JY photoproduction in ultraperipheral collisions Mt Csand Etvs

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J/Y photo-production in ultraperipheral collisions Máté Csanád (Eötvös University, PHENIX) Zimányi School on Heavy

J/Y photo-production in ultraperipheral collisions Máté Csanád (Eötvös University, PHENIX) Zimányi School on Heavy Ion Physics Budapest, November 29 – December 4, 2009 • UPC physics • • Photon-photon interactions Photon beam in A+A • Measurements at RHIC Experimental signatures Background • Results • • • LHC?

Based on … • My previous talks on this subject • David d’Enterria for

Based on … • My previous talks on this subject • David d’Enterria for the PHENIX Coll. Quark Matter 2005, nucl-ex/0601001 • Zaida Conesa del Valle for the PHENIX Coll. Quark Matter 2009 • PHENIX publication (submitted to PLB) ar. Xiv: 0903. 2041 • A lot of thanks… M. Csanád, Zimányi School 2009 2

Introduction • Nonlinear QCD dynamics at small x and Q 2 is one of

Introduction • Nonlinear QCD dynamics at small x and Q 2 is one of the focal points of theoretical activity Q 2 for coupling quarks even smaller, ~ 1 Ge. V 2, black disk limit • Mixing of perturbative and nonperturbative effects at small x and Q 2 • Interested in gluon distributions G(x, Q 2) • • Photon to vectormeson processes: sensitivity to gluon distribution at small x, cross-section (with Q 2=MV 2/4, x=MV 2/W N 2): • Photon-photon processes: tested in e+e- or ep (HERA) • Fermi 1924: The effect of the electromagnetic field of a relativistic particle is equivalent to a flux of photons with a continous energy spectrum. • Possible new directions: higher energies • nuclear beams • M. Csanád, Zimányi School 2009 3

Photon-photon interactions • High-energy : complementary to "conventional" e+e-, ep (DIS), or pp collisions

Photon-photon interactions • High-energy : complementary to "conventional" e+e-, ep (DIS), or pp collisions (to study QCD/QED, or even beyond-SM) • High energy photon: point-like interaction or quantumfluctuation into a vector meson or quark-pair • 0 dominates, but V, qq fluctuations interact strongly and give largest contribution to cross-sections M. Csanád, Zimányi School 2009 4

How to make gg collisions? • EM field of relativistic charged particle = flux

How to make gg collisions? • EM field of relativistic charged particle = flux of “equivalent” photons. • Weizsacker-Williams formula for -spectrum in an e± beam (with z=E / Ee): • Scattered beam close to parent beam (kinematics) low pt products & quasi-real photons (Q 2~0) M. Csanád, Zimányi School 2009 5

gg in nucleon-nucleon collisions Central collision: Peripheral collision: Ultra-peripheral collision: • Two heavy nuclei

gg in nucleon-nucleon collisions Central collision: Peripheral collision: Ultra-peripheral collision: • Two heavy nuclei not overlapping b>bmin 2 R • Ultra-Peripheral Collision (UPC) • • Emitting a quasi-real photon z=Eg / EA, x=zm. Abmin, K … Bessel functions • flux: • • Interacts with the other nucleus • Large photon cross-sections (~Z 4) M. Csanád, Zimányi School 2009 6

Where all this is done: BNL@RHIC • RHIC: Au+Au @ Ecms = 200 Ge.

Where all this is done: BNL@RHIC • RHIC: Au+Au @ Ecms = 200 Ge. V/nucleon + … • • Au+Au, Cu+Cu, pp+pp, d+Au collisions, up to 500 Ge. V/nucl. 4 experimental collaborations: BRAHMS, PHENIX, PHOBOS, STAR • PHENIX: several hundred scientist, a lot of topics • See talks of David d’Enterria, John Koster, Raphael Granier de Cassagnac, Todd Kempel, Swadhin Taneja, Rachid Noucier, Yoshinori Fukao M. Csanád, Zimányi School 2009 7

J/Y production in UPC’s • Different type of processes Dielectron continuum: A+g+g A*+e+e •

J/Y production in UPC’s • Different type of processes Dielectron continuum: A+g+g A*+e+e • Coherent J/Y production: g+A A*+J/Y( e+e-) • • Incoherent production (Coulomb-breakup): g+A A’+x. N+J/Y( e+e-), much larger pt of the pair M. Csanád, Zimányi School 2009 8

Experimental signatures • Central rapidities: • • Low multiplicities: N<15 (well below 15) Low

Experimental signatures • Central rapidities: • • Low multiplicities: N<15 (well below 15) Low total pt (large wavelength, “coherence condition”): Ephoton, max~ g/R ~ 3 Ge. V (80 Ge. V at LHC) Zero net charge Narrow d. N/dy peaked at y=0 (tagging/triggering) • Forward rapidities: • Coulomb-excited A* dissociation via (forward) neutron (Xn) emission M. Csanád, Zimányi School 2009 9

