1. Participation in the HADES experiment
P.Fonte
for the HADES RPC group
Jornadas LIP 2014
Sixth framework programme

2. HADES RPC Group Current responsibilities Maintenance & Operation
USC
D. Belver
P. Cabanelas
E. Castro J.A. Garzón
M. Zapata
GSI
W. Koenig
TU Darmstadt
G.Kornakov
LIP
A. Blanco
N. Carolino
O. Cunha
P. Fonte
L. Lopes
A. Pereira
P.Bordalo
C. Franco
S. Ramos
L. Silva
A.Oliveira
C.Silva
Maintenance
&
Operation
Calibration
IFIC-Valencia
J. Diaz
Participation in
the physics
analysis

4. Spectrometer concept § Geometry Fast particle identification
Full azimuth, polar angles 18 o - 85
Pair acceptance
0.35
About detector channels
Fast particle identification
RICH
CsI
solid photo cathode, N ~ 80
, C 4 F 10
radiator
TOF (
scintillator
rods)
RPC-TOF
Pre
Shower
18 pad chambers & lead converters
Momentum measurement
ILSE ,
super conducting
toroid B r
= 0.36 Tm
MDC
multi
wire drift chamber,
single
cell resolution
100 m

5. Hexagonal geometry with 6 identical “sectors”
RICH
MDC I
MDC II
MDC III
MDC IV
Magnet
TOF
RPC
Shower
Hexagonal geometry with 6 identical “sectors”

6. Strong dilepton enhancement over hadronic cocktails

7. Unevenly distributed radially by a factor ~2
Heavy nuclei colisions
Lots of particles (up to 30/sector)
Unevenly distributed radially by a factor ~2
over the inner TOF area
C+C
Au+Au

8. RPC design criteria
Operational parameter matched to the HADES overall performance
Multi-hit capability hit-loss probability below 20%
Minimum 150 channels/sector  effective cluster size
resolution 100 ps () or better
In principle not difficult for a good detector
Potential problems: mechanics, crosstalk (hard to measure).
rate capability up to 1 kHz/cm2 in some areas
Not so easy for almost continuous beam
efficiency above 95% for single hits
In principle no problem, except for geometric coverage
Area ~8/6 m2/sector
Fast! no long R&D time available

9. Final design 2 layers of individual cells with partial overlap rows
187 cells/sector distributed in 29 rows and 6 columns, 3 on top and 3 on bottom
1122 cells total
124 different detectors with variable width, length and shape  no attempt at impedance matching

10. HADES cells Heat-tolerant materials Fully shielded
0.27 mm  4 gaps
minimum for good efficiency
Aluminum and glass 2mm electrods
minimize amount of glass for maximum rate capability
try to keep good mechanics
Heat-tolerant materials
Fully shielded
Spring-loaded pressure plate
Aluminium
Glass
HV & readout in
the center

11. Assembly in gas box HV capacitor (~1cm2) HV distribution PCB
50 signal
Feedthrough
PCB
Further
shielding
between
feedthrougs

12. Readout scheme t1 t2
FEE

13. FEE electronics t1 t2
4 channel 3GHz amp+timing comparator + QtoWidth conversion
Support motherboard (mechanics, services, signal routing)

14. TDC and DAQ (by GSI electronics group) TRB (Time Readout Board)
128 multihit TDC channels (CERN’s HPTDC)

15. Partially instrumented
Time frame
Concept validation, 2003
First prototype test, 2005
Partially instrumented
Final prototype test, 2007
Fully instrumented

16. Time frame
Final tests, 2009
Ready for beam, 2011

17. Data recorded, compared with previous beamtimes
Very successful DAQ upgrade

22. Sub-threshold produced K- clearly visible: robust multihit performance

24. Mind the internal spacers of the RPCs!

26. Motivation
The main goal of the LIP-HADES group is to study the mass properties of hadrons inside a very dense hadronic medium at low temperature
This region of the phase-space, which is still poorly known, is explored in Hades through Au+Au collisions at 1.25 GeV/nucleon

27. Motivation
Leptons are the ideal probe of the in-medium properties of hadrons: they are not disturbed by secondary interactions due to their lack of strong interaction
The final goal is to compare the experimental e+e- (coming from the in-medium hadronic decays) mass spectrum with the predictions of models describing the heavy ion collisions
The in-medium properties of the above mentioned mass spectrum are crucial for a better understanding of the mechanism responsible for the mass generation in hadrons

28. Flowchart of the method developed at LIP for the PID of leptons
variables
PID variables
Signal
Sample
(lepton tracks)
multivariate input
Background
Sample
(hadron tracks)
Multidimensional parame-
trisation: all correlations are
properly taken into account
Dynamic
Neural
Network
single network output (per track)
Network
Cut
Accepted Tracks
Rejected
Tracks

29. Velocity distribution as a function of the momentum times polarity (before and after a multidimensional cut in the Neural Network response)
All tracks Rejected tracks Accepted tracks
The selection of relativistic electrons and positrons is evident
The efficiency and purity of the lepton sample are both above 92%
The selection of leptons with a low velocity or a high momentum is made possible by
the use of a Neural Network

30. The invariant mass spectrum for dileptons
Combinatorial background is subtracted
e+e-
Preliminary
The physical background,   e+e-, was removed with the help of a Neural Network

31. Conclusion
The HADES spectrometer was upgraded and had a very successful data taking with the Au-Au system.
The new RPC TOF Wall performed flawlessly, in specs, and showing a robust multihit performance.
There will be another production beamtime this year, either with  beam or with the Ag-Ag system.
HADES will be part of the set of experiments of FAIR (the first one to run, actually).