Meson spectroscopy at LHCb
M. Kreps on behalf of the LHCb Collaboration
Physics Department
Outline:
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Study of DJ mesons
D(s) meson masses
Bc+ mass and Bc+ → Bs π + observation
ψ(4160) in B + → K + µ+ µ−
X(3872) quantum numbers
www2.warwick.ac.uk
LHCb detector
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2
23 July 2013
Good mass resolution
Good time resolution
High trigger rate on c
and b
Uniform running
conditions
Michal Kreps – Meson spectroscopy at LHCb
D+
Mass (MeV)
3000
−
D1*(2618) 1
−
D0(2558) 0
2500
2000
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3
D2*(2479)
D1(2469)
D1(2419)
D0*(2380)
+
2
+
1
+
1
+
0
jq=1/2
P
J
jq=1/2
L=0
0 1
+
0
*
D0
jq=3/2
L=1
+
+
1 1 2
*
D1 D1 D2
+
S-wave π
D-wave π
−
*
Godfrey, Isgur: PRD32, 189
−
1S
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−
3
−
2
−
2
−
1
+
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+
3
+
3
+
2
D*(2023) 1
D(1864) 0
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D3*(2806)
D2(2806)
D2(2801)
D1*(2796)
D4*(3084)
D3 (3079)
D3 (3074)
D2*(3074)
Mass [arbitrary units]
Open charm mesons
2S
1D
1P
Du,d
γ Du,d
1F
Spectrum for D0 mesons basically same
1S and narrow 1P states well established
Broad 1P states recently observed at B-factories
BABAR observed in e+ e− → cc̄ → D∗ πX four additional states
Some could be possibly assigned, but not all are clear
Further studies are needed
23 July 2013
Michal Kreps – Meson spectroscopy at LHCb
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We study processes:
pp → D+ π − X
pp → D0 π + X
pp → D∗+ π − X
D meson reconstructed as
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D+ → K − π + π + ; N = 15.1M
D0 → K − π + ; N = 20.4M
D∗+ → D0 π + ; N = 6.4M
Purity in all cases very high
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Resolutions 8.1, 8.8 and 0.69 MeV/c2
×103
(a)
1500
23 July 2013
D+
500
1800
1850
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1950
m(K π+π+) [MeV]
×103
1500
(b)
LHCb
1000
D0
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0
1800
1850
1900
1950
m(K π+) [MeV]
×103
600
(c)
LHCb
D∗+
400
200
0
2005
4
LHCb
1 fb−1
1000
0
Candidates / (0.15 MeV)
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Candidates / (2 MeV)
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arXiv:1307.4556
Candidates / (1.5 MeV)
DJ mesons
2010
2015
2020
m(D0π+) [MeV]
Michal Kreps – Meson spectroscopy at LHCb
DJ mass spectra
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D2∗ (2460)
and
Strong signals for
D1 (2420)
Activity in 2.6–2.8 GeV
Feedthrough in Dπ from decays
to D∗ π
NEW
Candidates / (4 MeV)
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arXiv:1307.4556
30000
D2∗ (2460)0
20000
10000
0
5
(∗)
DJ → D∗ π
LHCb
1 fb−1
60000
D2∗ (2460)0
40000
0
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2200
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2800
m(D π ) [MeV]
+ -
Candidates / (4 MeV)
Candidates / (4 MeV)
D1 (2420)0LHCb
(a)
20000
Right sign data
Wrong sign data
(c)
80000
(∗)
DJ → D∗ π LHCb
(b)
60000
40000
D2∗ (2460)+
20000
2200
23 July 2013
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2800
m(D*+π-) [MeV]
0
2200
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2600
2800
m(D0π+) [MeV]
Michal Kreps – Meson spectroscopy at LHCb
D∗+π − fit
arXiv:1307.4556
NEW
Split sample by D∗ helicity angle
