Heavy ion physics with compact muon solenoid at large hadron collider
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Heavy-Ion Physics with Compact Muon Solenoid at Large Hadron Collider. Bolek Wyslouch Massachusetts Institute of Technology Los Alamos 25 October 2007. CMS. Quark Gluon Plasma. Data from SPS & RHIC show new and unexpected properties of hot nuclear matter

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Heavy-Ion Physics with Compact Muon Solenoid at Large Hadron Collider

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Heavy ion physics with compact muon solenoid at large hadron collider

Heavy-Ion Physics with Compact Muon Solenoidat Large Hadron Collider

Bolek Wyslouch

Massachusetts Institute of Technology

Los Alamos

25 October 2007


Quark gluon plasma

Quark Gluon Plasma

  • Data from SPS & RHIC show new and unexpected properties of hot nuclear matter

  • Jet quenching, strong elliptical flow, d+Au- control data indicate that we have produced strongly interacting color liquid

  • LHC will significantly increase energy density

    • New properties of the plasma

      • Continuation of strong coupling regime?

      • Weakly interacting Plasma?

    • New tools to study to hot and dense state

      • Hard probes

      • Access to very low-x

Los Alamos Bolek Wyslouch

Summary of physics opportunities

Summary of physics opportunities

  • LHC will accelerate and collide heavy ions at energies far exceeding the range of existing accelerators

    • The increase of beam energy will result in:

      • Extended kinematic reach for pp, pA, AA

      • New properties of initial state, saturation at mid-rapidity

      • A hotter and longer lived partonic phase

      • Increased cross sections and availability of new hard probes

  • New energy regime will open a new window on hot and dense matter physics: another large energy jump!

Los Alamos Bolek Wyslouch

Large hadron collider

Large Hadron Collider

  • LHC is about to start operations:

    • 2008:

      • proton-proton collisions at ~14 TeV

    • 2008:

      • p+p at 14 TeV

      • Pb+Pb at 5.5 TeV per nucleon pair

  • Heavy Ions

    • Expect ~1 month of heavy ion collisions each year

Beam Energy

Los Alamos Bolek Wyslouch

First rhic surprise multiplicities are low

PHOBOS Central Au+Au (200 GeV)



Compilation by K. Eskola

Rapidity Density

First RHIC Surprise: Multiplicities Are “Low”

  • Low, that is, compared to pre-data predictions of “cascading partons”

  • Consistent with predictions based on gluon saturation :

Kharzeev & Levin, Phys. Lett. B523 (2001) 79

Color Glass


Phys. Rev. Lett. 87, 102303 (2001)

From Eskola, QM 2000

Los Alamos Bolek Wyslouch

Lhc multiplicity is likely to be low

LHC multiplicity is likely to be low


Extrapolated to LHC:


Is it saturation that makes it so low?

Will it increase at higher energies?


Note: this is an important experimental issue!

Los Alamos Bolek Wyslouch

Rhic s two major discoveries

RHIC’s Two Major Discoveries

  • Discovery of strong “elliptic” flow:

    • Elliptic flow in Au + Au collisions at √sNN= 130 GeV, STAR Collaboration, (K.H. Ackermann et al.). Phys.Rev.Lett.86:402-407,2001

    • 307 citations

  • Discovery of “jet quenching”

    • Suppression of hadrons with large transverse momentum in central Au+Au collisions at √sNN = 130 GeV, PHENIX Collaboration (K. Adcox et al.), Phys.Rev.Lett.88:022301,2002

    • 357 citations

Flow strength

Suppresion Factor

Strongly interacting liquid with very low


Los Alamos Bolek Wyslouch

Elliptic flow at rhic


Elliptic Flow at RHIC



Flow (asymmetry in pT) is near to hydrodynamic limit,

LHC: can it grow even more ?

Los Alamos Bolek Wyslouch

Jet quenching at high p t will it continue at lhc



“Jet Quenching” at high pT: will it continue at LHC ?