Measured processes in Au+Au UPC STAR: PRL 89 272302 (02), Coherent r production, g+A

Measured processes in Au+Au UPC STAR: PRL 89 272302 (02), Coherent r production, g+A A*+r( p+p-) • PRC 70 031902 (04), Dielectron continuum at low minv, g+ g e + e – • • PHENIX: nucl-ex/0601001 (prelim. ), 0903. 2041 (final) • J/Y production: g+A A*+J/Y( e+e–) • Dielectron continuum at high minv : g+g e+e– • M. Csanád, Zimányi School 2009 10

Eliminating background sources • “Non-physical”: Cosmic rays: no ZDC, no good vtx. • Beam-gas

Eliminating background sources • “Non-physical”: Cosmic rays: no ZDC, no good vtx. • Beam-gas collision: no good vertex, large multiplicity, asymmetric d. N/dy final signal trigger level • • Physical processes: Peripheral nuclear A+A: “large” multiplicity, large pt • Hadronic diffractive (Pomeron-Pomeron): forward proton emission, larger pt: pt(gg)<pt(PP), like-sign pairs. Harddiffractive J/Y production. • Incoherent UPC g+n n+J/Y : pt(gg) < pt (g. P), wider & asymm. d. N/dy, ≥ 2 neutrons (induced nuclear break-up) with same direction as J/Y. • Other coherent UPC processes: gg e+e- (important , g. A jet+A (lower cross-sections) • M. Csanád, Zimányi School 2009 11

PHENIX detectors for UPC • DC + PC’s: Full centralarm charged tracking (e± momentum).

PHENIX detectors for UPC • DC + PC’s: Full centralarm charged tracking (e± momentum). • EMCal + RHIC: e± identification in central rapidity. • ZDC: Forward neutron detection (Au* dissociation): • BBC: charged tracks M. Csanád, Zimányi School 2009 12

Triggering on UPC’s • PHENIX Run-4 Au. Au UPC level-1 trigger: • Sensitive to

Triggering on UPC’s • PHENIX Run-4 Au. Au UPC level-1 trigger: • Sensitive to g+Au Au*+J/Y( e+e-) • Veto on coincident BBC (|y|~3 -4): • avoid periph. nuclear, beam-gas colls. • Neutron in ZDC (E>30 Ge. V) • sensitive to Au* Coulomb dissociation • Large energy (E > 0. 8 Ge. V) cluster in EMCal: • e+e- decay from J/Y • Trigger definition based on the above • Events collected (~0. 4% of MB trigger): UPC Au. Au: 8. 5 M • Min. Bias Au. Au (BBCLL 1): 1122 M (∫L = 120 mb-1) • M. Csanád, Zimányi School 2009 13

PHENIX UPC analysis cuts • Cuts made on the 8. 5 M UPC triggered

PHENIX UPC analysis cuts • Cuts made on the 8. 5 M UPC triggered events • Global cuts: Standard vertex cut: |zvtx| < 30 cm • Multiplicity (number of tracks) = 2, removes non-UPC • • Eletron ID cuts: RICH: # of photo-tubes within nominal ring radius >2 • Electrons: E 1>1 Ge. V or E 2>1 Ge. V, high-pt trigger threshold • • Pair cuts: • Dielectrons back-to-back (low sum pt) • Residual background subtraction: • unlike-sign pairs – like-sign pairs • Result: 28 unlike-sign pairs and no like-sign pairs of mee > 2 Ge. V/c 2: clean sample with 0 net charge M. Csanád, Zimányi School 2009 14

Transverse momentum distribution • J/Ψ: low pt region consistent with Au form factor fit

Transverse momentum distribution • J/Ψ: low pt region consistent with Au form factor fit • High pt region: also an incoherent component • Continuum: coherent nature M. Csanád, Zimányi School 2009 15

Invariant mass distributions • Continuum in good agreement with theoretical input • J/Y peak

Invariant mass distributions • Continuum in good agreement with theoretical input • J/Y peak & width also (theoretical input + full MC resp. +reco) M. Csanád, Zimányi School 2009 16

Yields Sample, me+e- [Ge. V/c 2] Yield J/Ψ [2. 7, 3. 5] 9. 9

Yields Sample, me+e- [Ge. V/c 2] Yield J/Ψ [2. 7, 3. 5] 9. 9 ± 4. 1 (stat) ± 1. 0 (syst) e+e- continuum [2. 0, 2. 8] 13. 7 ± 3. 7 (stat) ± 1. 0 (syst) e+e- continuum [2. 0, 2. 3] 7. 4 ± 2. 7 (stat) ± 1. 0 (syst) e+e- continuum [2. 3, 2. 8] 6. 2 ± 2. 5 (stat) ± 1. 0 (syst) M. Csanád, Zimányi School 2009 17

