# Presentation: 009455

## Atlas Heavy Ions

**Mark D. Baker for**
**R. Debbe, J.H. Lee, J. Jia, P. Nevski, R. Nouicer, ****P. Steinberg, H. Takai, F. Videbaek, S. White**
**(BNL)**

## Some Lessons from RHIC	

**Strongly interacting matter interacts strongly!**
**20 GeV and higher jets can be stopped.**
**Hard probes are essential for quantifying strong interaction physics**
**Reconstruct and study jets in ********+jet and jet+jet events.**
_**Quantify**_** partonic energy loss, fragmentation effects and excited-medium modes using direct-********-tagged jets**

## How?

- P. Steinberg

**Direct ********’s (pp@5.5TeV****)**

**Build a world-class calorimeter for the LHC **
**Large acceptance**
**Good resolution**
**Longitudinal segmentation for ************ separation**
**Spend $100M’s & person-millenia of effort**
**Local experts at BNL (HW&SW)**
**Start ~15 years ago so that it’s ready on time!**

**Direct ********’s (pp@200GeV)**

- 99+104 GeV dijet in a b=2fm PbPb sim.

## Nearly Done!

**Nearly Done!**
**Thanks to BNL **
**ATLAS (HEP) effort!**

## Large Acceptance (CMS similar)

## Large Acceptance

## Unique (@LHC) ATLAS feature:  ID

**Longitudinally segmented ****large-acceptance**** EMCAL w/ precision strips (in ********direction).**
**Factor of ~5 S/N improvement**** for direct photons for ************~45% in 20-70 GeV E****T**** range.**
**Over and above usual isolation and overall shower shape cuts**

- ET=44 GeV  particle rejected due to
- double-peaked structure in strips

## What do we need?

**Modest support for people **
**Modest NP-specific computing (<<RCF)**

**ATLAS Zero Degree Calorimeter **
**Stationed @ +/-140m from I.P.**

- S. White et al.

- Insert PHENIX
- Caterpillar plot...

**20 GeV ******

**5.5 A TeV Pb**

**Jets into ATLAS!**

-  Measure
-  Centrality & luminosity
-  Low-x parton densities
- 10x lower than HERA     after 1 nominal month

- Hard Ultraperipheral:

**Strikman, Vogt, White, PRL 96 (2006) 082001**

- &

## Conclusions

**ATLAS@LHC presents an amazing opportunity to study strongly interacting matter with a world class detector.**
**Complementary to RHIC. **
**Tremendous synergy with other activities of the department:**
**Physics center**
**USATLAS center**
**Computing center**
**Leaders in ATLAS calorimeter hardware/software**
**Experience in zero-degree calorimetry**
**Proximity to Columbia & Stony Brook collaborators**

## US ATLAS HI activities

**BNL **
**Debbe – High multiplicity tracking**
**Debbe – forward physics**
**Videbaek, Steinberg – computing**
**Baker, Steinberg, Jia – ********+jet**
**Steinberg – global observables & pp**
**Columbia – jets & ********+jet**
**Iowa State – heavy flavor**
**StonyBrook – jets & global observables.**

## Backups

## Why Should BNL Participate?

**Programmatic argument**
**BNL has declared its intent to lead the field of strong interaction physics for the foreseeable future: **QCD Lab.
**BNL can’t afford to **_not_** participate in the next major program in QCD physics.**
**But, with a modest manpower investment in ATLAS, BNL **can play a significant role in the LHC physics program
**That complements RHIC and e-RHIC**
**That **leverages BNL investment in ATLAS

## Probing small x parton densities

- After 1 nominal month of PbPb:
**“****~10 times  the x reach of **
**  ****HERA for fixed virtuality”**

**20 GeV ******

**5.5 A TeV Pb**

**Jets into the large acceptance calorimeter!**

**Probing small x parton densities**

**Ultraperipheral AA collisions**

**Preview of eRHIC**

- _Strikman, Vogt, White, PRL 96(2006) 082001_