# Presentation: 913230

## Heavy Ion Physics at ATLAS and CMS

- Marzia Rosati
- Iowa State University
- for
- and

**Workshop on Physics at the LHC era**
- Aspen Center for Physics, Colorado
- February 8, 2009

## Outline

- Heavy Ion Physics
- From RHIC to LHC
- Performance in ATLAS and CMS
- Outlook

- Marzia Rosati  -  Iowa State University

## Why Heavy Ions at the LHC?

- QCD is the fundamental theory of strong interactions.
- QCD is well studied/tested in the few particles and large Q2– i.e. in perturbative limit
- Heavy Ions provide a new opportunity to study **QCD in small **Q2** and many-particle regime**

- Marzia Rosati  -  Iowa State University

## QCD Coupling Constant

**asymptotic**** freedom at           short range / high energy**

**non perturbative at  long range/low energy**

**NP**

**HEP**

- Marzia Rosati  -  Iowa State University

## Phases of Nuclear Matter

**Normal Nuclear Matter**

**Quark Gluon Plasma**

- Nuclei behave like a liquid.
- Nucleons are like molecules.

- Deconfined phase in which nucleons dissolve in a plasma of quarks and gluons.

- Heat
- Compression

- Marzia Rosati  -  Iowa State University

## Matter under Extreme conditions

- Quark-Gluon Plasma (QGP) is the State of Matter under high temperature and pressure
- QGP is ground state of QCD and considered to be the primordial matter of the Universe
- Quarks and gluons are deconfined
- Chiral symmetry is restored (quarks are massless)
- Mission of Ultrarelativistic Heavy Ion studies
- Search, discover the QGP
- Measure the properties of the QGP
- Discover QCD in its natural, non-perturbative regime

- Marzia Rosati  -  Iowa State University

## Lattice QCD calculations

- The nature of this bath of quarks and gluons cannot be calculated directly with Quantum Chromodynamics.
- Teraflop-scale computers  simulate equilibrium QCD (assume thermal system)

- Predict phase transition:
**    ****hadrons ******** quark/gluon**
**   ****(QUARK GLUON PLASMA)**

- Marzia Rosati  -  Iowa State University

## LHC Heavy Ion Program

- Machine
- Energy
- E(beam)=7* Z/A→√s = 5.5.TeV/A or 1.14 PeV for Pb-Pb
- Heavy Ion Running
- Typically 4 weeks/ year
- Luminosity  10-27  cm-2 s-1 (Pb)
- 				 10 kHz rates
- Experiments
- ALICE: dedicated ‘general purpose’ HI experiment
- ATLAS and CMS: this talk

- Marzia Rosati  -  Iowa State University

## Stages during HI Collision

**hard collisions**

**pre-equilibrium**

**QGP**

**hadron gas**

**freeze-out**

- Marzia Rosati  -  Iowa State University

## Heavy Ion Physics at LHC

- LHC: factor 30 jump in center of mass energy with respect to RHIC

**4-10**

**1.5- 4.0**

**< 1**

******QGP ****(fm/c)**

**2x10****4**

**7x10****3**

**10****3**

**V****f****(fm****3****)**

**15- 40**

**3.5-10**

**2.5**

****** ****(GeV/fm****3****)**

**2- 8  x10****3**

**700**

**430**

**dN****ch****/dy**

**5500**

**200**

**17**

**s****1/2****(GeV) **

**LHC**

**RHIC**

**SPS**

**Central collisions**

****** ****3**

****** ****4 -10**

- Marzia Rosati  -  Iowa State University

## The ATLAS and CMS detectors

**Unprecedented acceptance for A+A physics both in pT and rapidity, with full azimuth**

**The ATLAS and CMS detectors**

- ECAL, PbWO4
- 0.0174x0.0174

- Inner detector

- HCAL (sampling)
- 0.087x0.087 (HB)
- 0.087->0.17 (HE)

- HF

- HF

- Muon Spectrometer

- Castor

- Castor

**Inner detector (|********|<2.5)**
**ECAL  (|********|<3)**
**HCAL (|********|<3)**
**HF (3<|********|<5)**
**Muon (|********|<2.4)**
**Castor (5<|********|<6.7)**
**ZDC (|********|>8)**

**CMS:**

**Inner detector (|********|<2.5)**
**ECAL  (|********|<3.2)**
**HCAL (|********|<3.2)**
**HF (3.2<|********|<5)**
**Muon (|********|<2.7)**
**Lucid (5.5<|********|<6)**
**ZDC (|********|>8)**

**ATLAS:**

- Marzia Rosati  -  Iowa State University

## Heavy Ion Physics Program at LHC

- Some examples of what we hope to do:
- first 15 minutes of running at low luminosity ~ 10**5** events:** **
**     ****global event properties and hadronic observables**
**multiplicity**
**elliptic flow**
- first few days of running ~ 10**7** events:** **
**     ****high-pt, heavy flavor**
**jet quenching, heavy-flavour energy loss**
**charmonium production**
**   **

- Marzia Rosati  -  Iowa State University

## GLOBAL EVENT PROPERTIES:
Characterize gross properties of initial state
Test saturation predictions
Probe early collective motion

- Characterize gross properties of initial state
- Test saturation predictions
- Probe early collective motion

- Marzia Rosati  -  Iowa State University

## Charged Particle Density vs c.m. energy

**First estimate of energy density**
**Saturation, CGC ?**

- Marzia Rosati  -  Iowa State University

## Multiplicity measurements

**hits count in pixels accomplished with dE/dx cut**

**tracklets with vertex constraint**

**ATLAS**

- Marzia Rosati  -  Iowa State University

## Collective flow in heavy ion collisions

- dN/d ~ 1 + 2 v2(pT) cos (2) + ...
-     “elliptic flow”

