Tapan Nayak For the ALICE Collaboration

Nov 18, 2006 QM06: pp physics in ALICE 1

Tapan NayakFor the ALICE Collaboration

Proton-proton physics in ALICE


1.Rich pp-physics program at unexplored energies:• Soft physics (low pT) program• First time: above the cosmic “knee”• Min. bias events, constraints for under-lying event• Multi-parton interactions (high multiplicity pp events)• Interplay of non-perturbative vs. perturbative physics• New x-Bjorken region (10-3-10-5)

• Heavy Flavour • mini-jets and jets

o Hadronization processeso Fragmentation processes

• Collision energy dependence all above• Potential for new physics

2. pp collisions provide basis for understanding heavy-ion collisions

p

p

Motivation


Low Luminosity (pp)Low (Ions)

• pp @ 14TeV• Luminosity (Lmax): 1034 cm-2 sec-1

• Lmax for ALICE: 3x1030 cm-2 sec-1

(200 kHz rate limit as TPC drift time is 90sec)

LHC Schedule:• Aug 2007: Collider Closure • Nov 2007: FIRST collisions: pp @ 900 GeV

• Dec 2007: pp @ 2200 GeV(?)

• 2008: pp @ 14TeV at low luminosity (~6x1026 cm-2sec-1)

• LOW LUMINOSITY runs are ideal for ALICE

CERN - Large Hadron Collider (LHC)


ITSLow pt trackingVertexing

ITSLow pt trackingVertexing

TPCTracking, dEdxTPCTracking, dEdx

TRDElectron IDTRDElectron ID

TOFPIDTOFPID

HMPIDPID (RICH) @ high pt

HMPIDPID (RICH) @ high pt

PHOS,0 PHOS,0

MUON -pairs MUON -pairs

PMD multiplicityPMD multiplicity

V0, T0Trigger + multiplicity

ACORDEcosmics

FMDch multiplicityFMDch multiplicity

ALICE layout

EM Calorimeter (future)


• Soft (100MeV) to hard (>100GeV) physicsSoft (100MeV) to hard (>100GeV) physics• low pT cut-off (~100 MeV):

=> Low magnetic field: 0.2-0.5 T & Low material budget: 7%=> Low magnetic field: 0.2-0.5 T & Low material budget: 7%• excellent tracking and PIDexcellent tracking and PID• dedicated di-electrons and di-muonsdedicated di-electrons and di-muons• high resolution calorimeter for direct photonshigh resolution calorimeter for direct photons

(charged particles)

• Central Barrel (-0.9 < < 0.9)• tracking, PID (ITS, TPC, TRD, TOF)• single arm RICH• single arm EM cal (PHOS)

• Multiplicity• charged (barrel+FMD): (-5.4 < < 3)• photons in PMD (-2.3 < < -3.7)

• Forward muon arm (2.4 < < 4.0)• absorber, dipole magnet• tracking and trigger chambers

• Trigger, timing, luminosity:• ZDC, V0, T0, CRT

• EM Calorimeter (future)

Unique features of ALICE


ROOT

AliRoot

STEER

Virtual MC

G3 G4 FLUKA

HIJING

MEVSIM

PYTHIA6

PDF

EVGEN

HBTP

HBTAN

ISAJET

AliE

n +

LC

G

EMCAL ZDCITS PHOSTRD TOF RICH

ESD

Analysis

AliReconstruction

PMD

CRT FMD MUON TPCSTART RALICESTRUCT

AliSimulation

JETAN

1. Event Generators

4. Analysis

2. Simulation

3. Reconstruction

Physics Data Challenge (2006)• 100M pp events being produced using GRID

• 10M already produced• Configuration:

• min. bias events with Pythia • addition of special physics events

• Most of the Analysis framework exists

Offline Framework


Momentum Resolution

central Pb–Pbpp

pT/p

T (

%)

pT (GeV/c)

central Pb–Pb

pppT/p

T (

%)

pT (GeV/c)

For pT < 2GeV: 0.5-0.8% For 2 < pT < 100GeV: 1-5%

Detector Performance


separation @ 3 separation @ 2

Stable hadrons (, K, p): 100MeV<p<5 GeV (few 10GeV)

Topological identification (K0, K+, K-, ): up to ~ 10 GeV

Leptons (e, ), photons, 0, electrons in TRD: p > 1 GeV, muons: p > 5 GeV 0 in PHOS: 1 < p < 80 GeV

Particle Identification


dN

/d

UA5, ZPC 33 (1986), CDF, PRD 41 (1990)

All chargedparticles

All Charged particles

PDC06 data:400K events (corrections)100K events (analysis)Different event sample!

