# Presentation: 268039

## Exclusive Central Production at the Tevatron ( LHC)

**Mike Albrow (Fermilab)**
**for the CDF Collaboration**

- Introduction, definitions, prehistory & other places
- Exclusive lepton pairs:
- Photoproduction,    + IP 
- D IP E : IP + IP 
-               IP + IP 
-               IP + IP  J+J, bJ + bJ
-               IP + IP  H         or WW/ZZ

_***+ some diffraction***_

## Central Exclusive Production

**x > 0.95**

**x > 0.95**

- ... both protons coherently scattered. Central state fully specified and measured.
- As distinct from “inclusive” production: e.g. J/psi + “anything”

**M up to about   3 GeV at ISR**
**                        ****100 GeV at Tevatron**
**                        ****700 GeV at LHC**

- Exchanged 4-momentum must
- have no electromagnetic charge
- or strong charge (colour), spin >=1
-                                                         (W,Z allowed, but from q’s)
- Central state Quantum Numbers restricted:

**“****Vacuum Excitation”**

**H,WW**

- p

- p

**> 3 rap-gap**

**> 3 rap-gap**

## Low Mass Central Exclusive Production

_***Low Mass Central Exclusive Production***_

**ISR          = 63 GeV ... then SPS at lower**

**Structures still not well **
**understood beyond f(980).**
**Not studied at higher **

**pp ******** p    X    p**
**X fully measured**

- p

- p

**+ nothing else**

- Search for “Glueballs”

**G(1710)??**

- ... and

- coherence!

**R807: NP B264 (1987) p.154**

**> 3 rap-gap**

**> 3 rap-gap**

**(rho just visible in moment analysis)**

**Angular correlations ******** spins**

## In          collisions (LEP energies  I L C) :

-                                  hadrons, and at high energy:
- WW  WW, WW  Z , WZ  W ?
**In ep collisions** (HERA) :
- gamma-IP  vector mesons
-                    (         too but buried?)
**In                    **(ISR  Tevatron and LHC) :
- IP IP  hadrons (can be single hadron), Higgs,
**   ****-IP ******** vector mesons (... Y,** Z(allowed but tiny)?)
**      ******** ****l+l-** (         too but buried?)
- In AA (RHIC, LHC) mainly                       (E-fields)
-     -IP and IP+IP

_***Central Exclusive Production in Different Machines***_

**New in **
**CDF**

## Central Exclusive Production 

**pp ******** p    X     p    where X is *****a simple system completely measured***

- p

- p

**At CERN ISR**
**Glueball Search**

**At Tevatron & LHC**

**through q-loops (box) + color bleaching (g)**

**W**

**W**

## Central Exclusive Production of Higgs Bosons (LHC)

_***Central Exclusive Production of Higgs Bosons (LHC)***_

- Gluon-gluon fusion + bleaching gluon exchange

**H**

**t**

- Hadrons with same quantum
- numbers as Higgs.

- Advantage: F.S. not strongly interacting
- Disadvantage: v.small cross section,
- experimentally difficult.

## CDF Detector at Fermilab Tevatron

**MiniPlug calorimeters**

**980 GeV p**

**980 GeV pbar**

- Coverage –7.5 < |eta| < +7.5

**Roman pots not used in the**
**data in this talk (acceptance)**
**except exclusive di-jets**

## Search for Exclusive Lepton Pairs I : e+e-

**Motivation was search for exclusive                   (cf H)**
**Trigger: 2 EM showers + forward BSC veto (p not visible) ~ 1M on tape**
**Off-line, exactly 2 showers, ET > 5 GeV and |eta| < 2**
**All CDF calorimetry and counters in “noise”**
**Example: Miniplug, hottest tower ****ET < 10 MeV**
**                                                ****Empty events**
**                                               ****Active events**
**19 superclean events, **
**16 had exactly 2 (+-) tracks (e+e-)**

***Exclusive***
***signature***

## LPAIR: MC, QED + p form factors

_***Exclusive Two Electron Event ***_

**M(ee) = 30 GeV!**
**(another has M = 38.4 GeV!)**

**Run/Event 195762/3788 **

**Central track chamber hits**

**Calorimeter “lego plot”**

-                                     distributions agree
**16 events b/g = 2.1+07-.3 **

**Phys Rev Lett 98, 112001 (2007)**

**First observation of                     in had had**

## Search for Exclusive Lepton Pairs II : 

- Continue study of         collisions :
- QED and luminosity calibration at LHC,           easier than e+e- (?)
- (must be done with pile-up).
- Forward p-spectrometer calibration if p detected (FP420!)
- Look for exclusive vector mesons (photoproduction      -IP  V)

- Two triggers in CDF:

- Low mass: continuum &                   , superclean (no pile-up)
- High mass: continuum & Y(1S), Y(2S), Y(3S) ... allow pile-up
- Can we select exclusive events among others?
- Does final sample contain “supercleans” (4% - 8% expected)?

