Observation of Exclusive Charmonium Production and <em>γγ -&gt; μ⁺μ⁻</em> in <em>pp</em> Collisions at s√=1.96  TeV

Article

Reference

Observation of Exclusive Charmonium Production and γγ -> μ

μ

in pp Collisions at s√=1.96  TeV

CDF Collaboration

CLARK, Allan Geoffrey (Collab.), et al.

Abstract

In CDF we have observed the reactions p+p→p+X+p, with X being a centrally produced J/ψ, ψ(2S), or χc0, and γγ→μ+μ− in pp¯ collisions at s√=1.96  TeV. The event signature requires two oppositely charged central muons, and either no other particles or one additional photon detected. Exclusive vector meson production is as expected for elastic photoproduction, γ+p→J/ψ(ψ(2S))+p, observed here for the first time in hadron-hadron collisions. We also observe exclusive χc0→J/ψ+γ. The cross sections dσdy|y=0 for J/ψ, ψ(2S), and χc0 are 3.92±0.25(stat)±0.52(syst)  nb, 0.53±0.09(stat)±0.10(syst)  nb, and 76±10(stat)±10(syst)  nb, respectively, and the continuum is consistent with QED. We put an upper limit on the cross section for Odderon exchange in exclusive J/ψ production.

CDF Collaboration, CLARK, Allan Geoffrey (Collab.), et al . Observation of Exclusive

Charmonium Production and γγ -> μ

μ

in pp Collisions at s√=1.96  TeV. Physical Review Letters , 2009, vol. 102, no. 24, p. 242001

DOI : 10.1103/PhysRevLett.102.242001

Available at:

http://archive-ouverte.unige.ch/unige:38551

Disclaimer: layout of this document may differ from the published version.

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Observation of Exclusive Charmonium Production and !

in p p Collisions at ffiffiffi

p s

¼ 1:96 TeV

T. Aaltonen,²⁴J. Adelman,¹⁴T. Akimoto,⁵⁶M. G. Albrow,¹⁸B. A´ lvarez Gonza´lez,¹²S. Amerio,^44a,44bD. Amidei,³⁵ A. Anastassov,³⁹A. Annovi,²⁰J. Antos,¹⁵G. Apollinari,¹⁸A. Apresyan,⁴⁹T. Arisawa,⁵⁸A. Artikov,¹⁶W. Ashmanskas,¹⁸ A. Attal,⁴A. Aurisano,⁵⁴F. Azfar,⁴³P. Azzurri,^47d,47aW. Badgett,¹⁸A. Barbaro-Galtieri,²⁹V. E. Barnes,⁴⁹B. A. Barnett,²⁶ V. Bartsch,³¹G. Bauer,³³P.-H. Beauchemin,⁶²F. Bedeschi,^47aD. Beecher,³¹S. Behari,²⁶G. Bellettini,^47b,47aJ. Bellinger,⁶⁰

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J. C. Yun,¹⁸L. Zanello,^52b,52aA. Zanetti,^55aL. Zhang,⁶²X. Zhang,²⁵Y. Zheng,⁹and S. Zucchelli^6b,6a

(CDF Collaboration)

1Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China

2Argonne National Laboratory, Argonne, Illinois 60439, USA

3University of Athens, 157 71 Athens, Greece

4Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain

5Baylor University, Waco, Texas 76798, USA

6aIstituto Nazionale di Fisica Nucleare Bologna, I-40127 Bologna, Italy

6bUniversity of Bologna, I-40127 Bologna, Italy

7Brandeis University, Waltham, Massachusetts 02254, USA

8University of California, Davis, Davis, California 95616, USA

9University of California, Los Angeles, Los Angeles, California 90024, USA

10University of California, San Diego, La Jolla, California 92093, USA

11University of California, Santa Barbara, Santa Barbara, California 93106, USA

12Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain

13Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

14Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA

15Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia

16Joint Institute for Nuclear Research, RU-141980 Dubna, Russia

17Duke University, Durham, North Carolina 27708, USA

18Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

19University of Florida, Gainesville, Florida 32611, USA

20Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy

21University of Geneva, CH-1211 Geneva 4, Switzerland

22Glasgow University, Glasgow G12 8QQ, United Kingdom

23Harvard University, Cambridge, Massachusetts 02138, USA

242001-2

24Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland

25University of Illinois, Urbana, Illinois 61801, USA

26The Johns Hopkins University, Baltimore, Maryland 21218, USA

27Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany

28Center for High Energy Physics: Kyungpook National University, Daegu 702-701, Korea;