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Unnatural parity (0− , 1+ , 2− , ...) 1 + h cos2 θH
Natural parity (0+ , 1− , 2+ , ...) sin2 θH
First fit sample enhanced in unnatural parity
Then sample enhanced in natural parity with unnatural parity
contributions fixed
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-5
-5
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2200
5000
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2800
LHCb
| cos θH | > 0.75
0
2200
2400
2600
2800
3000
Candidates / (4 MeV)
Candidates / (4 MeV)
500
3000
m(D*+π-) [MeV]
6
23 July 2013
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2200
2400
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2600
2800
3000
LHCb
| cos θH | < 0.5
0
2200
2400
2600
2800
3000
m(D*+π-) [MeV]
Michal Kreps – Meson spectroscopy at LHCb
D∗+π − fit
Resonance
D1 (2420)0
D2∗ (2460)0
DJ∗ (2650)0
DJ∗ (2760)0
DJ (2580)0
DJ (2740)0
DJ (3000)0
arXiv:1307.4556
NEW
Mass
2419.6 ±
2460.4 ±
2649.2 ±
2761.1 ±
2579.5 ±
2737.0 ±
2971.8 ±
(MeV)
0.1 ± 0.7
0.4 ± 1.2
3.5 ± 3.5
5.1 ± 6.5
3.4 ± 5.5
3.5 ±11.2
8.7
Width (MeV)
35.2 ± 0.4 ± 0.9
43.2 ± 1.2 ± 3.0
140.2 ± 17.1 ± 18.6
74.4 ± 3.4 ± 37.0
177.5 ± 17.8 ± 46.0
73.2 ± 13.4 ± 25.0
188.1 ± 44.8
-5
Significance (σ)
24.5
10.2
18.8
7.2
9.0
-5
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5000
2400
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LHCb
| cos θH | > 0.75
0
2200
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3000
Candidates / (4 MeV)
Candidates / (4 MeV)
500
3000
m(D*+π-) [MeV]
6
23 July 2013
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5000
2600
2800
3000
LHCb
| cos θH | < 0.5
0
2200
2400
2600
2800
3000
m(D*+π-) [MeV]
Michal Kreps – Meson spectroscopy at LHCb
Test natural vs. unnatural
parity vs. 0−
dN/d(cosθH)
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15000
LHCb
(a) DJ(2580)
arXiv:1307.4556
NEW
14000
12000
dN/d(cosθH)
16000
LHCb
*
0
(a) DJ (2650)
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-1
-0.5
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-1
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cosθH
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LHCb
(b) DJ(2740)
LHCb
*
(b) DJ (2760)0
2500
8000
dN/d(cosθH)
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D∗ π allows spin-parity
analysis
Fit mass in bins of cos θH
dN/d(cosθH)
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dN/d(cosθH)
Spin-parity analysis
-0.5
0
0.5
1
0.5
1
cosθH
5000
4000
LHCb
(c) DJ(3000)
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5000
1000
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-1
-0.5
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0.5
1
cosθH
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23 July 2013
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-1
-0.5
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0.5
1
cosθH
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-1
-0.5
0
cosθH
Michal Kreps – Meson spectroscopy at LHCb
Spin-parity results
Resonance
D 1(2420)0
D 2∗(2460)0
D J∗(2650)0
D J∗(2760)0
D J (2580)0
D J (2740)0
D J (3000)0
8
23 July 2013
JP
Function
1+
1+ hcos2 θH
2+
sin2 θH
N atural
sin2 θH
N atural
sin2 θH
Natural
sin2 θH
Natural
sin2 θH
Natural
sin2 θH
χ2/ ndf
JP
Function
arXiv:1307.4556
NEW
χ2/ ndf
JP
χ2/ ndf
Function
0.67/ 8
h Parameter
3.30 ± 0.48
8.5/ 9
6.8/ 9
5.8/ 9
151/ 9
34/ 9
36.6/ 9
Unnatural
Const.
Unnatural
Const.