##  Exclusive             candidates (Low mass)

-  _***Exclusive             candidates (Low mass)***_

**Photoproduction**
**(1****st**** time in hadron-hadron)**

**(2S)(3686)**

**Continuum **

**Acceptance rising strongly through mass range**
**Calculations of acceptance, and possible background**
**from                                     underway.**

**     ****(1S)(3097)**

***Khoze,Martin,Ryskin***
***Eur.Phys.J C24 (2002) 459***

## Q: Can exclusives be found using nassoc_tracks = 0 & kinematics ?

- Q: Can exclusives be found using nassoc_tracks = 0 & kinematics ?

-  _***Exclusive               candidates (High mass)***_

- Trigger: 2 central muons with pT > 4 GeV/c         L = 890/pb
- ~ 2.3 M events. Remove cosmic rays (timing + colinearity)
- Require on beam-line. Count additional (associated) tracks n_ass
- within 5 cm of           vertex.

- n_ass 

- n_ass 

**Y region 9.2 – 10.5 GeV**

**All masses**

## 7.0 < M(+-) (GeV/c2) < 9.2

-         Below Upsilon region

***M(************+************-) (GeV/c******2******) > 10.5 ***
-   Above Upsilon region

_***Number of associated tracks on mumu vertex***_

- Excesses in bin 0 : candidates for
- Cleanliness, backgrounds and acceptances being studied.
- Number of events “reasonable” for QED process, Luminosity.

- n_ass 

- n_ass 

## Invariant Mass Distribution - Upsilon Region

- Clearly visible peaks
- Y(1s) and Y(2s),
- perhaps Y(3S) too.
- + continuum

- For PR Blessing

**All (inclusive)**
**in sample in Y region**

**(n****assoc_tracks**** = 0)**

**Exclusive *****candidates***

## Now apply “superclean” exclusivity cuts as in ee and low mass

**Run/Event: 204413/8549136**

- Lego, threshold ET > 10 MeV

**M ~ 9.4 GeV**

- i.e. no pile-up, and no detected particles except

- 145 events in 8 GeV – 12 GeV region 
- 6 events + 4 M(            ) > 12 GeV.
**(Most of reduction is killing pile-up)**

**Use these to understand backgrounds**
**        ****of full (pile-up) sample.**

**Superclean Upsilon**

## {Measuring forward p  central quantum numbers

- {Measuring forward p  central quantum numbers
-                         2+ forbidden at t=0 for         state}

- Predictions for Tevatron
- F.Yuan ds/dy ~ 150 nb
- Khoze,Martin,Ryskin,Stirling:
- Eur.Phys.J. C35 (2004) 211

- Isotopic spin, spin, G-parity, parity same as Higgs boson

**Candidate events**

- Difficulty is soft photons, and “background”
- from photoproduction:

- M.Rangel et al **(+Royon,Peschanski)**
- 60 pb with CDF cuts

## Central  Exclusive 2-Photon Production

- KMR+Stirling hep-ph/0409037
**QCD diagram identical to pHp**

**38 fb**

_***Central  Exclusive 2-Photon Production***_

**MGA et al. (2001) hep-ex/0511057**

**Tevatron**

- Claim factor ~ 4 uncertainty

**Cleanest test of p+H+p theory**

## Cannot detect protons.  Need to look for        + nothing.

- Trigger on 2 EM4 showers + forward BSC1veto.
- Require all calorimetry and Beam Shower Counters
- in pedestals except 2 EM showers > 5 GeV.                         ( 1.2 mrad )

_***Exclusive 2-photon Search in CDF***_

- 16 were the 2-photon  e+e- events (presented earlier).
- 3 were not, no tracks.
- Detailed study: 1 had characteristics of
- -- single narrow showers on each side.

- Can only use events with no other collisions in bunch crossing.
-  “exclusive efficiency” = 0.086

**Exactly as in exclusive e+e- observation:**

## KMR : 38/fb (x4/4)

- 2 (+1         ) events were like this:

**QCD +QED process**

**ExHuME Monte Carlo**
**Durham Gp, James Monk &**
**Andy Pilkington**

**arXiv:0707.2374 submitted to PRL**

## cf

- If 2 of the 3 candidates are
- events we obtain a cross section:

**Durham Group Khoze, Martin, Ryskin & Stirling  **
**hep-ph/0507040 Eur.Phys.J C38 (2005) 475 : **
**38 fb with factor ~ 3 uncertainty**

**Conclusion: We have observed:**

**Existence of exclusive        implies that exclusive H must exist** **(if H exists)**
**Agreement with Durham group suggests**** ****H cross section at LHC in reach**

## Double Pomeron Exchange  Di-Jets in CDF

**GAP**

_***Double Pomeron Exchange  Di-Jets in CDF***_

- (p not seen)

