The ALICE muon spectrometer: trigger detectors and quarkonia detection in p-p collisions
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Transcript of The ALICE muon spectrometer: trigger detectors and quarkonia detection in p-p collisions
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The ALICE muon spectrometer:trigger detectors
and quarkonia detection
in p-p collisions
M. Gagliardi
Università degli Studi & INFN Torino
T. D.: Pr. E. Vercellin
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The ALICE experiment
A Large Ion Collider Experiment
muon spectrometer(2.5 < < 4)
LHC-CERN Collisions:
Pb-Pb( = 5.5 TeV )
Ar-Ar ( = 6.3 TeV )
p-p( = 14 TeV)
lighter A-A hybrid systems
(p-A, d-A…)
s
NNs
NNs
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Outline
• Quark-Gluon Plasma, Heavy Ion Collisions, Quarkonia
• Trigger detectors for the ALICE muon spectrometer:
- Resistive Plate Chambers for the ALICE muon spectrometer - Testing and characterisation of the final detectors - Results and status
• Quarkonia in p-p collisions - Motivation - Quarkonia detection in the muon spectrometer in p-p at 5.5 TeV - Extrapolation of quarkonia cross sections from 14 TeV to 5.5 TeV - Conclusions, outlook
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Phase diagram of nuclear matter and QGP
F. Karsch, QM 2006
Location and nature of phase transitions still debated
QGP
QCD asymptotic freedom at high energy and/or density, transition to a deconfined phase with partonic DF: the Quark-Gluon Plasma
B=0:Crossover hadrons-QGP at Tc 150÷200 MeV (LQCD)B 1 GeVc 5 10 0 )
Critical energy density:
1 GeV/fm3
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QGP in Heavy Ion Collisions
1 fm/c
20 fm/c
QGP
Space-time evolution of a heavy-ion collisionEnergy density at thermalisation: 3 GeV/fm3 at SPS
5 GeV/fm3 at RHIC
(estimated from ET)
Time
Final state measurements: QGP signatures “hidden” by hadronisation
QGP studied through a set of probes:- Thermal photons - Jet quenching- Elliptic flow- Strangeness- Quarkonia
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Quarkonia suppression by QGPcc: J/ , ’,c…bb: , ’, ’’…
D = Debye screening length, ~ T-1/2
Confinement: QGP:
rr
rVQQ
)(
D
r
QQe
rrV
)(
(T. Matsui – H. Satz, 1986)
When D decreases below a critical value ~ rQQ, the bound states are expected to be suppressed by colour screening: sequential suppression of resonances with increasing T > TC
Recent estimates: TJ/ 2TC , T’ TC
Interpretation of data is not straightforward:- which states are actually suppressed? - regeneration?
J/ suppression observed at SPS and RHIC in central Pb-Pb, In-In, Au-Au collisions (NA50/60, PHENIX)
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The ALICE muon spectrometer• Studying heavy quark
production via their muonic and semi-muonic decays.
