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

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

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

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

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

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)

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

Trigger detectors

•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)

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

• 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

- 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

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

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

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 %

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

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)

• 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

Test results

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%

Efficiency maps: results

Cells 2x2 cm2

We want this…… not this!

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

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

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)

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

Quarkonia detection in p-p collisions

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

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

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)

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:

Input pT distributions

J/

J/

Input rapidity distributions(R. Vogt, NLO CEM)

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

Reconstructed y distributions at 5.5 TeV

J/

J/: fine bins, statistical error < 2% : larger bins, statistical error < 8%

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

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

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

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/

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

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

F = 2.4 GeV 2mc F = 9 GeV 2mb

Gluon distribution functions

J/ rapidity distributions

(NLO)(NLO)

rapidity distributions

(NLO) (NLO)

Results with different PDFs

No PDF dependence of the pT distribution taken into account (same relative spread for all pT bins )

(NLO) (NLO)

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/

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

Backup slides

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

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

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

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

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

Cells (2x2 cm2)

Efficiency disuniformities

at ~ 90% eff. HV…

HV = 8000VEfficiency maps

Cells

…can be recovered100 ÷ 200 V above.

HV = 8200V

Resolution ~ 1 cm, efficiency = (13)%

Spacers ( 1 cm)

Correlation: resistivity vs noise and I

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!

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)

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)

• 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

Cross section vs scale