- “Almost” exclusive di-jet,
- Two jets and nothing else

**Jet <ET> spectra ~ same in SD and DPE**

**JET**

**JET**

**JET**

**JET**

**Detected in RP**

**No pile-up essential; low-L**
**(at LHC if both p detected, some PU allowed)**

## exclusive di-jets. 

**exclusive di-jets****.**

_***CDF Search for Exclusive Dijets ***__***(2 central jets + “nothing”)***_

**Apparent b-jet suppression**
**as they become exclusive ?**
**(Theoretically ******** 0 as Rjj ******** 1, Jz=0 rule)**
**Greatly reduces QCD background**

- p

- p

**J**

**J**

- detected

- inferred

**Relative to R < 0.4 fraction of b-bbar**

## Exclusive di-jet Cross section (integral)

## Value of CDF Central Exclusive Program for p+H+p at LHC

-        that exclusive Higgs must happen (if H exists ) at ~ KMR level.
-        Cross section > 10x higher at LHC, but still difficult.
- 2)                                     . Luminosity calibration
-      will be very hard, but p-calibration of p-spectrometers will work
-      as long as have trigger in good kinematic region (high M, forward).
- 3) Photoproduction of Y,Y’,Y” : cross section higher than continuum
-      and good p-calibration tool (pile-up allowed).
- 4)  Can exclusive         states be measured (Y+   ) as another
-        calibration of p+H+p cross section? Low-L, no pile-up,
- 5) Evidence for exclusive di-jets, with suggestion of depletion of
-      exclusive b-bbar dijets as expected.

- 1) Exclusive         **(if confirmed ... more data being analysed) **implies

## This field started with          at ISR, motivation glueball search.

**striking structures, narrow scalars, glueball nature still unclear.**
- Analogue for LHC is W+W- : guaranteed from 2-photon collisions,
**hopefully striking structures, narrow scalars, Higgs or even not.**
**Note: pp ******** p+(W+W-)+p **
**measures M(WW) even with 1(2) neutrinos and jets (UNIQUE)**
**as well as (WW) quantum numbers (spin) if enough statistics.**
**For pp ******** p+(ZZ)+p 2-photon continuum absent, ****only “H”-like states**

## Forward Proton Spectrometers: ISR  LHC

- p (beam)

- p (scattered)

**Gas Cerenkovs and tracking**

- Magnets and Spark Chambers

**~ 15m,  dp/p ~ 0.5%**

- ISR (1971)

- LHC (2009?)

**420m,  dp/p ~ 0.01%**

**120m of 8T dipoles**

**QUADS, SEPs**

**FP420**

**20cm x 20cm**

**~ 2m**

**24mm x 8mm**

**3-24 mm**

**10m**

**High Precision**
**(5-10um) tracking**

**High Precision**
**(~10ps) timing Cerenkovs**

**30 GeV/c**

**7000 GeV/c**

- SEPTUM

## Determining Quantum Numbers of Central State (H?)

- In gg  X only **CP = ++** is allowed.
- (a CP –ve A (MSSM) is highly suppressed)
- gg  vector (J = 1) forbidden, Yang’s theorem.
- J = 0, 2 can be distinguished by angular distributions
-  partial wave analysis. Can even see states hidden in overall M distribution!

**“****g”**

**“****g”**

**W+**

**W-**

**IP**

**IP**

- Moments H(LM) of the cos(   ) distributions  M(J=0), M(J=2).

**e.g.  ISR/R807 glueball search in                                         NPB264 (1986) 154 **

**Is it J = 0, CP = ++?**

## Not Central Exclusive, but : Diffractive W and Z Production : Run 1

_***Not Central Exclusive, but : Diffractive W and Z Production : Run 1***_

- p

- W

***W produced but p “stays intact”***
- CDF:

- D0 sees diffractive W and Z
- all consistent with 1% diff./ND

**D0**

- “quasi-elastic”

- W

- Z

## Update (Run 2) on CDF diffractive W,Z

_***Update (Run 2) on CDF diffractive W,Z***_

- Events with Roman Pot     (        < 0.1) and central W
- Calculate from full calorimetry        . Only “agree” if no PU
- Very small fraction of all events. Cannot use PU events.

- For no PU events, can find
- by balancing        and        (unique in pp)

**M(W) (not transverse mass!)**

- + Some Diffractive Z candidates

## Conclusions

- Central Exclusive Production in hadron-hadron collisions
- is a rich field, with very clean initial and final states.
- Initial:
- Final: lepton pairs, vector mesons, scalar          states, H, WW.
- CDF studies of all above CE processes (except H,WW !) are an
- important stepping stone. First observation of                         ,
- likely first observation of photoproduction in had-had of onium states,
- Candidates for exclusive          production, 2-jet production.
- Goal of FP420/220 of studying electroweak physics (H etc) in
- a unique situation looks feasible.