Jerzy Pietraszko

Transkrypt

Jerzy Pietraszko

Dielectron production in C+C
collisions with HADES
Jerzy Pietraszko, GSI Darmstadt
for the Hades Collaboration
12/1/2006
Jerzy Pietraszko, MESON 2006,
Krakow, Poland, 9 - 13 June 2006
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Introduction
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Physics motivation.
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Hades Spectrometer.
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In-medium modifications (predictions)
Vector mesons @ SIS energy regime
Detector concept
Experimental results.
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C+C 2.0 AGeV (2002)
P+P @ 2.2 GeV (2004)
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C+C 1.0 AGeV (2004) PRELIMINARY
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12/1/2006
See talk: S. Spataro June 10-th Session A 17:50
See talk: T. Christ June 12-th Session A 15:00
C+C @ 2.0 AGeV and C+C @ 1.0 AGeV comparison
Summary and Outlook.
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Physics Motivation
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Chiral symmetry broken in vacuum.
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Quark condensate – order parameter
Partial restoration of chiral symmetry
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At high temperatures (RHIC, LHC)
At large baryon density (SIS, AGS)
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Properties of hot and dense matter.
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Model predictions (one example) for VM
¾ „Melting” of the rho meson
¾ Mass shift and broadening of the ω
¾ Small effects on the φ-meson
12/1/2006
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Physics Motivation
DLS Ca+Ca 1AGeV
full spectral function[*]
DLS C+C 1AGeV
full spectral function[*]
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CERN data (Ceres/NA45) explaind
by medium effects
12/1/2006
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[*]R.Rappat al.., Nucl. Phys.. A617 (1997) 472
DLS puzzle
Models failed to explain DLS data for
0.15 ≤ M ≤ 0.4 GeV
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Probes for hot/dense medium
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cτ ≈10-15 fm/c
Ideal probes for medium effects:
Short life time
Decay inside hadronic medium
Decay channel into lepton pairs
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e+
No strong final interaction
Reconstruction of in-medium properties possible
e-
me + e −
ϑe + e −
= pe + pe − sin
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Meson
Mass (MeV/c2)
Γ (MeV/c2)
cτ (fm)
Main decay
e+e- BR
ρ
768
152
1.3
π+ π−
4.4 x 10-5
ω
782
8.43
23.4
7.2 x 10-5
φ
1019
4.43
44.4
π+ π− π0
K+ K-
12/1/2006
3.1 x 10-4
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Meson production at SIS energy regime
(1-2 AGeV)
NN → N∆
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πN
VM production (1-2 AGeV):
at or below threshold
⇒ multi step processes
⇒ production confined to the
high density phase
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πN → ρ N
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Meson multiplicity:
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π0, η known from TAPS
F.D.Berg.
F.D.Berg. At al., PRL 72,977 (1994)
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ρ, ω, ϕ - mt scaling
M.Bourquin,
M.Bourquin, Nucl.
Nucl. Phys. B114, 334 (1976)
12/1/2006
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Experimental challenges
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Small production rates:
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Large background:
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1 dilepton rho decay / 107 central collisions
Hadronic (particle misidentification)
Electromagnetic ( conversion, mainly from π0 )
Combinatorial (false combination of e+e–)
Detector requirements:
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Excellent particle id
Perfect lepton identification (hadron-blind
detector)
Low mass/low Z- design for reduced background
Highly selective trigger
High performance data acquisition.
12/1/2006
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HADES
A High-Acceptance Di-Electron Spectrometer
(expanded view)
Start-Veto detector
¾ Diamond, 8 strips, widths 1.55 – 5.4mm
¾ Time res.: 29.2 ps (Chromium beam)
Meta detector,TOF
θ <detector
45 deg.
¾ of:
Meta
at θ > 45
deg.
¾Consists
Tofino,
Pre-Shower
¾ Time res. 190 ps (electrons)
¾Time res:
350 ps.
¾ Position res. 27 mm.
¾Spatial res: 1.5 cm (low res. tracking)
¾Limitation: multihit capability (-> RPC)
12/1/2006
Rich detector
¾ Radiator gas:
¾C4F10, γthr = 18 (hadron blind)
¾ photon detector: CsI photo cathode
Low mass tracking system
¾ single cell resolution: 100 µm
¾ 4 planes / sector (high res. mode)
¾2 planes + META
