Extrapolation of J/ cross sections

from p-p 7 TeV to p-p 2.75 TeVin LO CEM

F. Bossù, M. Gagliardi

INFN & Università degli Studi Torino

Outline

• Color Evaporation Model

• d/dy for J/ in pp at 7 and 2.75 TeV

• Rescaling factors for total and y-differential cross sections: PDF and F dependence , evaluation of systematics

• Comparison with LO CSM

• Conclusions and outlook

• Perspectives for a pp run at 2.75 TeV

MotivationOne of the main observables for quarkonia suppression studies: the nuclear modification factor RAA

X = J/, c = a centrality-related quantity

)()()(cNcNcR

coll

AAX

ppX

ppinelAA

X

Pb-Pb: = 2.75 TeVNNsp-p: = 7 TeVs

At the LHC startup:

Task: evaluate (pp -> X) at

= 2.75 TeVppsRAA meaningful if: ppNN ss EXTRAPOLATION

?

MEASUREMENT?

Leading Order Color Evaporation Model

Cross section for prompt quarkonia production: some fraction F of the QQ cross section below the open heavy flavour meson threshold.F independent of kinematics, process, . CS not explicitely requireds

ji

Fy

BjFy

Aiij

m

m

OLCEM e

ssfe

ssfssd

sF

dyd H

Q,

2,

2,

4

4

..

),ˆ

(),ˆ

()ˆ(ˆˆ2

2 yOL e

ssxˆ..

2/1

ji

ijBjAi

m

m

CEM sxxssxfxfdxdxsdF H

Q,21

22,

21,21

4

4)ˆ()ˆ(ˆ),(),(ˆ

2

2

LO formulae for the rapidity distributions can be used to estimate uncertainty related to the choice of PDF set and of F. Dominant diagram gg->QQ only. Assuming no R dependence of ratios of cross sections at LO

Gluon distribution functions

hep-ph/0201195

hep-ph/9803445

hep-ph/9903282

hep-ph/0201127

yOL essx ˆ..

2/1

Leading Order fit for F = 2mc

Prompt J/ rapidity distributions in LO CEM

F = 2mc

J/ rapidity distributions in LO CEM (2)

Caveat 1: data include J/ from B-decay, curves don’t

Caveat 2: curves are normalised to same integral in 2.5 < y < 4 (= measured )

Data do not seem to prefer nor discard any of these curves

9.0

9.0

dydydCB

Rescaling factors for cross sections in ALICE acceptance

)75.2()7(

TeVTeV

S CB

CBCB

Central Barrel

PDF SCB

CTEQ5L 1.99CTEQ6L 1.69

MRST98L 1.79MRST01L 1.86GRV98L 2.16

4

5.2

dydydMS

)75.2()7(

TeVTeVS MS

MSMS

Muon Spectrometer

PDF SMS

CTEQ5L 2.22CTEQ6L 1.96

MRST98L 2.11MRST01L 1.97GRV98L 2.36

Spread / median 24% Spread / median 18%

F = 2mc

F dependence: cross sections

ALICECentral barrel

ALICEMuon spectrometer

F dependence: rescaling factors

ALICECentral barrel

ALICEMuon spectrometer

Variation in 2mC < F < 2mD: 4% to 10% (depending on PDF)

Comparison with CSM

J. P. Lansberg arXiv:1006.2750v1 [hep-ph]

LO CSM with CTEQ6L PDF: 1.87 < SCB < 2.07 and 2.31 < SMS < 2.52

LO CEM with CTEQ6L PDF and F = 2mC SCB = 1.69 and SMS = 1.96

)75.2()7(

TeVTeV

S CB

CBCB

)75.2()7(

TeVTeVS MS

MSMS

Rescaling factors for y-differential cross section

ALICECentral barrel

ALICEMuon spectrometer

Conclusions

• Rescaling factors from 7 to 2.75 TeV evaluated in LO Color Evaporation Model for total and y-diffferential cross sections, with 5 different PDFs

• Variation of rescaling factors with PDF: 24% in ALICE central barrel acceptance 18% in ALICE muon spectrometer aceptance

• Variation related to factorisation scale F: 4%÷10% (depending on PDF) for 2mC < F < 2mD

• CSM (lower bound) vs CEM: 10% for central barrel, 16% for muon spectrometer

NB: Variation = Full spread / median

Outlook and hints for discussion

• Take into account J/ from B-decay

• NLO CEM

• Newer PDFs (can we discard some of those used here?)

• Explore more models (CSM, NRQCD..)

• Should we expect theory to reduce systematics with combined use of LHC@7 TeV and Tevatron data?

A pp run at 2.75 TeV?LHCC102 minutes (shown at LPC meeting 27/09/2010)

in part (~50%)

May be scheduled in 2011 http://indico.cern.ch/conferenceDisplay.py?confId=108493

One colliding bunch in IP2LHC Programme coordinator says:

A pp run at 2.75 TeV? (2)Maximum luminosity (no beam displacement) with nominal emittances, 1 colliding bunch, 7x1010 p and * = 3.5 m : ~ 0.2 Hz/b (vdM scan)

Thus, in 20 h with * = 10 m we should expect (at most): 20 h * 3600 s/h * (3.5/10) * 0.2 Hz / b = 5600 b-1

Using measured cross sections at 7 TeV and a rescaling factor to 2.75 TeV of 0.5, we get:~ 2400 J/ in e+e- in -0.9 < y < 0.9~ 1200 J/ in +- in 2.5 < y < 4

Can we do something with this? Next slides: very preliminary feasibility studyin the muon spectrometer (signal analysis only!)

Generate 1200 J/ with “realistic ”input distributions at 2.75 TeV:

Perspectives for a pp run at 2.75 TeV

LO

LO

NLONLO

dyd

dyd

dyd

dyd

5.5

75.2

5.575.2

Obtained as:Rescaled from CDF fit according to CEM evolution

Perspectives for a pp run at 2.75 TeVAfter reconstruction: about 500 detected J/

Can we appreciate the J/ signal in such a low statistics scenario? Full physics performance coming soon