Post on 13-Mar-2018
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
2/22 R. Marki Heavy flavour spectroscopy at LHCb
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
3/22 R. Marki Heavy flavour spectroscopy at LHCb
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)
4/22 R. Marki Heavy flavour spectroscopy at LHCb
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
5/22 R. Marki Heavy flavour spectroscopy at LHCb
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.).
6/22 R. Marki Heavy flavour spectroscopy at LHCb
⌅�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)
7/22 R. Marki Heavy flavour spectroscopy at LHCb
⌅�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
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⌅�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
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⇤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).
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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
14/22 R. Marki Heavy flavour spectroscopy at LHCb
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 !
15/22 R. Marki Heavy flavour spectroscopy at LHCb
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
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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.
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Thank you for your attention
18/22 R. Marki Heavy flavour spectroscopy at LHCb
BACKUP SLIDES
19/22 R. Marki Heavy flavour spectroscopy at LHCb
⌅�b and ⌦�
b mass measurements
Theory, CDF and LHCb agree but DØ does not.
Measurements and prediction still have large uncertainties.
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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)
21/22 R. Marki Heavy flavour spectroscopy at LHCb
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
22/22 R. Marki Heavy flavour spectroscopy at LHCb