Baryon Spectroscopy at COMPASS HK 77.2

Transcription

Baryon Spectroscopy at COMPASS
HK 77.2
Tobias Weisrock
Johannes Gutenberg-Universität Mainz
DPG-Frühjahrstagung Dresden
7. März 2013
COMPASS
International Summer School
Symmetries, Fundamental Interactions and Cosmology
Introduction
Why study baryons?
I
I
3-quark bound states
⇒ excellent probe to study QCD
baryon spectrum only poorly known
I
I
many states with ∗ or ∗∗ in PDG listings
many missing states
COMPASS
Tobias Weisrock (JGU Mainz)
7. März 2013
1 / 15
Introduction
Why study baryons?
I
I
3-quark bound states
⇒ excellent probe to study QCD
baryon spectrum only poorly known
I
I
many states with ∗ or ∗∗ in PDG listings
many missing states
How to study baryons?
I
πN scattering
I
I
I
no new data available
still dominates PDG listings
γN scattering
I
MAMI, ELSA
I J/ψ
decays
I
BESIII
I
I
(HK 84.2),. . .
(HK 61.1)
NN scattering
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HADES (HK 1.2)
COMPASS
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Introduction
What do we measure at COMPASS?
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2009 data taking
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190 GeV/c proton beam on liquid hydrogen target
So far only two channels investigated:
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pp → pf π + π − precoil
pp → pf K+ K− precoil
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Introduction
I
2009 data taking
I
I
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I
pfast
π + , K+
pbeam
π − , K−
precoil
ptarget
COMPASS
Introduction
I
2009 data taking
I
I
I
I
pfast
π + , K+
pbeam
π − , K−
precoil
ptarget
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The COMPASS Experiment
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COmmon Muon and Proton Apparatus for Structure and Spectroscopy
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Located at SPS at CERN
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I
I
75% p
24% π +
190 GeV/c
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I
75% p
24% π +
190 GeV/c
CEDARs
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I
75% p
24% π +
190 GeV/c
CEDARs
Target
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I
75% p
24% π +
190 GeV/c
Large Angle Spectrometer
CEDARs
Target
RICH
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I
I
75% p
24% π +
190 GeV/c
Small Angle Spectrometer
Large Angle Spectrometer
CEDARs
Target
RICH
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Cuts
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minimum bias trigger
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incoming beam + recoiling proton
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exactly 1 primary vertex reconstructed inside the target
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identified incoming proton
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1 reconstructed recoil proton
3 outgoing charged particles
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P
Q = +1
outgoing π + or K+ identified by RICH
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Exclusivity and Coplanarity
Exclusive events selected by 2 cuts:
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energy sum of outgoing system around peak value (exclusivity)
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azimuthal angles of outgoing system and recoil proton differ by π (coplanarity)
Exclusivity
Coplanarity
×10
×10
7
6
before cut
after coplanarity cut
COMPASS
2009
pp → p π+π ps
f
(no acceptance correction)
preliminary
6
5
4
Events / 0.02 rad
Events / 0.5 GeV
6
COMPASS
2009
-
before cut
after exclusivity cut
6
pp → p π+π ps
f
preliminary
5
4
3
3
2
2
1
1
0
175
180
185
190
195
200
205
Total Energy of p π+π-ps System (GeV)
f
0
-3
-2
-1
0
1
2
3
Φπ+π-p -Φp -π
f
s
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Invariant Mass of π + π − pf
×10
Events / 5 Mev/c2
6
COMPASS
2009
pp → p π π ps
0.35
+
I
more than 56M events
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small structure at
≈ 1450 MeV
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dominant structure at
≈ 1700 MeV
possible candidates:
f
preliminary
0.3
0.25
0.2
0.15
I
0.1
I
I
0.05
I
0
1
1.2
1.4
1.6 1.8
2
2.2 2.4 2.6 2.8
3
Invariant Mass of π+π-p System (GeV/c2)
I
N(1700)3/2− (∗∗∗)
∆(1700)3/2− (∗∗∗∗)
N(1710)1/2+ (∗∗∗)
N(1720)3/2+ (∗∗∗∗)
shoulder at ≈ 2200 MeV
f
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Invariant Mass of π + pf -subsystem
×10
pp → p π π ps
+
f
2
preliminary
1.8
1.6
1.4
1.2
1
0.8
0.6
3
2.8
2.6
8
2.4
2.2
6
2
1.8
4
1.6
COMPASS
2009
pp → p π+π ps
1.4
0.4
f
2
1.2
0.2
0
1
×10
10
3
COMPASS
2009
-
++
∆ (1232)
f
2.2
Invariant Mass of π +π -p (GeV/c 2)
Events / 5 Mev/c2
6
2.4
1.2
1.4
1.6
1.8
2
2.2 2.4 2.6 2.8
3
Invariant Mass of π+p System (GeV/c2)
f
I
∆++ (1232) dominates