• invariant mass spectrum
• Forward rapidity (2.5 < y < 4), xBj 10-5
• Large quarkonia acceptance down to p
T 0
• Measurement of quarkonia production - as a function of centrality- as a function of pT, y- for different colliding systems (including p-A)- versus global observables- together with open charm/beauty
Mass resolution: 70 MeV/c2 at 3 GeV c2 – 100 MeV/c2 at 10 GeV/c2
TRIGGER SYSTEM(Resistive Plate Chambers)
TRACKING SYSTEM (Cathode Strip Chambers)
FRONT ABSORBER(composite material)
FILTER (Fe)
BEAM SHIELDING
(W) DIPOLEMAGNETB = 0.7 T19 m
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Trigger detectors
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•Low-pT muons mainly come from light meson decays: muon pT cut is performed to reduce the trigger rate (DAQ rate: 1 kHz)
• pT is estimated via the muon deviation in magnetic field
• trajectory is reconstructed by two trigger stations: each station is made of two planes of position sensitive detectors
Muon trigger system
- Cuts: pT > 1 GeV/c (J/) pT > 2 GeV/c ()
- 3 / 4 fired planes condition (redundancy)- Efficiency of the trigger algorithm: 75 % for J/, 90% for y2-y2, ~ (Z2-Z1)(ZF/Z1)(1/ pT)
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Trigger detectors (RPC)
•Muon efficiency 95%
• Fast response ( 2 ns)
• Low sensitivity to and n
• Minimise cost/area
• Time resolution 1 ns
• Spatial resolution cm
RESISTIVE PLATES: BAKELITE
INSULATOR
GRAPHITE
READOUT STRIPS
HV
GND
2 mm
2 mm
2 mm
GAS GAPSPACERS(PVC)
Requirements for the trigger detectors satisfied by standard single-gap Resistive Plate Chambers
AVALANCHE vs STREAMER- time resolution - spatial resolution - detector lifetime - no amplification- rate capability - signal/background
Two operation modes
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• Spatial resolution = 1 cm (A-A)• Occupancy as low as possible (A-A)• Rate capability 100 Hz/cm2 (A-A)• Time resolution 1 ns (A-A)• Detector lifetime (107 s/year) (p-p)
A-A collisions: streamer mixture50.5% Ar, 41.3% i-C4H10, 7.2% C2H2F4, 1% SF6 ; RH=50%
p-p: highly saturated-avalanche 89.7% C2H2F4, 10% i-C4H10, 0.3% SF6 ; RH=50%
SameADULT front-end electronics(Clermont-Ferrand)
R. Arnaldi et al., Nucl. Instr. and Meth. 451 (2000) 462, * NIM 457 (2001) 117, NIM 490 (2002) 51, NIM 508 (2003) 106, NIM 533 (2004) 112
* * R. Arnaldi, MG et al., Nucl. Phys. B (Proc. Suppl.) 158 (2006) 149
Streamer mode
Low (few 109 cm)
R&D on the ALICE RPCs
Dual threshold discrimination (ADULT)
Requirements in terms of both performance and lifetime fulfilled for A-A * and p-p **
Collision-specific requirements:
Avalanche mode
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- 3 different shapes: L (Long), C (Cut), S (Short)
- 5 different types of segmentation - Strip width: 1 cm, 2cm, 4cm
L1
L2
L3
C
S
The trigger stations MT1 and MT2
L1
L2
L3
C~ 5.5 m~
6.5
m
• 16 and 17 m from the IP
• Each station features two RPC planes
• Each plane is made of 18 RPCs read on both sides with orthogonal strips. Total: 72 RPCs.
• Area covered by each plane: about 6x6 m2
• RPC area : 70x280 cm2
Bending plane C,S: lower resistivity and finer segmentation
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Goal: characterise all detectors produced ( 120) and select the 72 final detectors (+ spares) according to well-defined criteria
• Preliminary tests:
- Gas leakage detection
- Electrodes resistivity (argon method)
- V-I curve: detection of possible leakage currents
• Efficiency measurements:
- Local measurement of efficiency as a function of HV
- Fit, estraction of parameters from curves: HV50%, slope
- High granularity measurement of efficiency at working HV
• Noise and current measurements:
- Mean hit rate and noise map (autotrigger method)
- Constant monitoring of dark current at working HV
Testing the final detectors
Streamer mixture
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Efficiency measured with cosmic rays (). The test station is composed of 3 scintillator planes for triggering and 2 RPCs for tracking, with an active area of 90×150 cm2 (enough to test one half-chamber).
