1. Quarkonium in the ALICE Muon Spectrometer
E. Scomparin (INFN Torino, Italy)
for the ALICE Collaboration
EMMI Workshop
"Quarkonium and deconfined
matter in the LHC era" 
Martina Franca (Italy)
June

2. Introduction ALICE (A Large Ion Collider Experiment):
the dedicated heavy-ion experiment at the LHC
Main focus on Pb-Pb collisions  QGP studies
at the nominal LHC luminosity, 51026 cm-2s-1
p-p collisions are a crucial aspect of the physics program
Reference for heavy-ion collision studies
Genuine p-p physics
Maximum luminosity limited to a few 1030 cm-2s-1
due to pile-up in TPC
Faster detectors may stand a higher luminosity
Running conditions appropriate for quarkonium studies
(both charmonium and bottomonium)

3. Quarkonia in the muon channel
Quarkonia measurement via muon pair decays
Well-known (and tested) detection technique
Hadron absorber(s) to filter out muons
Muon tracking in a magnetic spectrometer
Triggering on muon (pairs) to enrich the signal
Advantages
Fast detectors can be used  work at high luminosity
Soft background can be rejected at trigger level
Drawbacks
Careful design needed to have a satisfactory mass resolution
 Possibility of separating  states
Concept of a muon arm for ALICE present
(almost) from the beginning (TP)

5. ALICE muon arm - tracking
5 stations of two Cathode Pad Chambers ~ 100 m2
1.1106 channels, smallest pads 4.26.3 mm2
(<5% occupancy in PbPb)
Chamber thickness ~3% X0
Beam test results for spatial resolution  50 m
(<100 m required)
Measurement of detectors displacement with an
accuracy <50 m (GMS)
St 3,4,5: 140 slats
(max size 40280 cm2)
St 1,2: 16 quadrants

6. ALICE muon arm - trigger
4 detector planes subdivided in 2 stations (16 and 17 m from IP)
18 RPCs per plane, read on both sides with
orthogonal strips
Each plane ~5.56.5 m2
21k strips (1,2,4 cm pitch) and readout
channels
Projective geometry: different strip pitch
and length on each plane

7. Muon trigger - principle
Muon pT cut helps reducing the background from light meson decays
Two programmable pT cuts
Latency time ~800ns  used as one
of the L0 triggers
5 trigger signals: Single , UnLike and
Like-Sign dimuon high and low pT
Max muon trigger rate ~2 kHz
Trigger principle
pT cut using correlation between
position and angle
Deflection in dipole +
vertex constraint

8. Absorber(s) Beam shield Front absorber Muon filter
Front absorber: mainly carbon (also concrete, steel) (10 I)
 limit scattering and energy loss in the muon path
Muon filter: iron (7.2 I)  remove hadronic punch-through
Beam shield (along the pipe, tungsten): protect detectors
Muon momentum cut: p = 4 GeV/c

9. Acceptance Rapidity coverage: 2.5<y<4
Good transverse momentum coverage: down to pT=0 !
Effect of muon trigger pT cut not too strong

10. Physics performance, nominal LHC running conditions
Simulations for quarkonium physics performance study are based on
CEM calculations with MRST HO PDF
mc=1.2 GeV/c2, =2mc  for J/
mb=4.5 GeV/c2, =2mb  for 
CEM predictions, with these parameters, are in agreement with Tevatron data for the , but they underestimate by a factor ~2 the J/  J/ yields from these simulations may represent a pessimistic estimate
Inclusive cross section, including higher resonances feed-down
ppJ/ = 31 b
pp = 0.50 b
ppJ/ = 53.4 b
pp = b
5.5 TeV
14 TeV
PbPbJ/ obtained assuming
- binary scaling (Glauber model)
- nuclear shadowing (using EKS parametrization)
y, pT differential distributions
obtained from CEM predictions and from the extrapolation of the
CDF data at √s=2TeV, respectively
(ALICE-INT , ALICE-INT )