  • Energy loss of partons in hot and dense matter

  • E.g. charged particle RAA for multi-100 GeV/c pT

Parton Energy loss

Los Alamos Bolek Wyslouch

Quarkonia in heavy ions

Regeneration ?




Suppression ?

Energy Density

Quarkonia in Heavy Ions

  • J/ suppression in heavy ion collisions has been heralded as a discovery of Quark Gluon Plasma at CERN SPS circa 2000: there are fewer J/’s produced as energy density is increasing

  • There is a lot of detailed experimental data from SPS. RHIC is now releasing new information, it is consistent with SPS

  • Theoretical interpretation is difficult: we possibly need to look towards LHC:  family can provide important hints, there are three states with differing binding energy

Los Alamos Bolek Wyslouch

Post rhic dream heavy ion detector


Post-RHIC Dream heavy-ion detector

  • Large acceptance for charged and neutral hadrons, muons, photons, electrons covering wide pT range hermeticity

  • Good resolution for high pT probes (jets, J/,  family) resolution

  • Good trigger to allow selection of rare events speed

  • Good particle identification p0, b-, c-quarks, muons, electrons, photons, L, Ks, p, K , p particle ID

  • Most likely it does NOT have to handle extreme multiplicities

  • Relatively low luminosity of LHC as a heavy-ion accelerator

Los Alamos Bolek Wyslouch

High density qcd with heavy ions

“High density QCD with heavy-ions”

170 pages

10 chapters

~90 figures, ~20 tables

~20 CMS-AN-Notes

~25 CMS-HI institutions

~100 collaborators

Athens, Auckland, Budapest, CERN, Chongbuk, Colorado, Cukurova, Ioannina, Iowa, Kansas, Korea, Lisbon, Los Alamos, Lyon, Maryland, Minnesota, MIT, Moscow, Mumbai, Seoul, Vanderbilt, UC Davis, UI Chicago, Vilnius, Zagreb

D.d'E (ed.) CERN-LHCC-2007-009; J.Phys.G. to appear.

Los Alamos Bolek Wyslouch

Cms as a heavy ion experiment

  • Calorimeters: high resolution and segmentation

    • Hermetic coverage up to ||<5

    • (||<6.6 with the proposed CASTOR)

    • Zero Degree Calorimeter

  • Muon tracking:  from Z0, J/, 

    • Wide rapidity coverage: ||<2.4

    • σm 50 MeV at the  mass in the barrel

  • Silicon Tracker

    • Good efficiency and purity for pT~>0.3 GeV

    • Pixel occupancy: <2% at dNch/d 3500

    • p/p  1-2% for 1<pT <100 GeV

    • Good low pT reach using pixels

  • DAQ and Trigger

    • High rate capability for A+A, p+A, p+p

    • High Level Trigger: real time HI event reconstruction

CMS, as a heavy ion experiment


(5.2 < |η| < 6.6)


(z = 140 m, |η| > 8.2 neutrals)

Functional at the highest expected multiplicities:

studied in detail at dNch/d3000-5000 and cross-checked at 7000-8000

Los Alamos Bolek Wyslouch

Cms coverage


Sub detector


Tracker, muons

|  | < 2.4


|  | < 3.0

Forward HCAL

3 .0< |  | < 5.2


5.2 < |  | < 6.6

ZDC (neutrals)

8.2 < ||

CMS coverage

HCAL (Barrel+Endcap+Forward)

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Cms under construction

CMS under construction

Silicon Tracker





Muon Absorber


Si tracker &


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Centrality and forward detectors

Centrality and forward detectors

Centrality (impact parameter) determination is needed for most physics analyses

Zero Degree Calorimeter

Energy in the forward hadronic calorimeter

Tungsten-quartz fibre structure

electromagnetic section: 19X0

hadronic section 5.6λ0

Rad. hard to ~20 Grad (AA, pp low lum.)

