Quarkonium production in AA collisions with CMS · Quarkonia '06, 27/06/2006 1 / 2 4 David...

1/24Quarkonia '06, 27/06/2006 David d'Enterria (CERN)

Quarkonium production inAA collisions with CMS

International Workshop on Heavy Quarkonium – 2006BNL, Jun 27th 2006David d'Enterria

➢ Physics: Color screening (QGP), low-x QCD (CGC) at LHC➢ Experimental setup: CMS muon system (J/ψ,ϒμμ)➢ AA @ 5.5 TeV simulation studies: µ ident., QQbar reco. ➢ Results: efficiencies, J/ψ,ϒ mass resolutions, S/B, rates➢ Summary

CERN, Geneva


Quarkonia: probe of high-density QCD media

➢ Dissociation (color screening) = hot QCD matter thermometer

➢ Probe of low-x gluon structure/evolution:

Lattice QQ free energy vs T:Spectral function vs T:

Suppression pattern vs ε :

[H.Satz, hep-ph/512217]

production via gg fusion: x~10-3 (10-5)Q2~10 GeV2

gluon saturation,non-linear QCD

[See e.g. K.Tuchin, this workshop]

_


Quarkonia: from SPS and RHIC to LHC

➢ PbPb @ √sNN=5.5 TeV, pPb @ √sNN=8.8 TeV:

● Factor x30-45 increase in energy compared to AuAu,dAu @ RHIC

● 30-45 times lower Bjorken x=2pT/√s, ~ 10-3 (10-5)

● Large perturbative cross-sections.

● High luminosities (high rates).

Heavy-ion physics at LHC:

- Plasma hotter, longer-lived than @ RHIC

- Access to lower x, higher Q2

- Unprecedented gluon densities

- Availability of new probes (Y,Y',Y'')

ϒ

LHCRHIC

Vogt, hep-ph/0205330


J/ψ production in AA at the LHC

➢ J/ψ at LHC will clarify SPS/RHIC suppression:

SPS

30

enhanced suppression ?

enhanced regeneration ?

[H.Satz, hep-ph/512217]

RHICLHC

● Onset of direct J/ψ suppression (TD~1.5 -2 Tc) ?● Large(r) regeneration by ccbar recombination ?

Energy density (GeV/fm3)


ϒ production in AA at the LHC

➢ Large cross-sections: dσ /dy ~ 20 x RHIC➢ ϒ melts only at LHC: TD~ 4 Tc

➢ ϒ unaffected by final-state interactions: - Null hadronic absorption

- Small # bbar pairs small ϒ regeneration

➢ ϒ spectroscopy: TD (ϒ’) ~ TD (J/ψ): ϒ’/ ϒ vs pT very sensitive to system temperature & size

Gunion, Vogt, NPB 492 (1997) 301

“Cleaner” probe than J/ψ}


Compact Muon Solenoid (|η|<5)


CMS Muon system

➢ 3 types of gaseous particle detectors for muon identification: - Drift Tubes (DT) in central barrel region - Cathode Strip Chambers (CSC) in endcap region - Resistive Plate Chambers (RPC) in barrel & endcaps

precise measurement of

muon position (momentum)

fast info for LVL-1 trigger

}


CMS Muon system

• Drift Tubes (DT) in central barrel• Resistive Plate Chambers (RPC) in barrel and endcaps

• Cathode Strip Chambers (CSC) in endcap region


Muon reconstruction

Tracking + ( Ecal + Hcal ) + Muon-chambers for |η |<2.4

Silicon Microstripsand Pixels

Si TRACKER CALORIMETERS ECAL

HCALPlastic Sci/Steel sandwich

MUON BARRELDrift Tube Chambers (DT)

Resistive Plate Chambers (RPC)PbWO

4


Muon reconstruction

● Best muon spectrometer at LHC (CMS)

● Excellent coverage: ~5 units of rapidity and 2π

● Strongest magnetic field: 4 T, 2 T (return yoke)

● Tag from mu-chambers, momentum resolution from Silicon tracker

● Ecal + Hcal + Magnet Iron absorbs hadrons

● Barrel: pTµ > 3.5 GeV/c

● Endcap: pLµ > 4.0 GeV/c


Simulation studies

➢Signals (J/ψ ,ϒ ): CEM, NLO-pp, EKS98 PDF, TAA

-scaled

➢ Light-q background (π ,K): HIJING normalized to dNch

/dη=2500, 5000

➢Heavy-Q background (c,b): NLO-pp, CTEQ5M1 PDF, TAA

-scaled

(1) (2) (3)

(0) Reconstruct single decay muons (efficiencies, acceptances, trigger ...).