(low res. mode, 10% at 0.7 GeV/c)
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Spectrometer concept
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Geometry: Six sectors form a hexagonal structure:
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Cross section
Acceptance: 2π in φ ; 18 0 < θ < 85 0
Pair acceptance ≈ 35 %
¾ Tracking: Magnet, MDC
¾ Superconducting toroid magnet (6 coils)
Bmax = 0.7 T, Bending power 0.34 Tm
¾ low-mass MDC (multiwire drift chamber)
¾ PID and Lepton Identification
¾ RICH
¾ hadron blind
¾ photon detector: CsI photo cathode
¾ META (TOF, TOFino, Pre-Shower)
¾ Start detector
¾ diamond. (time res. 30 ps)
START
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Selective multi-level trigger system
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12/1/2006
Pair enhancement factor close to 10
No bias on data
LVL2 efficiency (pairs) 82 %
Suppression 10 - 100
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C+C @ 2.0 AGeV
Low res
High
res. .mode
mode
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Experimental Setup:
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Full HADES set-up with low
res. tracking.
Low resolution tracking:
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Target: 2 x 2.5 %
Data and trigger:
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12/1/2006
Inner Mdc,
Meta detector (spatial. res.
1.5 cm)
mom. res. 10% @ 0.7 GeV/c
220 Mevents
56 % LVL1 trigger, 44 %
LVL2 trigger
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Pion spectra (C+C, 2 AGeV)
2 parameter fit
Multiplicity
"Temperature"
HADES
N< π -π+>/Apart = 0.148 ± 0.018
Tπ+
Tπ-
TAPS
N< π 0>/Apart = 0.138 ± 0.014
KaoS
N< π ->/Apart = 0.126 ± 0.010
12/1/2006
=
=
41 ± 3; 87 ± 3
51 ± 3; 91 ± 4
Tπ- = 40 ± 3; 86 ± 3
1 dσ
− mT / T1
− mT / T2
=
C
⋅
e
+
C
⋅
e
1
2
mT2 dmT
good agreement with
TAPS/KaoS results!
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Raw e+e– mass spectrum (C+C, 2 AGeV)
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S/CB
Raw exp. Spectrum
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Comb. Background (CB)
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all e+e¯
comb. background
signal
No eff. correction
No acc. correction
Like-sign pairs
Formula: 2• Ne+e+Ne−e−
Signal:
Formula: S+-= Ne+ee+e- - CB+Counts:
S+- < 140 MeV/c2: 20 971 counts
S+- > 140 MeV/c2: 1 937 counts
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* Measured rates span over 5
orders of magnitude
* Good Signal/CB ratio
12/1/2006
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e+e– mass spectrum (C+C, 2 AGeV)
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Efficiency corrected spectra
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in HADES acceptance
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Detector efficiency
Reconstruction efficiency
normalized to the pion yield
Nπ0 = ½ (N π- + N π+)
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low resolution tracking
(10% at 0.7 GeV/c)
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systematical errors
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Norm. to the pion mult.(11 %)
Eff. corrections (20 %)
CB construction (20 %)
Simulated cocktail (PLUTO)
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Based on known (TAPS) or mtscaled meson multiplicities and
their vacuum decay properties.
* Only π0 , η not sufficient.
12/1/2006
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pp collisions @ 2.2 GeV (2004)
See talk: S. Spataro June 10-th Session A 17:50
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Experimental goal:
Verify dielectron efficiency:
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dielectron and hadron channels of π0, η
Conditions:
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Beam intensity: 107 p/second
Target: LH2 (5 cm length)
⇒ Dielectron efficiency well under control
total
signal
background
pp→ppη→ ppπ+π-π°
Mη 548 MeV/c2
total
η
π°
bg
M 549 MeV/c2
σ/M 2.5 % (3.6)
η yield
24845 ± 348
12/1/2006
pp→ppη→ ppe+e-γ
Mπ° 135 MeV/c2
M 140 MeV/c2
Mη 548 MeV/c2
σ/M 18 %
π° yield
7580 ± 454
η yield
2322 ± 118
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C+C @ 1.0 AGeV (2004)
See talk: T. Christ June 12-th Session A 15:00
¾Raw exp. Spectrum
¾No eff. Correction
¾No acc. correction
¾Comb. Background (CB)
¾Like-sign pairs
¾Formula: 2• Ne+e+Ne−e−
¾Signal: Formula: S+–= Ne+e–
e+e - CB+ –
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Experimental Setup:
¾ Full HADES set-up
¾ high res. Tracking.
¾ Target: 3 x 1.5 % target.
* Only π0 , η not sufficient.
C+C @ 1.0 AGeV
C+C @ 1.0 AGeV
in HADES acceptance
no eff. correction
prel
imin
ary
12/1/2006
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C+C @ 2.0 and @ 1.0 AGeV - comparison
x 2.5
PLUTO
C+C @ 2.0 AGeV
in HADES acceptance
C+C @ 2.0 AGeV
in HADES acceptance
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x 5.0