Continuum cross-sections • Cross-sections after efficiency corrections: me+e- interval [Ge. V/c 2] d 2σ/dmeedy|y=0

Continuum cross-sections • Cross-sections after efficiency corrections: me+e- interval [Ge. V/c 2] d 2σ/dmeedy|y=0 [μb c 2/ Ge. V] e+e- continuum [2. 0, 2. 8] 86 ± 23 (stat) ± 16 (syst) 90 e+e- continuum [2. 0, 2. 3] 129 ± 47 (stat) ± 28 (syst) 138 e+e- continuum [2. 3, 2. 8] 60 ± 24 (stat) ± 14 (syst) 61 STARLIGHT • Results agree with QED theoretical (STARLIGHT) calculations even though we are in a strongly interacting regime ! • Lacking of other model comparisons on this kinematical region… input from theorists is most welcome ! M. Csanád, Zimányi School 2009 18

J/Ψ cross-sections • Agreement with theoretical results • But: coherent + incoherent production •

J/Ψ cross-sections • Agreement with theoretical results • But: coherent + incoherent production • Main systematic error: coherent continuum • Statistical errors: larger luminosity • Present status: detailed study of GA(x, Q 2), J/Ψ absorption in cold nuclear matter not possible [1] [2] [3] [4] [ 1]P. R. L. 89, 012301 (2002) [ 2] P. L. B 72, 626 (2005) [ 3] ar. Xiv 0706. 2810 [hep-ph] [ 4] ar. Xiv: 0706. 1532 [hep-ph] M. Csanád, Zimányi School 2009 19

LHC prospects Cross-sections from J. Nystrand, hep-ph/0412096, NPA 752(2005)470 M. Csanád, Zimányi School 2009

LHC prospects Cross-sections from J. Nystrand, hep-ph/0412096, NPA 752(2005)470 M. Csanád, Zimányi School 2009 20

Summary • UPC collisions: high energy photon beam • Precision QCD Low background, simple

Summary • UPC collisions: high energy photon beam • Precision QCD Low background, simple initial state • Complimentary to conventional e+e- or ep • • First results from RHIC Efficient trigger, simple analysis • Good theoretical description • Main systematic uncertainity: dielectrons • No strong constraint on model ingredients yet • • To be continued at LHC Incoherent procecesses, continuum cross-section • Higher rates and energies • M. Csanád, Zimányi School 2009 21

Thank you for the attention! ar. Xiv: 0903. 2041 M. Csanád, Zimányi School 2009

Thank you for the attention! ar. Xiv: 0903. 2041 M. Csanád, Zimányi School 2009 22

Incoherent J/Y production • Via Coulomb-breakup • How to separate from the coherent? Strikman:

Incoherent J/Y production • Via Coulomb-breakup • How to separate from the coherent? Strikman: Via t distribution Via neutron tagging Coherent Incoherent ~ e-bt b=2. 6 Ge. V-2 Strikman et al. , hep-ph/0505023 • Limited statistics … M. Csanád, Zimányi School 2009 23

Background substraction J. Nystrand, hep-ph/0412096, NPA 752(2005)470 • Starlight Monte Carlo simulation • Determine

Background substraction J. Nystrand, hep-ph/0412096, NPA 752(2005)470 • Starlight Monte Carlo simulation • Determine continuum shape • 700 k e+e− pairs with minv>1. 5 Ge. V, 500 μb− 1 M. Csanád, Zimányi School 2009 24

Resulting distributions • • • Invariant mass distribution with continuum background Pair transverse momentum

Resulting distributions • • • Invariant mass distribution with continuum background Pair transverse momentum distribution Unlike-sign (red) and like-sign (yellow) pairs M. Csanád, Zimányi School 2009 25

Theoretical calculations • Cross-section is consistent with different model predictions • … though current

Theoretical calculations • Cross-section is consistent with different model predictions • … though current precision precludes yet any detailed conclusion on the basic ingredients: shadowing and nuclear absorption [ 1) ] [ 2) ] [ 3) ] [ 4) ] Rough comparison with HERA e-p data, p = A If coh. incoh. ratio is 50% - 50% • coh = 1. 01 0. 07 • incoh = 0. 92 0. 08 ~ 1, good agreement with HERA data hard probes scaling! [ 1) P. R. L. 89 012301 (2002)…] [ 2) P. L. B 626 (2005) 72 ] [ 3) ar. Xiv 0706. 2810 [hep-ph] ] [ 4) ar. Xiv: 0706. 1532 [hep-ph] ] • Similar comparison with STAR measurement gives coh = 0. 75 0. 02, closer to A 2/3 soft scaling [ZEUS, Eur. Phys. J. C 24 (2002) 345] [H 1, Eur. Phys. J. C 46 (2006) 585] [STAR, Phys. Rev. C 77 (2008) 034910] M. Csanád, Zimányi School 2009 26