Seoul National University, Seoul 151-742, Korea;

Sungkyunkwan University, Suwon 440-746, Korea;

Korea Institute of Science and Technology Information, Daejeon, 305-806, Korea;

Chonnam National University, Gwangju, 500-757, Korea

29Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

30University of Liverpool, Liverpool L69 7ZE, United Kingdom

31University College London, London WC1E 6BT, United Kingdom

32Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain

33Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

34Institute of Particle Physics: University of Alberta, Edmonton, Canada, T6G 2G7;

McGill University, Montre´al, Que´bec, Canada H3A 2T8;

Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6;

University of Toronto, Toronto, Ontario, Canada M5S 1A7;

and TRIUMF, Vancouver, British Columbia, Canada V6T 2A3

35University of Michigan, Ann Arbor, Michigan 48109, USA

36Michigan State University, East Lansing, Michigan 48824, USA

37Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia

38University of New Mexico, Albuquerque, New Mexico 87131, USA

39Northwestern University, Evanston, Illinois 60208, USA

40The Ohio State University, Columbus, Ohio 43210, USA

41Okayama University, Okayama 700-8530, Japan

42Osaka City University, Osaka 588, Japan

43University of Oxford, Oxford OX1 3RH, United Kingdom

44aIstituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy

44bUniversity of Padova, I-35131 Padova, Italy

45LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France

46University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

47aIstituto Nazionale di Fisica Nucleare Pisa, I-56127 Pisa, Italy

47bUniversity of Pisa, I-56127 Pisa, Italy

47cUniversity of Siena, I-56127 Pisa, Italy

47dScuola Normale Superiore, I-56127 Pisa, Italy

48University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

49Purdue University, West Lafayette, Indiana 47907, USA

50University of Rochester, Rochester, New York 14627, USA

51The Rockefeller University, New York, New York 10021, USA

52aIstituto Nazionale di Fisica Nucleare, Sezione di Roma 1, I-00185 Roma, Italy

52bSapienza Universita` di Roma, I-00185 Roma, Italy

53Rutgers University, Piscataway, New Jersey 08855, USA

54Texas A&M University, College Station, Texas 77843, USA

55aIstituto Nazionale di Fisica Nucleare Trieste/Udine, I-34100 Trieste, Italy

55bUniversity of Trieste/Udine, I-33100 Udine, Italy

56University of Tsukuba, Tsukuba, Ibaraki 305, Japan

57Tufts University, Medford, Massachusetts 02155, USA

58Waseda University, Tokyo 169, Japan

59Wayne State University, Detroit, Michigan 48201, USA

60University of Wisconsin, Madison, Wisconsin 53706, USA

61Yale University, New Haven, Connecticut 06520, USA

62Institute of Particle Physics: University of Alberta, Edmonton, Canada T6G 2G7;

McGill University, Montre´al, Que´bec, Canada H3A 2T8;

Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6;

University of Toronto, Toronto, Ontario, Canada M5S 1A7;

and TRIUMF, Vancouver, British Columbia, Canada V6T 2A3 (Received 16 February 2009; published 15 June 2009)

In CDF we have observed the reactionspþp!pþXþp, with Xbeing a centrally producedJ=c, cð2SÞ, or_c0, and!^þ inpp collisions at ffiffiffi

ps

¼1:96 TeV. The event signature requires two oppositely charged central muons, and either no other particles or one additional photon detected.

Exclusive vector meson production is as expected for elastic photoproduction,þp!J=cðcð2SÞÞþ p, observed here for the first time in hadron-hadron collisions. We also observe exclusive_c0!J=c þ . The cross sections^d_dyj_y¼0 forJ=c, cð2SÞ, and _c0 are 3:920:25ðstatÞ 0:52ðsystÞnb, 0:53 0:09ðstatÞ 0:10ðsystÞnb, and7610ðstatÞ 10ðsystÞnb, respectively, and the continuum is consistent with QED. We put an upper limit on the cross section for Odderon exchange in exclusiveJ=cproduction.