U nnatural
1+ hcos2 θH
U nnatural
1+ hcos2 θH
U nnatural
1+ hcos2 θH
200/ 9
26/ 9
3.4/ 8
0−
cos2 θH
0−
cos2 θH
0−
cos2 θH
342/ 9
94/ 9
23/ 9
4.2 ± 1.3
6.6/ 8
3.1 ± 2.2
10/ 8
1.5 ± 0.9
Michal Kreps – Meson spectroscopy at LHCb
D0π + and D+π − Fits
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arXiv:1307.4556
NEW
Fits more involved due to reflections from D∗ π final states
Reflections fixed based on D∗+ π − results
See clear D2∗ (2460), DJ∗ (2760) and DJ∗ (3000)
Resonance parameters consistent with D∗+ π −
For DJ∗ (2760) only fit to D∗+ π − reliable for resonance parameters
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LHCb
20000
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2500
2200
23 July 2013
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Candidates / (4 MeV)
Candidates / (4 MeV)
60000
3000
m(D0π+) [MeV]
2000
0
40000
2500
3000
LHCb
20000
0
2200
2400
2600
2800
3000
m(D+π-) [MeV]
Michal Kreps – Meson spectroscopy at LHCb
Ground state D(s) mesons
Candidates/ (2 MeV/c2)
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LHCb
(a)
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30000
LHCb
1 fb−1
25000
20000
15000
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1850
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2000
− +
M(K K π ) [MeV/ c2]
+
pull
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JHEP 06 (2013), 065
Candidates/ (2 MeV/c2)
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Huge samples available at LHCb
Dominant systematic uncertainty from
momentum and energy loss calibration
Smaller Q value of the decay ⇒ smaller
sensitivity to momentum calibration
Have large samples of other particles to
calibrate momentum
Candidates/ (2 MeV/c2)
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LHCb
(b)
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1840
1860
1880
pull
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23 July 2013
−
M(K K π π )
+
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-2
-4
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− +
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1820
1920
1840
1860
1880
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0
-2
-4
-6
−
1900
1920
− +
M(K K K π ) [MeV/ c2]
+
[MeV/ c2]
pull
0
1820
Michal Kreps – Meson spectroscopy at LHCb
Ground state D(s) mesons
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Direct results
JHEP 06 (2013), 065
M (D0 )
= 1864.75 ± 0.15 (stat) ± 0.11 (syst) MeV/c2 ,
M (D+ ) − M (D0 ) =
4.76 ± 0.12 (stat) ± 0.07 (syst) MeV/c2
98.68 ± 0.03 (stat) ± 0.04 (syst) MeV/c2
M (Ds+ ) − M (D+ ) =
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Adding PDG information, we derive
M (Ds+ ) = 1968.19 ± 0.20 ± 0.14 ± 0.08 MeV/c2
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Mass difference best in world
D0 mass matches in precision existing best measurement
For D0 knowledge of kaon mass becomes important
CLEO
ACCM
LGW
E691
KEDR
CLEO2
MRK2
CLEO
CDF2
PDG Average 4.74 ± 0.28
PDG Average 1864.92 ± 0.16
BABAR
PDG Average 98.85 ± 0.25
LHCb
LHCb
D
11
0
1863.5
LHCb
New average 4.76 ± 0.12
New average 1864.84 ± 0.12
1864
23 July 2013
1864.5
1865 1865.5 1866
D0 mass [MeV/c2]
D
+
New average 98.69 ± 0.05
4
4.2 4.4 4.6 4.8
5 5.2 5.4 05.6 5.8 6
M(D+ ) - M(D ) [MeV/c2]
Ds+
97
97.5
98
98.5 + 99
99.5 100
M(Ds ) - M(D+ ) [MeV/c2]
Michal Kreps – Meson spectroscopy at LHCb
Bc mass
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Mass of the Bc currently determined from J/ψ π decays
They have rather large Q value ⇒ large systematic uncertainty from
momentum scale
Benefits from precise masses of daughters
Recently we observed new decay Bc → J/ψ Ds+
Q value here is about same as B 0 → J/ψ K ∗
Candidates/(25 MeV/c2 )
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PR D87, 112012
+
60
50
40
Candidates/(10 MeV/c2 )
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25
LHCb
+
B+
c → J/ψ Ds
20
3 fb−1
15
10
5
30
0
6.2
6.25
6.3
m(J/ψ D+
s )
20
6.35
GeV/c2
10
0
5.6
5.8
6
6.2
m(J/ψ D+
s )
12
23 July 2013
6.4
6.6
GeV/c2
Michal Kreps – Meson spectroscopy at LHCb
Bc mass
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PR D87, 112012
m(Bc ) − m(Ds ) = 4307.97 ± 1.44 ± 0.20 MeV/c
Using our determination of m(Ds ) including correlations
m(Bc ) = 6276.28 ± 1.44 ± 0.36 MeV/c2
Consistent with PDG
Uncertainty about same as PDG
Potential for improvement as statistically dominated
D0
CDF
LHCb (J/ ψ π+ )
Old average: 6274.51 ± 1.80
LHCb (J/ ψ D+s )
Average: 6275.14 ± 1.30
6260
13
23 July 2013
6270
6280
6290
6300 6310 6320
B+c mass [MeV/c2]
Michal Kreps – Meson spectroscopy at LHCb
Observation of Bc+ → Bsπ +
NEW
c
∗
Vcs
W+
π
d
+
Bc+
b
s
Bs0
b
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000
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000
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000
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00
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000
00
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000
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000
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14
Bc can decay via b-, c-quark decay
or weak annihilation
Up to now all decays through
c-quark decay
b-quark decay should give larger
rate
Bc → Bs π decay first of this kind
Statistical significance 7.7σ
fc
+
+
→
B
π
)=
×
B(B
s
c
fs
+0.17
2.38 ± 0.35 ± 0.11 −0.12 × 10−3
23 July 2013
LHCb-PAPER-2013-044
40
LHCb
Data
B+c → B0s(→ J/ ψφ)π+
Comb. bkg.
