quarkonia results at cmsweb.mit.edu/.../5-1450/covarelli/275-0-panic11_quarkonia.pdfquarkonia...

28-Jul-11 R. Covarelli 1

R O B E R T O C O V A R E L L I ( U N I V . O F R O C H E S T E R )

QUARKONIA RESULTS AT CMS

19TH PARTICLE AND NUCLEI INTERNATIONAL CONFERENCE MIT (CAMBRIDGE), 24-29 JULY 2011

QUARKONIUM MEASUREMENTS IN CMS

• pp collisions at 7 TeV (2010-2011)

• J/y, y(2S) differential cross-sections and cross-section

ratio in transverse momentum (pT) and rapidity (y)

• Measured separately in “prompt” (coming from the pp

collision point) and “non-prompt” (displaced, i.e. from

B-hadron decays) charmonium contributions

• Y(1S), Y(2S), Y(3S) differential cross-sections and

cross-section ratios in pT

• Studies on ccJ

• Measurement of X(3872) to y(2S) cross-section ratio

• Pb-Pb collisions at 2.76 TeV (2010)

• Several interesting results including studies on suppression of excited bottomonium states


Manuel

Calderon’s

talk on Monday

PHYSICS MOTIVATIONS (I)

• Quarkonium prompt production:

• Includes feed-down for J/y

(ccJ, y(2S) → J/y) and Y (cbJ → Y)

• Direct only in the y(2S) case:

theoretically cleaner

• Recent calculations at NLO in NRQCD (O(as

4v4)), including both color-singlet

and color-octet contributions, are

available for charmonium

• Good agreement with TeVatron and first

(low-pT) LHC measured cross-sections

• Interesting to investigate:

• 1/pTn dependence at high pT

• y(2S) vs. J/y with same LDMEs

• Ratios to reduce experimental uncertainties

Roberto Covarelli 3

Y.-Q. Ma et al.

Phys. Rev. Lett. 106, 042002 (2011)

28-Jul-11

PHYSICS MOTIVATIONS (II)

• cc studies

• Measurement of s(cc2)/s(cc1) and the fraction of J/y coming from cc

decays (cc → J/y g) provide additional important “handles” for

comparison to NRQCD predictions

• “Exotic states” (e.g. X(3872))

• A wide range of measurements possible: cross-sections, non-prompt fraction, quantum numbers… and new states


J/y non-prompt production:

Test FONLL approach

at 7 TeV

Test improved

b- fragmentation function

(fitted from data of several

experiments)

M . Cacciari et al.,

JHEP 0407, 033 (2004)

M . Cacciari et al.,

JHEP 0604, 006 (2006)

THE CMS DETECTOR


• Muon triggers: • segments found in muon detectors (Level 1)

• fast regional track reconstruction (High-Level Trigger)

Muon

reconstruction

from

combined

information of

silicon tracker

and external

detectors

(DT, CSC,

RPC)

J/Y , Y(2S) AND Y CROSS-SECTIONS

• A = acceptance determined from

simulation using unpolarized

production as a default. Maximum

variations are given based on “extreme” polarization scenarios

• e = efficiency determined from

J/y data (see next slide)

• L = luminosity

• DpT, Dy = sizes of pT, y bins


𝑑2𝜎

𝑑𝑝𝑇𝑑𝑦𝑄𝑄 𝐵𝑅(𝑄𝑄 → 𝜇+𝜇−) =

𝑁𝑓𝑖𝑡(𝑄𝑄 )

𝐿𝑑𝑡 ∙ 𝐴 ∙ 𝜖 ∙ ∆𝑝𝑇∆𝑦

𝑁𝑓𝑖𝑡 J/y, y(2S) = 1 − 𝑓𝐵 𝑁𝑡𝑜𝑡 (prompt)𝑓𝐵𝑁𝑡𝑜𝑡 (non prompt)

𝑁𝑓𝑖𝑡 𝑌 = 𝑁𝑡𝑜𝑡 (prompt only)

Y(1S) acceptance

Unpolarized

MUON EFFICIENCY MEASUREMENTS

• Use data-driven measurements of the

muon efficiency (“tag-and-probe”

method)

• In events with a J/y candidate, ask for

one well-identified muon (“tag”)