11. Other dimuon sources Background consists of Correlated dimuons
 both muons originate from the same heavy quark pair
Uncorrelated dimuons
combination of decay muons from uncorrelated sources
Muons from  and K decay (uncorrelated bck)
 simulation based on HIJING assuming a pessimistic estimate of dNch/d|=0 ~ 8000
muons produced after a first hadronic
interaction in the absorber (secondary , K
decays) <10% (after pT and vertex cut)
From CEM  and PYTHIA simulation
(tuned to reproduce NLO pQCD)

12. Pb-Pb collisions, nominal LHC energy
Expected yields for the yearly ALICE Pb-Pb data taking period
Time = 106 s
L = cm-2s-1
Number of expected events (integrated over centrality)
assuming no medium effects apart from shadowing and no enhancement in the quarkonium production due to statistical hadronization or cc recombination
J/
(2S)
(1S)
(2S)
(3S)
N. ev.
7 105
2 104
7 103
2 103
1 103
With this statistics we can study
centrality and pT-dependence of J/ and  yields
(2S) more difficult  low significance
A measurement of J/ elliptic flow can also be carried out

13. Pb-Pb collisions, mass spectrum
J/ region  strong background centrality dependence (uncorrelated bck dominates)
 region  weaker background centrality dependence (correlated bck dominates)
central
Mass resolution:
J/ ~ 70MeV
 ~ 100 MeV
 the  states can be clearly separated
peripheral
Uncorrelated background to be subtracted through event mixing techniques

14. First heavy-ion run, end 2010
Future difficult to predict, but for the moment 4 weeks of Pb beam
at √s=2.76 TeV/nucleon are foreseen, with maximum luminosity
Lmax = 5  1025 cm−2 s−1
Baseline scenario
1.2  106 s data taking (12 hours  28 days, L=Lmax)
Lint = 6  10-2 nb-1
NJ/ ~ 8.5  104, N(1S) ~ 8.5  102
(Slightly more) pessimistic scenario
5  105 s data taking (6 hours  22 days, L=0.02Lmax)
Lint = 5  10-4 nb-1
NJ/ ~ 7  102, N(1S) ~ 0
Could be enough to distinguish suppression vs
enhancement scenarios ?!
Warning: RAA estimate would profit a lot from a (long enough)
pp run at 2.76 GeV

15. p-p collisions, nominal LHC energy
Expected yields for the yearly ALICE Pb-Pb data taking period
Time = 107 s
L = cm-2s-1
S [x103]
S/B
S/√(S+B)
J/
2807 12
1610 ’ 75
0.6
170  27
10.4
157 ’
6.8
3.4 73
’’
4.2
2.4 55
It will be possible to study J/ pT distribution with
reasonable statistics up to (at least) 20 GeV/c
(and down to pT= 0!)
The good  statistics will allow a study of its
differential distributions

16. p-p collisions, mass spectrum
MC, 107 s running time, L=31030
Contrary to Pb-Pb , the continuum is dominated by correlated
background (due to the low hadron multiplicity, the uncorrelated
contribution is small)

17. Forward-y physics Gluon PDF distributions have
large uncertainties at very low x,
since they rely on extrapolations
(no data available in this region)
LO CEM calculations show that
the shape of the quarkonium
rapidity distribution is strictly
related to the PDF. Since the
region 2.5<y<4 corresponds to
x < 10-5
 it will be possible to put
constraints on the gluon PDF
at low x

18. Other physics topics: polarization
J/
(J/ bck subtr)
(J/ + bck)
Bias on the evaluation of the
J/ polarization due to the
background is not very large
(as expected)
With 200K J/, the error on
J/ is < 0.02 
With the  statistics collected in
one year we can evaluate the
polarization with a statistical error
between 0.05 – 0.11
 = 0
Statistical errors, for the pT
dependence of the polarization, vary
between
ALICE expected statistics in 1 year ~ 3 times  CDF statistics (Run I, 3 yr)

19. First LHC p-p run First pp run at 7 TeV currently ongoing
Luminosity is increasing step by step
Depending on the maximum luminosity chosen for ALICE,
and assuming, tentatively, LHC=0.12
L= 3 1029 cm-2s-1 (beginning)  104 J/ month-1
L= 3 1030 cm-2s-1  105 J/ month-1
Expected statistics at the end of 2011 similar to that expected
for a 1-year run at top LHC energy
See later for the statistics cumulated up to now....

