# Presentation: 717983

## New Diffractive Results 

**from the Tevatron**

- Michele Gallinaro
- The Rockefeller University
- (CDF collaboration)

- Introduction
- Exclusive production (dijets,c, ,...)
- Diffractive structure function
- Flavor dependence (W/Z)

## Hadronic Diffraction

- the exchange (“pomeron”) is colorless
-  rapidity gap

- Elastic and diffractive processes:
- leading hadron emitted at small angle

- Small transferred momentum

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Diffractive processes

**Diffractive processes**

- gaps are exponentially suppressed

- Poisson statistics:
- P(y)=e-y   (particle density)

-  large rapidity gaps are signatures for diffraction

- rapidity gaps are formed by
- multiplicity fluctuations

-  rapidity gaps survive (y>3)

**  **_**Non-diffractive interactions**_**:**

**  **_**Diffractive interactions**_**:**

- colorless exchange

- y~ln 1/  (****momentum loss fraction)

- non-diffractive collisions

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Run II detectors

**~57 m**

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Diffractive dijets

**  ************=**

**********all********towers)********E****T**** e******

******s**

**** momentum loss fraction of pbar

- Approx. flat at <0.1

- const

- overlap events

- MP energy scale: ±25% →Δlogξ = ±0.1
- RP acceptance (0.03<ξ< 0.1) ~ 80% (Run I)

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Exclusive Higgs at LHC

- H

- Attractive Higgs discovery channel at the LHC

- _Bialas, Landshoff_:
- PLB 256,540 (1991)
- _Boonekamp, Peschanski, Royon:_
- PRL 87, 251806(2001)
- _Khoze, Martin, Ryskin_:
- Eur. Phys. J. C23, 311 (2002); C25,391 (2002);C26, 229 (2002)

- hard gg→H  process
- color neutral exchange
-     rapidity gap signature
- clean process
- MH= “missing mass” = (s 1 2)1/2

- _Theory predictions_:
- H(LHC)~3 fb, signal/bkg~3 (if Mmiss=1 GeV)
- 			    Khoze, Martin, Ryskin

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Exclusive Dijets at Tevatron

- similar to exclusive Higgs
- much larger cross section

- _Goal:_
- find exclusive dijet production (if it exists)
- measure cross section/upper limit
- calibrate Higgs predictions at LHC

- ...not observed yet...

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Exclusive Dijets in Run I

**Exclusive Dijets in Run I**

- (not detected)

- Exclusive dijet limit:
- Run I: PRL 85 (2000) 4215
****** **jj (excl.) < 3.7 nb (95% CL)

- Mass fraction:

- Rjj=

- Mjj

- Mx

**Expected shape of signal events**

- theory expectns ~1 nb (Run I kinematics)

- PRL 85 (2000) 4215

- Mx

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Dijet Mass Fraction

**Dijet Mass Fraction**

| Minimum ET(Jet1) | Cross section (Rjj>0.8) |
| --- | --- |
| 10 GeV | 1.1 ± 0.1(stat) ± 0.5(syst) nb |
| 25 GeV | 25 ± 3(stat) ± 10(syst) pb |

- independent of rapidity gap size

- rate falls smoothly as Rjj→ 1
- no excess at large Rjj

- exclusive region

- Double Pomeron Exchange (DPE)

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Exclusive Dijet Events ?

- Rjj=0.36

- Rjj=0.81

- ETjet1(2) = 33(31) GeV

- ETjet1(2) = 36(33) GeV

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Limits on Exclusive production

- Martin, Kaidalov, Khoze, Ryskin, Stirling
- (hep-ph/0409258): ~ 40 pb (ET>25 GeV) (factor ~2 uncertainty)

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Heavy flavor exclusive dijets

**Heavy flavor exclusive dijets**

- Experimental method:
- normalize Rjj for qq to Rjj for all jets
- look for event suppression at large Rjj
- _Pros:_	many systematics cancel out
- 	good HF quarks id
- 	small g mistag O(1%)
- _Cons:_	heavy quark mass:
- 	contribution from exclusive b/c

-  use b-quark jets

- illustration

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## HF tagged jet fraction

- Rbtag(>0.7)/Rbtag(<0.4)=0.59 ± 0.33 (stat) ± 0.23 (syst)

- exclusive production?
- need:
- to compare to MC
- more data !

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Future plans

- Increase data sample:
- new exclusive b-jet trigger
- ~ 80% efficiency for SecVtx tagged jets
- expect 900 tagged b-jets in 300 pb-1 at L=3x1031cm-2s-1

- how does Rbtag(>0.7) /Rbtag(<0.4) look like in bb events?

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Diffractive dijets

**Diffractive dijets**

- x10

- x0.1

- no appreciable Q2 dependence  observed within 100 < Q2 < 1,600 GeV2
- pomeron evolves similarly to proton

- ratio of SD/ND dijet event rates
- slope and normalization agree with Run I result
- no dependence observed 0.03<<0.1
- confirms Run I results

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Diffractive W

**Diffractive W**

- Study diffractive W-boson production, and the partonic structure of
- the Pomeron by a comparison to the diffractive di-jet production

- hard-gluon dominated Pomeron
- (rate lower by s)

- hard-quark dominated Pomeron

- or

- Run I: 8,246 W(ev) events - PRL 78 (1997), 2698
- RW (SD/ND)= 1.15 ± 0.51(stat) ± 0.20(syst) %

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Exclusive low-mass states

-  excl (J/ ) = 49 ± 18(stat) ± 39(syst) pb

- bkg from multiplicity fluctuations (under threshold)
- difficult to estimate noise contribution

- ~70 pb Khoze, Martin, Ryskin, Stirling
-             Eur. Phys. J. C 35, 211 (2004)

- pp **** pp

- J/****** **

- ( is soft)

- (same quantum numbers as Higgs boson)

**

**Exclusive low-mass states**

- new trigger implemented

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Exclusive diphotons

**Exclusive diphotons**

- (gg →ET>5 GeV)=40 fb
-  in 100 pb-1 expect ~5 events

- _Work in progress:_
- estimate background
- study low-pt photon ID
- study efficiencies
- ...more data

- new trigger implemented

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Summary

- forward detectors working well
- dedicated diffractive triggers

- improved limits for exclusive production (dijets, c)

- attempted to extract signal using b-quarks
- new DPE b-trigger

- diffractive structure functions, W/Z, etc. (gluon/quark ratio, q2,  dependence)

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## BACKUP

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005

## Proton-Antiproton Collisions

**~25% of the time the proton and antiproton ****elastically scatter**

**~56% of the time a ****“hard”**** collision occurs**

******tot**** = ********e****l ****+ ********in**

**~10% of the time ****single diffraction**** occurs**

**~1% of the time ****double diffraction**** occurs**

******in**** = ********SD**** ****+ ********DD**** ****+ ********HC**

- hard core

- Michele Gallinaro - "New diffractive results from the Tevatron" - Moriond - Mar. 2005