• The other muon (“probe”) can pass or

not pass the selection S under

investigation

• Invariant mass plots separate for the

two cases: the fitted Npass-S/Nall gives an

unbiased estimate of the efficiency eS


Limitation of the method: assumes efficiency

factorization, does not take into account

correlations due e.g. to trigger requirements

MC corrections

required

MASS DISTRIBUTION FITS

• Use unbinned maximum likelihood fits to extract yields (Ntot)

• Lineshapes: • Crystal Ball (+ Gaussian) functions for signal

• Exponentials or polynomials for background

• Some shape parameters in common when

fitting multiple peaks

• Typical mass resolutions:

• 20-50 MeV/c2 for J/y, y(2S), 80 MeV/c2 for Y


DECAY LENGTH FITS

• Used to determine the non-prompt fraction of J/y, y(2S)

• Fit simultaneously invariant mass and

• Lineshapes:

• Prompt: d-function

• Non-prompt: exponential with an effective

smearing due to J/y motion in the B frame

• Background: superposition of different

contributions determined from the mass

side-bands

• Use per-event errors (from s-matrices) as lJ/y resolution factors


Primary vertex

CROSS-SECTION RESULTS

• One example: J/y inclusive cross-section by merging CMS results with 0.3 pb-1 (low pT) and 37 pb-1 (high pT)


Main systematic

uncertainties:

Total cross sections

Efficiency correlations

Acceptance edge

effects

Luminosity uncertainty

Non-prompt fractions

Tracker alignment

B-lifetime model

Resolution model

Eur. Phys. J C71, 1575 (2011)

CMS PAS BPH-10-014 (2011)

PROMPT J/Y , Y(2S)

J/y y(2S)


Excellent agreement with NRQCD predictions (including feed-down in the J/y case)

NON-PROMPT J/Y , Y(2S) J/y y(2S)


Good agreement with FONLL predictions Overall shift in the y’ case (total B → y’ rate)

Spectra fall more rapidly than predictions at high pT

Y(1S), Y(2S), Y(3S)

• 3 pb-1 data, 0 < pT < 30 GeV/c

• Results compared only to Pythia simulation (including CSM and COM but only at LO) NLO results at 7 TeV not yet available

• Needs normalization to total (~factor 2 overestimation)


Phys. Rev. D83, 112004 (2011)

STUDIES

• Full 2011 sample (1.1 fb-1)

• Combine a prompt J/y candidate with a photon

converted to e+e- in the

silicon tracker

• Conversion selection

based on:

• Vertexing probability

• Large conversion radius

• pT

• p0 veto combining

candidates with photons

in the EM calorimeter


cc

cc0

cc2

cc1

X(3872) / Y(2S) CROSS-SECTION RATIO

• Both reconstructed in the J/y p+ p- channel

• Background reduction using: • 4-track vertex

• Di-pion pT

• Di-pion / J/y angular separation

• On a data sample of 40 pb-1, measurement of X(3872) to y(2S) ratio [cross-section x BR] :

for pT > 8 GeV/c, |y|< 2.2


CMS PAS BPH-10-018 (2011)

CONCLUSIONS

• Several results on quarkonia obtained with CMS, thanks to

the excellent performances in muon reconstruction down

to low transverse momentum:

• J/y / y(2S) / Y differential cross-sections measured with typical

uncertainties (statistical + systematic) of 5% / 20% / 15%

• Ranging from 0 to 70 GeV/c for the J/y

• For charmonium, prompt/non-prompt separation achieved using decay length information

• Good agreement with NLO NRQCD predictions at 7 TeV

• B → J/y, y(2S) in reasonable agreement with FONLL predictions, except for the very high pT region and for the total B → y(2S) rate

• cc studies in the J/y + converted g channel very promising

• Excellent signal-to-background ratio, good separation of the 3 states

• First CMS measurements in the field of “exotic” quarkonia

• X(3872) to y(2S) [cross-section x BR] ratio


BACKUP SLIDES


B-FRACTION RESULTS


• Increasing

monotonically

• fy(2S) generally larger

than fJ/y, becoming

equal at large pT

Y(2S) / J/Y CROSS-SECTION RATIO


CDF trend (increasing

with pT) for prompt

confirmed

No structure observed

within errors in non-prompt especially

true at high pT

TOTAL CROSS SECTIONS


POLARIZATION UNCERTAINTIES


• Polarization uncertainties not shown in the plots:

quoted as typical variations using the 4 extreme

acceptance scenarios

quarkonia results at cmsweb.mit.edu/.../5-1450/covarelli/275-0-panic11_quarkonia.pdfquarkonia...

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