(1) Construct dimuon inv. mass spectrum.

(2) Construct dimuon combinatorial background (like-sign muon pairs)

(3) Subtract combinatorial-bckgd. + yield integration (2σ around peak)

Olga Kodolova, Marc Bedjidian CMS AN-2006/011


PbPb ϒ + X μ+μ - + X in CMS

➢ MC simulation & visualization of Upsilon event (PbPb, dN/dη|η=0

= 3500) using pp software framework

ϒ µ+µ-


J/ψ , ϒ : μ reconstruction algorithm

➢ Primary vertex determination: - select pairs of pixel hits

with ∆φ giving 0.5 < pT < 5 GeV

- extrapolate each pair in RZ to the beam line.

➢ Track finding: - start from track candidate in muon stations - extrapolate inwards from plane to plane using vertex constraints

➢ Track selection by cuts: - fit quality (χ2) - vertex constraint

Si layers

Si pixels

σZ = 190mm

µ-track

µ-stations


J/Ψ, ϒ acceptances

➢ J/Ψ accepted above pT~2 GeV/c (low-p

T muons absorbed in material

at y=0, but punchthrough at y~2). High-pT acceptance ~15%

➢ ϒ accepted (~35%) down to pT=0 GeV/c. High-p

T acceptance ~15%

acce

pta

nce

acce

pta

nce

Improved low pT

J/Ψ acceptanceat forward rapidities

ϒ

J/Ψ J/Ψ

η

pT

pT (GeV/c)


J/ψ triggering (pT-η acceptance)

➢ Two different Level-1 settings:

L1 : optimized for high luminosity pp OL1 : low quality muon candidate (used in HI)➢Trigger condition: two L1 or L2 opposite-sign candidates

26000 J/ψ generated: (OL1,L2) 252 events, (L1,L2) 113 events.

➢ Total trigger efficiency: 0.97% (OL1-L2 chain)

0.44% (L1-L2 chain)

artificial dip(η Jacobian)


ϒ triggering (pT-η acceptance)

➢ Two different Level-1 settings:

L1 : optimized for high luminosity pp OL1 : low quality muon candidate (used in HI)➢Trigger condition: two L1 or L2 opposite-sign candidates

15700 Y generated: (OL1,L2) 3322 events, (L1,L2) 2590 events.

➢ Total trigger efficiency: 21% (OL1-L2 chain)

16.5% (L1-L2 chain)

artificial dip(η Jacobian)


Dimuon efficiency & purity vs dNch/dη

➢ ϒμμ embedded in PbPb event.

➢Efficiency:

ε(p,η)=εtrack-1

εtrack-2

εvtx

>80% for all multiplic. (barrel)

~65% for all multiplic. (barrel+endcap)

➢Purity = [true ϒ reco]/ [all ϒ reco]

~90% for all multiplicities

“realistic” LHC multiplicity range


μμ mass spectra (signal+background)

➢Pb-Pb, dNch

/dη|η=0

= 5000 , L = 0.5 nb-1

➢ Background: π/K (90% of Nch

) μμ (BR=63%)

➢ Background: c-,b-hadrons μ+X (BR~18% ,~38%)➢ Combinatorial backgd (mixed sources):

➢ J/ψ ,ψ ' peaks seen (S/B~0.6) All 3 ϒ peaks seen (S/B~0.07)

1 µ from π /K + 1 µ from J/ψ 1 µ from b/c + 1 µ from π /K


μμ mass spectra (signal+background)