- In non central collisions there is large initial spatial anisotropy.
- The degree to which this translates into momentum space is a measure of the pressure

- Marzia Rosati  -  Iowa State University

## Flow at RHIC

- Hydrodynamics without any viscosity describes heavy ion reactions

- Marzia Rosati  -  Iowa State University

## Elliptic Flow in ATLAS and CMS

_**ATLAS**_
**    ****Flow was included in HIJING using parametrization from RHIC**

- b=10.7fm

_**CMS**_
**    ****Flow measured using two and multiparticle correlations**
-     standard Hijing

- tracker

- Marzia Rosati  -  Iowa State University

## Hard Probes

- Results with no medium (pp) and cold nuclear matter effects (pA) understood in pQCD define the benchmark for the probe;
- Results in hot medium and their difference with defined expectation provides a **characterization of the medium**.

- Marzia Rosati  -  Iowa State University

## Jet Tomography

- Partons are expected to lose energy via induced gluon radiation in traversing a dense colored medium.

- Marzia Rosati  -  Iowa State University

## Discovery of Jet Quenching  at RHIC

- Measure using (Leading) high-pT hadrons and photons

**Suppression Factor**

- Marzia Rosati  -  Iowa State University

## Jet Rates at LHC

- High pT, large rates
-  b jets, di-jet, -jet
- Also full jet measurement not leading hadrons

- Marzia Rosati  -  Iowa State University

## “Full” Jet Measurements at LHC

**E****T****rec**** vs E****T****gen**

**CMS**
**Iterative cone (R>=0.5) with **
**background subtraction**

**dN****ch****/d******** = 5000**

**ATLAS**
**Cone, R=0.4, **
**with background Subtraction**

- Marzia Rosati  -  Iowa State University

## Deconfinement

**Deconfinement**

- r

- V(r)/

- Lattice QCD calculation

- Different Quarkonia states test the degree of color screening and measure the temperature.

- Lattice QCD makes a clear prediction for the onset of deconfinement.

**T**

- Marzia Rosati  -  Iowa State University

## J/ suppression at RHIC

- Smooth suppression with increasing collision centrality
- Forward rapidity more suppressed than mid-rapidity
- very similar suppression at RHIC and SPS...

- Nuclear Suppression Factor

- Ratio **Blue **/ **Red**

- Marzia Rosati  -  Iowa State University

## J/ Measurement at the LHC

- both muons
-  with |<2.4

**Mass resolution **
**68 MeV/*****c*****2**

**Mass resolution **
**35 MeV/*****c*****2**

**~100k J/******** per month,**
**tagging method**

** ****ATLAS**

**  ****CMS**

**Expected rate**
** ****(per month,10****6****s, 0.5 nb****-1****):**
**     ****J/******** ~ 180 kevents**

- Marzia Rosati  -  Iowa State University

## Upsilon Measurement at LHC

**0.25 nb-1**

**|********|<1**

**mass resolution, 125 MeV**

**mass resolution, 54 MeV**

**|********|<2.4**

** ****ATLAS**

**  ****CMS**

- Marzia Rosati  -  Iowa State University

## Conclusions

**Conclusions**

- The LHC with Heavy Ions is a fantastic discovery machine with a very rich Physics program:
- The first 15 minutes; Lint=1b-1
- Event multiplicity, elliptic flow
- The first month; Lint=0.1-1nb-1
- Rare high pt processes: jets, quarkonia
- ATLAS and CMS have unprecendented capabilities to make measurements over a large kinematic range for important signatures of the Quark Gluon Plasma
- The experiments will be commissioned and ready (thanks to the proton run)
-    Important results already from the very start of running with nuclear beams

- Marzia Rosati  -  Iowa State University

## END

- Marzia Rosati  -  Iowa State University

## LHC: Cross-sections and Rates

**LHC: Cross-sections and Rates**

- Cross-sections of
- interesting probes
- expected to increase by factors
-  ~ 10  ( cc )  to
-  ~ 10**2**  ( bb )  to
-  ~  > 10**5** (very high pT jets)
- Hard probes of the medium accessible at LHC

- 

- Marzia Rosati  -  Iowa State University

## LHC: extending the low-x  Reach

**LHC: extending the low-x  Reach**

- RHIC as opened the
- low-x frontier finding indications for new physics  (Colour Glass Condensate    CGC)
- x = 2 p (parton) / √s
- LHC will lower the x- frontier by another factor 30 due to energy and by 3 due to larger rapidity
- Can reach x = 3 * 10**-6** in pp,
-                        10**-5**  in PbPb

- Marzia Rosati  -  Iowa State University

## Experimental Strategy

- Characterize the medium by studying the QCD probe in:
-  no medium p+p collisions
-  cold nuclear matter   d+Au collisions
-  hot medium Au+Au collisions

- Marzia Rosati  -  Iowa State University

## QGP 

**QGP **

- Energy Density

- R2

- Marzia Rosati  -  Iowa State University

## Summary of Ions

| Collision | R
(fm) | Luminosity 
(cm-2s-1) | dNch/dy (maximum) | Interaction rate |
| --- | --- | --- | --- | --- |
| p+p | ~1 | 1x1034 | <250 | 1 GHz |
| 208Pb+208Pb | 7.1 | 1x1027 | <8000 | 8 kHz |
| 40Ar+40Ar | 4.1 | 6x1028 | <800 | 200 kHz |
| p+208Pb |  | 1x1030 | <150 | 2 MHz |
| p+40Ar |  | 1x1031 | <120 | 6 MHz |

- The desired species for a systematic HI study are as follow

- Marzia Rosati  -  Iowa State University