C+C @ 1.0 AGeV
in HADES acceptance
no eff. correction
prel
imin
ary
12/1/2006
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HADES data compared with Pluto model.
¾ C+C @ 2.0 AGeV
¾ C+C @ 1.0 AGeV
Substantial yield above the η contribution
factor 2.5
¾ 2.0 AGeV
¾ 1.0 AGeV
factor 5 ( preliminary ! )
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Comparison with transport: HSD*
Mass Spectrum (C+C, 2 AGeV).
*HSD – Hadron-String-Dynamics (Gießen, E. Bratkovskaya, W. Cassing)
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efficiency-corrected data compared with model.
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folded with HADES filter:
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geometrical acceptance
momentum resolution (low resolution mode, 10% at 0.7 GeV/c)
HSD vacuum
12/1/2006
HSD in-medium
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Comparison with transport:
HSD, Pluto, UrQMD.
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Model vacuum calculations:
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UrQMD Frankfurt (M. Bleicher, D. Schumacher)
Pluto Hades
HSD Giessen (E. Bratkovskaya, W. Cassing)
π0, η sources in agreement (20 %),
Only π0, η sources not sufficient to explain the data,
Discrepancy for full cocktail.
12C
+ 12C 2 AGeV
only π0, η sources
vacuum calculations
12/1/2006
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Summary
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C+C, 2 AGeV
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Final spectrum available.
Comparison with transport models ongoing.
C+C, 1 AGeV
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Preliminary spectrum,
⇒ Substantial yield above the η contribution
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P+P, 2.2 GeV
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Dielectron efficiency under control.
Outlook
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Collected data, ongoing data analysis:
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Upgrade of Tofino subsystem with RPC (2007)
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12/1/2006
C+C 1.0 AGeV, Ar+KCl 1.757 AGeV, P+P 1.25 GeV
Ni+Ni, Au+Au runs feasible
Hades at FAIR: 2-8 AGeV runs.
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The collaboration
SIS
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12/1/2006
Bratislava (SAS, PI), Slovakia
Catania (INFN - LNS), Italy
Cracow (Univ.), Poland
Darmstadt (GSI), Germany
Dresden (FZR), Germany
Dubna (JINR), Russia
Frankfurt (Univ.), Germany
Giessen (Univ.), Germany
Milano (INFN, Univ.), Italy
Munich (TUM), Germany
Moscow (ITEP,MEPhI,RAS),
Russia
Nicosia (Univ.), Cyprus
Orsay (IPN), France
Rez (CAS, NPI), Czech Rep.
Sant. de Compostela (Univ.),
Spain
Valencia (Univ.), Spain
Coimbra (Univ.), Portugal
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12/1/2006
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Hades@GSI and DLS@LBL
π0→e+e–γ
Hades
DLS
mid-rapidity
Pluto vs Hades data
preliminary
η→e+e–γ
Hades
DLS
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design
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π0, η acceptance
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C+C @ 1AGeV
mid-rapidity
Pluto vs DLS data
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12/1/2006
Comparison with Pluto
cocktail
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Selective multi-level trigger system
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Fast First Level Trigger:
(50 ns, up to 20 kHz)
¾ Meta multiplicity
¾ Start detector (time signal)
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Second Level Trigger
Second Level Trigger:
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Online hit finders (Rich, Tof, Shower)
Online hit matching (MU)
Trigger decision (within 20 µs)
~3 Gbyte/s raw data
Events transported to the mass storage
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Performance:
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12/1/2006
Pair enhancement factor close to 10
No bias on data
LVL2 efficiency (pairs) 82 %
Suppression 10 - 100
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Comparison with models: Pluto
Transverse momentum (C+C, 2 AGeV)
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efficiency-corrected data compared with Pluto model.
PLUTO
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Mee < 150 MeV/c2
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150 < Mee < 550 MeV/c2
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Data well described,
Underestimation over whole p⊥
range (factor 2.5).
Mee > 550 MeV/c2
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Underestimation for high p⊥
* Factor 2,5 missing in the
η region
12/1/2006
24

Jerzy Pietraszko

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