➢Pb-Pb, dNch

/dη|η=0

= 2500 , L = 0.5 nb-1

➢ Background: π/K (90% of Nch

) μμ (BR=63%)

➢ Background: c-,b-hadrons μ+X (BR~18% ,~38%)➢ Combinatorial backgd (mixed sources):

➢ J/ψ ,ψ ' peaks seen (S/B~1.2) All 3 ϒ peaks seen (S/B~0.12)

1 µ from π /K + 1 µ from J/ψ 1 µ from b/c + 1 µ from π /K


Heavy-quarks decays: b,c → µ / J/ψ +X

δr is transverse distance between the intersection points with the beam line belonging two different muon tracks

I. Lokhtin, CMS-NOTE 2001/008

➢ J/ψ from B decays: ~20% all J/ψ at LHC➢ Secondary vertex finding and correlated background rejection:

primary J/ψ

J/ψ from Bμ

μ


J/ψ mass spectra (like-sign subtraction)

➢ Best mass resolution at LHC:

σJ/ψ

= 35 MeV/c2 in barrel+endcap (both muons |η| < 2.4)

“high” multiplicity dN

ch/dη|

η=0 = 5000

“low” multiplicity dN

ch/dη|

η=0 = 2500


ϒ mass spectra (like-sign subtraction)

➢ Best mass resolution at LHC:

σϒ= 54 MeV/c2 (barrel), and σϒ= 90 MeV/c2 (barrel+endcap)

Barrel+ Endcap:(both

muons

|η| < 2.4)

Barrel:(both

muons

|η| < 0.8)

“high” multiplicity dN

ch/dη|

η=0 = 5000


QQbar rates at CMS (1 nominal PbPb run)

➢ Pb-Pb 5.5 TeV: 1-month, L = 0.5 nb-1

➢ J/ψ ,ϒ statistics = O(105),O(104): differential studies (dN/dpT, dN/dy,

centrality, ...) possible


Summary

➢ J/ψ ,ϒ = unique probes of QCD media in A+A: - Step-wise “melting” pattern = absolute QGP thermometer - Production via gg fusion = probe of low-x QCD structure&evolution (CGC)

➢ Simulation studies of J/ψ ,ϒμμ in CMS (PbPb @ √sNN=5.5 TeV):

● Geometrical acceptances: ~15% (at high pT)

● Dimuon efficiency ~80% and purity ~90%, for all multiplicities● Best mass resolutions at LHC: σ

QQ ~ 1% m

QQ (barrel+endcap)

σJ/ψ

= 35 MeV/c2 (barrel+endcap), σϒ= 54 MeV/c2 (barrel alone)

● Full separation of ϒ family: bottomonium spectroscopy● Signal/Background: ~ 1(5), ~0.1(1) for J/ψ ,ϒ in barrel (+endcaps)● High rates expected (per year):

J/ψ ~ 180 kevents, ϒ ~ 25 kevents, ϒ ’ ~ 7 kevents, ϒ ’’ ~ 4 kevents

➢ Detailed differential studies (dN/dpT, dN/dy, centrality, ...) possible !


Backup slides


Charmonia Performances

ψ, ψ’ψ, ?ψ’ψ, ??ψ’ψ, ?ψ’perf.--few-20 GeV0-10 GeV0-20 GeVpt J/ψ

|η| < 2|η| < 2.5|η| < 0.9-4 < η < -2.5acc. η

60, --313, --245, --150, 7J/ψ , ψ ’

65 MeV

ALICE µ +µ - ATLAS µ +µ -CMS µ +µ -ALICE e+e-

70 MeV37 MeV35 MeVM res.

Bkg input: dNch/dy~2500-4000 in central Pb-Pb. for 1 month

central central central

BSS +/

min. bias

BSS +/

35

A.Dainese (HP'06)


Bottomonia Performance

➢

ϒ, ?ϒ’, no ϒ’’

ϒ, ϒ’, ϒ’’ϒ, ?ϒ’, no

ϒ’’ϒ, ϒ’, ?ϒ’’perf.