DOI:10.1103/PhysRevLett.102.242001 PACS numbers: 13.85.Fb, 12.38.Qk, 12.40.Vv, 13.60.r

In central exclusive production processes,pþp !pþ Xþp, the colliding hadrons emerge intact with small transverse momenta,p_T [1], and the produced state X is in the central region, with small rapidity jyj, and is fully measured. If regions of rapidity exceeding about 5 units are devoid of particles, only photon and Pomeron [2], P, exchanges are significant, where P consists mostly of two gluons in a color singlet state with charge parityC¼ þ1. Odderon, O, exchange, with 3 gluons in a C¼ 1 state [3–5], is allowed in pp, but not ep, collisions, and would appear as an enhancement in exclusive J=c ^and cð2SÞproduction inppcompared to the expectation from pure photoproduction inep. Using the CDF II detector at the Fermilab Tevatron, we previously observed [6] pþ

p!pþe^þeþp in agreement with QED, and found candidates [7] for pþp !pþþp consistent with QCD expectations [8]. In this Letter we report measure- ments of exclusive dimuon production,X¼^þ, with M2 ½3:0;4:0 GeV=c², directly [QED, Fig. 1(a)], or from photoproduced J=cð3097Þ or cð2SÞð3686Þ [Fig.1(b)] decay, and_c0ð3415Þ !J=c þ!^þ [Fig.1(c)]. Lower masses were excluded by muon range, and higher masses by trigger rate limitations. Exclusive photoproduction of vector mesons has been measured in epcollisions at HERA [9], but not previously observed in hadron-hadron collisions. The theoretical uncertainty on the QED cross section is <0:3%; this process is distinct from Drell-Yan production (qq!^þ), which is neg- ligible in this regime.

At the LHC, in pp collisions with ffiffiffi ps

¼10–14 TeV, central exclusive production of states such asX¼H and W^þW, whereHis a Higgs boson, are allowed [10]. Apart from their intrinsic interest, our measurements confirm the viability of the proposed LHC studies. The pþ_c0þp [Fig.1(c)] and pþHþp[as in Fig.1(c)but with a top quark loop] cross sections are related [11], and pþ ^þþp can be used to calibrate forward proton spectrometers.

We used pp collision data at ffiffiffi ps

¼1:96 TeV with an integrated luminosityL¼1:48 fb¹delivered to the CDF II detector. This is a general purpose detector described elsewhere [12]. Surrounding the collision region is a track- ing system consisting of silicon microstrip detectors and a cylindrical drift chamber in a 1.4 Tesla solenoidal field.

The tracking system has 100% efficiency for recon- structing isolated tracks with p_T 1 GeV=c and jj<

0:6[1]. A barrel of 216 time-of-flight counters outside the cylindrical drift chamber is surrounded by calorimeters with separate electromagnetic (EM) and hadronic sections covering the range jj<3:6. Drift chambers outside the calorimeters were used to measure muons withjj<0:6 [13]. The regions 3:6<jj<5:2 are covered by lead- liquid scintillator calorimeters [14]. Gas Cherenkov coun- ters covering 3:7<jj<4:7 determined the luminosity with a 6% uncertainty [15]. We did not have detectors able to measure the forwardpandp, but beam shower scintil- lation counters (BSC1–BSC3), located along the beam pipe, detected products of pðpÞ fragmentation, such as p!p, withjj<7:4.

The level 1 trigger required at least one muon track with p_T>1:4 GeV=c and no signal in BSC1 (5:4&jj&

5:9), and a higher level trigger required a second track with opposite charge. The offline event selection closely followed that described in Ref. [6], where we observed exclusive e^þe production. We required two oppositely charged muon tracks, each with p_T>1:4 GeV=c and jj<0:6, accompanied by either (a) no other particles in the event or (b) only one additional EM shower with E^EM_T >80 MeV and jj<2:1. Condition (a) defines an exclusive dimuon event. The exclusivity efficiency"_exc is the probability that the exclusive requirement is not spoiled by another inelastic interaction in the same bunch crossing, or by noise in a detector element. This efficiency was measured [6] as the fraction of bunch crossing triggers that pass the exclusivity requirement (a). We found"_exc¼ 0:093 with negligible uncertainty. The product "_excL¼ L_eff¼1398 pb¹ was the effective luminosity for single interactions.

FIG. 1. Feynman diagrams for (a) !^þ, (b) P!J=cðcð2SÞÞ, and (c) PP!_c, with the 2-gluon exchange forming a Pomeron.

