Post on 20-Dec-2015
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Recent results from SVD-2 experiment
1. Current status2. Pentaquark search3. Charmed mesons
A.Kubarovsky, V.Popov SINP MSU Moscow
(for SVD collaboration)
Talk at QFTHEP 2004, Peterhof, St.Petersburg, Russia 17-23 May 2004
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
SVD-2 experiment
• The main goals (when started in 2000):– Cross section of charm creation at near-threshold
energies– A-dependencies– Searches for intrinsic charm of nucleons (Brodsky,...)
• Most of statistics was collected in 2002• Pentaquark analysis since ‘2003 fall
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
SVD-2 detector layout
1 2
3 54
1.a
P-beam
K-
K-
p+
1 High precision microstrip vertex detector. 5 Gamma detector.1a Active target with Si, C and Pb planes2 Multiwire proportional chambers. 3 Magnet ( 1.18 T over 3m long region). 4 Multicell threshold Cherenkov counter.
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
SVD-2 tracking detector
Si active target1 mm pitch
Pb C
Tracking detectors
25 μm50 μm
X Y
X Y
X Y U W X Y
10 mm
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
SVD-2 trigger
Level I• Based on energy depositions in 58 Si active target strips• Basic principle is to look for the >2...3 MIPs depositions in
consecutive planes• Decision time: 220 ns• "Non-usable" events contamination: < 10%
Level II• Not implemented yet...• Basic idea - a search of "secondary" activity• A simplified "fast" information from vertex tracking detector
to be used
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
SVD-2 run I (April '2002)
• IHEP Protvino U-70 accelerator• Proton beam 70 GeV/c• Intensity 5-6×105 1/cycle (1.2 sec)• Total target thickness ~0.5% of hadronic length• 400…600 events/cycle registered• 53,000,000 events stored
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Experimental accuracies
• X,Y-resolutions for tracks fitted: 8…10 m• Z-resolution:
– for the primary vertex: 70… 130 m– for the secondary vertex: 200… 300 m
• Impact parameter resolution: ~ 14 m• Momentum resolution for the 5 GeV tracks: 1%• Effective mass resolution:
– K0: 4.4 MeV : 1.6 MeV
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Primary vertex Z-coordinate in SVD-2 active target
SVD-2 data analysis
Si Si
Pb
Si
C Si
Si
Si – 300m; Pb – 220 m; С – 500 m
z = 70÷130µm, x,y = 7÷10µm
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
K0s and Λ0 effective masses
• K0s M = 497.61 ± 0.09 (stat.), σ=4.4 MeV/c2
• Λ0 M = 1115.32 ± 0.05 (stat.), σ=1.6 MeV/c2
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
u
ud +2/3
+2/3−1/3
p
K−s−1/
3
u−2/3
Meson: quark-antiquark
+
u
u
d
ds+1/3 −1/
3+2/3
−1/3
+2/3
Pentaquark: 4 quarks + 1 antiquark
Exotic if antiquark is of the different flavour
Baryon: three quarks
Hadron nicknames
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
A start of pentaquark history
An idea of five-quark states was discussed since late 60’s (Jaffe, Lipkin, Strotteman, …)
First estimates in the Skyrme model (Chemtob, Praszalowicz, Walliser) – 1985...
There were no conclusive results from experimental searches
“The general prejudice against baryons not made of three quarks and the lack of any experimental activity in this area make it likely that it will be another 15 years before the issue is decided”. (PDG, 1986)
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
PDG – in “Particle listings under revision”
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
In the ‘2003 fall...
• uudds quark content• Predicted by Diakonov,Petrov and Polyakov
Z.Phys A 359, 305(1997)• Supposed to be of 1530 MeV/c2 mass, width <15
MeV/c2 and to decay into nK+ or pK0 • Observed by several experiments
(LEPS,DIANA,CLAS,…) in both decay modes• The pK0 mode can be searched for by SVD-2:
good resolution for K0s and proton identification
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Anti-decuplet of q4q-bar states
DPP model modified
(DP hep-ph/0310212)(1530) < 15 MeV
M=1760-1810
M=1650-1690
M=1862 = 5 +
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Data sample
• ~35,000 events sample for D-meson searches was used
• Primary selection mainly based on the presence of well-defined secondary vertices in the close-to-target region
• Secondary tracks are measured by vertex detector
• Allowed decay length is 1…35 mm (av. 20 mm), means that only ~10% of K0
s to be reconstructed
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Events selection for pentaquark analysis
• ≤ 5 charged tracks from primary vertex to reduce combinatorial background
• K0s selection:
– 2 oppositely charged tracks from secondary vertex
– 490 ≤ Mππ ≤ 505 MeV/c2
– Mpπ ≥ 1120 MeV/c2 (→ not Λ0)
• Proton selection:– Positive track from primary vertex– Momentum of 4…21 GeV/c– Absence of a Cerenkov detector hit
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
pK0s spectrum analysis
• Cut applied: pK0s
system goes forward in center-of-mass system
• Narrow peak at 1526 MeV/c2 is observed
• FRITIOF simulated background fails to reproduce the real shape
• Peaks in higher mass region can be attribu-ted to Σ*+ bumps
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Cut applied: Pp>PK0 to eliminate bumps (cf. B.Levchenko, arXiv:hep-ph/0401122)
• Background can be described in different ways:– FRITIOF simulations– Plain polynom fitting– Random-star (not
shown)
• All three give the shape compatible to the experimental one
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Pentaquark parameters at SVD-2
• Number of events within a peak: 50 over background of 78, gives a significance of 5.6 σ
• Mass: 1526 ± 3(stat.) ± 3(syst.) MeV/c2
• Width Γ < 24 MeV/c2 (below experimental resolution)
• Strangeness could not be defined directly, but there are no reported S= -1 states in this mass region
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Cross section and A-dependence
• We estimate the total cross-section of pA→Θ+ + X as30÷120 μb/nucleon
• We fail to find the difference in A-dependence of Θ+ events from that of total for inelastic events (~A0.7)
0
0,01
0,02
0,03
0,04
C Si Pb
The ratio of Θ+ peak events to the total of K0 events for different target materials
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Theta mass with another set of cuts applied
• Peak width:
24
18 MeV/c2
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Experiments zooSpring8
ELSA
JLab-p
HERMES
ITEP
pp ++.
COSY-TOF
DIANA
SVD-2
JLab-d
ZEUSCERN/NA49H1
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Pentaquark observations
A table from E.Klempt, hep-ph/0404270
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Theta masses from different experiments
• Certain mass shift can be observed between the K+n and K0p modes
Spring-8
CLAS-d
CLAS-p
SAPHIR
ITEP
HERMES
COSY
ZEUS
SVD-2
1520 1540 1560
K0p
K+n
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
H1: charmed pentaquark?
• M = 3099 ± 3 ± 5 MeV• Minimal quark content:
uuddc• To be confirmed!
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Near-threshold D0 production
• Search for the D0 K+π- decays
• Different reconstruction methods used (not cross-checked yet…)
• 24 events over background of 12
V.Volkov 15/06/04
A.Kubarovsky, V.Popov. Recent results from SVD-2 experiment QFTHEP17 June 2004
Current status
• New analysis software is able to process “distant” V0s : – K0 - 10 times more statistics (for Θ+ analysis
and charm searches)– Λ – up to 100 times more statistics, allowing
Ξ - decays reconstruction to search for Ξ 3/2
pentaquark claimed by NA49• Better kinematical fitting for secondaries to
improve effective mass resolution