The ALICE experiment at LHC

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The ALICE

experiment at LHC

Domenico Di Bari

Dipartimento Interateneo di Fisica INFN-Bari

4th Summer School on THE PHYSICS OF LHC

14-19 jun 2010 Martignano, Grecìa Salentina (Lecce, Italy)

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P. Giubellino

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PLC 20J.

Schukraft

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HI @LHC: Constraints and Solutions

 Extreme particle density : dN

_ch

/dh ~ 2000 – 8000

x 500 compared to pp@LHC; x 30 compared to ³²S@SPS

 high granularity, 3D detectors

 Silicon pixels and drift detectors, TPC with low diffusion gas mixture (Ne-CO₂)

 conservative & redundant tracking

 up to ~200 space points per track

 large distance to vertex

 e.g. emcal at 4.5 m (typical is 1-2 m !)

 Large dynamic range in p

_t

:

from very soft (0.1 GeV) to fairly hard (100 GeV)

 very thin detector, modest field 0.5 T (low p_t),

 ALICE: ~ 10%X₀ in r < 2.5 m (typical is 50-100%X₀)

 vertex detector works as ‘standalone low p_t spectrometer’ (tracking & PID)

 large lever arm + good hit resolution (large p_t)

 B= 0.5T, tracking L ~ 3.5m, BL² ~ like CMS !

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PLC 20J.

Schukraft

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HI @LHC: Constraints and Solutions

 Both partons & hadrons matter:

fragmentation (i.e. hadrons) is part of the signal, not of the problem

 partons (heavy quarks): secondary vertices, lepton ID

 hadrons: use of essentially all known PID technologies

 dE/dx, Cherenkov & transition rad., TOF, calorimeters, muon filter, topological

 Modest Luminosity and interaction rates; short runs

10 kHZ (Pb-Pb), (< 1/10000 of pp@10³⁴) ~ 1 month/year

 allows slow detectors (TPC, SDD), moderate radiation hardness

 moderate trigger selectivity, no pipelines (mostly ‘track & hold’ electronics)

 large event size (~ 100 MB) + short runs => high throughput DAQ (> 1GB/s)

 Single dedicated heavy ion experiment

combine capabilities of a handful of more specialized HI expts at AGS/SPS/RHIC

 18 detector technologies, several smaller ‘special purpose’ detectors

(HMPID, PHOS, PMD, FMD, ZDC..)

 central barrel (~ STAR) + forward muon arm (~PHENIX)

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5 Detector:

Size: 16 x 26 meters Weight: 10,000 tons

Collaboration:

> 1000 Members

> 100 Institutes

> 30 countries

ALICE

ACORDE V0

T0 ZDC FMD PMD

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Are you asking me if

QGP was here? I

don’t know. Please,

call the CSI experts…

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AHA, AHA, here is the

Higgs!!!

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21/4/2010 28^th RRB J. Schukraft

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ALICE Status

Complete:

ITS, TPC, TOF, HMPID, FMD, T0, V0, ZDC,

Muon arm, Acorde PMD , PHOS(3/5), DAQ

Partial installation:

7/18 TRD 4/10 EMCAL

~ 60% HLT

ALICE Detector Installation mid 2009

New (‘post Chamonix’) LHC schedule: Likely configuration until end 2011

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Material budget distribution in ALICE

Radial distance from beam line

X/X

₀

<10% up to 250 cm

from IP

Good precision 

for e/

measurements

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Photon convertion

point distrib.

@7TeV

Actual agreement

of data with MC

< 8%

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11

some anxious minutes waiting for collisions..

~ 16:35

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12

The first ‘event’ pops up in the ACR

~ 16:41

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Relief and jubilation..

Collisions in ALICE !!

.. and some celebration.. ~ 16:42

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‘First Physics’ in the making

After years of looking at simulated data, there was no holding back:

First physics results examined,

ca 1 hour after data taking finished (284 events !)..