Efficiency measurements: the test station in Torino
Tracking RPCs
Scintillator Planes
Test slots (4 different positions)
MUON TRACK
EXPECTED IMPACT POINT
Tracking RPC 1
Tracking RPC 2
RPCsunder test
Local measurement of efficiency
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About the local measurement of efficiency- Resolution: ~ 1 cm (FWHM)
RMS 4 mm
Systematic error evaluated with a dedicated analysis on a few runs (cross-checks with more detectors)
- Aim of the efficiency test: verify uniformity, not absolute efficiency- Actual RPC efficiency shall be measured online during data-taking in ALICE
TESTED RPC’S
TRK 1
TRK 2RECONSTRUCTED TRACK
- Systematic error due to fake tracks: 3÷5 %
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Slope: 0.16/100V
50% eff. HV: 7467 V
Slope: 0.14/100V
50% eff. HV: 7564 V
Efficiency measured as a function of HV in cells of 20x20 cm2
Efficiency curves
Parameters unaffected by the systematic error:- HV at 50% efficiency- Slope of the curve
All voltages corrected for T and p p
bar
K
TVVeff
1
2930
Goal: evaluate the uniformity of the detector through the spread of the parameters of the curve in different cells fit
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Cells 2x2 cm2
PVC spacers( 1 cm)
Efficiency maps at working HV
•Area divided in smaller cells (~ 2 x 2 cm2): -about 500 events in central cells ( statistical error < 1%)- about 100 events in peripheral cells ( s. e. < 3%)-about 50 events in side cells (s.e. ~ 3÷4%)
All efficiency maps examined to detect imperfections, defined as: raw efficiency < 90% at working HV (8100 and 8200 V)
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• Trigger: events with at least one hit on both planes of the RPC.
• Count the number of hits at every strip crossing
• Divide by elapsed time and crossing area to obtain single counting rate (Hz/cm2)
• Correct for DAQ dead time• Repeat the measurement over a
wide range of HV’s• Measure the mean rate• Count the number of hot spots
(rate > 5,10,20 Hz/cm2)
Noise measurements: autotrigger
Strip x
Strip y
Hz/cm2
Strip xStrip y
HV: 8200V
(A few) problematic detectors may present hotspots with rates up to several tens of Hz/cm2
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Test results
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Efficiency curves: results
Distribution of the voltage range in which all cells reach 50% efficiencyMean voltage range: (300 ± 70) V
Cells
HV at 50% efficiency (V)
Evaluation of the uniformity
For each detector, plot HV50 distribution over all cells. Find the spread of HV50
200 V
RMS/MEAN < 1%
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Efficiency maps: results
Cells 2x2 cm2
We want this…… not this!
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Efficiency maps: results (II)
57% of all produced detectors: uniform, high efficiency throughout the whole surface
17% of all produced detectors: small regions (max 6x6 cm2) with raw efficiency slightly below 90%
12% of all produced detectors: many small regions slightly below 90% , or larger zones below 90%
6% of all produced detectors: very large regions below 90%; regions well below 90%
The population of tested detectors can be divided in four classes:
8%: discarded during preliminary tests, efficiency not measured
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Noise and current measurements: results
Both distributions: peak + tail (problematic detectors lie in the tail)
Mean rate: peak around 0.1 Hz/cm2
Peak around 0.10÷0.15 nA/cm2 ( 2A)
Both rate and current: no correlation with resistivity was observed
Mean # of hot spots: 5÷10 Hz/cm2: 6 10÷20 Hz/cm2: 3 > 20 Hz/cm2 :2
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Selection criteria and final results Detectors evaluated on the basis of efficiency maps (inspected one by one) uniformity (RMS of HV50), noise (mean rate and number of hot spots), current
Common to all detectors rated 2:only very small (if any) imperfections in the efficiency map
(> 20 Hz/cm2)
Rated 0: construction flawsRated 1: insufficient performances Rated 2: sufficient performances Rated 3: good performancesRated 4: excellent performances
