The ALICE experiment at LHC

Domenico Di BariDipartimento Interateneo di Fisica

INFN-Bari

4th Summer School on THE PHYSICS OF LHC 14-19 jun 2010 Martignano, Grecìa Salentina (Lecce, Italy)

P. Giubellino

PLC 20J. Schukraft3

HI @LHC: Constraints and Solutions

Extreme particle density : dNch/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 pt: from very soft (0.1 GeV) to fairly hard (100 GeV)

very thin detector, modest field 0.5 T (low pt), ALICE: ~ 10%X0 in r < 2.5 m (typical is 50-100%X0) vertex detector works as ‘standalone low pt spectrometer’ (tracking & PID)

large lever arm + good hit resolution (large pt) B= 0.5T, tracking L ~ 3.5m, BL2 ~ like CMS !

PLC 20J. Schukraft4

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 experimentcombine 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)

5

Detector:Size: 16 x 26 metersWeight: 10,000 tons

Collaboration:> 1000 Members> 100 Institutes > 30 countries

ALICEACORDEV0T0ZDCFMDPMD

Are you asking me if QGP was here? I

don’t know. Please, call the CSI experts…

AHA, AHA, here is the

Higgs!!!

21/4/2010 28th RRB J. Schukraft8

ALICE StatusComplete: 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

Material budget distribution in ALICE

Radial distance from beam line

X/X0<10% up to 250 cm

from IP

Good precision for

e/ measurement

s

Photon convertion

point distrib. @7TeV

Actual agreement of data with MC

< 8%

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some anxious minutes waiting for collisions..

~ 16:35

21/4/2010 28th RRB J. Schukraft12

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

21/4/2010 28th RRB J. Schukraft14

‘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

12/3/2010 Yale J. Schukraft15

A few days later…

TPC trackTRD track HMPID

Cherenkov Ring

Muon Spectrometer

ITS

TPC, TRD, TOF, HMPID

On 6th December, ‘stable beams’ were declared & we could switch onall ALICE detectors for the first time..

21/4/2010 28th RRB J. Schukraft16

Data Taking Summary

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

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ALICE efficiency

ALICE PHYSICS RUN TIME

cum

mul

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LHC STABLE BEAMS

efficiency (%)

>15 Million interactions

> 150 kMuon triggers

Inter. rate~ 30 – 90 Hz

Integrated Data taking efficiencysince 30.3 ~ 85%

12/3/2010 Yale J. Schukraft17

Tracking works beautifully

Beam spot at 2.36 TeV

TPC pt spectrumPreliminary

preliminary alignment !

SPD Vertex resolution versus # tracks

Plots as shown on 18 Dec ‘LHC’ jamboree

21/4/2010 28th RRB J. Schukraft18

alignment with cosmics only

s=181 mmafter alignment

before alignment

DataMC

pT = 1 – 1.5 GeV/c

DataMC

Impact parameter DCA

pT = 1 – 1.5 GeV/c

cosmics + pp ( = 0 and π)

Getting to know ALICE: Shape

18

SPD

21/4/2010 28th RRB J. Schukraft19Results shown on 17 Febr LHCC

PID (or 6 ways to measure Kaons)

ALICE - Work in Progress

ALICE - Work in Progress

ALICE - Work in ProgressK ® mn

ALICE Work in Progress

K0s ® pp

# 6:HMPID Cherenkov

p

K p

12/3/2010 Yale J. Schukraft20

Plots as shown on 18 Dec ‘LHC’ jamboree

The Particle Zoo Revisited:

PDG: 1115.7 MeV

L ® pp

PDG: 497.6 MeV

K0s ® pp

PDG: 1115.7 MeV

L ® pp

… National Geographic was sort of correct..

F ® K+K- PDG: 1019.5 MeV

21/4/2010 28th RRB J. Schukraft21W(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 pApril 2010

12/3/2010 Yale J. Schukraft22

Plots as shown on 18 Dec ‘LHC’ jamboree

More Particles..

p0 ® ® e+e- e+e-

p0 ® 1 < pt < 1.5 GeV

PHOS (9 m2)

X ® Lp ® pp p

Reconstruction from conversion

12/3/2010 Yale J. Schukraft24

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

TOFProtons

Kaons

Pions

all plots:preliminary calibration & alignment !

TPCNo vertex cut !

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(Anti)Nuclei

P. Giubellino

Event Classess = 0.9 and 2.36 TeV

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

Non-single diffractive (NSD) = ND+DDUse measured cross sections for diffractive processes

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

s = 7 TeVDiffraction is quite unknownHadron-level def. of evts to minimize model

dependenceAll events that have at least one charged primary particle

in |η| < 1: “INEL>0”27

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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 particlescreated 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) ofmany numbers we need to (re)measure toget confidence in our detectors, tune thesimulations, 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 ALICEhas started for good !

dN/dh: comparison to exp.

NSD 2.36 TeV NSD 900 GeV INEL 900 GeVALICE preliminary 4.43 ± 0.01 ± 0.16 3.58 ± 0.01 ± 0.12 3.02 ± 0.01 ± 0.07ALICE EPJC 65 111 (2010) 3.51 ± 0.15 ± 0.25 3.10 ± 0.13 ± 0.22CMS 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 ± ?

Multiplicity distributions @ 0.9,2.36,7 TeV

0.9 TeV: consistent with UA5Fit 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 !

21/4/2010 28th RRB J. Schukraft33

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 pT

Identified particles pT (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, ………

P. Giubellino

P. Giubellino

P. Giubellino

Charmed Mesons

m+ m- invariant mass as measured by the Muon

Spectrometer

2.5 < h < 4

Femtoscopy (HBT correlation)0-9 TeV

By correlating two (or more) particles (i.e. Bose-Einstein enhancement for pairs of pions at low pT), 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

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.

P. Giubellino

Thanks for your patience…

Backup slides

Rapidity Rapidity Rapidity

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