Energy resolution (n,g): E~E·10%

Position resolution: ~2 mm (EM sect.)

~140 meters from CMS IP

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Zero degree calorimeter

Zero Degree Calorimeter

Los Alamos Bolek Wyslouch



T2 Tracker TOTEM

5.2< η < 6.6

CASTOR: Tungsten-Quartz

5.2< η < 6.6

Los Alamos Bolek Wyslouch

Charged particle multiplicity


Charged particle multiplicity

  • high granularity pixel detectors

  • pulse height measurement in each pixel reduces background

  • Very low pT reach, pT>26 MeV (counting hits)

Will be one of the first results,

important for initial energy density,

saturation, detector performance etc.

Simple extrapolation from RHIC data

W. Busza, CMS Workshop, June 2004

Muon detection, tracking, jet finding performance

checked up or larger than dNch/dh=5000

Los Alamos Bolek Wyslouch

Elliptic flow measurements in cms

Elliptic Flow measurements in CMS

  • Use calorimeters and tracker

    • Event plane reconstruction

    • v2 measurements

  • Very large acceptance

v2(h) tracker

Los Alamos Bolek Wyslouch

Jets at rhic





Jets at RHIC

Find this……….in this

Los Alamos Bolek Wyslouch

Production of qcd jets









Production of QCD jets



“Clean” Jet

Quenched, absorbed, modified jet

“Soft QCD”

“Hard QCD”



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High p t leading charged hadrons

nhit > 12

pchi2 > 0.01

dca <3

High-pT (leading) charged hadrons

C.Roland, CMS-AN06-001

  • Excellent tracking performances (PbPb, dNch/dh = 3500):

  • Efficiency

  • Fake Rate

Momentum resolution

Expected dN/dpT

reach pT~300 GeV/c

(high ET HLT)

Impact parameter


Displaced vertexes from heavy-Q decays measurable

Los Alamos Bolek Wyslouch

Pixel tracking low p t reach of cms

Pixel tracking

All tracker fitting

Pixel Tracking, low pT reach of CMS

800 MeV

Los Alamos Bolek Wyslouch

Pixel tracking

F. Sikler

Pixel tracking

Track finding efficiency vs pT and for p+p and central Pb+Pb

Fakes are controlled using pixel hit shape

Los Alamos Bolek Wyslouch

High p t leading charged hadrons1

High-pT (leading) charged hadrons

C.Roland et al., CMS-AN06-110

Nuclear modification factor (= AA-yield / pp-yield) at the LHC:

PbPb (PYQUEN) 0.5 nb-1

extended reach ~300 GeV/c

w/ high-ET (jet)trigger

×5 suppr.

Strong discriminationpower for parton energy loss models:

- Initial parton medium density: dNg/dy~O(2-4·103)

- Medium transport coefficient: <q>~O(10-100) GeV2/fm

Los Alamos Bolek Wyslouch

Pb pb full jet reconstruction

1. Subtract average soft background

2. Find jets: iterative cone algorithm

3. Recalculate pileup outside cone

4. Recalculate jet energy

jet energy: reco vs. MC

energy resolution

efficiency, purity

Pb-Pb full jet reconstruction

I. Vardanyan et al. CMS-Note-2006-50

  • Iterative-cone + backgd subtraction. [New developments (fast-KT) under study]

Los Alamos Bolek Wyslouch

Pb pb full jet reconstruction1

Pb-Pb full jet reconstruction

C.Roland et al., CMS-AN06-110

  • Jet spectra up to ET~ 0.5 TeV (PbPb, 0.5 nb-1, HLT-triggered).

  • Detailed studies of medium-modified (quenched) jet FF possible.


Gluon radiation:

large-angle (out-of-cone)

vs. small-angle emission



I. Lokhtin et al., PLB567 (03)39

Los Alamos Bolek Wyslouch

G g z jet tagging cms

g- , g*- , Z- jet tagging (CMS)

  • Possibility to calibrate jet-energy loss (and Fragmentation Functions) with back-to-back gauge boson (large cross-sections, good detection capabilities):

  • Dominant (heavy-Q) dimuon backgd.

