Bottomonium first results from LHC experiments Nuno Leonardo - - PowerPoint PPT Presentation

Bottomonium first results from LHC experiments

Nuno Leonardo (Purdue University) for the LHC Collaborations Hadron2011 Munich, June 15, 2011

XIV International Conference on Hadron Spectroscopy

bottomonia@LHC,

• N. Leonardo

HADRON’2011

di-lepton signals

• μμ, ee spectra
• detector resolution

2

• verview

pp @ 7TeV

• data-driven efficiency
• cross section
• prospects

PbPb @ 2.76TeV

• RAA, cross section
• ϒ’ suppression

introduction

• LHC
• motivations

bottomonia@LHC,

• N. Leonardo

HADRON’2011

LHC luminosity

3

pp@7TeV

2011 (2010) . ATLAS, CMS: L~1k (40) pb-1 LHCb: L~300 (40) pb-1 ALICE: L~2 (<1) pb-1

pp@2.76TeV

ATLAS, CMS: L~ 241 nb-1 LHCb: L~ 67 pb-1 ALICE: L <1 pb-1

PbPb@2.76TeV

ALICE, ATLAS, CMS: L~9 μb-1 LHCb: n/a

Lpp ≈ 1030 - 1033 cm-2 s-1 LPbPb ≈ 1025 - 1027 cm-2 s-1 [lpc.web.cern.ch]

f b-1 !

bottomonia@LHC,

• N. Leonardo

HADRON’2011

ALICE, ATLAS, CMS, LHCb

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bottomonia@LHC,

• N. Leonardo

HADRON’2011

LHC experiments (cont’d)

• all four detectors have the capability to study bottomonia
• complementary phase space and physics coverage
• e.g. central vs forward rapidities, pp vs heavy-ion environments
• based on different: B field, detector technologies, DAQ

capabilities, emphasis on hermeticity or particle ID

5

bottomonia@LHC,

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HADRON’2011

then... & now

6

Fermilab Summer 1977 CERN, Summer 2010

... a spectroscopists delight!

bottomonia@LHC,

• N. Leonardo

HADRON’2011

CDF

2.9 fb-1

large set of results

7

CESR- 1980/90s CUSB, CLEO Tevatron-2000s CDF, D0 D0

1.3 fb-1

BaBar: ϒ(3S)→ηb(1S)γ Belle: ϒ(5S)→ ϒ(2S)ππ

➥ ➥

PEPII/KEKB-2000s BaBar, Belle Zb→ϒ(nS)π±

(Bottomonium-like exotica: 2 charged states just above

• pen beauty B*B, B*B*

thresholds)

bottomonia@LHC,

• N. Leonardo

HADRON’2011

direct production indirect production

contribution from feed down transitions from heavier bottomonia

➥ 30-50% of full ϒ(1S) productions no contribution from long-lived states

bottomonium spectroscopy

(below open beauty threshold)

bottomonia@LHC,

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HADRON’2011

phenomenology

9

• heavy quarkonia constitute an ideal

laboratory for testing interplay between perturbative and non-perturbative QCD

• bottomonium (and in general, quarkonium)

production not satisfactorily understood

• theoretically and experimentally puzzling
• no theory has simultaneously explained

Tevatron measurements of both cross section and polarization

• non-relativistic QCD (incl. color octet), color

singlet model, color evaporation model, etc

(note: NNLO* is not a complete NNLO, possibility of large uncanceled logs) (note: drastic change of CSM predicted polarization from LO to NLO/NNLO*)

T L

bottomonia@LHC,

• N. Leonardo

HADRON’2011

bottomonia at the LHC?

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• phenomenology
• large b-quark mass ➩ non-relativistic effective approaches better realized
• no feed-down from long-lived b-hadrons
• unprecedented energy regime
• extended reach, eg probe pT>20GeV, best discriminate between models
• high cross section (and luminosity) ➩ bottomonia produced copiously
• allow new era of bottomonium precision measurements
• heavy ion
• 1 month per year dedicated to heavy-ion physics run
• cross sections ~50 times larger, energy density ~3 times higher than at

RHIC ➩ will allow first significant measurements of the ϒ resonance family

• improve overall understanding of the cold and hot nuclear matter effects
• LHC calls for precision studies of bottomonia at high temperature

di-lepton signals

bottomonia@LHC,

• N. Leonardo

HADRON’2011

L~0.6pb-

1

LHCb

12

Nϒ≈48k

bottomonia@LHC,

• N. Leonardo

HADRON’2011

ATLAS

13

Nϒ≈23k

bottomonia@LHC,

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HADRON’2011 14

)

2

(GeV/c

µ µ

m

10

2

10

)

2

Events/(GeV/c

1 10

2

10

3

10

CMS Preliminary = 2.76 TeV

NN

s PbPb

• 1

b µ = 7.28

int

L

• J/

(1,2,3S)