--few-10 GeV--0-8 GeVpt ϒ

|η| < 2|η| < 0.8(2.4)|η| < 0.9-4 < η < -2.5acc. η

45, --, --50, 17, 1221, 8, --30, 12, 8ϒ ,ϒ ’,ϒ’’

90 MeV

ALICE µ +µ - ATLAS µ +µ -CMS µ +µ -ALICE e+e-

145 MeV54(85) MeV90 MeVM res.

|η|<2.4

|η|<0.8

central central min. bias central

BSS +/

Bkg input: dNch/dy~2500-4000 in central Pb-Pb. for 1 monthBSS +/

A.Dainese (HP'06)


J/ψ from B in CMS & ALICE

➢

primary J/ψ

J/ψ from B

energy LHCat 2.0~J/ψ all

B from J/ψ

J/ψ → µ+µ-

J/ψ → e+e-

CMS: CMS/NOTE 2001/008, ALICE: CERN/LHCC 99-13

A.Dainese (HP'06)


QQbar at the LHC

➢ Quarkonia measurements in heavy-ion collisions in CMS◆ Authors: ◆ Detailed study of background, reconstruction, signal extraction◆ Extended acceptance and higher efficiency triggering◆ Study as a function of bulk multiplicity◆ Increased acceptance and efficiency, include forward regions


Quarkonia at LHC: experimental challenges

● Important contribution to ψ production from B → J/ψ (ψ ’) + X ● ~20% of J/ψ● ~40% of ψ’

● Normalization:

Drell-Yan not available for normalization (from qq, while quarkonia from gg at LHC; and small cross section at LHC)

W, Z?● Different Q2, x

Open heavy flavour, but …● Energy loss?● Thermal charm production?

Possible alternative: RAA (à la PHENIX)

Need to measure this!


Quarkonia acceptances at LHC

➢

µ+µ-µ+µ- µ+µ-

e+e-

-4<η<-2.5

ϒJ/ψ

-4<η<-2.5

ac

ce

pta

nc

e (

%)

J/ψ ϒ

A.Dainese (HP'06)


Low-x at the LHC (nucleus)

➢PbPb @ 5.5 TeV, pPb @ 8.8 TeV:

(i) Very high √s → Bjorken x=2pT/√s, ~30-45 times lower than AuAu,dAu @ RHIC

(ii) Very large perturbative cross-sections.

Nuclear xG(x,Q2) is basically unknown for x<10-3 !

Armesto, nucl-th/0410161


Experimental access to low-x parton distrib. (II)

➢ Kinematical (x,Q2) domains covered experimentally:

➢ Most existing low-x nPDFs measurements are in the non-perturbative regime

e-p, p-p

e-A, p-A

much less nuclear PDF dataavailable:

Dd'E, nucl-ex/0404018


Colour Glass Condensate

PomeronReggeon

MesonsIllustration only. There is no “PDFs” nowin the sense of pQCD factorization

➢ CGC: Effective field theory of QCD in high-energy (high density, small-x) limit.

• hadrons = classical fields (saturated gluon wave-function) below new scale: Q2<Qs

2

• “Sat. momentum”: A-“amplified”: Qs2 ~ A1/3 ~ 1.5,3 GeV2 RHIC,LHC

• Perturbative calculations (strong Fµν field ⇒ weak coupling αs<<1).

• had.+had: collision (amplitude level) of 1(2) gluon wave function(s): “resums” all mult. scatts. • Color Glass (“static” color sources = quarks) Condensate (high gluon occupation values).

➢ Quantum evolution: BK, JIMWLK: Non-linear, all-twist eqs. in saturation region

xG(x,Q2)= dNg/dy

Q2 = 10 GeV2


Compact Muon Solenoid (|η|<5)


Local Pattern Recognition (I)

● Barrel (DT):● Reconstruct position of each channel above threshold using

effective drift velocity● Reconstruct φ super-layer hits (time-space conversion)