Five quality classes (0 to 4)
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Conclusions and status-All RPCs characterised, data stored in a database
- Of all produced detectors: 17% : discarded for construction flaws (8%) or insufficient performances (9%) 26%: sufficient, selected for use in peripheral regions or as spares 57%: good (33%) or excellent (24%) performances- 72 final detectors selected and installed in ALICE- Commissioning start date: December 2007- A few spares ( 15) missing- More RPCs to be produced and tested
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Quarkonia detection in p-p collisions
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MotivationOne of the main observables for quarkonia suppression studies: the nuclear modification factor RAA
X = J/, c = a centrality-related quantity
)(
)()(
cN
cNcR
coll
AAX
ppX
ppinelAA
X
Pb-Pb: = 5.5 TeVNNsp-p: = 14 TeVs
At the LHC:
Task: evaluate (pp -> X) at
= 5.5 TeVppsRAA meaningful if: ppNN ss EXTRAPOLATION
MEASUREMENT
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Strategy # 1:direct measurement
in a dedicated p-p run at 5.5 TeV
• Input parametrisations
• Reconstruction
• Expected yields and efficiencies
• Measurement of differential cross sections
Evaluation of the physics performance of the ALICE muon spectrometer in a p-p run at 5.5 TeV by means of simulation
Not in the present LHC schedule, may be available in a subsequent phase
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Simulation approach and input
- Reconstruction with fast simulation
- Quarkonia generation according to Color Evaporation Model (CEM) predictions:
• Total cross section (NLO, MRST PDF)
• pT distribution: rescaling of CDF results ( = 1.96 TeV) according to CEM prescription
• Rapidity distribution: NLO CEM, MRST
- Quarkonia decay in +- (PYTHIA)
s
Same frame as for the 14 TeV case*:
* ALICE Collaboration, J. Phys. G: Nucl. Part. Phys. 32 (2006)
AssumeL = 3 x 1030 s-1cm-2,
106 s data taking
bBR promptJ 8.1* /
nbBR 12*
(R. Vogt)
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Input quarkonia pT distribution: rescaling from CDF
CEM gives predictions* for the evolution of with*Accardi et al.,hep-ph/0308248
s2tp
Rescaling to 5.5 TeV: n kept constant K2 increased to match CEM value
2
22
n
Kpt
Fit of pt distribution as measured by CDF ( = 1.96 TeV)
nK
pp
dp
dNt
t
t ])(1[ 2
s
New value fed back in dN/dpT to obtain rescaled distribution
Y
TeVt
Y
TeVt pp96.1
2
5.5
2 *33.1 /
96.1
2/
5.5
2 *26.1J
TeVt
J
TeVt pp CEM:
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Input pT distributions
J/
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J/
Input rapidity distributions(R. Vogt, NLO CEM)
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2.5 < y < 4
pT
yJ/
Quarkonia detection probability in pT and y bins
J/
Non-vanishing efficiency at pT = 0
2.5 < y < 4
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Reconstructed y distributions at 5.5 TeV
J/
J/: fine bins, statistical error < 2% : larger bins, statistical error < 8%
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Reconstructed pT distributions at 5.5 TeV
J/
J/: fine bins up to 15 GeV/c, statistical error < 8% : fine bins up to 10 GeV/c, statistical error < 10%
2.5 < y < 42.5 < y < 4
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Efficiencies & yields at 5.5 TeV - Conclusions
Quarkonia yields in the muon spectrometer in 106 s at 3 x 1030 s-1cm-2:
152400 ± 400 prompt J/ 1300 ± 40
Total muon spectrometer acceptance x efficiency: (over all phase space)- for J/: 2.8%- for : 3.6%
Similar values were found at = 14 TeVs
CAVEAT: signal analysis only, prompt J/ onlyMore refined study: background, J/ from B-decay
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Strategy # 2Extrapolation of quarkonia
cross sections from 14 TeV to 5.5 TeV
• Rescaling factors (total and in pT bins) evaluated
in the frame of NLO CEM
• LO investigation of the effect of PDFs and F on the uncertainty
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If p-p measurement is only performed at 14 TeV, need to compute a scaling factor (models). Muon spectrometer acceptance: 2.5 < y < 4.