30
B+c → B0sρ+
B+c → B*s π+
20
10
0
6000
Candidates / (10 MeV/c2)
Vud
Candidates / (10 MeV/c2)
u
6200
6400
m(B0sπ+)
6600
[MeV/ c2]
LHCb
50
Data
−
B+c → B0s(→ Ds π+)π+
Comb. bkg.
40
30
B+c → B0sρ+
B+c → B*s π+
20
10
0
6000
6200
6400
m(B0sπ+)
6600
[MeV/ c2]
Michal Kreps – Meson spectroscopy at LHCb
cc̄ above DD̄ threshold
000
111
000
111
111
000
000
111
000
111
000
111
000
111
000
111
000
111
Practically all information on 1−− cc̄ states from
σ(e+ e− → hadrons)
R=
σ(e+ e− → µ+ µ− )
Interferences rarely taken into account
Best knowledge from BES (PLB 660, 315) which takes interferences
into account
State
Mass [ MeV ] Width [ MeV ]
χ /d.o.f=1.05
ψ(3770) 3773.2 ± 0.3
27.2 ± 1.0
ψ(4040) 4039.6 ± 4.3
84.5 ± 12.3
R
ψ(4160) 4191.7 ± 6.5
71.8 ± 12.3
R
R
ψ(4415) 4415.1 ± 7.9
71.5 ± 19.0
R
111
000
000
111
000
111
000
111
000
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000
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000
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000
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000
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000
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000
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000
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000
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000
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000
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000
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000
111
5.5
2
5.0
4.5
4.0
3.5
R
3.0
exp
2.5
the
2.0
con
int
1.5
Rres
1.0
RBW
0.5
0.0
-0.5
-1.0
3.7
3.8
3.9
4.0
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5.0
Ecm(GeV)
15
23 July 2013
Michal Kreps – Meson spectroscopy at LHCb
B + → K +µ+µ− decays
00
11
00
11
000
111
00
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000
00
11
000
111
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11
000
111
000
111
00
11
00
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000
00
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00
11
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00
11
000
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000
111
Significant effort goes into study of
b → sl+ l− FCNCs
In measurements, J/ψ and ψ(2S) is
removed
cc̄ states above ψ(2S) kept,
expected to contribute about 2%
of non-resonant (Beylich, Buchalla,
LHCb-PAPER-2013-039
dB/dq2 [10-7 × c 4/GeV2]
00
11
111
000
00
11
000
111
00
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00
11
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000
111
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
LHCb
1 fb−1
0.4
0.2
5
10
15
20
q2
Events / (12 MeV/c2)
00
11
11
00
000
111
00
11
000
111
00
11
000
111
00
11
000
111
000
111
We are getting to point when B +
data can test such contributions
Have 1830 B + decays with
m(µ+ µ− ) > 3770 MeV/c2
Very low background
Binned theory
0.6
0
0
Feldmann: EPJ C71, 1635)
00
11
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
Theory
LHCb
[GeV2/c 4]
data
LHCb
sum
signal
background −1
400
3 fb
200
0
5400
5600
mK+µ+µ− [MeV/c2]
16
23 July 2013
Michal Kreps – Meson spectroscopy at LHCb
Dimuon spectrum
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
LHCb-PAPER-2013-039
2
See signal at ≈ 4.2 GeV/c
Fit Breit-Wigner for observed peak
Non-resonant contribution according to latest theory (Khodjamirian et al.,
JHEP 09, 089; Bouchard et al., arXiv:1306.2384; Bobeth et al., JHEP 01, 107)
00
11
111
000
00
11
000
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00
11
000
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00
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000
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000
111
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
Non-B background
Fit takes into account interference between BW and non-resonant
contribution
Parameters
data
LHCb
+0.9
−9
sum
150
B[×10 ]
3.5 −0.8
−1
non-resonant
3 fb
Mass [ MeV/c2 ] 4190 ± 5
interference
2
resonances
100
Width [ MeV/c ] 66 ± 12
background
Events / (25 MeV/c2)
00
11
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
50
0
3800
4000
4200
4400
4600
mµ+µ− [MeV/c2]
17
23 July 2013
Michal Kreps – Meson spectroscopy at LHCb
Interpretation
ψ (4160)
LHCb best fit
Y(4260)
30
25
100
20
15
80
/L)
width [MeV/ c2]
00
11
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
Consistent with ψ(4160)
Interpretation as Y (4260) excluded at 4σ
Contributes about 20% above ψ(2S) mass
best
00
11
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
LHCb-PAPER-2013-039
2log(L