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small shoulder at ≈ 1900 MeV
1
1
preliminary
1.2
1.4
1.6
1.8
2
2.2 2.4 2.6 2.8
3
Invariant Mass of π+p (GeV/c2)
0
f
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Invariant Mass of π − pf -subsystem
×10
f
preliminary
0.6
0.5
0.4
0.3
0.2
f
pp → p π π ps
+
0.7
3
2.8
8
2.6
7
2.4
6
2.2
5
2
4
1.8
3
1.6
COMPASS
2009
-
1.4
pp → p π+π ps
2
preliminary
1
f
0.1
0
1
×10
3
COMPASS
2009
-
0
∆ (1232)
Events / 5 Mev/c2
6
0.8
1.2
1.2
1.4
1.6
1.8
2
2.2 2.4 2.6 2.8
3
Invariant Mass of π-p System (GeV/c2)
1
1
1.2
1.4
1.6
1.8
f
I
∆0 (1232)
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N(15??) ← dominant decay mode of 1700 MeV structure
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N(16??), ∆(16??)
2
2.2 2.4 2.6 2.8
3
Invariant Mass of π-p (GeV/c2)
0
f
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Invariant Mass of π + π − -subsystem
×10
×10
5
3
pp → p π+π ps
f
preliminary
ρ(770)
0.4
0.3
0.2
f 0(980)
0.1
f 2(1270)
f
COMPASS
2009
-
Events / 5 Mev/c2
6
0.5
3
2.8
2.6
4
2.4
2.2
3
2
1.8
2
1.6
COMPASS
2009
pp → p π+π ps
1.4
f
0
0
0.2
0.4
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ρ(770)
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f0 (980)
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f2 (1270)
0.6
0.8
1
1.2 1.4 1.6 1.8
2
Invariant Mass of π+π- System (GeV/c2)
1
1.2
1
0
preliminary
0.2
0.4
0.6
0.8
1
1.2 1.4 1.6 1.8
2
Invariant Mass of π+π- (GeV/c2)
0
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Cuts
Exclusivity
Coplanarity
×10
×10
0.12
6
before cut
after coplanarity cut
COMPASS
2009
+ pp → p K K ps
f
preliminary
0.1
Events / 0.02 rad
Events / 0.5 GeV
6
0.16
COMPASS
2009
+ -
before cut
after exclusivity cut
pp → p K K ps
f
0.14
preliminary
0.12
0.08
0.1
0.08
0.06
0.06
0.04
0.04
0.02
0
175
0.02
180
185
190
195 200
205
Total Energy of p K+K ps System (GeV)
f
-3
-2
-1
0
1
2
3
ΦK+K-p -Φp -π
f
s
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Invariant Mass of K+ K− pf
×10
Events / 5 MeV/c2
3
COMPASS
2009
+ pp → p K K ps
2.5
f
preliminary
2
more than 900k events
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no clear structures seen
some pion contributions still
visible
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1.5
1
⇒ RICH selection still to be
optimised
0.5
0
1.5
I
2
2.5
3
3.5
4
4.5
Invariant Mass of K+K p System (GeV/c2)
f
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Invariant Mass of K+ pf -subsystem
×10
Events / 5 MeV/c2
3
4
COMPASS
2009
+ pp → p K K ps
3.5
f
preliminary
3
2.5
I
no resonances expected for
q = +2 and s = +1
I
no structures seen
2
1.5
1
0.5
0
1
1.2
1.4
1.6
1.8
2
2.2 2.4 2.6 2.8
3
Invariant Mass of K+p System (GeV/c2)
f
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Invariant Mass of K− pf -subsystem
×10
Events / 5 MeV/c2
3
16
Λ(1520)
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2009
+ pp → p K K ps
f
14
preliminary
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12
10
clear Λ(1520) contribution
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8
I
6
good resolution
further structure at
≈ 1800 MeV (Λ(18??)?)
4
2
0
1
1.2
1.4
1.6
1.8
2
2.2 2.4
2.6 2.8
3
Invariant Mass of K p System (GeV/c2)
f
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Invariant Mass of K+ K− -subsystem
×10
Events / 5 MeV/c2
3
16
φ(1020)
14
COMPASS
2009
+ -
I
pp → p K K ps
f
clear φ(1020) contribution
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preliminary
good resolution
12
I
shoulder by a2 (1320)?
10
I
structure at ≈ 1500 MeV
(f0 (1500)? f20 (1525)?)
8
6
PWA of centrally produced
system performed by A.
Austregesilo (HK 2.5)
4
2
0
0.6
0.8
1
1.2 1.4 1.6 1.8
2
2.2 2.4
+ Invariant Mass of K K System (GeV/c2)
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Conclusion and Outlook
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COMPASS has large datasets for baryon spectroscopy in pp scattering
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so far pp → pπ + π − p and pp → pK+ K− p analysed
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rich structures visible in most mass spectra
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Conclusion and Outlook
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COMPASS has large datasets for baryon spectroscopy in pp scattering
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so far pp → pπ + π − p and pp → pK+ K− p analysed
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rich structures visible in most mass spectra
Next steps:
I Extend to further channels
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pπ 0 π 0 p, pK0 K̄0 p
pπ 0 p, pηp, pωp, ΛK+ p,. . .
start of partial wave analysis (PWA)
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15 / 15
Thank you for your attention
COMPASS
7. März 2013
16 / 15

Baryon Spectroscopy at COMPASS HK 77.2

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