242001-4

After these selections, cosmic rays were the main back- ground. They were all rejected, with no significant loss of real events, by timing requirements in the time-of-flight counters and by requiring the three-dimensional opening angle between the muon tracks to be_3DðÞ<3:0 rad. Within a fiducial kinematic region (FKR) [jðÞj<0:6, andM2 ½3:0;4:0GeV=c²], there are 402 events with no EM shower. TheMspectrum is shown in Fig.2. The J=c ^andcð2SÞare prominent, together with a continuum.

The spectrum is well fitted by two Gaussians with expected

masses and widths (dominated by the resolution) and a continuum whose shape is given by the product of the QED spectrum (!^þ), acceptance, and efficiency, as shown in Fig.2(inset). The numbers of events from the fit are given in Table I, with statistical uncertainties. The numbers given in Table I for backgrounds, acceptances, and efficiencies show systematic uncertainties estimated by varying parameters within acceptable bounds.

Backgrounds to exclusive^þevents are (see TableI) (a) proton fragmentation, if the products are not detected in the forward detectors, (b) for the J=c^,c0 events with a photon that did not give an EM shower above 80 MeV, and (c) events with some other particle not detected. The probability of aporp fragmenting at theppðpÞvertex was calculated with the LPAIRMonte Carlo (MC) simula- tion [17] to be0:170:02ðsystÞ, and the probability that all the fragmentation products havejj>7:4to be0:14 0:02ðsystÞ. If a proton fragments, the decay products may not be detected through BSC inefficiency, estimated from data to be0:080:01. The fragmention probability at the pPpðpÞvertex was taken from the ratio of single diffrac- tive fragmentation to elastic scattering at the Tevatron [18]

to be0:240:05.

We compared the kinematics of the muons, e.g.

p_Tð^þÞ and , with simulations for the three classes: J=c^, cð2SÞ [19], and QED [17] with M2

½3:2;3:6 and ½3:8;4:0GeV=c² to exclude the J=c ^and cð2SÞ. The distributions agree well with the simulations;

the few events that are outside expectations are taken to be nonexclusive background. Figure3shows the distributions of p_Tð^þÞ. As expected,hp_Ti is smaller for the QED process, and the data agree well withSTARLIGHT[19], apart from two events withp_T>0:8 GeV=cwhere no events are expected. Comparing data withLPAIRwe estimate that the nonexclusive background is ð95Þ% of the observed

TABLE I. Numbers of events fitted to classesJ=c,cð2SÞ,_c0, and QED. Backgrounds are given as percentages of the fit events, and efficiencies are to be applied to the events without background. The stated branching fractionBfor the_c0is the product of the _c0!J=c þandJ=c !^þbranching fractions [16]. For events (fit) the uncertainty is only statistical; all other uncertainties are purely systematic except when both are given. The cross sections include a 6% luminosity uncertainty.

Class J=c cð2SÞ c0ð1PÞ !^þ

Acceptances:

Detector (%) 18:82:0 543 192 41:81:5

Efficiencies:

-quality (%) 33:41:7 456 332 41:82:3

Photon (%) 834

Events(fit) 28617 397 658 779

Backgrounds:

Fragmention (%) 92 92 112 82

Nonexclusive (%) 33 33 33 95

c0ð%Þ 4:01:6

B!^þð%Þ 5:930:06 0:750:08 0:0760:007

B_FKRðpbÞ 28:42:0ðstatÞ 6:0ðsystÞ 1:020:17ðstatÞ 0:19ðsystÞ 8:00:9ðstatÞ 0:9ðsystÞ 270:3ðstatÞ 0:4ðsystÞ

d

dyjy¼0ðnbÞ 3:920:25ðstatÞ 0:52ðsystÞ 0:530:09ðstatÞ 0:10ðsystÞ 7610ðstatÞ 10ðsystÞ

/ ndf χ2orb 36.25 / 549.0697 P 0 .431 p 1 72.35 ±.000 p 3 3.09 ±.1620 p 4 9.187 ±.000 p 6 3.68 ±.468

p 37.86 ±

2) ) (GeV/c µ-

µ+

M(

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4

2 Events per 10 MeV/c

0 10 20 30 40 50 60 70

/ ndf χ2orb 36.25 / 549.0697 P 0 .431 p 1 72.35 ±.000 p 3 3.09 ±.1620 p 4 9.187 ±.000 p 6 3.68 ±.468

p 37.86 ±

2) ) (GeV/c µ- µ+ M(

3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 2Events per 100 MeV/c

2 4 6 8 10 12 14 16 18 20

FIG. 2 (color online). MassMdistribution of 402 exclusive events, with no EM shower (histogram), together with a fit to two Gaussians for theJ=c andcð2SÞ, and a QED continuum. All three shapes are predetermined, with only the normalizations floating. Inset: Data above the J=c and excluding 3:65<

M<3:75 GeV=c²[cð2SÞ] with the fit to the QED spectrum times acceptance (statistical uncertainties only).