● Drift velocity depends on B field and impact angle

● Cluster hits (linear fit): 2D segment● Fit 2D lines separately in r-φ and r-z through the 8+4 layers

of chamber● L/R ambiguities solved by best χ 2

● Combine into 3D segments, use segment position and direction for tracking

● Resolution: 100 µ m in φ view, direction ~1mrad

● Apply impact angle correction on time-to-distance relation and refit

● Calculate position (center of gravity) of the track-segment and its angle in the super-layer (+error matrix)

up to 12 hits/station

DT’s and CSC’s are multi-layer detectors: First step of muon reconstruction is local pattern recognition Reconstruct track segments in the DT and CSC detectors

Norbert NeumeisterCERN PH / HEPHY Vienna


Local Pattern Recognition (II)

• Endcaps (CSC):– Reconstruct 3D hits

– Associate hits with linear fit (only one hit per layer)

– Fit “Gatti” function to the spatial shape of 3-strip charge distribution to determine centroid of cluster in layer

– Associate two projections by time coincidence

– Fit 3D segments through the collection of wire and strip clusters in chamber; linear fit

– Resolution: 120–250 µ m form bending coordinate, depending on chamber

up to 6 hits/station



Standalone Muon Reconstruction

● All muon detectors (DTBX, CSC and RPC) are used● Seed generation:

– external: Level-1 trigger (vector at 2nd station) → Level-2 reconstruction

– internal: track segments from local pattern recognition ● Fit:

● Kalman filter technique applied to DT/CSC/RPC track segments● Use segments in barrel and 3D hits in endcaps● Trajectory building works from inside out● Apply χ 2 cut to reject bad hits● Track fitting works from outside in● Fit track with beam constraint

● Propagation:● Non constant magnetic field● Iron between stations, propagation through iron (more difficult

than in tracker!)● GEANE used for propagation through iron



Global Muon Reconstruction

Start from standalone reconstructed muons:

• Seed generation– Get muon trajectory at innermost muon station– Propagate to outer tracker surface and to interaction point– Open window for track reconstruction

• define region of interest through tracker based on Level-2 track with parameters at vertex

• fixed/dynamic region– Create one or more seeds for each Level-2 muon

• Construction of trajectories for a given seed● Propagate from innermost layers out, including hits in muon chambers– Resolve ambiguities– Final fit of trajectories

tremendous gain in resolution

Inclusion of Tracker Hits



Tracking Strategy

Rely on few measurement layers, each able to provide robust (clean) and precise coordinate determination

2 to 3 Silicon Pixel, and 10 to 14 Silicon Strip Measurement Layers

6 layersTOB

4 layersTIB

3 disks TID 9 disks TEC

R-phi (Z-phi) onlyR-phi (Z-phi) onlymeasurement layersmeasurement layers

R-phi (Z-phi) & StereoR-phi (Z-phi) & Stereomeasurement layersmeasurement layers

Radius ~ 110 cm, Length ~ 270 cm η~1.7

η~2.4

At high luminosity (~ 20 min. bias events every 25 ns):

R = 10 cm 25 cm 60 cm

Nch/(cm2*25ns) = 1.0 0.10 0.01



Muon pT Resolution

Level-2:

Level-3:σ = 0.013 σ =

0.015σ = 0.018

σ = 0.12 σ = 0.14 σ = 0.17

barrel endcapsoverlap

Order of magnitude improvement



Muon pT Resolution Norbert NeumeisterCERN PH / HEPHY Vienna


HLT muon track reconstruction

(G. Bagliesi – EPS 2003)

43

Inclusion of Tracker Hits: “Level-3”•Define a region of interest through tracker based on L2 track with parameters at vertex• Find pixel seeds, and propagate from innermost layers out, including muon

Standalone Muon Reconstruction: “Level-2”• Seeded by Level-1 muons• Kalman filtering technique applied to DT/CSC/RPC track segments•GEANE used for propagation through iron• Trajectory building works from inside out• Track fitting works from outside in• Fit track with beam constraint