Reconstruction with TPC

Reconstruction with SPD

pp @ 14TeVMin biasALICE

dN

/d

dN

/d

Pseudo-rapidity distributions

Good agreement in central region


Violation of KNO scaling:Multiplicity distributions expected to “scale” as per to single parton-parton interactions. Deviations attributed to multiparton interactions, jet-minijets.

Multiplicity distributions

E735: Phys. Lett. B 435 (1998) 453

N/<N1>

546GeV

900GeV

1800GeV <N1>=31

200GeV<N1>=20

Walker PRD 69 (2004)

>80>60

>40

High multiplicity trigger (threshold on # of SPC chips hit

Multiplicity reaching to >10 times the mean value – interesting for multi-parton interactions, event structure, HBT, multiplicity correlations, rapidity gaps ….

Multiplicity reach

Nch

900GeV

14TeV5.5TeV

2.2TeV

Probability for an event to have larger than Nch multiplicity

(||<0.9)

ALICE

Full phase space


CDF: PRL 61, 1819 (1988)

Charged particles

pT distributions

pT reach

pp @ 14TeVMin biasALICE

• With 100k events, up to 10 GeV/c • With 100M events, up to 50 GeV/c

pT (GeV/c)


CDF: PRD 65,72005(2002)

Nch

<p

T>Mean pT vs. Multiplicity

ALICEpp @ 14TeV

E735 Fermilab

Nch

<p

T>

• <pT> vs. multiplicity shows different behavior for different identified particles.• In ALICE: inclusive and identified particles will be used in the study with low to high pT range

Protons

Kaons

Pions

CDF data

All pT

pT>0.4GeV/c


K0s

pp @ 14TeV

Strangeness: Baryons, Mesons

reconstruction

pp@14TeV

(p,-)

(

)/K

0 s

• PYTHIA for min. bias and underlying events (with different settings) give different results.• Flavour dependence of the ratio

• Baryon production mechanism • Constraints for underlying events

K0s p p

Yield per event

0.1 0.01 2X10-4 10-5 0.4 0.4


in %

Proton – antiproton asymmetry

H1: Δη ~ 7

– 9.61 ← η

Rossi & Veneziano: gluons carry baryon number resulting in substantial baryon production in central rapidity region. (Kopeliovitch & Zakharov Z. Phys. C43 (1989) 241). Expectation at LHC:

Baryon # transfer in rapidity

ALICE advantages:

• Large rapidity gap• Asymmetry vs. multiplicity• With protons, ….. • Statistics: 108 events (one month):

109 , 107 p, 106 , 104 , 103

q

q qStandard case

This is suppressed exp (-1/2 y)

String Junction


• Motivation: - small xBJ physics- pQCD in a new energy domain- HQ fragmentation functions- gluon shadowing- quarkonia production mechanism, charm and beauty cross sections

• ALICE advantages: - combination of electronic, muonic and hadronic channels:

Central barrel (-0.9<<0.9) and Muon arm (2.5<<4)- coverage close to pT~0 for quarkonia and open charm- high precision vertexing

• Physics analysis:- hadronic decays: D0K , D+-K, DsK K*, Ds, …

- Leptonic decays: - B l (e or ) + anything. - Inv. mass of lepton pairs: BB, DD, J/, ’, family, B J/+ anything.- BB (J/ )- e- correlations.- W+- l+- , Z0l+l-.