~ 18:00

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12/3/2010 Yale J. Schukraft

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A few days later…

TPC track

TRD track HMPID Cherenkov Ring

Muon Spectrometer ITS

TPC, TRD, TOF, HMPID

On 6^th December, ‘stable beams’

were declared & we could switch on all ALICE detectors for the first time..

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Data Taking Summary

30/03/20100 09/04/2010 19/04/2010

1 2 3 4

0 10 20 30 40 50 60 70 80 90 100 ALICE efficiency

ALICE PHYSICS RUN TIME

cummulative time (days)

LHC STABLE BEAMS

efficiency (%)

>15 Million interactions

> 150 k

Muon triggers Inter. rate

~ 30 – 90 Hz

Integrated Data taking efficiency since 30.3 ~ 85%

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1 7

Tracking works beautifully

Beam spot at 2.36 TeV

TPC p_t spectrum Preliminary

preliminary alignment !

SPD Vertex resolution versus # tracks

Plots as shown on 18 Dec ‘LHC’ jamboree

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alignment with cosmics only

s=181 mm

after

alignment before alignment

Data MC

p_T = 1 – 1.5 GeV/c

Data MC

Impact parameter DCA

p_T = 1 – 1.5 GeV/c

cosmics + pp ( = 0 and π)

Getting to know ALICE:

Shape

18

SPD

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19 Results shown on 17 Febr LHCC

PID

(or 6 ways to measure Kaons)

ALICE - Work in Progress

ALICE - Work in Progress ALICE - Work in Progress

K ® mn

ALICE Work in Progress

K

⁰_s

® pp

# 6:

HMPID Cherenkov

p

K p

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2 0

Plots as shown on 18 Dec ‘LHC’ jamboree

The Particle Zoo Revisited:

PDG: 1115.7 MeV

L ® pp

PDG: 497.6 MeV

K

⁰_s

® pp

PDG: 1115.7 MeV

L ® pp

… National Geographic was sort of correct..

F ® K

⁺

K

^- PDG: 1019.5 MeV

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W

(^sss)

® LK ® pp K

April 2010

More Particle Appearances

K

^*

® Kp

February 2010

Work in progress

h ®  ®

e⁺e^- e⁺e^-

X(

^ssd

) ® Lp ® pp p

April 2010

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2

2 Plots as shown on 18 Dec ‘LHC’ jamboree

More Particles..

p

⁰

®  ® e

⁺

e

^-

e

⁺

e

^-

p

⁰

® 

1 < p_t < 1.5 GeV

PHOS (9 m²)

X ® Lp ® pp p

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 Reconstruction from conversion

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2

4 Plots as shown on 18 Dec ‘LHC’ jamboree

ALICE special: Particle Identification

(very important for heavy ion physics later in 2010)

15/2/2006 LHCC Status Report J. Schukraft

.. ‘lots’ of data..

ITS

‘Good pp interactions’: (rate few Hz) - 300 k : √s = 900 GeV

- 30 k : √s = 2.36 TeV

TRD

Electrons

Pions

velocity v/c

TOF

Protons

Kaons Pions all plots:

preliminary calibration & alignment !

TPC

No vertex cut !

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(Anti)Nuclei

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P. Giubellino

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Event Classes

 s = 0.9 and 2.36 TeV

 Inelastic (INEL) = Single-diffractive (SD) + Double-diffractive (DD) + Non-diffractive (ND);

 Non-single diffractive (NSD) = ND+DD

 Use measured cross sections for diffractive processes

 Change MC generator fractions (SD/INEL, DD/INEL) such that they match these fractions

 s = 7 TeV

 Diffraction is quite unknown

 Hadron-level def. of evts to minimize model dependence

 All events that have at least one charged primary particle in |η| < 1: “INEL>0”

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Physics exploitation of ALICE has started for good !

Phase 1: rediscovering the standard model

(QCD in the case of ALICE)

The average number of charged particles created perpendicular to the beam

in pp collisions at 900 GeV is:

dN/dh = 3.10 ± 0.13 (stat) ± 0.22 (syst)

This is the first (and easiest) of

many numbers we need to (re)measure to get confidence in our detectors, tune the simulations, study background, ....