• Z

> 4.0 GeV/c

µ T

p

CMS

ee μμ μμ

PbPb@2.76TeV

Nϒ≈138k (|η|<2.4)

N1S=23,390±194 N1S=7,298±133 N1S=3,999±113

bottomonia@LHC,

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HADRON’2011

momentum/mass resolution

15

|η| < 0.8

CERN-PH-EP-2011-041 CERN-PH-EP-2011-057

L~13 nb-1

σ~94MeV σ~46MeV

(up to 110 MeV at higher rapidities)

σ~21MeV

(up to 50 MeV at higher rapidities)

σ~13 MeV

L~5.2 pb-1

CERN-PH-EP-2011-018 CERN-PH-EP/2010-046

Alice Atlas LHCb CMS

CMS-PAS-TRK-10-004

bottomonia@LHC,

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HADRON’2011

prior expectations (before LHC startup)

16

arXiv:nucl-ex/0702045v1

⎛ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ⎝ ｜ ｜ ｜ ⎛ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ⎝ ｜ ｜ ｜

ATLAS simulation CMS simulation LHCb simulation ALICE simulation

pp @ 7TeV

• LHCb-CONF-2011-016, 32pb-1
• CMS-BPH-10-003 (arXiv:1012.5545,PRD), 3pb-1

➪ see also talks by B.Akgun and G.Sabatino

• n Tuesday parallel session Quarkonia/3

bottomonia@LHC,

• N. Leonardo

HADRON’2011

cross-section ingredients

18

(1S) (GeV/c) !

• f

T

p 2 4 6 8 10 12 14 (1S) ! y of 2 2.5 3 3.5 4 4.5

Acceptance

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

A c c e p t a n c e ε f f i c i e n c y s i g n a l y i e l d s

polarization: LHCb LHCb LHCb CMS CMS

bottomonia@LHC,

• N. Leonardo

HADRON’2011

ϒ(nS) differential cross sections

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ϒ(2S)/ϒ(1S): 0.26±0.02±0.04 ϒ(3S)/ϒ(1S): 0.14±0.01±0.02

(|y|<2)

CMS LHCb

(1S) (GeV/c) !

• f

T

p

2 4 6 8 10 12 14

dy [nb/(GeV/c)]

T

(1S)X)/dp ! " (pp #

2

d

• 4

10

• 3

10

• 2

10

• 1

10 1 10

2.0 < y < 2.5 2.5 < y < 3.0 3.0 < y < 3.5 3.5 < y < 4.0 4.0 < y < 4.5 2.0 < y < 2.5 2.5 < y < 3.0 3.0 < y < 3.5 3.5 < y < 4.0 4.0 < y < 4.5

= 7 TeV s

Preliminary LHCb

• 1

L = 32.4 pb

$

(unpolarized case)

ϒ(1S)

unpolarized stat+syst no lumi.

bottomonia@LHC,

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HADRON’2011 20

comparison: theory

bottomonia@LHC,

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HADRON’2011

comparison: experiment

LHC vs Tevatron LHC

bottomonia@LHC,

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HADRON’2011

polarization

• detector acceptance sensitive to unknown

polarization ➭ σ(ϒ) variations of about 20%

• measure full angular distribution of leptons
• in complementary reference frames
• also frame independent
• results binned in pT and rapidity
• measurements being currently finalized

22

➙

Acceptance test λ’s

bottomonia@LHC,

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HADRON’2011 LHCb- CONF-2011- 020

• ther measurements, prospects

23

ATLAS simulation

• prompt bottomonium reconstruction

includes feeddown from higher states

• eg 40-50% of ϒ(1S) production from decays
• f excited 2S,2P,3S states [CDF,
PRL84
(2000)
2094]
• desirable to separate direct production
• eg reconstruct χb → ϒ γ decays
• (plots show examples already achieved for charmonia)
• search for exotica, bottomonia-like states?
• ➭ more data required

X(3872)

L~36pb-1 L~40pb-1

PbPb @2.76TeV

• CMS-PAS-HIN-10-006
• CMS-HIN-11-007 (arXiv:1105.4894, submitted PRL)

a . k . a . U p s i l

• n

s u p p r e s s i

• n

.

bottomonia@LHC,

• N. Leonardo

HADRON’2011

• at high temperatures, strongly interacting matter becomes a plasma of quarks and gluons
• suppression of quarkonia is a classical prediction of QGP signature
• color screening of the binding potential [T

.Matsui, H.Satz PLB178, 416 (1986)]

• suppression pattern indicates the medium temperature (‘QGP thermometer’)
• role of cold nuclear matter effects also emphasized at SPS and RHIC
• bottomonium measurements at LHC help characterize the dense matter produced in

heavy-ion collisions beyond the SPS and RHIC charmonium results

• the ϒ family of states is an expected powerful probe
• ϒ(1S) is the most tightly bound state ➪ last to melt down
• provide 3 different states/handles for probing the hot medium
• quantitative bottomonium measurements accessible for first time
• large production rates ➪ sizable datasets
• exploit excellent mass resolution
• bottomonia as QGP probe