Single muons10<Pt<100 GeV/c

Level-3Algorithmic efficiency

η


Residuals and Pulls in r-φ / ndf2

χ 49.27/17

Constant 129

Mean 0.0436

Sigma 0.9774

xσ)/sim-xrec

(x-5 -4 -3 -2 -1 0 1 2 3 4 5

0

200

400

600

800

1000

1200

1400

2

-1000 -500 0 500 1000

X0sim X0

f it µm

0

200

400

600σ = 109 µm

residual pull

DT

CSC

/ ndf2χ 1231/23

Constant 1.272e+04

Mean 0.0002398

Sigma 0.02302

(cm)φsim-x

φrecx

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.20

2000

4000

600

800

1000

1200

1400 / ndf2χ 210.4/57

Constant 6310

Mean 0.01169

Sigma 1.238

φxσ )/φ

sim-xφ

rec (x

-5 -4 -3 -2 -1 0 2 3 4 50

1000

2000

3000

4000

5000

6000

7000

1


The CMS experiment (|η|<5)

Physics program: Higgs (EWSB), Beyond SM, Heavy-Ions, low-x QCD …

Silicon Tracker (|η| < 2.5):Si pixels, Si stripsGood eff. & purity for pT>1 GeV

Pixel occupancy (PbPb): 1-2%

∆p/p ≈ 2% for pT<70 GeV

Calorimeters (|η| < 5): EM: PbW0

4

HCAL: Scint.+steel

Magnet :4 T solenoid

Muon tracking (|η| < 2.5):

µ from Z0, J/ψ , ϒ

σm ≈ 50 MeV at the ϒ mass DAQ & Trigger

High rate capability for A+A, p+A, p+p

HLT: real time HI event reco


Muon trigger system

➢

G. Bagliesi – EPS 2003 – Aachen 17-24/7/2003 46

Level-1 (~µs) 40 MHz High-Level ( ms-sec) 100 kHzEvent Size ~ 106 Bytes

40 MHzClock drivenCustom processors

100 kHzEvent drivenPC networkTotally software

100 HzTo mass storage

two trigger levelstwo trigger levels

All charged tracks with pt > 2 GeV

Reconstructed tracks with pt > 25 GeV

Operating conditions:one “good” event (e.g Higgs in 4 muons )

+ ~20 minimum bias events)

Combines information from the three independent trigger systems


Silicon Tracker Layout

➢

6 layersOuterBarrel

9 Disks in the End Cap

1 Single detector 2 detectors back to back

4 layersInnerBarrel3 layersPixel Barrel

3 Disks2 Pixel Disks

70M Pixel channels, 11M Strip channels

Pixel: 100x150µm2, Inner Strips: 80µmx6.1cm, Outer Strips: ~150µmx9.1cm


Tracker in heavy-ion environment

➢Simulated Central Pb+Pb Event

(HIJING+OSCAR+IGUANA)

Simulation dNch/dy ~ 3000

Channel Occupancy

Pixel Detector Occupancy of < 2%

(less than 10% for outermost layers)

Including Pulse Height Information

Key for successful tracking Excellent soft physics capabilities

Pixels InnerStrips

OuterStrips

Allows correction of detector effects Provides useful dE/dx information


Suppression scenario (ALICE)

➢• Suppression-1

Tc =270 MeVΤD/Tc=1.7 for J/Ψ ΤD/Tc= 4.0 for ϒ.

• Suppression-2 Tc=190 MeVΤD/Tc=1.21 for J/Ψ ΤD/Tc= 2.9 for ϒ.PRC72 034906(2005)

Hep-ph/0507084(2005)

Good sensitivity J/ψ , ϒ & ϒ ’


γ γ , γ A : physics topics

➢ Typical diagrams for γγ and γA collisions:

Pomeron, gluon, or meson

QED, precision QCD

l +l -, C-even cc bb, W+W -...

QED in strong regime (Zαem

~1),heavy-Q spectroscopy, [quartic GC (W Wγγ), ...]

Precision QCD(low bckgd, simpler initial state than p,A+A)

Quarkonia, heavy-Q, jets ...

Nuclear GA(x,Q2), low-x physics,

QQbar in cold nuclear matter

➢ Physics:

➢ Measurements:

➢ Topics:

_ _

➢ All UPC measurements at RHIC: ZDC-triggered (neutron tagging) !

Dd'E, nucl-ex/0601001

Quarkonium production in AA collisions with CMS · Quarkonia '06, 27/06/2006 1 / 2 4 David...

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