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
10
60
4180
LHCb
4200
4220
4240
5
4260
mass [MeV/c2]
18
23 July 2013
Michal Kreps – Meson spectroscopy at LHCb
X(3872) quantum numbers
00
11
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
00
11
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
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000
111
00
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000
00
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00
11
000
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00
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19
Not all hypotheses work
with any J P C
Restricts its position in
spectrum
PC
In 2006 CDF restricted J to
1++ or 2−+
BABAR favours 2−+ from
observation of X(3872) →
J/ψ ω
23 July 2013
1200
1000
450
X(3872) yield / bin volume
11
00
00
11
000
111
00
11
000
111
00
11
000
111
00
11
000
111
000
111
Its 10 years since observation of
X(3872)
Triggered renewed interest to cc̄
states
Lot of speculations what X(3872) is
Determination of quantum
numbers important
Number of candidates / (2.5 MeV)
00
11
111
000
00
11
000
111
00
11
000
111
00
11
000
111
000
111
400
|cos(θJ/ ψ)| < 0.6
600
-1
L ≈ 780 pb
X(3872)
data points
300
250
acc. corrected
prediction for
0++
p
200
150
100
1-s
50
1++
p
0
0 0.63 1.15 π/2
0 0.63 1.15 π/2
0 0.63 1.15 π/2
0 0.63 1.15 π/2
2-+
p
||∆ Φ - π| - π/2|
1200
ψ (2S)
70
X(3872)
60
1000
50
40
600
30
400
20
200
400
10
0 550
200
0
CDF Run II
350
800
800
|cos(θJ/ ψ)| > 0.6
|cos(θπ π)| |cos(θπ π)| |cos(θπ π)| |cos(θπ π)|
< 0.5
> 0.5
< 0.5
> 0.5
600
313 ± 26
600
800
0
LHCb
750
800
1000
1200
1400
M(π+π-J/ψ ) - M(J/ ψ ) [MeV]
PRL 110, 222001
Michal Kreps – Meson spectroscopy at LHCb
X(3872) quantum numbers
00
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000
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000
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00
11
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000
111
+
+
LHCb uses B → J/ψ K decays
Full angular analysis performed
Introduces “production” polarization
PRL 110, 222001
Number of candidates / 0.4
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
120
100
LHCb
all candidates
1 fb−1
80
60
40
Data
PC
20
Simulated J =1++
PC
Simulated J =2-+
50
|cosθππ| > 0.6
40
30
20
10
0
-1
20
23 July 2013
-0.5
0
0.5
1
cosθX
Michal Kreps – Meson spectroscopy at LHCb
X(3872) quantum numbers
00
11
000
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000
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000
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111
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111
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000
00
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000
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00
11
000
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000
111
Use likelihood ratio −2 ln[L(2 )/L(1 )]
Allows to distinguish between 1++ and 2−+ hypotheses
Excludes 2−+ at 8.2σ
Only cc̄ possibility is χc1 (23 P1 ), but mass is off
New D0 mass weakens pure molecule interpretation
Number of experiments / bin
00
11
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
++
−+
PRL 110, 222001
107
LHCb
6
10
Simulated JPC=1++
Simulated JPC=2-+
105
104
t data
3
10
102
-200
21
23 July 2013
-100
0
100
200
-+
++
t = -2 ln[ L(2 )/ L(1 ) ]
Michal Kreps – Meson spectroscopy at LHCb
Conclusions
00
11
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111
00
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000
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111
00
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000
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00
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00
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000
111
Significant improvement to experimental knowledge of DJ mesons
We find additional states
Some information on parity available
We improve on ground state D(s) masses
00
11
00
11
000
111
00
11
111
000
00
11
000
111
00
11
000
111
000
111
Implication for X(3872)
Observed Bc → J/ψ Ds and improved Bc mass measurement
Observe ψ(4160) in B + → K + µ+ µ− at unexpectedly high rate
Finally after almost 10 years pinpointed X(3872) J P C
List of available results at
http://lhcbproject.web.cern.ch/lhcbproject/CDS/cgi-bin/index.php
Many other topics in progress and in some cases not all data analysed
⇒ More news to expect
00
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00
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22
23 July 2013
Michal Kreps – Meson spectroscopy at LHCb