20. p-A collisions, too.... They are in the program, but not
as first priority....
Very important for our understanding
of A-A results, seen the large
uncertainties on shadowing
Eskola et al., JHEP 0904:065 (2009)
p-Pb collisions, LHC single magnet ring with two beam apertures
imposes
for p-Pb √s=8.8 TeV
for p-Pb y=0.47
Extrapolations needed when comparing p-p/p-Pb/Pb-Pb

21. Shadowing and CGC in pA Large uncertainties on the ratio
R. Vogt, PRC81(2010)044903
Large uncertainties on the ratio
depending on the chosen PDF set
J/
Inclusion of CGC-related effects gives
systematically lower ratios at all y and
a steeper variation of Rp-Pb as a function
of pT (again with large uncertainties)
CTEQ6 gluon pdf + kT kick
EKS98
A measurement
is mandatory
CGC, kT kick power
CGC, kT kick gauss.

22. Moving from first signals.....
Spectrometer installed in 2007 and then commissioned step by
step during the 2008 cosmic run
From the first
cosmic muon....

23. ..towards real data ..to the first muon pair in 900 GeV pp collisions
Not yet a J/, anyway

24. Trigger is alive... Fine tuning of detector parameters EfficienciesHV
Thr
Dec
Commissioning results
10 mV
Mar
Fine tuning and intervention on electronics
May
Few more electronic interventions
7 mV
Efficiencies
Data collected in May
Threshold 7 mV
All RPCs have efficiency >90%
on both cathodes
Mean value above 95%

25. ...and working
For the moment (low luminosity) , use for data taking the lowest
possible trigger threshold pT = 0.5 GeV/c
Distance of closest approach (DCA) to the vertex for tracks
in the muon spectrometer
DCA(cm)
PYTHIA
7 TeV
No trigger
requirement
With trigger
Muons
Hadrons
Total
Muon tracking-trigger matching very effective in rejecting
Hadronic contribution
Soft (background related) component

26. Alignment is important, too...
First J/ signal has started to pop out in the invariant mass
spectrum a few weeks after the beginning of the 7 TeV data
taking...
...but with a bad
resolution, due to the
absence of an
alignment with
straight tracks

27. ...and of course very helpful
Resolution on the J/ peak in agreement with
expectations from Monte-Carlo (J/ ~ 80 MeV
for an alignment resolution m)

28. Towards the first physics results
Next step: produce physics results
On our list
Cross section
Differential distributions (pT, y)
Polarization
being studied just now
needs higher statistics
Obtain the cross section in the standard way
A · trig
High values down to pT =0
Does not depend very
strongly on pT
track close to 100%
Which is the main source of systematic error ?

29. Effect of unknown polarization
The full angular distribution of decay muons is given by
Assuming =0 (as measured by
all previous experiments) we can
calculate the systematic error on
 due to our ignorance of  and 
The effect is rather strong
+12.2, % (Collins-Soper) 
+10.6, % (Helicity) 
Most of the effect is related to the uncertainty on ,
 plays a weaker role

30. Conclusions ALICE is measuring quarkonium production in p-p collisions
at √s=7 TeV, at the LHC
The muon spectrometer, covering the rapidity region 2.5<y<4,
is currently taking data with satisfactory detector performance
First physics signal (J/) are popping out and will lead soon to
first physics publications
We are eagerly waiting for the first Pb-Pb run scheduled at
the end of A meaningful J/ signal seems within reach....
...stay tuned!