 R. Marki Heavy flavour spectroscopy at LHCb

The ⌅0b baryon

)2) (MeV/c-pK0M(D5400 5600 5800 6000

)2Ev

ents

/ ( 1

5 M

eV/c

0

10

20

30

40

50

60

70

80

90

= 7 TeV DatasPreliminaryLHCb

-1 = 333 pbintL

signal-pK0 D→0bΛ

signal-pK0 D→0bΞ

bkg.-πp0 D→0bΛ

bkg.0bΛLow-mass

Random bkg.A signal has been ob-served for the first timein the ⌅0

b ! D0pK�

channel with a signif-icance of 2.6 standarddeviations.

The fit gives [CERN-LHCb-CONF-2011-036]

M⌅0b

= 5802.0 ± 5.5 (stat) ± 1.7 (syst) MeV/c2


⇤0b ! ⇤+

c ⇡� at LHCb

)2c) (MeV/!"

+c#(M

5400 5500 5600 5700 5800 5900

)2c

Can

did

ates

/ (

10 M

eV/

2000

4000

6000

8000

10000

12000

14000

16000

18000

LHCb

!"

+c#$

0b#

!K+

c#$0b#

Part-rec. bkg.

Random bkg.

Within the full 2011 statistics (1 fb�1):

Huge samples of hadronic decays of ⇤0b collected !

70’540 ± 330 signal events6

Signal-to-background (±25 MeV/c2 around the nominal ⇤0b mass)

S/B = 11

6arXiv:1205.345211/22 R. Marki Heavy flavour spectroscopy at LHCb

Excited ⇤0b-baryons

Excited ⇤0b states: two states with JP = 1/2� and 3/2�

Orbital excitations with L = 1

First observation at LHCb

Predictions exist:

Reference M[⇤0⇤b (1/2�)] M[⇤0⇤

b (3/2�)]Capstick, Isgur 5912 5920[PRD 34 2809 (1986)]Baccouche, et al. 5920 (spin-averaged)[hep-ph/0105148]Garcilazo, et al. 5890 5890[hep-ph/0703257]Ebert, et al. 5930 5947[arXiv:0705.2957]Karliner, et al. 5929 ± 2 5940 ± 2[arXiv:0804.1575]Roberts, Pervin 5939 5941[arXiv:0711.2492]

Predicted mass above ⇤0b⇡

+⇡� threshold (5900 MeV/c2) butbelow the ⌃b⇡ one (around 5950 MeV/c2).


First observation of excited ⇤0b baryons

Kinematic fit - ⇤0b and ⇤+

c mass constraint

)2c) (MeV/!

"+

"0

b#(M

5900 5910 5920 5930 5940 5950

)2c

Can

did

ates

/ (

0.5

MeV

/

5

10

15

20

25

30

LHCb

)2c) (MeV/±!±!b

0"(M

5900 5910 5920 5930 5940 5950

)2c

Can

did

ates

/ (

0.5

MeV

/

5

10

15

20

25

30

LHCb

Left ⇤0b⇡

+⇡� and right ⇤0b⇡±⇡± (WS) combinations7

M⇤0b(5912) = 5911.95 ± 0.12 (stat) ± 0.03 (syst) ± 0.66 (⇤0

b mass) MeV/c2

M⇤0b(5920) = 5919.76 ± 0.07 (stat) ± 0.02 (syst) ± 0.66 (⇤0

b mass) MeV/c2

The significances of the observations are 4.9 and 10.1 standarddeviations, respectively.

7arXiv:1205.345213/22 R. Marki Heavy flavour spectroscopy at LHCb

Current status of cs mesons

[Xiang Liu, Charm 2010]

D⇤s0(2317)+ and

Ds1(2460)+ statesdiscovered in the D+

s ⇡0

channel in 2003 but werepredicted to have muchhigher masses

D⇤s1(2700)+, D⇤

sJ(2860)+ and DsJ(3040)+ excited statesobserved in DK and D⇤K decay modes and in three-bodyb-hadron decays at the B-factories between 2006 and 2009