25

Sequential melting

decreasing binding energy TC ~ 150-170MeV

bottomonia@LHC,

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HADRON’2011

datasets

26

PbPb run 2010 @2.76TeV (7.28μb-1) pp run 2011 @2.76TeV (225 nb-1)

• same online+offline selection applied to both datasets
• muon selection: quality cuts, pT>4GeV/c, |ημ|<2.4

PbPb pp

bottomonia@LHC,

• N. Leonardo

HADRON’2011

invariant yields

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Centrality % Number of events

1 10

2

10

3

10

4

10

5

10

6

10

7

10 20 40 60 80 100

Minimum Bias Trigger Dimuon Trigger

=2.76 TeV

NN

s CMS PbPb

A c c e p t a n c e ε f f i c i e n c y s i g n a l y i e l d s

bottomonia@LHC,

• N. Leonardo

HADRON’2011

ϒ(1S) invariant yields in PbPb

• Systematic uncertainties
• yield extraction: 8-14%
• acceptance: 1-5%
• efficiency: 14%
• TAA: 4.3-15%
• Statistical uncertainties: 5-20%

28 y

• 2.5
• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 2.5

dN/dy (nb)

AA

1/T

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 (1S)

• CMS Preliminary

= 2.76 TeV

NN

s PbPb

0-100% < 20.0 GeV/c

T

0.0 < p

(GeV/c)

T

p

2 4 6 8 10 12 14 16 18 20

(nb c/GeV)

T

N/dydp

2

d

AA

1/T

• 2

10

• 1

10 (1S)

• CMS Preliminary

= 2.76 TeV

NN

s PbPb

0-100% 0.0 < |y| < 2.4 0-100% 0.0 < |y| < 2.4

pT rapidity centrality

bottomonia@LHC,

• N. Leonardo

HADRON’2011

nuclear modification factor, RAA

• RAA(1S) in 20% most central bin
• 0.60 ± 0.12stat. ± 0.10 syst.
• 1S yields affected by large feeddown
• suppression might be due to melting
• f excited states (2S, 2P, 3S)

29

part

N

50 100 150 200 250 300 350 400

AA

R

0.2 0.4 0.6 0.8 1 1.2 1.4

• Prompt J/

(0-100%)

• Non-prompt J/

(0-100%) (1S)

• (0-100%)

CMS Preliminary = 2.76 TeV

NN

s PbPb

0.0 < |y| < 2.4 < 30.0 GeV/c

• J/

T

6.5 < p < 20.0 GeV/c

• T

0.0 < p

bottomonia@LHC,

• N. Leonardo

HADRON’2011

ϒ(1S) differential RAA

30

pT rapidity centrality

• 1S inclusive (minimum bias) RAA
• 0.62 ± 0.11stat. ± 0.10 syst.
• no clear dependency on rapidity or

centrality; high pT not as suppressed?

• will be answered with more data
• also separate 2S, 3S measurements

bottomonia@LHC,

• N. Leonardo

HADRON’2011

ϒ(2S+3S) vs ϒ(1S)

• measure fraction of excited states ϒ(2S+3S) relative to ϒ(1S)
• extracted directly from fit to PbPb and pp data samples

31

PbPb pp

bottomonia@LHC,

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HADRON’2011

• extract double ratio directly from

simultaneous fit to both samples

• advantages of double ratio
• acceptance, efficiency, luminosity cancel
• remaining systematics 9% from fit

lineshape model

• measurement is statistics dominated

ϒ(2S+3S) suppression

32

first observation of suppression of excited ϒ states

bottomonia@LHC,

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HADRON’2011

ϒ’ suppression: p-value

• ‘what is probability for a background

fluctuation to mimic the observed result?’

• generate pseudo-experiments assuming

the null hypothesis (ie no suppression)

• fit pseudo-data samples with nominal fit
• count fraction of occurrences for which

ratio (taken as test statistic) is same or lower than observed

• p-value: 0.9%, or
• significance 2.4σ (1-sided Gaus. test)

33

null hypothesis: ( (no suppression) p-value < 1%

bottomonia@LHC,

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HADRON’2011

Summary

• first measurements of ϒ(nS) differential cross sections and ratios

at √s=7TeV have been performed

• very good agreement between all LHC results, contributing to an improved

understanding of quarkonium production

• polarization studies being finalized, will shed further light on existing puzzles
• bottomonia also studied in PbPb collisions at √sNN=2.76TeV
• first observation of relative suppression of excited ϒ states
• 40% suppression of Y(1S) ➭ consistent with melting of excited states only
• pp and PbPb 2011 LHC runs will allow to:
• probe high pT spectrum
• improve precision and significance of the measurements
• measure further bottomonia/-like states

34