HI
CMS Heavy Ion Physics
Pablo Yepes
Rice University
Hadronic Collisions
 Quarkonia Production
 Jet Collisions
Coherent Interactions
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
0
Why HI at LHC
HI
Jurgen Shukraft, Quark Matter 2001
Pb+Pb, central collisions (b=0)
SPS RHIC LHC
dNch/dy
500
3
V f(Kfm )
800 3000
1
7
20 Bigger
2.5
5
20 Hotter
QGP(fm/c)
1
3
0(fm/c)
1
0.5
(GeV/fm3)
May 19, 2001May 19, 2001.
Before
7 Longer
Pb
Pb
After
0.2
Pablo Yepes, Rice U
1
J/Y Melting
HI
J/Y c c p- Hadron
p+
K gas
u,d
u,d
c c d
d
u,d
May 19, 2001.
J/Y Yield
NA50 Collaboration, CERN
QGP
u
L(fm): Average distance travel by
the J/Y inside tNuclear Matter.
u,d
Pablo Yepes, Rice U
2
Quarkonia Acceptance in
CMS m-Chambers
J/Y at CMS
Acceptance
Full Detector
10%
Barrel
Pt(GeV)
Upsilon at CMS
20%
Full Detector
Barrel
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
HI
•CMS: J/Y mainly pT>5
GeV with barrel, due
to m cutoff.
•ALICE: h>2.5 with m
•ATLAS (if they do HI) lower
acceptance due to
higher m pT cutoff.
3
Quarkonia Reconstruction
Essential sub-detectors:
 Tracking devices
 Muon system
Pessimistic assumptions
for background estimates:
 dNch/dy=8000
(most generators < 5500)
 <pt>p=0.48 GeV/c
(HIJING 0.39 GeV/c)
 <pt>k=0.67 GeV/c
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
HI
Special Heavy
Ion Tracking
Algorithm
Significant
Muon
background
from p and K
decays
4
# events/25 MeV/c2
J/Y Signal
10
10
4
Pb-Pb
# events/25 MeV/c2
L= 1027 cm2 s-1
Y/cont.= 1.0
Ca-Ca Pb-Pb
# J/Y 2.2 105
3
2
10
Min bias collisions - 1 month run - barrel only
muons with P > 3.5 GeV/c
HI
1 month running at
top Luminosity:
J/Y’s detected and
reconstructed in the
Barrel:
5
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
S/B
Ca-Ca
104
9.7
1.0
L= 2.5 1029 cm2 s-1
Y/cont.= 9.7
10
4
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
Opposite-sign di-muon invariant mass (GeV/c2)
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
ALICE: ~2K
events with ms
5
HI
L= 1027 cm-2 s-1
# Events/25 MeV/c2
Upsilon/cont.= 1.6
104
Total
Decay-Decay
103
Decay-b
3
b-b
# Events/25 MeV/c2
Upsilon in Pb-Pb
1 month: 22000  and 7500 ’
detected in the barrel
7000
Combinatorial
background
subtracted
after
reconstructio
n
6000
5000
4000
Decay-c
102
3000
2
2000
c-c
1000
8.5
8.75
9
9.25
9.5
9.75
10
10.25
10.5
Opposite-sign di-muon Invariant Mass
Background contributions
May 19, 2001May 19, 2001.
10.75
11
(GeV/c2)
Pablo Yepes, Rice U
0
8.5
8.75
9
9.25
9.5
9.75
10
10.25 10.5
10.75
11
Di-muon Invariant Mass (GeV/c2)
6
HI
# Events/25 MeV/c2
Upsilon in Ca-Ca
L= 2.5 1029 cm-2s-1
Upsilon/cont.= 9.4
105
• 1 month:
• 340000 
104
• 115000 ’
• Only barrel used.
Total
b-b
Decay-Decay
Decay-b
103
Decay-c
8.5
8.75
9
9.25
9.5
9.75
10
10.25
10.5
10.75
11
Opposite-sign di-muon invariant mass (GeV/c2)
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
7
HI
Upsilon’/Upsilon
ratio as a
Thermometer
(Ramona Vogt)
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
8
Quarkonia Reference
HI
At SPS, J/Y is compared to
Drell-Yan.
At LHC Drell-Yan
contribution is negligible.
Z0 proposed as reference to 
production.
 MZ>M
 Different production mechanisms:
Z0: antiquark-quark, quark-gluon
and antiquark-gluon.
: gluon-gluon.