4
5.2
5.5
)5.5( dydy
dTeV
TeVXppMS
X
Definitions
)14(
)5.5(
TeV
TeVS
MSX
MSX
X
J/
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Scaling factors
63.0)14(
)5.5(
/
//
TeV
TeVS
MSJ
MSJ
J
43.0
)14(
)5.5(
TeV
TeVS
MS
MS
2,
1,
2,
1,
14
5.5
14
5.5]2,1[ T
T
T
T
p
p
TT
p
p
TT
MS
MS
dpdpdN
dpdp
dN
S
Scaling factor in the pT bin [pT,1, pT,2]:
dN/dpT
normalised to unity
pT bin (GeV/c) SJ/ S[0,2] 0.81 0.55
[2,4] 0.64 0.51
[4,6] 0.47 0.45
[6,8] 0.38 0.39
[8,20] 0.32 0.33
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Leading Order Color Evaporation Model
Cross section for quarkonia production: some fraction Fc of the QQ cross section below the open c/b threshold.Fc independent of kinematics, process, .s
LO formulae used to investigate theoretical uncertainty by varying F and by using different PDF sets (dominant diagram gg->QQ only)
ji
Fy
BjFy
Aiij
m
m
COL
CEM es
sfe
s
sfssd
s
F
dy
d H
Q,
2,
2,
4
4
..
),ˆ
(),ˆ
()ˆ(ˆˆ2
2 yOL e
s
sx
ˆ..2/1
ji
ijBjAi
m
mCCEMC sxxssxfxfdxdxsdF
H
Q,21
22,
21,21
4
4)ˆ()ˆ(ˆ),(),(ˆ
2
2
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F = 2.4 GeV 2mc F = 9 GeV 2mb
Gluon distribution functions
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J/ rapidity distributions
(NLO)(NLO)
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rapidity distributions
(NLO) (NLO)
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Results with different PDFs
No PDF dependence of the pT distribution taken into account (same relative spread for all pT bins )
(NLO) (NLO)
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Relative spreads
• LO relative spreads: 4% for J/, 8% for
• Spreads compatible with luminosity uncertainty (5÷10%)
•15% discrepancy between LO and NLO scaling factors
•Uncertainty arising from F negligible w. r. t. PDF
• J/ y-distribution at 14 TeV can constrain PDF* * ALICE-INT-2006-029
PDF SJ/ SCTEQ5L 0.52 0.33
CTEQ6L 0.56 0.35
MRST98L 0.54 0.36
MRST01L 0.56 0.39
(Max – Min) /2 Ave 4% 8%
J/
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Conclusions and outlook
•Both measurement and extrapolation investigated
-Measurement feasible
- Statistics: 152000 J/ (stat err. on total < 1%) 1300 (stat err. on total ~ 3%)
- Differential cross sections may be measured with statistical errors < 10%- Systematics not considered yet
- Outlook: p-p like systems
-First estimate of the scaling factors
- LO uncertainty from PDF: < 10%
- NLO to be fully investigated
- Outlook: vary production model
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Backup slides
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R & D on ageing effects
the R&D program to understand the RPCs ageing
problems was focused on two aspects:
•effects due to flowing the RPCs with dry gas
increase of bakelite resistivity
•effects due to long-term operation of the detector in condition of high counting rates increase of bakelite resistivity, due to the conduction mechanism surface damaging, due to streamer discharge
RPCs for the ALICE Muon Trigger System
• 2 linseed oil layers
• low resistivity (109
cm)• wet gas mixture
ageing proportional to integrated current per surface unit (mC/cm2), i.e. to the integrated hits per surface unit (Mhit/cm2)
possible effects: -increase of dark current and single rate-efficiency loss
Ageing tests already performed for the streamer mode:
The detector lifetime was found to be compatible with the ALICE heavy ions data-taking program* * R.Arnaldi et al., Nucl. Instr. and Meth.A 533 (2004) 112
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Saturated Avalanche mixture
Irradiation at GIF (CERN), to simulate ALICE working conditions
Test in Torino with cosmic rays,to check efficiency map:
First results presented @ RPC2005, proceedings on Nucl. Phys. B 158 (2006)