(QED) events. The cð2SÞ data are well fitted by the

STARLIGHTphotoproduction simulation [19]. The distribu- tion ofp_TðJ=cÞis well fitted bySTARLIGHT, apart from five events with p_TðJ=cÞ>1:4 GeV=c [Fig. 3(b)]. These could be due to nonexclusive background, some_c0radia- tive decays with an undetected photon, or an Odderon component.

To measure_c0production we required one EM shower withE^EM_T >80 MeVin addition to the two muons; if two adjacent towers had enough energy, they were combined.

There are 65 events in theJ=c peak and eight continuum events; these are likely to be!^þwith a brems- strahlung. We interpret the 65 events as_c0!J=c þ production and decay. The distribution of the mass formed from theJ=c and the EM shower energy, while broad, has a mean value equal to the_c0 mass. TheE^EM_T spectrum is well fitted by an empirical function which extrapolates to only 3:61:3ðsystÞ _c0 candidates with showers below 80 MeV. The p_TðJ=cÞ and distributions for the events with an E^EM_T signal are consistent with all these J=c ^{being from}c0 decay, as simulated byCHICMC [20].

Additional photon inefficiency comes from conversion in material, 72%, and dead regions of the calorimeter, 5:02:5%, giving a total inefficiency 174%, which gives a background to exclusiveJ=c ^of 4:01:6% (all errors systematic).

We calculated acceptances and efficiencies using the

LPAIR [17] andSTARLIGHT[19] MC generators for QED, J=c ^and cð2SÞ, and CHICMC [20] for _c0 production.

Generated events were passed through a GEANT-based [21] simulation of the CDF detector. The trigger efficiency for muons rose steeply between 1:4 GeV=c and 1:5 GeV=c, where it exceeded 90%. As we triggered on one muon, the trigger efficiency for events with two muons was>99%forM>3 GeV=c².

Figure2(inset) shows the subset of the Fig.2data above 3:15 GeV=c² (to exclude the J=c), excluding the bin 3:65–3:75 GeV=c² which contains the cð2SÞ. The curve shows the product of the QED spectrum and acceptance efficiency,A", with only the normalization floating, from the 3-component fit to the full spectrum. The continuum data agrees with the QED expectation. The integral from

3 GeV=c² to 4 GeV=c² is 779ðstatÞ events, and after correcting for backgrounds and efficiencies (Table I), the measured cross section for QED events with jðÞj<

0:6 and M2 ½3:0;4:0GeV=c² is ¼2:7 0:3ðstatÞ 0:4ðsystÞpb, in agreement with the QED pre- diction2:180:01 pb[17].

For the promptJ=c ^andcð2SÞcross sections, we took the number of events from the Gaussian fits, subtracted backgrounds, and corrected for A" to obtain B_FKR for both muons in the fiducial kinematic region (see Table I).

To obtain ^d_dyj_y¼0 from_FKR we used theSTARLIGHTMC program, which gives the ratio of these two cross sections for each resonance, and divided by the branching frac- tions B. We found ^d_dyjy¼0ðJ=cÞ ¼3:920:25ðstatÞ 0:52ðsystÞ nb. This agrees with the predictions2:7^þ0:6_0:2 nb [19] and 3:40:4 nb [22] among others [23,24]. We found ^d_dyj_y¼0ðcð2SÞÞ¼0:530:09ðstatÞ 0:10ðsystÞnb compared with a prediction [19] 0:46^þ0:11_0:04 nb. The ratio R¼^c_J=^ð2S_c^Þ¼0:140:05 is in agreement with the HERA value [9]R¼0:1660:012at similar ffiffiffiffiffiffiffiffiffiffiffiffi

sðpÞ

p .