    “removable” via secondary-vtx. cut

C.Mironov et al.

Dimuon trigger




Away side

Associated Hadrons

pT >25 GeV/c

sr=50 mm

sj=20 mm

3s vtx. cut

Los Alamos Bolek Wyslouch

Balancing or z 0 g vs jets

g, Z0


Events/ 5 GeV

ETo - ETJet (GeV)

Balancing  or Z0/g* vs Jets

  • Jet quenching with calibrated energy

    • On average Z/ ET and jet ET should balance (unquenched jets)

    • Z ->  and  can be reconstructed with very good ET resolution

    • Dominated by quark jets

      q + g -> q + Z0/

  • -Jet:

    • Need to control the background from leading 0 in QCD dijets

    • Reject 0 by cluster isolation cuts in the calorimeters

    • Quenching will help

      • Lower Thresholds

  • Z0 - Jet

    • Cleaner but lower rates

ETjet, g > 120GeV in Barrel,

1 month at 1027 cm-2s-1 Pb+Pb

new studies to appear shortly

dN/dy ~7000, unquenched Jets

Los Alamos Bolek Wyslouch

Quarkonia probe of high density qcd media

Quarkonia: probe of high-density QCD media

  • Dissociation (color screening) = hot QCD matter thermometer

  • Probe of low-x gluon structure/evolution:


[H.Satz, hep-ph/0512217]

Spectral function vs T:

Lattice QQ free energy vs T:

Suppression pattern vs e :

gluon saturation,

non-linear QCD

production via gg fusion:

x~10-3 (10-5)

Q2~10 GeV2

Los Alamos Bolek Wyslouch

Heavy ion mc event in cms

Heavy Ion MC Event in CMS

Pb+Pb event (dN/dy = 3500) with  -> -

Pb+Pb event display: Produced in CMS software framework

(simulation, data structures, visualization)

Los Alamos Bolek Wyslouch

J suppression

regeneration ?




suppression ?

Energy Density

J/ψ suppression

O.Kodolova, M. Bedjidian, CMS-AN06-116

J/ acceptance

Best mass resolution @ LHC

J/,' S/B

= 35 MeV/c2


pT reach (0.5 nb-1)


Los Alamos Bolek Wyslouch





O.Kodolova, M. Bedjidian, CMS-AN06-116

 family S/B

 acceptance

Best mass resolution @ LHC

= 54 MeV/c2

 spectroscopy (seq. suppr.)

pT reach (0.5 nb-1)

’/  stat. reach (HLT)

Strong models constraint



Los Alamos Bolek Wyslouch

Ultra peripheral collisions g pb

Ultra-Peripheral collisions g Pb

  • Quarkonia photoproduction

  • Probes nuclear PDF in unexplored (x,M2) range

  • Uses ZDC to trigger on forward emitted neutrons

  • Measurement --> m+m-, e+e- in the central detector

Los Alamos Bolek Wyslouch

Bolek Wyslouch

Cms trigger and daq in p p

CMS Trigger and DAQ in p+p

Level 1 trigger

- Uses custom hardware

- Muon tracks + calorimeter information

- Decision after ~ 3μsec

High level Trigger

- ~1500 Linux servers (~10k CPU cores)

- Full event information available

- Runs “offline” algorithms

Los Alamos Bolek Wyslouch

Cms trigger daq in pb pb vs p p

CMS Trigger+DAQ in Pb+Pb vs p+p

Level 1 trigger

- Uses custom hardware

- Muon tracks + calorimeter information

- Decision after ~ 3μsec

High level Trigger

- ~1500 Linux servers (~10k CPU cores)