Cross check di-muon
reconstruction algorithm
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
9
Jet Quenching
HI
• Large pT quarks affected by hot hadronic media
• Jets at RHIC buried in low pT background
• Look at particle pt spectrum
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
10
Jets at LHC are Easy for High
Multiplicity PbPb
Total Calorimeter Energy
Jet quenching
HI
monojet/dijet enhancement
jet-Z0mm or jet-g
dNch/dy=8000
Jet Finding
100 GeV ET
- ~100%
- s(ET)/ET=11.6%.
f
May 19, 2001May 19, 2001.
h
Pablo Yepes, Rice U
11
Etjet, g>120
GeV in the
barrel
1 month:
 900 events
for Pb-Pb
 104 events
for Ca-Ca
May 19, 2001May 19, 2001.
# Events/4 GeV
Balancing Photons and Jets
2 weeks at
L=1027 cm-2s-1
Pablo Yepes, Rice U
HI
<E>=0 GeV
<E>=4 GeV
<E>=8 GeV
Background
ETg//p0-ETJet (GeV)
12
Ultra Peripheral Collisions
HI
(Coherent Interactions)
A
g or P
g or P
A
Low pT
Low Energy
pT < 1/R 50 MeV
ECMMax < g/R
 CERN SPS
 RHIC
 CERN LHC
May 19, 2001May 19, 2001.
ECMMax =0.5 GeV
ECMMax =6 GeV  Detected
ECMMax =160 GeV
Pablo Yepes, Rice U
13
STAR Ultra-Peripheral Event
HI
(DNP 2000)
AuAu  gP (gAu) r pp
Trigger: Low multiplicity and zero energy at Zero Degree
Calorimeter (ZDC)
Side view
End view
May 19, 2001May 19, 2001.
ZDC
ZDC
Pablo Yepes, Rice U
14
HI
gg Physics
Mainly studied at e+ecolliders.Typically
p0<mgg<hc. stot up to 70
GeV by LEP.
Non perturbative QED,
coupling Z2.
New Physics:
e+e- Cross Sections
Ethr
s(Pb+Pb) s(Ca+Ca)
(GeV) (barn)
(barn)
0.5
1,500
5.5
1.0
500
1.8
5.0
30
0.1
 Standard Model H production marginal for HI
 Any exotic particle coupling to gg.
 Supersymmetric Higgs for some areas of parameters space.
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
15
Ultra-Peripheral Collisions
gg Cross Sections
HI
A
107
hadrons
10-2
cc
106
1
10-4
105
103
10
108
10-6
bb
1010
10-8
events/year/GeV
e +e -
events/sec/G
eV
sAA(M) (barn/GeV)
102
102 m+ m-+ 104
10-2
A
A
1
p0
10-1
10-4
10-6
hf
h a2
2
f2'
107
10
hc
c
105
cc0
10-2
cc2
H'
hb
hh2b0b
10-8
10-4
10-6
10-10
1014
10-12
1
10
102
M (GeV)
May 19, 2001May 19, 2001.
10-5
Pablo Yepes, Rice U
103
10
10-1
10-10
10-8
HSM
10-12
10-3
10-10
10-3
1012
events/year
Meson or
lepton/quark pair
102
events/sec
g
g
100
sAA(barn)
A
10-5
10-14
10-1
100
10
102
M (GeV)
10-12
16
gg Physics, Hadron Spectroscopy
HI
Light quark: Difficult at CMS because of low pT,
challenge for triggering, unless a multiplicity
trigger is used.
 Heavy quark
spectroscopy.
Very large
numbers
expected
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
17
Photon Nucleus (gA)
HI
gp studied in HERA: Wgp<200 GeV
gA at LHC: Wgp<900 GeV
Vector meson production: gp(A) Vp(A),
V=r,w,f,J/Y
 Very large rates, for example >104 Hz f in Ca-Ca
 Interface QCD and hadronic physics
 LHC will be a meson factory. Competitive with other meson
factories like f factory at Frascatti (CP, QM tests, etc).
 Can CMS trigger on these events. Clean events with only a few
tracks.
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
18
Conclusions
HI
CMS is provides unique tools to study Heavy Ion
Collisions at LHC.
Some physics topics:
 Quarkonium production:  and J/Y families.
 Jet quenching.
 Ultra-Peripheral collisions.
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
19
HI
Addendum: Tracking
60
Occupancy (%)
Developed for
50
ch
dN /dy=8000 and
dN0/dy=4000.
40
Track only particles
with tracks in m
30
detector.
Use m-chambers tracks20
as seeds.
10
Use only tracking
detector providing 3D 0 60
space points.
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
Detector Pitch mm
MSGC
200
MSGC
240
Silicon 147
70
80
90
100
110
120
Radius of MSGC layer (cm)
20
Interference
HI
Nuclei can emit or scatter q q pair
 two indistinguishable possibilities
Amplitudes add
 Vector meson has negative parity
 s ~ |A1 - A2eip·b|2
Destructive interference when pT << 1/b
May 19, 2001May 19, 2001.
Pablo Yepes, Rice U
21