- J/ polarization

Heavy flavour in pp


D0 Kc = 124m)

PrimaryVertex B

e

Xd0

rec. track

B e + X

Pb+Pb at 5.5TeV

109 events

pp @ 14TeV

up to 11–14 GeV/c with 70M evts


e+e- Minv

+- Minv

+- Minv

Electronic channel Muonic channel

Quarkonia

Statistics: in one year of data (109 min bias events):• 8.5x106 J/ and 6.5x103 in the muonic chanel• 5x105 J/ in the electronic channel


hadrons

hadrons

leading particle

a

b

c

d

c

chbbaa

abcdba

T

hpp

z

Dcdab

td

dQxfQxfdxdxK

pdyd

d

0

/222

)(ˆ

),(),( Parton distribution functions Hard scattering c.s. Fragmentation function

• Motivation: - test of perturbative QCD predictions- Jet fragmentation properties- understanding the hadronization processes

• Jet rates:- pT>100GeV:

• Physics analysis: Jet trigger (for >100GeV)high pT spectra Jet reconstruction & jet structure observables:

- jT , fragmentation function, jet-shape- di-hadron correlations-Jet correlations

High pT and jets in pp


2-Jet in pp

Displays forpT

threshold

00.20.40.60.81.01.21.41.61.82.0


• Motivation: - thermal photon spectrum- QCD tests, PDF determination- pp: initial stages

• Physics analysis: - thermal photon identification- prompt photons: isolation method- photon HBT- Photon tagged jets (-jet correl.)

- E = Ejet ( energy provides independent

measure of jet energy)- emitted in opposite direction PHOS

R

ALICE can measure photon tagged jets with• E > 20 GeV (PHOS + TPC)• E > 40 GeV (EMCAL+TPC)

Dominant processes (pQCD contributions)

g + q → γ + q (Compton)

q + q → γ + g (Annihilation)

Direct photons in pp


• ALICE advantages at LHC: Low pT, excellent PID & vertex; and reconstruction of high pT jets Ideal to study min. bias & underlying events at low luminosity

• Unique physics with one year data: Global event characteristics:inclusive and identified

distributions multiplicity distributions, fluctuations/correlations pT distributions

Particle ratios, strangeness Baryon transport, rapidity gap <pT> vs. multiplicity Heavy quarks (total c and b cross sections) high pT spectra, jets direct photons ………

• pp study provides important benchmark for all heavy-ions topics

• ALICE pp program is complementary to dedicated pp experiments @ LHC

Summary


TPC sector test: Cosmic rays

Single event display of one pp event


Thanks to many of the colleagues who have helped to put the talk together

- ALICE Physics working groupsand in particular to

ALICE First Physics working group,

Main references:1. ALICE PPR – Vol-12. 2. ALICE PPR – Vol-2


Luminosity & cross sections

• Luminosity is related to the rate & cross section:• L in pp measured by: V0, T0, ITS and Luminometers• Reduction in luminosity at ALICE IP from LHC max: 1034

• Final L from theoretical c.s. and TOTEM measurements• Expected uncertainty in estimated L : ~5%

.Ldt

dNR

5.05.97177132610314

4.34.955609.519895.5

3.5441457.615752.2

33.432356.312.5660.9

dN/d (=0) (inel)

dN/d (=0) (ND)

<Nch> (inel)

<Nch> (ND)

(SD)

(el) (total)

Sqrt(S) TeV

QGSM model predictions: A.B. Kaidalov

Total cross section

Compilation by R.M. Godbole et al.


Beam Energy (TeV) 0.45 1.2 6 to 7 6 to 7 6 to 7

Number of bunches 43 43 43 43 156

* [m] 10 10 10 10 10

Crossing Angle [rad] 0 0 0 0 0

Transverse emittance [m] 3.75 3.75 3.75 3.75 3.75

Bunch spacing [ns] 2025 2025 2025 2025 525

Bunch Intensity 1x1010 1x1010 1x1010 4x1010 4x1010

Luminosity [cm–2 s–1] 4x1027 1x1028 6x1028 1x1030 3.5x1030

Inelastic Rate [Hz] 144 450 3600 57600 201600

LHC Beam Parameters


LHC

B factories

Tevatron


J/ψ

108

106

104

102

100

Q2 (

GeV

2)

100 GeV

Tapan Nayak For the ALICE Collaboration

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