PRELIMINARY
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Ageing in p-p collisions
Higher beam intensity beam-gas interaction! ageing effects more important in p-p:
Study of a highly-saturated avalanche gas mixture (89.7% C2H2F4, 10% i-C4H10, 0.3% SF6 ; RH=50%)
Signal amplitude > 10 mV (min. threshold of Front End Electronics)Mixture performances tested with -beam (SPS), with and without irradiation (GIF): efficiency, space and time resolution fulfill the requirements
Detector occupancy and trigger rate much smaller in p-p w.r.t. A-A: space resolution requirements less strict in p-p
Integrated hits: • ~20 Mhit/cm2 per year • ~100 Mhit/cm2 per year in the hot spot
• mean rate: <2 Hz/cm2
• hot spot (beam-gas interaction*) : 10 Hz/cm2 g 1-2
RPCs
R. Guernane et al., ALICE-INT-2003-041
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Ageing test with Higly Saturated Avalanche mixture
Irradiation at GIF (CERN), to simulate ALICE working conditions
Test in Torino with cosmic rays,to check efficiency map:IN PROGRESS
First results presented @ RPC2005, proceedings on Nucl. Phys. B 158 (2006)
PRELIMINARY
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xexp-xmeas
MUON TRACK
EXPECTED IMPACT POINT
TRK 1
TRK 2
Local efficiency measurement•Trigger: exactly one cluster per plane (85% of events) on both TRacKing chambers (no ambiguity in track choice).
Require cluster size < 3 as well, to improve resolution and cut out showers. Compute impact points on TRK’s.
•Track the cosmic ray and project the trajectory on testing plane. Find expected impact coordinates on tested RPC’s.•Look for corresponding hit on tested RPC and compute position. If there is more than one cluster, choose the nearest
•RPC is efficient only if , on both planes:|Xexp – Xmeas| < tolerance
•Plot xexp – xmeas to check tracking accuracy and resolution
•Divide the tested area in cells
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Cells (2x2 cm2)
Efficiency disuniformities
at ~ 90% eff. HV…
HV = 8000VEfficiency maps
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Cells
…can be recovered100 ÷ 200 V above.
HV = 8200V
Resolution ~ 1 cm, efficiency = (13)%
Spacers ( 1 cm)
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Correlation: resistivity vs noise and I
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Heavy ion collisions: ageing tests with streamer mixture
Irradiation at GIF (CERN), to simulate ALICE working conditions
Test in Torino with cosmic rays,to check efficiency map
Detector lifetime is compatible with ALICE data-taking scenario!
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0
0.2
0.4
0.6
0.8
1
1.2
10000 10500 11000 11500 12000
HV (V)
efficiency
streamer contamination
600 V
efficiency and streamer contamination correlation:V=600 V between the knee and the threshold HV for streamer contamination > 20%
Highly Saturated Avalanche operation
source-off
Irradiation
rate 80
Hz/cm2
Test with cosmic rays Beam test (SPS -beam + GIF)
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Cross section for quarkonia production
CEM predictions for p-p at = 5.5 TeV (PPR vol. II):
s
barnBR promptJ 8.1* /
5.5 x 106 from prompt J/36000 from over all rapidities
nbarnBR 12*
If L = 3 x 1030 s-1cm-2, in 106 s data taking:
(R. Vogt)
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• Quarkonia generation
• Muon decay kinematics generated with Pythia
• Detection probability evaluated for each particle:
• Reconstructed (pt,•AliFastMuonTrackingRes
•AliFastMuonTriggerEff
•AliFastMuonTrackingAcc
•AliFastMuonTrackingEff
• Reconstructed pt bins filled with weight given by trigger and tracking acceptances and efficiencies
Signal analysis
J/, y > 0
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Cross section vs scale