Quantum numbers of D⇤s1(2700)+ need further confirmation

Existence of the D⇤sJ(2860)+ resonance still unclear and its

spin-parity unknown


D0, D+ and K 0S at LHCb

Very clean samples of D0, D+ and K 0S at LHCb

]2 invariant mass [GeV/c+π+π-K1.84 1.86 1.88 1.9

2C

andi

date

s / 1

.7 M

eV/c

0

10000

20000

30000

40000 (a)LHCb

]2 invariant mass [GeV/c+π-K1.84 1.86 1.88 1.9

2C

andi

date

s / 1

.7 M

eV/c

0

200

400

600

310×

(b)LHCb

]2 invariant mass [GeV/c-π+π0.48 0.5 0.52

2C

andi

date

s / 1

.3 M

eV/c

0

5000

10000

15000

20000 (c)LHCb

]2 invariant mass [GeV/c-π+π0.48 0.5 0.52

2C

andi

date

s / 1

.3 M

eV/c

0

10000

20000

(d)LHCb

(a) D+, (b) D0 , (c) K 0S decaying inside and (d) outside the vertex detector

K 0S ! ⇡+⇡� mass resolution down to 3.5 MeV/c2 !


DsJ states observations

]2 invariant mass [GeV/c0SK+D

2.5 3

2C

andi

date

s / 5

MeV

/c

0

200

400 (c)LHCb

]2 invariant mass [GeV/c+K0D2.5 3

2C

andi

date

s / 5

MeV

/c

0

1000

2000 (d)LHCb

Combined fit8 - background subtracted (first peak is D⇤s2(2573)+)

m(D⇤s1(2700)+) = 2709.4 ± 1.9 (stat) ± 4.5 (syst) MeV/c2

�(D⇤s1(2700)+) = 121.7 ± 7.3 (stat) ± 12.1 (syst) MeV

m(D⇤sJ(2860)+) = 2866.7 ± 1.0 (stat) ± 6.3 (syst) MeV/c2

�(D⇤sJ(2860)+) = 64.5 ± 3.2 (stat) ± 6.6 (syst) MeV

All compatible with previous results from the B-factories, D⇤sJ(2860)+ confirmed

Precision dominated by systematic e↵ects

No statistically significant DsJ resonance above 3 GeV/c2 observed

Spin-parity assignment still need angular analysis of D⇤K

8LHCb-PAPER-2012-016


Summary and plans

LHCb gives most precise ⇤0b mass measurement

⌅�b and ⌦�b masses measured at LHCb and CDF observationof ⌦�b confirmed

Excited ⇤0b state observed and measured for the first time at

LHCb

LHCb confirms existence of D⇤sJ(2860)+ and D⇤

s1(2700)+,mass + decay width measured

New measurements are soon to come with 2011 data (1 fb�1):⇤0

b, ⌅�b and ⌦�b lifetimes

Excellent prospects for further spectroscopy at LHCb in theyears to come: expect 2.5 fb�1 by end of 2012 + additional5 fb�1 at least by 2017 with a b-hadron production crosssection twice as large.


Thank you for your attention


BACKUP SLIDES


⌅�b and ⌦�

b mass measurements

Theory, CDF and LHCb agree but DØ does not.

Measurements and prediction still have large uncertainties.


M(⇡+⇡�) spectrum in ⇤0⇤b ! ⇤0

b⇡+⇡�

)2c) (MeV/!"

+"(M

280 290 300

)2c

Can

did

ates

/ (

2.5

MeV

/

0

2

4

6

8

10

12

14

16

LHCb

M(⇡+⇡�) spectrum is consistent with the result ofphase-space decay simulation (�2/ndf = 1.6 for ndf = 9)


DsJ states observations

]2 invariant mass [GeV/c0SK+D

2.5 3

2C

andi

date

s / 5

MeV

/c

0

2000

4000

6000(a)LHCb

]2 invariant mass [GeV/c+K0D2.5 3

2C

andi

date

s / 5

MeV

/c

0

20000

40000

(b)LHCb

D+K 0S and D0K+ mass distributions without background

subtraction

The low signal-to-background ratio is responsible for the largesystematic uncertainties


Heavy ﬂavour spectroscopy at LHCb - LPHElphe.epfl.ch/publications/2012/ICHEP_b-baryons.pdf ·...

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