Central Exclusive Di Muon Production Ronan Mc Nulty

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Central Exclusive Di. Muon Production Ronan Mc. Nulty (UCD Dublin) On behalf of the

Central Exclusive Di. Muon Production Ronan Mc. Nulty (UCD Dublin) On behalf of the LHCb collaboration SM@LHC, Durham, 11 th-14 th April 2011 Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 1

Motivation Usually proton collisions produce very many final state particle because the gluon is

Motivation Usually proton collisions produce very many final state particle because the gluon is a coloured object. But if a colourless object is exchanged…. . • • • Results can be related to HERA and Tevatron Understand QCD in a clean environment Unambiguous evidence for pomeron. Search for odderon Constrain unintegrated parton distributions at very small x (2 x 10 -6) Search for saturation effects Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 2

Central Exclusive Production y=-10 y=-2 y=0 y=2 y=10 Elastic Scattering Single Diffraction Double Diffraction

Central Exclusive Production y=-10 y=-2 y=0 y=2 y=10 Elastic Scattering Single Diffraction Double Diffraction Central Exclusive Production (elastic) Central Exclusive Production (inelastic) Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 3

LHCb: a forward spectrometer y Interaction Point Tracking Stations Muon Chambers 250 mrad 10

LHCb: a forward spectrometer y Interaction Point Tracking Stations Muon Chambers 250 mrad 10 mrad VELO Magnet RICH detectors ECAL HCAL Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 l 20 mz 4

Use of backwards tracks Clearly not exclusive Ronan Mc. Nulty, SM@LHC, Durham 11 -14

Use of backwards tracks Clearly not exclusive Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 5

Trigger on two muons and <20 SPD hits Requiring a gap, there is evidence

Trigger on two muons and <20 SPD hits Requiring a gap, there is evidence for central exclusive production decaying to two muons. Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 6

Simple Selection Criteria n n n No backward tracks (gap of ~2 units of

Simple Selection Criteria n n n No backward tracks (gap of ~2 units of rapidity) Precisely two forward muons No photons (for J/psi and diphoton process) One photon (for Chi. C analysis) p. T of dimuon <900 Me. V (<100 Me. V for pmmp). Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 7

Dimuon Mass Spectrum af te r tr ig ge r demand gap Ronan Mc.

Dimuon Mass Spectrum af te r tr ig ge r demand gap Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 8

J/ψ and ψ’ n n n No backward tracks Precisely two forward muons No

J/ψ and ψ’ n n n No backward tracks Precisely two forward muons No photons Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 9

J/ψ and ψ’: Number of Photons J/ψ ψ’ Estimated feeddown from Chi_c Ronan Mc.

J/ψ and ψ’: Number of Photons J/ψ ψ’ Estimated feeddown from Chi_c Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 10

J/ψ and ψ’: Number of Tracks ψ’ J/ψ ψ’ feeddown Tempting to fit the

J/ψ and ψ’: Number of Tracks ψ’ J/ψ ψ’ feeddown Tempting to fit the background under the peak using straight line/exponential. Better if we can understand the physics giving background. Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 11

Inelastic backgrounds Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 12

Inelastic backgrounds Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 12

Fit elastic and inelastic components Estimate purity below 900 Me. V to be 80+-3

Fit elastic and inelastic components Estimate purity below 900 Me. V to be 80+-3 % Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 13

J/ψ Non-resonant background & misid This is not background subtracted ! Ronan Mc. Nulty,

J/ψ Non-resonant background & misid This is not background subtracted ! Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 14

ψ’: Non-resonant backgrounds & misid Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011

ψ’: Non-resonant backgrounds & misid Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 15

pp->pmmp n n n No backward tracks Precisely two forward muons. mmm>2. 5 Ge.

pp->pmmp n n n No backward tracks Precisely two forward muons. mmm>2. 5 Ge. V No photons Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 16

Fit elastic and inelastic components Shape for inelastic events Fit to signal events Note:

Fit elastic and inelastic components Shape for inelastic events Fit to signal events Note: this time we have simulation that predicts the shape for the three contributions. Background shape from data Signal shape from simulation. Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 17

χc n n n No backward tracks Precisely two forward muons Precisely one photon

χc n n n No backward tracks Precisely two forward muons Precisely one photon Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 18

χc: Di. Muon Invariant Mass About half the background that was observed in the

χc: Di. Muon Invariant Mass About half the background that was observed in the exclusive J/ψ analysis (since no continuum process). Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 19

χc: Di. Muon+Photon Invariant Mass (Caveat: Inelastic contribution appears to be much larger than

χc: Di. Muon+Photon Invariant Mass (Caveat: Inelastic contribution appears to be much larger than for J/ψ) Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 20

Cross-section calculations n σ=(p. N/ε) / L n ε: Trigger, tracking, photon & selection

Cross-section calculations n σ=(p. N/ε) / L n ε: Trigger, tracking, photon & selection efficiencies are estimated from simulation, with size of systematics taken from data/simulation agreement. n p: Feed-down for ψ’, χc subtracted. Uncertainty on fit to p. T spectrum taken as systematic on inelastic contribution. n L: Analysis only uses single-interaction events. Need to know average number of pile-up interactions. Currently translates into 20% uncertainty on L. Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 21

Summary Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 22

Summary Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 22

Comparison to Theory J/ψ: 474 +-103 pb Starlight (Klein & Nystrand) 292 pb Super.

Comparison to Theory J/ψ: 474 +-103 pb Starlight (Klein & Nystrand) 292 pb Super. Chic (Harland-Lang, Khoze, Ryskin, Stirlin) 330 pb Motyka & Watt 330 pb Schäfer & Szczurek 710 pb ψ’: 12. 2 +- 3. 2 pb Starlight (Klein & Nystrand) 6 pb Schäfer & Szczurek ~ 17 pb σ(ψ’)/σ(J/ψ): 0. 20 +- 0. 03 Starlight (Klein & Nystrand) 0. 16 Schäfer & Szczurek ~ 0. 2 HERA: 0. 166 +- 0. 012 (lower √( p) ) CDF: 0. 14 +- 0. 05 (lower √( p) ) χ0: 9. 3 +- 4. 5 pb Super. Chic: 14 pb pμμp: 67 +- 19 pb χ1: 16. 4 +- 7. 1 pb 10 pb χ2: 28. 0 +-12. 3 pb LPAIR (J. Vermaseren) 42 pb Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 23

Summary n n First Observation of CEP at LHC First separation of χc spin

Summary n n First Observation of CEP at LHC First separation of χc spin states in CEP Good agreement with theory predictions Consistency with HERA and CDF results. Ronan Mc. Nulty, SM@LHC, Durham 11 -14 April 2011 24