ACR X UNAUTHORIZED UNCOORD AIRSPACE ENTRY HAD LTSS FROM SMA Y. SYS ERROR.

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I WAS WORKING THE S SECTOR WITH APPROX 7 ACFT WHEN I REALIZED THAT 1 OF MY ACFT; ACR X; ENTERED CHICAGO CENTER (ZAU) AIRSPACE WITHOUT BEING HANDED OFF. I IMMEDIATELY BEGAN AN AUTOMATED HDOF (FLASHED HIM AT ZAU) AND SIMULTANEOUSLY ATTEMPTED TO CALL ZAU ON THE LANDLINE. WHEN ZAU ANSWERED THE LANDLINE; I ASKED IF THEY HAD RADAR CONTACT WITH ACR X. THEY SAID; NO. WHAT ALT IS ACR X AT?' WHILE ZAU WAS ASKING ME THIS QUESTION; I NOTICED ANOTHER TARGET AT 6000 MSL IN THE IMMEDIATE VICINITY OF ACR X. I TOLD ZAU '6000'; CAME OFF THE LANDLINE AND ISSUED TFC TO ACR X; 'TFC 12 O'CLOCK ALSO AT 6000'; GOT BACK OFF THE LINE WITH ZAU TO HEAR THEM TELL ME TO TURN ACR X TO A 180 HDG. I CAME BACK OFF THE LINE WITH ZAU AND ISSUED ACR X THE HDG. I WENT BACK ON THE LANDLINE WITH ZAU; COMPLETED A HDOF AND TRANSFERRED COM TO ZAU. TO MY KNOWLEDGE; NEITHER ACR X; NOR SMA Y EVER SAW EACH OTHER. THE MAIN CAUSE OF THIS INCIDENT WAS A LACK OF SCANNING ON MY PART. HAD I BEEN PRACTICING A GOOD SCAN TECHNIQUE; I WOULD HAVE NOTICED ACR X STILL ON MY TAG AND HANDED HIM OFF SOONER. ZAU DOES NOT GET A FULL DATA BLOCK OF INFO ON THEIR RADAR UNTIL WE START AN AUTOMATED HDOF. IF THEY HAD SEEN A FULL DATA BLOCK; IT IS HIGHLY POSSIBLE THAT THEY COULD HAVE WARNED ME THAT ACR X WAS APCHING THEIR AIRSPACE (NO EXCUSE HOWEVER). ALSO; I WAS APCHING 1 1/2 HRS ON POS. DURING THE FIRST 30 MINS OF MY SESSION; I WORKED AN EXTREMELY BUSY DEP RUSH. I FEEL I MAY HAVE BEEN IN A RELAXED STATE KNOWING THAT THE BUSY TFC WAS BEHIND ME AND A BREAK WAS ALMOST HERE.