- Full event information available

- Runs “offline” algorithms

Los Alamos Bolek Wyslouch

Trigger daq architecture

Trigger/DAQ Architecture

Standard rack servers

Dual CPU - dual core

2008/09: quad/8 core

8 “DAQ slices”


~1500 “Filter Unit” servers

~12000 1.8GHz Opteron


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High level trigger simulations

Acceptance, BR







Acceptance, efficiency, backgrounds

measured and parametrized from

full offline simulation + algorithms




Table x

DAQ rate

Rate to tape

Trigger rate

(signal + bkg)

1 +


Signal rate

Output Rates

to tape

Timing of offline algorithms and event size

bias measured on full simulations

High Level Trigger Simulations



Los Alamos Bolek Wyslouch

Minimum bias vs hlt

Minimum bias vs HLT

HLT CPU time

Budget ~ 8 CPUsec

per event

(1.8GHz Opteron)

Strawman trigger

table for design lumi

with HLT

with HLT


(106 sec @

design lumi)

Rates to


Min bias

Min bias

Los Alamos Bolek Wyslouch

Activities of hi physicists

Activities of HI physicists

  • Exploration of the capabilities of CMS as a heavy ion detector and preparations for data taking

    • Development of analysis tools and reconstruction algorithms

      • Development of generators

      • Reconstruction algorithms

    • Development of trigger algorithms

      • HLT Farm operations

      • Trigger algorithms

    • Simulation studies

      • Studies of detector behavior in HI collisions

  • Design and construction of “HI motivated” detectors

    • Zero Degree Calorimeter

    • CASTOR

Los Alamos Bolek Wyslouch

Heavy ion physicists within cms collaboration

Heavy Ion Physicists within CMS Collaboration

  • Overall CMS Collaboration

    • 38 Countries, 181 Institutions, ~2500 Scientists

  • Heavy Ion Institutions

    • Athens, Auckland, Budapest, CERN, Chongbuk, Colorado, Cukurova, Ioannina, Iowa, Kansas, Korea, Lisbon, Los Alamos, Lyon, Maryland, Minnesota, MIT, Moscow, Mumbai, Seoul, Vanderbilt, UC Davis, UI Chicago, Vilnius, Zagreb

    • Total of about 65 PhDs, 35 Students, 50% from the US

Los Alamos Bolek Wyslouch

Physics plan

Calendar Year

Physics (known physics)

Total on tape


Preparations: HLT, Reconstruction, first p+p physics at low energy



Reference p+p, global observables, jets ET<200 GeV, charged particle spectra, first dimuon events,

0.3 k


Centrality and event plane dependence of global obs., charged particle spectra to 200 GeV, multi-100 GeV jets, open b,c, first quarkonia



Detailed jet fragmentation studies, multi-jets, quarkonia physics, first tagged jet studies, detailed open b,c studies



Extensive studies of rare channels, centrality, event plane dependence of quarkonia, tagged jets, heavy quarks



Detailed studies of rare channels


Physics Plan

  • Comprehensive heavy ion physics program with emphasis on hard probes

  • Program follows increasing luminosity

    • Continuously extend pT range

    • New probes

    • Increase level of precision and detail

    • Tighten and optimize trigger

  • Pb+Pb for the first few years, expect other ions and p+Pb later, in close coordination with ALICE

Los Alamos Bolek Wyslouch



  • LHC will extend energy range and in particular high pT reach of heavy-ion physics

  • CMS is preparing to take advantage of its capabilities

    • Excellent rapidity and azimuthal coverage and high resolution

      • Quarkonia

      • Jets

    • Centrality, Multiplicity, Energy Flow reaching very low pT

    • Essentially no modification to the detector hardware

    • New High Level Trigger algorithms specific for A+A

    • Zero Degree Calorimeter, CASTOR and TOTEM will be important additions extending forward coverage

    • Heavy-Ion program is well integrated into the overall CMS Physics Program

  • The knowledge gained at RHIC will be extended to the new energy domain

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