After correcting the 65_c0 candidates for backgrounds and efficiencies, and applying the branching fraction Bð_c0 !J=cþÞ ¼0:01280:0011 [16], we found

d

dyj_y¼0ð_c0Þ ¼7610ðstatÞ10ðsystÞnb. The _c2ð3556Þ may be present, although it is strongly suppressed by the J_z¼0 rule [11] and is forbidden at 0 scattering angle.

Exclusive gg!_c1ð3511Þ, J^PC ¼1^þþ is forbidden by the Landau-Yang theorem, but may occur with off-shell gluons [25]. It is nevertheless forbidden by symmetry arguments [26] when bothpandp scatter at 0 . Because of the limited MðJ=c þÞ resolution we cannot distin- guish these states; we assume _c1 and _c2 to be negli- gible. If several states _ci are present, P

Bi_i;FKR¼ 8:00:9ðstatÞ 0:9ðsystÞ pb. Theoretical predictions have large (often unstated) uncertainties, but are com- patible with our measurement. Reference [11] predicted

d

dyj_y¼0ð_c0Þ ¼130 nb; however, the Particle Data Group (PDG) value [16] of the_c width has since been reduced by a factor 1.45, correcting their prediction to 90 nb. Yuan [27] predicted 160 nb (again the factor _1:45¹ should be applied) and Bzdak [28] 45 nb.

) (GeV/c) µ-

µ+ T ( p

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.61.8 2

Events per 0.1 GeV/c

0 5 10 15 20 25 30

µ-

µ+

→ γγ (a)

) (GeV/c) µ-

µ+ T ( p

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0

µ-

µ+

→ ψ (b) J/

) (GeV/c) µ-

µ+ T ( p

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0

2 4 6 8

µ-

µ+

→ ψ(2s) (c)

FIG. 3 (color online). pT distribution of ^þ (points with statistical error bars) for (a) QED, M2 ½3:2;3:6 þ

½3:8;4:0GeV=c², (b) J=c, and (c) cð2SÞ. The MC predictions (with no background) are shown by the histo- grams, normalized to the data.

242001-6

If theJ=c ^and cð2SÞ cross sections were larger than expected for photoproduction, it would be evidence for Odderon exchange. Taking a theoretical value of

d

dyj_y¼0ðJ=cÞ ¼3:00:3 nb for photoproduction, com- patible with the predictions, we give a 95% C.L. upper limit^d_dyjy¼0ðJ=cÞ<2:3 nbfor Odderon exchange (OP! J=c^{). Bzdak et al.} [29] predicted the ratio of Odderon:

photon exchange inJ=c production to be 0.3–0.6, consis- tent with our limit.

In conclusion we have observed, for the first time in hadron-hadron collisions, exclusive photoproduction of J=c ^andcð2SÞ, exclusive double Pomeron production of _c0, and the QED process !^þ. The photo- production process has previously been studied in ep collisions at HERA, with similar kinematics ( ffiffiffiffiffiffiffiffiffiffiffiffi

sðpÞ

p

100 GeV), and the cross sections are in agreement. We put an upper limit on an Odderon contribution to exclusive J=c production. Our observation of exclusive_c0produc- tion implies that exclusive Higgs boson production should occur at the LHC [10] and imposes constraints on thepþ p!pþHþpcross section.

We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions.

This work was supported by the U.S. Department of En- ergy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A. P.

Sloan Foundation; the Bundesministerium fu¨r Bildung und Forschung, Germany; the Korean Science and Engineering Foundation and the Korean Research Foundation; the Science and Technology Facilities Council and the Royal Society, UK; the Institut National de Physique Nucleaire et Physique des Particules/CNRS; the Russian Foundation for Basic Research; the Ministerio de Ciencia e Innovacio´n, and Programa Consolider-Ingenio 2010, Spain; the Slovak R&D Agency; and the Academy of Finland.

*Deceased.

[1] A cylindrical coordinate system is used with the z axis along the proton beam direction;is the polar angle and is the azimuthal angle. Transverse momentum isp_T¼ jpjsin, and transverse energy isE_T¼EsinwhereEis the energy. Pseudorapidity is¼ lnðtan₂Þ, and for the charmonium states we use longitudinal rapidity y¼ ln^EþpEp^zz.

[2] See, e.g., J. R. Forshaw and D. A. Ross,Quantum Chromo- dynamics and the Pomeron(Cambridge University Press,

Cambridge, England, 1997); S. Donnachieet al.,Pomeron Physics and QCD (Cambridge University Press, Cambridge, England, 2002).

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