Phase 2 is still a long way to go..

last time measured at the ISR for pp

» p

National Geographic News (4 Dec.)

‘….a machine called ALICE....

found that a ^(!) proton-proton collision recorded on November 23

created the precise ratio

of matter and antimatter particles predicted from theory..’

submitted to EPJC 28 Nov 2009

Physics exploitation of ALICE has started for good !

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dN/dh: comparison to exp.

NSD 2.36 TeV NSD 900 GeV INEL 900 GeV ALICE preliminary 4.43 ± 0.01 ± 0.16 3.58 ± 0.01 ± 0.12 3.02 ± 0.01 ± 0.07 ALICE EPJC 65 111 (2010) 3.51 ± 0.15 ± 0.25 3.10 ± 0.13 ± 0.22 CMS JHEP 02 (2010) 041 4.47 ± 0.04 ± 0.16 3.48 ± 0.02 ± 0.13

UA5 Z. Phys. C33 1 (1986) 3.43 ± 0.05 ± ? 3.09 ± 0.05 ± ?

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Multiplicity distributions @ 0.9,2.36,7 TeV

 0.9 TeV: consistent with UA5

 Fit with NBD (Negative Binomial Distrib.) ok in a limited h-regions

 7 TeV: NBD fit slightly deviate

at highest multiplicities

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Life starts getting interesting..

Increase .9 to 2.3 TeV (%) NSD

ALICE preliminary* 23.7 ± 0.5 +4.6-1.1 %

CMS 28.4 ± 1.4 ± 2.6 %

Pythia D6T (109) 18.7 % Pythia ATLAS CSC (306) 18.3 % Pythia Perugia-0 (320) 18.5 %

Phojet 14.5 %

QGSM 19 %

Larger increase of multiplicity at mid-rapidity than in MC generators

Tail grows faster ! Good news for the Heavy Ion program:

More charged particles will create a denser and hotter system !

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Physics Analysis

 Papers published

 ‘First Physics’, EPJC 65 (2010) 111

 Papers submitted

 Detailed analysis of charged particle multiplicity (0.9 & 2.36 TeV) EPJC, 18.4

 First look at multiplicity at 7 TeV

 Papers almost ready (900 GeV Data)

 Charged particle p_T

 Identified particles p_T (π, K, p)

 Strangeness production (K⁰, Λ, Ξ,Φ)

 Baryon-antibaryon asymmetry

 Bose-Einstein correlations

 Other ongoing Analysis

 π⁰ spectra, event structure, azimuthal correlations, h-φ correlations, high multiplicity events, ………

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P. Giubellino

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P. Giubellino

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P. Giubellino

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Charmed Mesons

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m

⁺

m

^-

invariant mass as measured by the Muon

Spectrometer

2.5 < h < 4

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Femtoscopy (HBT correlation)

0-9 TeV By correlating two (or more) particles

(i.e. Bose-Einstein enhancement for pairs of pions at low p_T), the ALICE

experiment will probe the space-time substructure of the dynamic matter at the femtometer (10 ^-15 m) scale.

These measurements are of great interest both for heavy ion and for proton-proton collisions. Indeed, the

space-time substructure of the "system"

created in proton collisions is not well understood, and may reveal information on the confinement process inaccessible through momentum-space probes alone

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In 1956, Robert Hanbury Brown and Richard Q. Twiss published A test of a new

type of stellar interferometer on Sirius, in which two photomultiplier tubes (PMTs), separated by about 6 meters, were aimed at the star Sirius. Light was collected into the PMTs using mirrors from searchlights. An interference effect was

observed between the two intensities, revealing a positive correlation between the two signals, despite the fact that no phase information was collected. Hanbury

Brown and Twiss used the interference signal to determine the apparent angular size of Sirius, claiming excellent resolution.

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P. Giubellino

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Thanks for your patience…

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Backup slides

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Rapidity Rapidity Rapidity

Single Diffraction (SD) Double Diffraction (DD) Double Pomeron Exch. (DPE)