status of heavy ion

1Sasha Milov ATLAS IL meeting Jan 03, 2011

Status of Heavy Ion

Sasha Milov

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LHC run2010 with Pb+Pb

At the end of 2010 LHC took a very successful data with Pb+Pb @ √sNN = 2.75 TeV

Both LHC and ATLAS performances were beyond expectations. ChronologicallyNov 2: end of p+p+2days: injecting Pb+2days: first collisions+2days: stable beams+2days: 4x4 bunches+2-3days 64x64bunchesNov 24: first PRL. 9.2ub-1 (7.7b cross section)Dec 24: J/psi & Z paper

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A HI event

Sasha Milov ATLAS IL meeting Jan 03, 2011

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The HI event.

Sasha Milov ATLAS IL meeting Jan 03, 2011

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A oicture needs to be expained

Find a high-pT particle

Look around it in p+p and find a jet

Look at 180o and find its back-to-back partner

The same in d+Au

Find the near-side jet in A+A

And no back-to-back partner

Partners of the hard-scattered probes are absorbed in the media.

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Pictures which do not...

Sasha Milov ATLAS IL meeting Jan 03, 2011

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The results

Sasha Milov ATLAS IL meeting Jan 03, 2011

p+p reference (open circles) the same in all plots.MC (yellow histogram) does not imply the media effectsSmall asymmetry di-jets reduce with centrality, large asymmetry di-jets increase with centrality.All jets peak at -π Possibly there is some broadening of the jets

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MultiplicityarXiv:1012.1657v1

arXiv:1011.3916v2

ATLAS: analysis ongoingThe most central bin well agrees With ALICE paper

Better rapidity coverage

Several independent methods

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MultiplicityUse Pixel detector only: low occupancy, low pT cut, wide coverage.Method 1: Combine all hits and confirm B-layer hit with layer 1 hit. Method 2: Combine all hits then flip the detector and subtract the combinatorialMethod 3: use standard pixel tracks with (in no field runs)

Columbia U.

Sasha Milov ATLAS IL meeting Jan 03, 2011 10

MultiplicityUse Pixel detector only: low occupancy, low pT cut, wide coverage.Method 1: Combine all hits and confirm B-layer hit with layer 1 hit. Method 2: Combine all hits then flip the detector and subtract the combinatorialMethod 3: use standard pixel tracks with (in no field runs)

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FlowThe Fourier transform of azimuthal distributionThere all odd coefficients especially important is v2Known to be large at RHIC

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Flow

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17 Nov: arXiv:1011.3914, acc. PRL

STAR at RHIC

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Spectra. dNAA/dpT

σpp<TAB> dNpp/dpT RAA=

Phys. Rev. Lett. 91, 072301 (2003)

~2008 -- 2010

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Spectra.ALICE 1012.1004v1

Approximately 20%of run statistics

Central (0-10%)

Peripheral(60-80)%

Figure is 2 weeks old. There is lot more statistics

BNL; WIS

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Data vs. MC (HIJING)Data and MC look different:Total number of tracks above

pT=0.5 GeV is similar, but HIJING has lower pT (no flow).

As a result the tracks with pT<0.5 produce more hits per track above the threshold

Data MC

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Hit statistics in MinBiasPer track hit statistics reflects

the detector occupancy Pixel<SCT<TRT

The effects are also consistent to what is expected from HIJING

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Hit statistics in Data and MC look different:Total number of tracks above

pT=0.5 GeV is similar, but HIJING has lower pT (no flow).

As a result the tracks with pT<0.5 produce more hits per track above the threshold

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Hit statistics in centrality

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Vertex pointing in pT

Selecting primary particles using the p+p cuts gives good resultspT dependent

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Further optimization.

Need to look at centrality and (may be) in charge.

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Further optimization.And in rapidity?

Main questions:1. How to clean the secondaries?2. How far in pT can we go before being overwhelmed by feed-downs3. How to correct for efficiency?

neg posdifferent cuts

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Two particle correlations

SUNYSB (chem)